Abstract 4371: PELP1-TFAP2C crosstalk promotes endocrine resistance in breast cancer cells

Background: A significant proportion of estrogen receptor positive (ER+) breast cancer (BC) initially respond to antiestrogens or aromatase inhibitors but become therapy resistant-BC. Development of effective therapies for endocrine therapy resistant BC represent the highest unmet need. PELP1 is a nuclear receptor coregulator, commonly overexpressed in BC, contributes to therapy resistance and correlate with poor survival. TFAP2C (transcription factor AP-2 gamma) is a known regulator of ER activity and high expression of TFAP2C is associated with a decreased response to Fulvestrant. The objective of this study is to examine the significance of PELP1-TFAP2C crosstalk in the development of breast cancer therapy resistance.

Methods: We used yeast two-hybrid screen to identify PELP1 interacting transcription factors. Interaction of PELP1 and TFAP2C was confirmed by immunoprecipitation and GST pull down assays. Functional significance of the cross talk was tested using CellTiter-Glo, MTT and colony formation assays in the presence or absence of endocrine therapy. Mechanistic studies were conducted using shRNA, overexpression, Western blotting, reporter gene assays, RT-qPCR, ChIP-seq and RNA-seq analysis. Biological significance of PELP1 and TFAP2C in endocrine therapy resistance was examined using overexpression and under expression models of PELP1 and TFAP2C in multiple BC models including MCF7 and ZR75.

Results: Yeast based screening of a mammary gland cDNA expression library using PELP1 as the bait identified TFAP2C as a novel interacting protein of PELP1. Immunoprecipitation assays using multiple BC cell lysates confirmed the interaction of PELP1 with TFAP2C. Using various deletions of PELP1, and by using GST pull down assays, we identified N-terminal 400-600aa region of PELP1 as the major interaction site for TFAP2C. Using RNA-seq of PELP1 knockdown BC model cells, we predicted TFAP2C as an enriched transcription factor in PELP1 regulated genes. The GSEA results from RNA-seq showed TFAP2C and PELP1 induce a subset of common genes. Reporter gene assays confirmed that PELP1 functions as a coactivator of TFAP2C. Mechanistic studies showed that TFAP2C activates both AKT and ERK pathways in ER+ cell lines, while knock down of PELP1 attenuated these effects. Overexpression of TFAP2C contributed to increased cell proliferation and endocrine therapy resistance in MCF7 and ZR75 models, while knock down of PELP1 attenuated these effects. Utilizing ZR75-TFAP2C xenograft models with WT PELP1 or PELP1 knock down, we provided genetic evidence that endogenous PELP1 is essential for TFAP2C drive n breast cancer progression in vivo.

Conclusions: Collectively, our studies demonstrated that PELP1 functions as a coactivator of TFAP2C in modulating a set of ER target genes, TFAP2C functions as a transcription factor of PELP1 regulated genes and blocking the PELP1-TFAP2C axis could have therapeutic utility for treating therapy resistance. Supported by VA grant I01BX004545 (R.K. Vadlamudi)

Citation Format: Junhao Liu, Suryavathi Viswanadhapalli, Mengxing Li, Uday P. Pratap, Weiwei Tang, Zexuan Liu, Yiliao Luo, Kristin A. Altwegg, Xiaonan Li, Gangadhara R. Sareddy, Rajeshwar R. Tekmal, Ratna K. Vadlamudi. PELP1-TFAP2C crosstalk promotes endocrine resistance in breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4371.

Abstract P6-04-14: The role of PELP1-TFAP2C crosstalk in mediating endocrine-therapy-resistance in breast cancer

Background: A significant proportion of estrogen receptor (ER) positive (ER+) breast cancer (BC) initially respond to endocrine therapies, such as antiestrogens or aromatase inhibitors. However, ER+ BC can build up resistance to treatment progressing into therapy resistant-BC (TR-BC). Development of effective therapeutics for endocrine-therapy-resistant BC represents a significant unmet need in BC treatment options. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is oncogenic nuclear receptor coregulator, commonly overexpressed in BC. PELP1 overexpression is correlated with poorer patient survival and is associated with development of TR-BC. TFAP2C (AP2Gamma) is a known regulator of ER activity. In addition, high expression of TFAP2C is associated with a decreased response to the steroidal antiestrogen, Fulvestrant. However, it remains unknown whether PELP1 and TFAP2C crosstalk and if the PELP1/TFAP2C axis behaves synergistically to contribute to the development of therapy resistance in TR-BC. Methods: To gain insight into PELP1 signaling mechanisms, we used yeast two-hybrid screen to identify proteins that interact with PELP1. The interaction between PELP1 and TFAP2C was confirmed by immunoprecipitation using both endogenous and GFP tagged proteins. GST fusions of various domains of PELP1 were used to identify the TFAP2C interacting domain. Functional significance of the crosstalk was tested using Celltiter Glo, MTT, apoptosis, and invasion assays. Mechanistic studies were conducted using shRNA, overexpression, Western Blot, reporter gene assays, RT-qPCR, ChIP and RNA-Seq analysis. Biological significance of PELP1 and TFAP2C in endocrine-therapy-resistance was examined using overexpression and under-expression models of PELP1 and TFAP2C in multiple ER+ BC and TR-BC model cells (MCF-7, ZR-75, T-47D, MCF-7-TamR, MCF7-LTLT and ZR75-ERMT537S. Results: Screening of a mammary gland cDNA expression library using PELP1 as the bait identified TFAP2C as a novel interacting protein of PELP1. Immunoprecipitation assays utilizing multiple BC cell lysates confirmed interaction of PELP1 with TFAP2C. We also confirmed PELP1 and TFAP2C interactions using GFP and GST epitope tagged proteins. Using GST fusion of various domains of PELP1, we identified the PELP1 N-terminal domain (aa 400-600) as the major interaction site for TFAP2C. Using PELP1 knockdown BC model cell lines with RNA-Seq analysis, we identified a set of genes regulated by PELP1. The GSEA results from the RNA-Seq data predicted TFAP2C as an enriched transcription factor in a subset of PELP1 regulated genes. RT-qPCR analysis confirmed that PELP1 is needed for optimal regulation of the ER and associated ER target genes by TFAP2C. Reporter gene assays confirmed that PELP1 functions as a coregulator of TFAP2C. Overexpression of TFAP2C contributed to endocrine-therapy-resistance in BC model cells, while knockdown of PELP1 abolished TFAP2C mediated therapy resistance. Conclusions: Collectively, our studies identified PELP1 functions as a coregulator of TFAP2C in modulating ER target genes. TFAP2C functions as a transcription factor of PELP1 regulated genes and blocking the PELP1-TFAP2C axis will have therapeutic utility for treating TR-BC

Citation Format: Junhao Liu, Suryavathi Viswanadhapalli, Mengxing Li, Uday P Pratap, Yiliao Luo, Kristin A Altwegg, Xiaonan Li, Gangadhara R Sareddy, Rajeshwar R Tekmal, Ratna K Vadlamudi. The role of PELP1-TFAP2C crosstalk in mediating endocrine-therapy-resistance in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-04-14.

Abstract P3-11-08: Targeting LIFR enhances the activity of HDAC inhibitors for the treatment of triple negative breast cancer

Background: Triple-negative breast cancer (TNBC) is a heterogeneous disease. TNBC lacks targeted therapies and represents a disproportional share of the breast cancer (BC) mortality rate. Histone deacetylase inhibitors (HDACIs) are emerging as promising multifunctional agents in TNBC to elicit cytotoxic actions. Recent studies have shown that cancer cells elucidate feedback activation of leukemia inhibitory factor receptor (LIFR) which in turn curtails response to HDACIs. We developed a first-in-class inhibitor of LIFR, EC359 that directly interacts with LIFR and effectively blocks LIFR downstream signaling. Here, we examined whether the novel LIFR inhibitor, EC359, has the ability to counteract negative effects of LIFR signaling to enhance HDACIs therapeutic efficacy in the treatment of TNBC.

Methods: We tested multiple HDACIs currently in clinical trials including vorinostat, panobinostat, romidepsin, and givinostat using multiple TNBC models. The effect of combination therapy of HDACIs and EC359 on TNBC cell viability and invasion was examined using MTT assays and matrigel invasion assays respectively. The efficacy of combination therapy on cell survival and apoptosis was determined using clonogenic assays and Caspase 3/7 assays, respectively. Mechanistic studies were performed using Western blotting, qRT-PCR, and reporter gene assays. The efficacy of combination therapy in vivo was examined using Xenograft, patient-derived xenograft (PDX), and patient-derived explant (PDEX) models.

Results: We demonstrated that the treatment of TNBC models with HDACIs increased the expression of LIFR. Immunohistochemistry analyses of breast tumors using tissue microarrays revealed significant expression of LIFR in TNBC samples. Knockdown of LIFR or treatment with a small molecule inhibitor of LIFR (EC359) significantly enhanced the efficacy of HDACIs in reducing cell viability, colony formation ability, and invasiveness as well as promoted apoptosis compared to monotherapy of HDACIs or EC359 in TNBC cell lines. Mechanistic studies, reporter gene assays and biochemical studies using multiple TNBC models exhibited activation of the LIFR signaling pathway upon HDACIs treatment but was attenuated by EC359+HDACI combination therapy. Treatment of human breast tumors utilizing PDEX assays showed that EC359 enhanced the ability of HDACIs to decrease the proliferation (Ki-67 positivity) compared to monotherapy. Furthermore, using TNBC xenografts and PDX models, we demonstrated that EC359 treatment enhanced the ability of HDACIs to reduce in vivo tumor growth compared to monotherapy.

Conclusions: Our results suggest that the combination therapy of HDACIs and EC359 provides greater therapeutic efficacy than monotherapy. In addition, treatment with EC359 can overcome the feedback activation of LIFR currently observed in the treatment of TNBC with HDACIs.

Citation Format: Suryavathi Viswanadhapalli, Mengxing Li, Bindu Santhamma, Uday P Pratap, Yiliao Luo, Junhao Liu, Kristin A Altwegg, Xiaonan Li, Hui Yan, Zhenming Xu, Andrew Brenner, Gangadhara R Sareddy, Rajeshwar R Tekmal, Hareesh B Nair, Klaus J Nickisch, Ratna K Vadlamudi. Targeting LIFR enhances the activity of HDAC inhibitors for the treatment of triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-11-08.

Abstract P3-03-10: Targeting Wnt/β-catenin pathway by antidepressant imipramine for triple negative breast cancer treatment

Aberrant activation of Wnt signaling has been implicated in various human cancers including breast cancer. Several intra-cellular signal transduction pathways are induced by Wnt, notably by Wnt/β-catenin dependent pathway. In breast cancer, triple negative breast cancer (TNBC) subtypes have increased Wnt/β-catenin signaling associated with high grade tumors, metastasis, poor prognosis and tumor regression. Importantly, significant upregulation of Wnt/β-catenin pathway and overexpression of Wnt transcriptional targets have emerged in breast cancer stem cells (BCSCs) than normal mammary epithelial stem cells. Blockade of Wnt/β-catenin signaling has been reported to suppress breast cancer growth, invasion, migration and induced apoptosis and “stemness”. WNT pathway inhibition preferentially reduces stem cell like activity in patient-derived metastatic breast cancer compared to normal cells. Collectively, these studies suggest that Wnt/β-catenin pathway could be the potential target in inhibiting TNBC growth, metastatic progression and “stemness”. We recently identified that imipramine, an FDA approved antidepressant used to treat chronic depression, inhibits TNBC growth and progression. Imipramine treatment significantly reduced cell viability, migration and invasion of breast cancer cells in general and TNBC cells in particular. Our preliminary findings demonstrated that systemic delivery of imipramine suppressed TNBC growth in orthotopic mouse xenograft model. Our studies further show that imipramine inhibits several Wnt/β-catenin catenin pathway proteins including WNT1, FZD1, β-catenin, cyclin D1 and c-myc, which are reported to support breast cancer “stemness” and metastasis. Importantly, our preliminary studies revealed that imipramine inhibits TNBC stem cells as evidenced by reduced CD44+ population. Our results suggest the therapeutic efficacy of imipramine as a single/or neo-adjuvant agent for treating TNBC patients.

Citation Format: Subapriya Rajamanickam, Santosh Timilsina, Ismoil Jatoi, Virginia Kaklamani, Ratna K Vadlamudi, Manjeet K Rao. Targeting Wnt/β-catenin pathway by antidepressant imipramine for triple negative breast cancer treatment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-03-10.

Abstract P3-10-01: Development and characterization of a first-in-class small molecule inhibitor of PELP1

Background: Breast cancer (BCa) is the most commonly diagnosed cancer and the second leading cause of cancer death in women. BCa is composed of distinct molecular subtypes, such as ER positive BCa (ER+ BCa) and triple negative BCa (TNBC). Development of novel effective therapies for patients with therapy resistant breast cancer (TR-BC) and TNBC remains the highest unmet need in patient treatment and survivorship. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) plays a critical role in multiple nuclear receptor functions leading to TR-BC and TNBC progression. PELP1 expression is dysregulated in BCa, is a prognostic indicator of poorer BCa survival, and its deregulation contributes to BCa therapy resistance. The objective of this study is development and characterization of a small molecule inhibitor of PELP1 (SMIP) as novel therapeutic for treating BCa.

Methods: Using yeast two-hybrid screening, we identified PELP1 Inhibitory Peptide (PIP1) from a library of peptides. PIP1 binds PELP1 with high affinity and functions to inhibit PELP1 oncogenic activity. Direct binding of PIP1 to PELP1 was confirmed using biotin pull-down assays and inhibition of BCa proliferation confirmed using MTT assays. We used the Hit-Ligand interaction site with PIP1 hot spot residues based on 3D alignment and morphology to generate a library of peptidomimetics (small chemical molecules). In vitro activity was assessed using Celltiter Glo, MTT, and matrigel invasion chamber assays in multiple BCa models. Mechanistic studies were conducted using Western blot, reporter gene assays, and peptide competition assays. Xenograft and patient derived explant (PDEX) assays were used for preclinical evaluation and preliminary toxicity analysis.

Results: Bioactivity screens revealed PELP1 Inhibitory Peptide (PIP1) significantly attenuates PELP1-mediated proliferation with an IC50 of 10µM across multiple BCa cell lines. We confirmed PIP1 binding to PELP1 using peptide pull-down assays with nuclear lysates from BCa cells. Using Hit-Ligand-Based interaction site with the PIP1 hot spot residues, we identified 61 potential hits using a 10,000 Diverse Set. Screening of these 61 potential hits using the MTT assays lead to the selection of SMIP34 (tetrahydropyrazolo [1,5a) pyrazole) as lead inhibitor of PELP1. SMIP34 treatment reduced proliferation at an IC50 of 3-10µM in ER+ BCa (ZR-75, MCF-7, and T- 47D); TR-BC (MCF-7-TamR, MCF-7-LTLT, ZR-75-MT-ER537S, and ZR-75-MT-ER538G); and TNBC (MDA- MB-231, and BT549) models. Additionally, SMIP34 showed no activity in human mammary epithelial cells. Specificity of SMIP34 was confirmed using PELP1 knockdown BCa cell lines. Mechanistic studies using Western blot analysis confirmed that SMIP34 binding to PELP1 contributes to its degradation. In matrigel invasion chamber assays, SMIP34 significantly reduced the invasiveness of TR-BC and TNBC models. In combination studies, SMIP34 displayed synergy and enhanced the efficacy of current chemotherapeutics Cisplatin and Paclitaxel. In PDEX assays, Ki67 staining revealed SMIP34 significantly decreased tumor proliferation. In xenograft models, SMIP34 (10mg/kg/s.c.) treatment resulted in significant reduction in tumors compared to vehicle treatment. Furthermore, overall mouse body weight in both control and SMIP34 treated groups were similar, suggesting no overt signs of toxicity.

Conclusion: We have developed a first-in-class small molecule inhibitor of PELP1 (SMIP) displaying effectivity against TR-BC and TNBC in vitro and in vivo.

Supported by CPRIT Predoctoral Fellowship CPRIT RTA; RP170345 (K.A. Altwegg)

Citation Format: Kristin A Altwegg, Suryavathi Viswanadhapalli, Monica Mann, Uday P Pratap, Mengxing Li, Junhao Liu, Yiliao Luo, Gangadhara R Sareddy, Hariprasad Vankayalapati, Ratna K. Vadlamudi. Development and characterization of a first-in-class small molecule inhibitor of PELP1 [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-10-01.

Author Correction: Cancer Testis Antigen Promotes Triple Negative Breast Cancer Metastasis and is Traceable in the Circulating Extracellular Vesicles

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Estrogen receptor coregulator binding modulator (ERX-11) enhances the activity of CDK4/6 inhibitors against estrogen receptor-positive breast cancers

BACKGROUND

CDK4/6 inhibitors in combination with endocrine therapy (AE/AI/SERDs) are approved for the treatment of ER+ advanced breast cancer (BCa). However, not all patients benefit from CDK4/6 inhibitors therapy. We previously reported a novel therapeutic agent, ERX-11, that binds to the estrogen receptor (ER) and modulates ER-coregulator interactions. Here, we tested if the combination of ERX-11 with agents approved for ER+ BCa would be more potent.

METHODS

We tested the effect of combination therapy using BCa cell line models, including those that have acquired resistance to tamoxifen, letrozole, or CDK4/6 inhibitors or have been engineered to express mutant forms of the ER. In vitro activity was tested using Cell Titer-Glo, MTT, and apoptosis assays. Mechanistic studies were conducted using western blot, reporter gene assays, RT-qPCR, and mass spectrometry approaches. Xenograft, patient-derived explants (PDEs), and xenograft-derived explants (XDE) were used for preclinical evaluation and toxicity.

RESULTS

ERX-11 inhibited the proliferation of therapy-resistant BCa cells in a dose-dependent manner, including ribociclib resistance. The combination of ERX-11 and CDK4/6 inhibitor was synergistic in decreasing the proliferation of both endocrine therapy-sensitive and endocrine therapy-resistant BCa cells, in vitro, in xenograft models in vivo, xenograft-derived explants ex vivo, and in primary patient-derived explants ex vivo. Importantly, the combination caused xenograft tumor regression in vivo. Unbiased global mass spectrometry studies demonstrated profound decreases in proliferation markers with combination therapy and indicated global proteomic changes in E2F1, ER, and ER coregulators. Mechanistically, the combination of ERX-11 and CDK4/6 inhibitor decreased the interaction between ER and its coregulators, as evidenced by immunoprecipitation followed by mass spectrometry studies. Biochemical studies confirmed that the combination therapy significantly altered the expression of proteins involved in E2F1 and ER signaling, and this is primarily driven by a transcriptional shift, as noted in gene expression studies.

CONCLUSIONS

Our results suggest that ERX-11 inhibited the proliferation of BCa cells resistant to both endocrine therapy and CDK4/6 inhibitors in a dose-dependent manner and that the combination of ERX-11 with a CDK4/6 inhibitor may represent a viable therapeutic approach.

PELP1 signaling contributes to medulloblastoma progression by regulating the NF-κB pathway

Medulloblastoma (MB) is the most common and deadliest brain tumor in children. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein and its oncogenic signaling is implicated in the progression of several cancers. However, the role of PELP1 in the progression of MB remains unknown. The objective of this study is to examine the role of PELP1 in the progression of MB. Immunohistochemical analysis of MB tissue microarrays revealed that PELP1 is overexpressed in the MB specimens compared to normal brain. Knockdown of PELP1 reduced cell proliferation, cell survival, and cell invasion of MB cell lines. The RNA-sequencing analysis revealed that PELP1 knockdown significantly downregulated the pathways related to inflammation and extracellular matrix. Gene set enrichment analysis confirmed that the PELP1-regulated genes were negatively correlated with nuclear factor-κB (NF-κB), extracellular matrix, and angiogenesis gene sets. Interestingly, PELP1 knockdown reduced the expression of NF-κB target genes, NF-κB reporter activity, and inhibited the nuclear translocation of p65. Importantly, the knockdown of PELP1 significantly reduced in vivo MB progression in orthotopic models and improved the overall mice survival. Collectively, these results suggest that PELP1 could be a novel target for therapeutic intervention in MB.

PELP1 promotes glioblastoma progression by enhancing Wnt/β-catenin signaling

Background

Glioblastoma (GBM) is a deadly neoplasm of the central nervous system. The molecular mechanisms and players that contribute to GBM development is incompletely understood.

Methods

The expression of PELP1 in different grades of glioma and normal brain tissues was analyzed using immunohistochemistry on a tumor tissue array. PELP1 expression in established and primary GBM cell lines was analyzed by Western blotting. The effect of PELP1 knockdown was studied using cell proliferation, colony formation, migration, and invasion assays. Mechanistic studies were conducted using RNA-seq, RT-qPCR, immunoprecipitation, reporter gene assays, and signaling analysis. Mouse orthotopic models were used for preclinical evaluation of PELP1 knock down.

Results

Nuclear receptor coregulator PELP1 is highly expressed in gliomas compared to normal brain tissues, with the highest expression in GBM. PELP1 expression was elevated in established and patient-derived GBM cell lines compared to normal astrocytes. Knockdown of PELP1 resulted in a significant decrease in cell viability, survival, migration, and invasion. Global RNA-sequencing studies demonstrated that PELP1 knockdown significantly reduced the expression of genes involved in the Wnt/β-catenin pathway. Mechanistic studies demonstrated that PELP1 interacts with and functions as a coactivator of β-catenin. Knockdown of PELP1 resulted in a significant increase in survival of mice implanted with U87 and GBM PDX models.

Conclusions

PELP1 expression is upregulated in GBM and PELP1 signaling via β-catenin axis contributes to GBM progression. Thus, PELP1 could be a potential target for the development of therapeutic intervention in GBM.

Cancer Testis Antigen Promotes Triple Negative Breast Cancer Metastasis and is Traceable in the Circulating Extracellular Vesicles

Triple negative breast cancer (TNBC) has poor survival, exhibits rapid metastases, lacks targeted therapies and reliable prognostic markers. Here, we examined metastasis promoting role of cancer testis antigen SPANXB1 in TNBC and its utility as a therapeutic target and prognostic biomarker. Expression pattern of SPANXB1 was determined using matched primary cancer, lymph node metastatic tissues and circulating small extracellular vesicles (sEVs). cDNA microarray analysis of TNBC cells stably integrated with a metastasis suppressor SH3GL2 identified SPANXB1 as a potential target gene. TNBC cells overexpressing SH3GL2 exhibited decreased levels of both SPANXB1 mRNA and protein. Silencing of SPANXB1 reduced migration, invasion and reactive oxygen species production of TNBC cells. SPANXB1 depletion augmented SH3GL2 expression and decreased RAC-1, FAK, A-Actinin and Vinculin expression. Phenotypic and molecular changes were reversed upon SPANXB1 re-expression. SPANXB1 overexpressing breast cancer cells with an enhanced SPANXB1:SH3GL2 ratio achieved pulmonary metastasis within 5 weeks, whereas controls cells failed to do so. Altered expression of SPANXB1 was detected in the sEVs of SPANXB1 transduced cells. Exclusive expression of SPANXB1 was traceable in circulating sEVs, which was associated with TNBC progression. SPANXB1 represents a novel and ideal therapeutic target for blocking TNBC metastases due to its unique expression pattern and may function as an EV based prognostic marker to improve TNBC survival. Uniquely restricted expression of SPANXB1 in TNBCs, makes it an ideal candidate for targeted therapeutics and prognostication.

Abstract 4316: Targeting LIFR overcomes HDAC inhibitor resistance in ovarian cancer

Ovarian cancer (OCa) is the deadliest of all gynecologic cancers in the United States and a critical need exists for the development of novel therapies for the treatment of OCa. Leukemia inhibitory factor receptor (LIFR) and its ligand LIF play a critical role in cancer progression, metastasis, stem cell maintenance, and therapy resistance. Recent clinical studies showed that cancer cells elucidate feedback activation of LIFR that limits response to histone deacetylase (HDAC) inhibitors. Recently, we developed a first-in-class inhibitor of LIFR, EC359 that directly interacts with LIFR and effectively blocks LIF-LIFR interactions. Here, we examined whether LIFR inhibitor EC359 abrogate the side effects of histone deacetylase inhibitor SAHA (Vorinostat) for the treatment of OCa.

Methods: The effect of EC359 and SAHA as a combination therapy on OCa cell viability was examined by MTT assays. The efficacy of combination therapy on cell survival and apoptosis was determined using clonogenic assays and caspase3/7 assays respectively. The efficacy of combination therapy on OCa stem cells was determined using extreme limiting dilution assays. Mechanistic studies were performed using western blotting, qRT-PCR and Mass Spectrometry analyses. The effect of combination therapy on STAT3 signaling was examined using reporter gene assays. The in vivo efficacy of combination therapy on tumors was examined using ex vivopatient derived explants and mouse xenograft models.

Results: EC359 significantly enhanced the efficacy of SAHA in reducing cell viability, colony formation ability, and apoptosis compared to monotherapy of SAHA in multiple established and primary OCa cells. Further, EC359 enhanced SAHA ability to reduce self-renewal of OCa stem cells. As expected in STAT3 reporter assays, SAHA treatment activated STAT3 reporter and EC359 addition abrogated SAHA mediated STAT3 activation. Mechanistic studies using multiple OCa models and western blot analysis confirmed activation of LIFR signaling pathway upon SAHA treatment and its blockage by EC359 treatment. Treatment of human primary OCa tumor explants with EC359 enhanced ability of SAHA to decrease the proliferation (Ki-67 positivity) compared to monotherapy treated tumors. DIA based Mass Spectrometry analyses identified unique pathways modulated by combination therapy. Treatment of OCa xenografts with EC359 enhanced the ability of SAHA to reduce in vivotumor growth compared to monotherapy treated tumors.

Conclusions: Our results suggest that EC359 has therapeutic utility in overcoming the limitation of feedback activation of LIFR observed in the treatment of HDAC inhibitors in treating OCa.

Citation Format: Mengxing Li, Suryavathi Viswanadhapalli, Gangadhara Reddy Sareddy, Bindu Santhamma, Hui Yan, Zhenming Xu, Edward Kost, Rajeshwar Rao Tekmal, Hareesh B. Nair, Klaus J. Nickisch, Ratna K. Vadlamudi. Targeting LIFR overcomes HDAC inhibitor resistance in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4316.

Abstract 1008: S-Equol inhibits breast cancer growth by regulating phosphorylation status of estrogen receptor β

Background: Breast cancer is the most common malignancy in females and second most common cause of cancer related mortality in women. Since 70% of all breast cancers are estrogen receptor-positive (ER+ve), endocrine therapy such as anti-estrogens or aromatase inhibitors, targeting the estrogen receptor (ER) pathway is the most common treatment used for ER+ve breast cancers. However, patients will develop de novo or acquired resistance to therapy, leads to tumor progression, and metastasis. It is well documented that ERβ functions as tumor suppressor in different cancers including breast cancer. We recently showed that phosphorylation status of ERβ is important for its antitumor activity. However, little is known about the role of ERβ phosphorylation status in hormone therapy and resistance; therefore, we investigated whether phosphorylation status of ERβ has role in overcoming hormone therapy resistance in ER+ve breast cancers.

Experimental design: To elucidate the importance of phosphorylation status of ERβ, we used CRISPR-Cas9 system to knockout ERβ in MCF7-Aro (therapy-sensitive) and Letrozole resistant (MCF7aro-LTLT) cells. Several mutant clones were identified for both MCF7-Aro cells and LTLT cells and the depletion of ERβ protein in both cell clones was confirmed by immunoblotting. The parental and knockout cells with or without treatment of S-equol were analyzed for cell proliferation, protein (Western) and RNA (RT-qPCR) analysis.

Results: First we analyzed the cell proliferation in parental (MCF7 Aro and LTLT) and ERβ knock out cells. The proliferation rate is increased in the ERβ knockout cells compared to the parental cells. Treatment with ERβ agonist S-Equol to the parental cells inhibited the cell proliferation whereas in the knock out cells, the effect of S-equol is compromised. RNA-seq analysis of S-equol treated parental cells showed the downregulation of ERβ target genes involved in tumor progression and resistance to hormone therapies. In contrast, compared to parental cells, ERβ knock out cells showed diverse effects to S-equol treatment. RT-qPCR analysis revealed that S-Equol could not modulate the ERβ-target genes in ERβ knock out cells compared to parental cells.

Conclusions: Our findings provide evidence that phosphorylation status of ERβ is important for elucidating its antitumor activity in therapy-resistant cells. The differential effects of S-equol on parental and ERβ knockout cells suggest that the antiproliferative action of S-equol is partly mediated by ERβ. We believe that our ongoing studies may further validate the role of phosphorylation status of ERβ by using both ERβ agonists and phosphorylation-regulating compounds in both therapy sensitive and resistant cells.

Citation Format: Kumaraguruparan Ramasamy, Cathy Samayoa, Shaorong Chen, Rong Li, Ratna K. Vadlamudi, Rajeshwar R. Tekmal. S-Equol inhibits breast cancer growth by regulating phosphorylation status of estrogen receptor β [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1008.

Abstract 1712: Estrogen receptor beta signaling sensitizes glioblastoma cells to chemo and radiation therapy

Current treatment options for glioblastoma (GBM) are poor, the mortality rates are very high and therapy resistance is a major clinical problem. Standard treatment consists of surgical resection, external beam radiation therapy, adjuvant chemotherapy with temozolomide (TMZ), and tumor treating fields. Nonetheless, despite a heavy investment in therapy, all patients eventually succumb to their disease. Recent studies suggest that estrogen receptor beta (ERβ) may function as a tumor suppressor in GBM. However, the mechanism(s) by which ERβ contributes to chemo- and radiation therapy response remains unknown. The objective of this study is to examine whether ERβ sensitizes GBM to chemo- and radiation therapy and to understand the mechanistic insights of ERβ mediated tumor suppression in GBM.

Methods: To study the functions of endogenous ERβ in GBM cells, we have utilized multiple ERβ overexpressing GBM model (GBM- ERβ) cells using lentiviral transduction. As a second model we have also generated ERβ knockout (ERβKO) cells using CRISPR/Cas9 system, and as a third model we used lentiviral-ERβshRNA transfected primary GBM cells (ERβKD). We then examined the effect of TMZ and radiation on the expression of ERβ using qRT-PCR. The effect of TMZ and radiation on ERβ overexpression and knockout models was examined using MTT cell viability assays. Mechanistic studies were conducted using RNA-seq, HR reporter gene assays, confocal microscopy, western blot, and qRT-PCR analysis. The in vivo role of ERβ on chemo sensitivity of TMZ was studied using orthotopic models of GBM and mouse survival was determined using Kaplan-Meier survival curves.

Results: Cell viability and survival assays using multiple established and primary GBM cells demonstrated that ERβ sensitizes GBM cells to DNA damaging agents including TMZ and radiation therapy. qRT-PCR analysis demonstrated that ERβ expression was decreased following chemo- and radiation treatment. Combination analysis of RNA-seq studies using ERβ overexpression, and ERKO models, revealed an alteration in the number of genes involved in DNA recombination and repair, ATM signaling, and cell cycle check point control. Mechanistic studies showed that ERβ plays a significant role in homologous recombination (HR) mediated repair; and ERβ reduced expression and activation of ATM upon DNA damage. Generation of optimal γH2AX foci following TMZ treatment is dependent on the status of ERβ. More importantly, GBM cells expressing ERβ had increased survival when compared to control GBM cells in orthotopic GBM models. ERβ overexpression further enhanced the survival of mice to TMZ therapy in both TMZ sensitive and TMZ resistant GBM models.

Conclusion: Our results provided evidence that ERβ is required for optimal chemo- and radiation- induced DNA damage response in GBM cells.

Citation Format: Uday P. Pratap, Gangadhara Reddy Sareddy, Mengxing Li, Yiliao Luo, Mei Zhou, Suryavathi Viswanadhapalli, Rajeshwar Rao Tekmal, Andrew Brenner, Ratna K. Vadlamudi. Estrogen receptor beta signaling sensitizes glioblastoma cells to chemo and radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1712.

Abstract 3485: PELP1 is a novel mediator of medulloblastoma progression

Background: Medulloblastoma (MB) is the most common and deadliest primary brain tumor in children that accounts for 15-20% of all pediatric brain tumors. Despite recent advances in multimodal treatment, the 5-year overall survival of MB patients is approximately 60-70%. Unfortunately, improved outcome have been associated with significant long-term toxicities. Identifying novel targets that drive MB progression is urgently needed. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein that functions as a coregulator of several nuclear receptors. Oncogenic PELP1 signaling is implicated in the progression of several cancers including breast, ovarian, prostate, lung, pancreas and colon. However, its role in the progression of medulloblastoma remains unknown. Here, we examined the role of proto-oncogene PELP1 in the progression of MB.

Methods: The expression of PELP1 in tumor micro arrays was analyzed using validated PELP1 antibodies for immunohistochemistry. PELP1 expression was determined in vitro by western blotting. PELP1 knockdown cells were generated using PELP1 shRNA lentiviral particles or PELP1 siRNA. The effect of PELP1 knockdown or overexpression was studied using cell proliferation, colony formation and migration using established in vitro assays. Mechanistic studies were conducted using RNA-seq, RT-qPCR, immunohistochemistry, reporter gene assays and signaling analysis. Interaction of PELP1 with NF-κB was examined by immunoprecipitation. Mouse orthotopic xenografts models were used for preclinical evaluation of PELP1 knock down.

Results: Immunohistochemical analysis of MB tissue microarrays revealed that PELP1 is overexpressed in MB specimens compared to normal brain specimens. Knockdown of PELP1 using PELP1 specific siRNA or shRNA significantly reduced cell proliferation, cell survival, and cell migration of MB cell lines. RNA-seq analysis revealed that PELP1 knockdown significantly downregulated the pathways related to inflammation, angiogenesis and extracellular matrix. Further, gene set enrichment analysis (GSEA) confirmed that the PELP1-regualted genes were negatively correlated with NF-κB, extracellular matrix and angiogenesis. Mechanistic studies showed that PELP1 knockdown reduced the expression of NF-κB reporter gene activity and its target genes. Additionally, knockdown of PELP1 significantly reduced in vivo MB tumor progression in orthotopic models, and improved overall mice survival. IHC analysis demonstrated that the proliferation marker Ki67 and NF- κB targets were significantly downregulated in PELP1 knockdown tumors compared to controls.

Conclusions: Taken together, these results provide the evidence that PELP1 could be a potential therapeutic target for therapeutic intervention in medulloblastoma.

Citation Format: Yiliao Luo, Gangadhara Reddy Sareddy, Uday P. Pratap, Mengxing Li, Junhao Liu, Prabhakar Pitta-Venkata, Suryavathi Viswanadhapalli, Xiaonan Li, Manjeet Rao, Rajeshwar Rao Tekmal, Ratna K. Vadlamudi. PELP1 is a novel mediator of medulloblastoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3485.

EC359: A First-in-Class Small-Molecule Inhibitor for Targeting Oncogenic LIFR Signaling in Triple-Negative Breast Cancer

Leukemia inhibitory factor receptor (LIFR) and its ligand LIF play a critical role in cancer progression, metastasis, stem cell maintenance, and therapy resistance. Here, we describe a rationally designed first-in-class inhibitor of LIFR, EC359, which directly interacts with LIFR to effectively block LIF/LIFR interactions. EC359 treatment exhibits antiproliferative effects, reduces invasiveness and stemness, and promotes apoptosis in triple-negative breast cancer (TNBC) cell lines. The activity of EC359 is dependent on LIF and LIFR expression, and treatment with EC359 attenuated the activation of LIF/LIFR-driven pathways, including STAT3, mTOR, and AKT. Concomitantly, EC359 was also effective in blocking signaling by other LIFR ligands (CTF1, CNTF, and OSM) that interact at LIF/LIFR interface. EC359 significantly reduced tumor progression in TNBC xenografts and patient-derived xenografts (PDX), and reduced proliferation in patient-derived primary TNBC explants. EC359 exhibits distinct pharmacologic advantages, including oral bioavailability, and in vivo stability. Collectively, these data support EC359 as a novel targeted therapeutic that inhibits LIFR oncogenic signaling.See related commentary by Shi et al., p. 1337.

Estrogen receptor beta enhances chemotherapy response of GBM cells by down regulating DNA damage response pathways

Glioblastoma (GBM) is the most commonly diagnosed brain tumor that exhibit high mortality rate and chemotherapy resistance is a major clinical problem. Recent studies suggest that estrogen receptor beta (ERβ), may function as a tumor suppressor in GBM. However, the mechanism(s) by which ERβ contributes to GBM suppression and chemotherapy response remains unknown. We examined the role of ERβ in the DNA damage response of GBM cells, and tested whether ERβ sensitizes GBM cells to chemotherapy. Cell viability and survival assays using multiple epitope tagged ERβ expressing established and primary GBM cells demonstrated that ERβ sensitizes GBM cells to DNA damaging agents including temozolomide (TMZ). RNA-seq studies using ERβ overexpression models revealed downregulation of number of genes involved in DNA recombination and repair, ATM signaling and cell cycle check point control. Gene set enrichment analysis (GSEA) suggested that ERβ–modulated genes were correlated negatively with homologous recombination, mismatch repair and G2M checkpoint genes. Further, RT-qPCR analysis revealed that chemotherapy induced activation of cell cycle arrest and apoptosis genes were attenuated in ERβKO cells. Additionally, ERβ overexpressing cells had a higher number of γH2AX foci following TMZ treatment. Mechanistic studies showed that ERβ plays an important role in homologous recombination (HR) mediated repair and ERβ reduced expression and activation of ATM upon DNA damage. More importantly, GBM cells expressing ERβ had increased survival when compared to control GBM cells in orthotopic GBM models. ERβ overexpression further enhanced the survival of mice to TMZ therapy in both TMZ sensitive and TMZ resistant GBM models. Additionally, IHC analysis revealed that ERβ tumors had increased expression of γH2AX and cleaved caspase-3. Using ERβ-overexpression and ERβ-KO GBM model cells, we have provided the evidence that ERβ is required for optimal chemotherapy induced DNA damage response and apoptosis in GBM cells.

Abstract P2-06-02: Development of a first-in-class small molecule inhibitor (EC359) targeting oncogenic LIF/LIFR signaling for the treatment of triple negative breast cancer

Background: Leukemia inhibitory factor (LIF) and its receptor LIFR are over-expressed in multiple solid tumors and play a key role in tumor growth, progression, and resistance to standard anti-cancer treatments. Triple-negative breast cancer (TNBC) lacks targeted therapies and represents a disproportional share of breast cancer (BCa) mortality. TNBC exhibits autocrine stimulation of the LIF/LIFR axis and overexpression of LIF is associated with poorer relapse-free survival in BCa patients. LIF signaling also promotes maintenance of stem cells. Therefore, targeting the LIF/LIFR axis may have therapeutic utility in TNBC.

Methods: We rationally designed a small organic molecule (EC359) that emulates the LIF/LIFR binding site and functions as a LIFR inhibitor from a library of compounds. In silico docking studies were used to identify the putative interaction of the EC359 and LIF/LIFR complex. Direct binding of EC359 to LIFR was confirmed using surface plasmon resonance (SPR) and microscale thermophoresis technique (MST) assays. In vitro activity was tested using Cell-Titer Glo, MTT, invasion, and apoptosis assays. Mechanistic studies were conducted using Western blot, reporter gene assays, and RNA-seq analysis. Xenograft, patient-derived xenograft (PDX), and patient-derived explant (PDEX) models were used for preclinical evaluation and toxicity.

Results: Molecular docking studies showed that EC359 interacts at the LIF/LIFR binding interface. SPR and MST studies confirmed direct interaction of EC359 to LIFR. EC359 reduced the growth of TNBC cells with high potency (IC50 50-100nM) and promoted apoptosis. Further, EC359 treatment reduced invasion and stemness of TNBC cells. EC359 activity is dependent on the expression levels of LIFR and showed little or no activity on TNBC cells that have low levels of LIFR or ER+ve BCa cells. Further, EC359 significantly reduced the viability of cisplatin and taxane-resistant TNBC cells and enhanced the efficacy of HDAC inhibitors. Mechanistic and biochemical studies showed that EC359 interacts with LIFR and effectively blocking LIF/LIFR interactions. EC359 also blocked LIFR interactions with other LIFR ligands such as oncostatin M, ciliary neurotrophic factor, and cardiotrophin-1. EC359 treatment attenuated the activation of LIF/LIFR driven pathways including STAT3, mTOR, AKT, and MAPK. RNA-seq analysis identified regulation of apoptosis as one of the important pathway modulated by EC359. In TNBC xenograft and PDX assays, EC359 significantly reduced tumor progression. Further, using human primary BCa PDEX cultures, we demonstrated that EC359 has the potential to substantially reduce the proliferation of human BCa. Pharmacologically, EC359 exhibited high oral bioavailability and long half-life with a wide therapeutic window.

Conclusions: EC359 is a novel targeted therapeutic agent that inhibits LIF/LIFR oncogenic signaling in TNBC via a unique mechanism of action. EC359 has the distinct pharmacologic advantages of oral bioavailability, in vivo stability, and is associated with minimal systemic side effects. (DOD BCRP grant #BC170312)

Citation Format: Viswanadhapalli S, Luo Y, Sareddy GR, Santhamma B, Zhou M, Li M, Pratap UP, Altwegg KA, Li X, Srinivasan U, Ma S, Chang A, Riveros AC, Zhang KY, Dileep KV, Pan X, Murali R, Bajda M, Raj G, Brenner A, Manthati V, Rao M, Tekmal RR, Nair HB, Nickisch KJ, Vadlamudi RK. Development of a first-in-class small molecule inhibitor (EC359) targeting oncogenic LIF/LIFR signaling for the treatment of triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-06-02.

Abstract P5-04-23: Enhancing the activity of a novel estrogen receptor coregulator binding modulator (ERX-11) against ER-positive therapy resistant breast cancer

Background:We had previously reported a novel small molecule, ERX-11, that directly interacts with ER and blocks the interaction between a subset of coregulators with both native and mutant forms of ER. ERX-11 effectively blocks ER oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant human breast cancer cells. To enhance the clinical translation of ERX-11, we sought to pursue both lead optimization and evaluate combinations of ERX-11 with other approved agents in breast cancer.

Methods: We designed, synthesized and tested 500 derivatives of ERX-11 in multiple models of ER+ breast cancer. We also tested combinations of ERX-11 with multiple agents, including other ER targeting agents, chemotherapies and CDK4/6 inhibitors. We tested the effect of combination therapy using breast cancer cells with acquired resistance (Tamoxifen, Letrozole, Ribociclib resistant) and engineered models that express ER mutations. In vitro activity was tested using Cell titer glo, MTT, and apoptosis assays. Mechanistic studies were conducted using Western blot, reporter gene assays and RNA-seq analysis. Xenograft, patient derived xenograft (PDX), patient derived explant (PDE) and xenograft derived explant (XDE) models were used for preclinical evaluation and toxicity.

Result: Evaluation of 500 analogs of ERX-11 identified a number of leads with differential activity against ER+ and ER- breast cancer cells, identified several analogs including ERX-144, 208, 296, 315 with nanomolar potency against ER+ and therapy-resistant ER+ breast cancers. Validation of the mechanism of action of these analogs is ongoing. The combination of ERX-11 and palbociclib significantly blocked ER-mediated and ER-coregulators mediated oncogenic signaling and showed potent anti-proliferative activity against both endocrine therapy-sensitive and resistant breast cancer cells. In addition, ERX-11 inhibited ribociclib-resistant ER+ cell proliferation in a dose dependent manner. Mechanistic studies using IP-Mass spectrometry demonstrated that ERX-11 and palbociclib blocks the interaction between larger subset of coregulators with ER in therapy resistant breast cancer models. ERX-11 and palbociclib both exhibited potent anti-proliferative activity against therapy-sensitive and therapy-resistant ER+ve breast cancer cells, in xenograft models and in PDEs. Importantly, combination therapy of ERX-11 and palbociclib synergistically reduced the growth of tamoxifen and letrozole resistant xenograft tumors compared to either drug alone. Mass spec based DIA analyses and RNA-seq studies revealed that combinational treatment uniquely activated p53, unfolded response mediated apoptotic pathways, altered DNA damage response and suppressed E2F and Myc target genes. Biochemical studies confirmed combination therapy significantly altered E2F1, ER and DNA damage response pathways.

Conclusion: We have successfully pursued two avenues to improving ERX-11 for clinical translation. We have developed ERX-11 analogs with higher potency against ER+ breast cancer. We have shown that combinational treatment with ERX-11 and palbociclib may overcome endocrine therapy resistance and CDK4/6 inhibitor (ribociclib) resistance.

Citation Format: Viswanadhapalli S, Ma S, Lee T-K, Sareddy GR, Liu X, Ekoue D, Alluri A, Luo Y, Kassees K, Arteaga C, Alluri P, Weintraub SE, Tekmal RR, Ahn J-M, Raj GV, Vadlamudi RK. Enhancing the activity of a novel estrogen receptor coregulator binding modulator (ERX-11) against ER-positive therapy resistant breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-23.

Abstract P4-07-01: A small molecule inhibitor (ERX-41) induces endoplasmic reticulum stress in triple negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer and represents a disproportional share of the breast cancer mortality, primarily due to a lack of targeted therapies. There is a major unmet need for rationally designed novel therapies that can extend survival of patients with TNBC. TNBCs are characterized by a high basal level of endoplasmic reticulum stress, due to high protein turnover and need for proliferation. Recent studies revealed the role of several members of the Nuclear Receptor (NR) superfamily as molecular drivers in TNBC, including the androgen receptor (AR), glucocorticoid receptor (GR) and the orphan NR tailless (TLX).

Methods: Recently, using peptidomimetics, we have developed small molecules that specifically target and block interactions of multiple coregulators with oncogenic NRs. We performed a screen of our 500+ compound peptidomimetic library derived from our ERX-11 oligobenzamide (that was rationally designed to target ERα) for anti-proliferative activity in TNBC cell lines. Identified leads were then validated in multiple TNBC cell lines. In vitro activity was tested using Cell titer glo, MTT, matrigel invasion, and apoptosis assays. Mechanistic studies were conducted using Western blot, reporter gene assays, CRISPR/Cas9 KO and RNA-seq analysis. Xenograft, patient derived xenograft (PDX), patient derived explant (PDE) and xenograft derived explant (XDE) TNBC models were used for preclinical evaluation and toxicity.

Results: We have identified a first-in-class drug (ERX-41) that has potent activity (IC50 = 50-250nM) against all six molecular subtypes of TNBC. Systematic evaluation using CRISPR/Cas9 KO screen and overexpression screen comprising 48 NRs identified TLX as a preferred target of ERX-41. Analyses of primary breast tumors revealed TLX was highly expressed in TNBC. Further, TLX was amplified in nearly 50% of TNBC xenografts (cbioportal.org). Modelling, mechanistic and biochemical studies showed that ERX-41 interact with TLX and selectively blocks its interactions with coregulators. Gene expression analyses revealed both significant reduction of TLX-activated genes (CCND1, WNT7A) and significant activation of TLX-repressed genes (p21) upon treatment with ERX-41 in TNBC models. Gene ontogeny pathway analyses of RNA-seq data in TNBC cells showed that ERX-41 treatment positively correlated with apoptosis. Our ultrastructural studies indicated that ERX-41 enhances endoplasmic reticulum stress in TNBC inducing autophagic flux and subsequent apoptosis. ERX-41 has significant potency against multiple TNBC xenografts and PDXs in vivo, PDEs and XDEs ex vivo, indicating its potential for clinical translation. Pharmacologically, ERX-41 exhibited high oral bioavailability and associated with minimal toxicity upon oral gavage for up to 120 days in animal studies.

Conclusions: We believe that the ability of ERX-41 to block NR signaling and target a critical molecular vulnerability in TNBC and its ability to enhance endoplasmic reticulum stress in TNBC, will revolutionize the therapeutic landscape of TNBC. ERX-41 is oral bioavailable, potent against multiple TNBC molecular subtypes, and is associated with minimal systemic side effects. (supported by NIH grant RO1 CA223828-01)

Citation Format: Liu X, Viswanadhapalli S, Ma S, Lee T-K, Sareddy GR, Ekoue DN, Blatt EM, Zhou M, Li M, Tekmal RR, Ahn J-m, Vadlamudi RK, Raj GV. A small molecule inhibitor (ERX-41) induces endoplasmic reticulum stress in triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-07-01.

Abstract P2-02-03: FASN inhibition as a potential treatment for therapy of endocrine resistant breast cancer

INTRODUCTION: Fatty acid synthase (FASN) is a key enzyme in tumor cell biology controlling endogenous lipid biosynthesis. It is overexpressed in a biologically aggressive subset of tumors, including breast carcinoma. We previously reported prolonged stabilization of disease with TVB-2640 in patients with advanced metastatic breast cancer, including some endocrine resistant ER+ tumors. Using in vitro and in vivo models, we assessed the role of FASN inhibition by TVB-3166 (preclinical version of TVB-2640) for treatment of endocrine resistant breast cancer. METHODS: Breast tumor cells were incubated with TVB-3166 (200nM), imaged and analyzed by automated Live-Cell analysis system (IncuCyte). For tumor growth inhibition, cells (2X106)were subcutaneously injected into SCID mice implanted with estrogen pellets. Once tumors were measurable, mice were divided into treatment groups: tamoxifen (4mg/kg), TVB-3166 (60mg/kg) and the combination. Patient tumor explants were incubated for 72h on gelatin sponges in culture medium in the absence or presence of 200nM TVB-3166. Tissue were fixed in 10% formalin and processed into paraffin blocks. Sections were stained with H&E, ERα and Ki67. RESULTS: The effectiveness of FASN inhibition on the growth of tumor cells has been confirmed in a number of breast cancer cell lines such as MCF7, ZR75, MDA-MB-231 and others. TVB-3166 leads to a marked inhibition of growth in tamoxifen resistant (TamR) cells, which 15% greater than in the parent line. IHC and Western blot showed FASN inhibition leads to significantly reduction of ERα levels. Immunofluorescent confocal microscopy showed inhibition of FASN by TVB-3166 alters subcellular localization of ERα. TVB-3166 was able to significantly inhibit tamoxifen resistant breast tumor growth in mice (p<0.05). Additionally, TVB-3166 treatment of primary tumor explants decreased their proliferation (Ki67) compared to untreated controls (21% vs 38%, p<0.01). CONCLUSION: Our preclinical data provide evidence that FASN inhibition by TVB-3166 presents a promising therapeutic strategy for treating of endocrine resistant breast cancer. RNA sequencing of tumor explants is being performed to evaluate FASN inhibition impact on canonical and non-canonical ERα signaling pathways.

Citation Format: Gruslova A, Sareddy GR, Vadlamudi RK, Viswanadhapalli S, Brenner A. FASN inhibition as a potential treatment for therapy of endocrine resistant breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-02-03.

Abstract 5875: Development of LIFR inhibitor EC359 as a novel therapeutic for ovarian cancer

Background: Ovarian cancer (OCa) is the deadliest of all gynecologic cancers. OCa patients initially respond to standard combinations of surgical and cytotoxic therapy; however, ~80% will develop recurrence and inevitably succumb to chemotherapy-resistant disease. OCa stem cells are implicated in the tumor initiation and therapy resistance. LIFR signaling plays a critical role in OCa progression and stemness. Further, high circulating LIF levels correlate with tumor recurrence and chemoresistance. The autocrine loop involving LIF, LIFR and STAT3 axis drives sustained fibroblast production of inflammatory mediators. This represents a significant problem and a critical need exists for development of novel therapies targeting the LIFR axis for treating OCa.

Methods: We have rationally designed and synthesized a small organic molecule (EC359) that emulates the LIF-LIFR binding site and functions as a LIFR inhibitor from a library of compounds. In silico docking studies were used to identify the putative interaction of the EC359 and LIF/LIFR complex. Binding of EC359 to LIFR was confirmed using surface plasmon resonance (SPR) and IP assays. Mechanistic studies were conducted using Western, RT-qPCR, and RNA-Seq analysis. Xenograft models were used for preclinical evaluation and toxicity. The efficacy of EC359 was tested using Patient-Derived eXplants (PDeX).

Results: Global analysis of online databases revealed negative correlation of OCa survival with LIFR expression. Molecular docking studies showed EC359 interacts at the LIF-LIFR binding interface. SPR studies confirmed interaction of EC359 to LIFR. Western analysis of eight cells that represent four subtypes of OCa confirmed higher expression of LIF and LIFR. EC359 reduced the growth of eight OCa cells with high potency (IC50 10-50 nM) and promoted apoptosis. EC359 treatment reduced stemness of OCa cells. EC359 activity is dependent on the level of expression of LIFR with little activity on cells that do not express LIFR. EC359 significantly reduced the viability of carboplatin- and taxol-resistant OCa cells. Mechanistic studies showed EC359 interacts with LIFR and block its interaction with LIF. EC359 treatment reduced the STAT3 phosphorylation, mTOR and downstream survival signaling cascades. RNA sequencing revealed unique pathways blocked by EC359. Treatment of xenograft tumors with EC359 significantly reduced the tumor volume compared to control. Further, using PDeX of OCa, we demonstrated that EC359 has potential to reduce the proliferation. Pharmacologically, EC359 exhibited high oral bioavailability and long half-life with a wide therapeutic window.

Conclusions: EC359 is a novel agent that targets LIF-LIFR axis and has activity against chemotherapy-resistant and primary OCa tumors. EC359 has the distinct pharmacologic advantages of oral bioavailability, in vivo stability, and is associated with minimal systemic side effects.

Citation Format: Suryavathi Viswanadhapalli, Hareesh B Nair, Bindu Santhamma, Gangadhara R Sareddy, Yiliao Luo, Xinlei Pan, Edward R Kost, Ramachandran Murali, Rajeshwar Rao Tekmal, Klaus J Nickisch, Ratna K Vadlamudi. Development of LIFR inhibitor EC359 as a novel therapeutic for ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5875.

Abstract 2483: Estrogen receptor beta enhances chemotherapy response in GBM

Background: The incidence of developing glioblastoma (GBM) is greater in men than in women, and women of reproductive age have a survival advantage over men and postmenopausal women. These correlative findings suggest that estrogens play a significant role in suppression of GBM, but how they might do so is poorly understood. GBM cells express the estrogen receptor beta (ERβ) that functions as a tumor suppressor. However, the in vivo significance of endogenous ERβ and its role in GBM progression are incompletely understood. The objective of this study is to examine the role of endogenous ERβ in the progression and chemotherapy response of GBM.

Methods: To study the functions of endogenous ERβ in GBM cells, we have generated ERβ knockout (ERβKO) GBM cells using CRISPR/Cas9 system and lentivital-ERβshRNA transfected primary GBM cells (ERβKD). As a second model, we generated multiple ERβ overexpressing GBM model cells (both established and primary GBM cells) using lentiviral transduction. Effect of ERβ-KO, -KD or -overexpression was studied using cell proliferation, invasion and apoptosis using established in vitro assays. Mechanistic studies were conducted using RNA-seq, RT-qPCR and signaling analysis. In vivo role of ERβ was studied using orthotopic models of GBM and mouse survival was determined using Kaplan-Meier survival curves.

Results: ERβKO or ERβKD increased, while ERβ overexpression reduced the proliferation of GBM cells. To determine the effect of ERβKO on mice survival, U251-WT and U251-ERβKO cells were implanted intracranially into immunocompromised mice. Compared to control mice, ERβKO mice had significant reduction in survival. Further, IHC analysis of tumor sections from these mice revealed that ERβKO tumors had more expression of the proliferation marker Ki-67 than the control tumors. RNA-seq analyses using U87WT and U87ERβKO cells revealed that the ERβKO-modulated genes were related to DNA damage response, p53 pathway, NF-κB signaling, JAK-STAT, and mTOR pathways. Further, RNA-seq studies using U87 and U87ERβ overexpression models revealed downregulation of a number of genes involved in DNA repair, DNA damage response (DDR), ATM signaling and cell cycle checkpoint control. Mechanistic studies showed that ERβ modulates expression of genes involved in apoptosis and DDR, thus enhancing the response to chemotherapy drugs. Compared to control, ERβKO cells exhibited resistance to DNA-damaging agents including cisplatin and temozolomide, while ERβ-overexpressing cells were highly sensitive to these DNA-damaging agents. We also validated ERβ sensitization to temozolomide using orthotopic GBM models.

Conclusion: Using ERβ-KO and -KD GBM model cells, we have provided strong evidence demonstrating tumor suppressor and therapy sensitization potential of endogenous ERβ. Our results suggest that upregulation of ERβ expression/functions is an attractive therapy for treating GBM.

Citation Format: Mei Zhou, Gangadhara R. Sareddy, Jinyou Liu, Mengxing Li, Suryavathi Viswanadhapalli, Xiaonan Li, Rajeshwar R Tekmal, Andrew Brenner, Ratna K. Vadlamudi. Estrogen receptor beta enhances chemotherapy response in GBM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2483.

Abstract 3734: Estrogen receptor β agonists suppress the growth and progression of mammary tumors in immune-competent mouse models

Background: Despite medical advances in early detection and treatment, breast cancer still has a relatively high mortality rate in women due to recurrence and metastasis. Many human cancers are able to suppress the activity of the immune system. With the emerging importance of the immune system in tumor surveillance, the need to employ immunocompetent in vivo models to study breast cancer progression is evident. Syngeneic tumor mouse models are a useful tool to study drug development and therapeutic utility of novel drugs. Emerging evidence suggest that Estrogen receptor (ER) β functions as a tumor suppressor in many cancers including breast cancer. Therefore, targeting ERβ with selective agonists may provide therapeutic benefit in the treatment of breast cancer. Herein, we examined the therapeutic efficacy of ERβ agonists on the growth of syngeneic mouse mammary tumors. Experimental design: To test the effects of ERβ agonists on growth, we carried out cell proliferation, invasion and migration, and clonogenic assays in all three-mouse mammary tumor models with different genetic background. Cell cycle was analyzed using FACS analysis. D2A1 (BALB/c) and MM51 (FVB) syngeneic models and ex-vivo culture of E0771 (C57/B6) cells were used to evaluate the antitumor effects of ERβ agonists. Results: First, we assessed the effects of ERβ agonists on cell proliferation of these three mouse mammary tumor cells. Cells were treated with different concentrations of LY500307 (100nM-10µM) and S-Equol (1µM-100µM) for 72 and 96 hrs. D2A1 cells and E0771 cells showed IC50 of 2.5µM for LY500307 and 50 µM for S-Equol and MM51 cells had an IC50 of 2 µM for LY500307 and 40 µM for S-Equol. Our results also showed that ERβ agonists reduce the colony formation ability of D2A1 and MM51 cells. In D2A1 and MM51 cells, LY500307 treatment decreased colonies by 32% and 50%, and S-Equol reduced colonies to 18% and 40% as compared to control respectively. Cell cycle analysis showed that LY500307 and S-equol treatment in D2A1 and E0771 cells resulted in a significant accumulation of cells in S phase. Further, we analyzed the therapeutic efficacy of LY500307 in two syngeneic mouse tumor models from D2A1 and MM51 cells. Our results demonstrated that LY500307 inhibited the tumor growth and the effect was more pronounce in combination with aromatase inhibitor letrozole. Further, using ex-vivo model of tumor explants from E0771 cells, we showed that ERβ agonists inhibited the mammary tumor growth. Conclusions: Our results suggested that ERβ agonists have potential to prevent the progression mammary tumors in immunocompetent hosts.

Citation Format: Kumaraguruparan Ramasamy, Cathy Samayoa, Naveen K. Krishnegowda, Shaorong Chen, Ratna K. Vadlamudi, Rajeshwar R. Tekmal. Estrogen receptor β agonists suppress the growth and progression of mammary tumors in immune-competent mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3734.

17β-Estradiol Regulates Microglia Activation and Polarization in the Hippocampus Following Global Cerebral Ischemia

17β-Estradiol (E2) is a well-known neuroprotective hormone, but its role in regulation of neuroinflammation is less understood. Recently, our lab demonstrated that E2 could regulate the NLRP3 (NOD-like receptor protein 3) inflammasome pathway in the hippocampus following global cerebral ischemia (GCI). Here, we examined the ability of E2 to regulate activation and polarization of microglia phenotype in the hippocampus after global cerebral ischemia (GCI). Our in vivo study in young adult ovariectomized rats showed that exogenous low-dose E2 profoundly suppressed microglia activation and quantitatively shifted microglia from their "activated," amoeboid morphology to a "resting," ramified morphology after GCI. Further studies using M1 "proinflammatory" and M2 "anti-inflammatory" phenotype markers showed that E2 robustly suppressed the "proinflammatory" M1 phenotype, while enhancing the "anti-inflammatory" M2 microglia phenotype in the hippocampus after GCI. These effects of E2 may be mediated directly upon microglia, as E2 suppressed the M1 while enhancing the M2 microglia phenotype in LPS- (lipopolysaccharide-) activated BV2 microglia cells in vitro. E2 also correspondingly suppressed proinflammatory while enhancing anti-inflammatory cytokine gene expression in the LPS-treated BV2 microglia cells. Finally, E2 treatment abolished the LPS-induced neurotoxic effects of BV2 microglia cells upon hippocampal HT-22 neurons. Collectively, our study findings suggest a novel E2-mediated neuroprotective effect via regulation of microglia activation and promotion of the M2 "anti-inflammatory" phenotype in the brain.

Differential Effects of Estrogen Receptor β Isoforms on Glioblastoma Progression

The estrogen receptor β (ERβ) functions as a tumor suppressor in glioblastoma (GBM) cells. However, the in vivo significance of endogenous ERβ and the roles of its isoforms in GBM are incompletely understood. Using ERβ isoform-specific PCR screening, we found that GBM cells predominantly express ERβ1 and ERβ5, along with low levels of ERβ2 and ERβ4. We observed greater ERβ5 expression in higher grades of glioma than in lower grades. In CRISPR-based ERβ knockout (KO) cells and ERβ KO cells uniquely expressing ERβ1 or ERβ5 only, ERβ1 significantly reduced proliferation. Compared with parental GBM cells, ERβ KO cells exhibited high migratory and invasive potentials, and reexpression of ERβ1 resulted in the reduction of this phenotype. Interestingly, ERβ5 expression increased foci formation and anchorage-independent growth of NIH3T3 cells and increased motile structure formation, including filopodia and ruffles in GBM cells. Only ERβ1-expressing tumors resulted in longer mouse survival. RNA-Seq analysis revealed unique pathways modulated by ERβ1 and ERβ5. Compared with ERβ KO cells, ERβ1 cells exhibited lower activation of mTOR signaling molecules, including p-mTOR, p-S6K, and p-S6, and ERβ5-expressing cells had enhanced mTOR downstream signaling. Unique proteins including several that function as regulators of mTOR, immunomodulatory, and apoptosis pathways bound to ERβ1 and ERβ5 isoforms. Our work confirms the tumor-suppressive potential of ERβ1 and reveals the acquired oncogenic ability of ERβ5 in GBM cells. ERβ isoform status and their unique interactions with oncogenic pathways may have important implications in GBM progression.Significance: These findings suggest that only ERβ isoform 1 has tumor suppressor function in GBM and that ERβ isoform switching contributes to GBM progression. Cancer Res; 78(12); 3176-89. ©2018 AACR.

Abstract P6-06-04: Targeting replication stress in triple negative breast cancer treatment regimen: An emerging approach

Triple-negative breast cancers (TNBCs) represent aggressive heterogeneous subtype of breast cancer with poor clinical outcome. TNBCs have been reported to have high levels of replication stress due to i) various oncogene activations (C-myc or EGFR) ii) germline BRCA mutations iii) “BRCAness” in the absence of BRCA mutations in sporadic TNBCs. Replication stress is known to cause genomic instability, promote tumorigenesis and plays a critical role in therapy resistance in TNBCs. Therefore, targeting replication stress has emerged as an effective approach for better TNBC treatment through further downregulation of the remaining checkpoints to induce catastrophic failure of TNBC cells proliferation. Herein, we evaluated the anticancer efficacy of Carbazole Blue (CB), a synthetic analogue of Carbazole, on TNBC cells growth and progression. Our results demonstrated that CB inhibits short and long term viability of TNBC (MDA-MB-231, MDA-MB-468 and BT549) cells in a dose dependent manner without affecting normal mammary epithelial (MCF-10A) cells. In addition, CB treatment significantly reduced proliferation of TNBC cells, as evidenced by the BrdU proliferation assay. Consistent with this, our results further demonstrated that CB treatment induced G1/S cell cycle arrest and apoptosis in TNBCs. Importantly, systemic delivery of CB using nanoparticle-based delivery approach suppressed breast cancer growth without inducing toxicity, in preclinical orthotopic xenograft and PDX mouse models of TNBC. Furthermore, our gene microarray analysis revealed that CB treatment modulates the expression and activity of several genes known to be involved in DNA replication (CDC6, CDT1, MCMs, Claspin, POLE and PCNA) and associated DNA repair machinery such as (XRCC3, Exo1 and RAD51), which play pivotal roles in replication stress. Our results for the first time highlight the potential use of CB as a novel and potent therapeutic agent for treating TNBCs. As exploiting replication stress to treat cancer is gaining major interest, compound/s that may induce replication stress and inhibit DNA repair ability of cancer cells, has immense translational potential.

Citation Format: Rajamanickam S, Park JH, Bates K, Timilsina S, Eedunuri VK, Onyeagucha B, Subbarayalu P, Abdelfattah N, Jung KH, Favours E, Mohammad TA, Chen H-IH, Vadlamudi RK, Chen Y, Kaipparettu BA, Arbiser JL, Rao MK. Targeting replication stress in triple negative breast cancer treatment regimen: An emerging approach [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-06-04.

Abstract P1-09-09: Efficacy of estrogen receptor β agonists in the prevention of breast cancer progression to therapy resistance

Estrogen plays an important role in the initiation and progression of breast cancer (BCa). Approximately, 70% of breast tumors are estrogen receptor (ER) positive at the time of presentation. Endocrine therapy using aromatase inhibitors (AI), or anti-estrogen (AE) molecules are widely used for treating ER+ve BCa. However, their efficacy is limited by intrinsic and acquired therapy resistance and most patients develop resistance to these drugs. The transcriptional effects of estrogen are mediated by two ERs (ERα and ERβ) and both are expressed in normal breast tissue. Unlike ERα, ERβ functions as tumor suppressor. However, role of ERβ specific agonists in the prevention of BCa progression remains elusive. In this study, we investigated the effectiveness of two ERβ agonists (S-Equol and LY500307) in the prevention of BCa progression using endocrine therapy sensitive (MCF7-aro) and letrozole resistant (MCF7-aro-LTLT) cells. Our results demonstrated that treatment with ERβ agonists inhibit short-and long-term growth of both endocrine therapy sensitive and resistant BCa cells. In addition, ERβ agonists treatment inhibited invasion and migration of both MCF7-aro and MCF7-aro-LTLT cells. Importantly, cell cycle analysis revealed that ERβ agonists induced cell cycle arrest. Our gene microarray analysis demonstrated that both ERβ agonists significantly modulated genes involved in the cell cycle progression, DNA replication and cell death pathways. Further, gene enrichment analysis of differentially expressed genes revealed that genes involved in the cell cycle checkpoints emerged as significant pathway modulated by ERβ agonists treatment in MCF7-aro cells. Interestingly, in letrozole-resistant MCF7-aro cells, DNA replication was significantly affected by ERβ agonists treatment. Pathway analysis also identified enrichment for chemokine signaling pathways. We confirmed pathway analysis by qRT-PCR and western blot analysis. Accordingly, treatment of in vivo syngeneic xenografts with ERβ agonists significantly inhibited BCa progression. Collectively, these results from this study suggest that ERβ agonists have potential to prevent the progression of BCa progression.

Citation Format: Ramasamy K, Samayoa C, Krishnegowda NK, Vadlamudi RK, Tekmal RR. Efficacy of estrogen receptor β agonists in the prevention of breast cancer progression to therapy resistance [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-09-09.

Abstract P1-09-06: Blocking ER coregulator signaling enhances CDK4/6 inhibitor palbociclib therapy in ER-positive advanced breast cancer

BACKGROUND: Recently,CDK4/6 inhibitors in combination with endocrine therapy (AE/AI/SERDs) is approved for the treatment of ER+ advanced breastcancer (BCa). However, not all patients benefit from CDK4/6 inhibitors therapy. Emerging studies indicate many therapy-resistant tumors retainER signaling, via interaction with critical oncogenic coregulatorproteins. Considering complex signaling interplay of ER and CDK4/6 axis, combination therapy of CDK inhibitor with other potent ER-targeted agents that block ER coregulatory signaling may extend the efficacy and may prevent the development of resistance to the CDK4/6 inhibitors. We recently developed a small organic molecule, ER coregulator binding modulator ERX-11 (EtiraRx-11). The objective of this study is to test the utility of novel combination therapy of ERX-11 with CDK4/6 inhibitor palbociclib in treating therapy resistant advanced BCa.

METHODS: We have utilized multiple therapy sensitive and therapy-resistant BCa models with various genetic backgrounds. We tested efficacy using both acquired resistance and engineered models that express ER mutations or oncogenes. Efficacy of combination therapy was tested using established in vitro assays including, MTT, colony formation, apoptosis, and cell cycle progression. Mechanistic studies were conducted using reporter gene assays, gene expression, RNA-seq analysis and signaling alterations. Patient-derived BCa explant and Xenograft studies were used to determine the in vivo efficacy of the combination therapy.

RESULTS: ERX-11 effectively blocked ER-mediated and ER-coregulator mediated oncogenic signaling and has potent anti-proliferative activity against both endocrine therapy-sensitive and therapy-resistant BCa cells. Mechanistic studies using IP-Mass spectrometry showed that ERX-11 blocks the interaction between a subset of coregulators with ER in resistant BCa models. ERX-11 exhibited potent anti-proliferative activity against therapy-sensitive and therapy-resistant ER-driven BCa cells in vitro, in xenograft models in vivo and in patient-derived breast tumor explants ex vivo. Co-treatment of ERX-11 with palbociclib synergistically reduced cell viability and induced apoptosis of therapy sensitive and resistant BCa model cells. Importantly, combination therapy of ERX-11 and the palbociclib synergistically reduced the growth and induced apoptosis of tamoxifen and letrozole resistant xenograft tumors compared to either drug alone. RNA-seq studies revealed that combinational treatment with ERX-11 and palbociclib uniquely activated p53 and unfolded response mediated apoptotic pathways and suppressed E2F and Myc target genes. Biochemical studies confirmed combination therapy significantly altered E2F1 and ER signaling pathways and promoted apoptosis.

CONCLUSIONS: Our data support a critical role of blocking ER coregulator signaling in treating therapy resistance in advanced ER+ BCa. Combinational treatment with ERX-11 and palbociclib may overcome/delay endocrine therapy resistance.

Citation Format: Viswanadhapalli S, Sareddy GR, Zhou M, Ali E, Li X, Ma S-H, Lee T-K, Tekmal RR, Ahn J-M, Raj GV, Vadlamudi RK. Blocking ER coregulator signaling enhances CDK4/6 inhibitor palbociclib therapy in ER-positive advanced breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-09-06.

PELP1: a key mediator of oestrogen signalling and actions in the brain

Proline-, glutamic acid- and leucine-rich protein 1 (PELP1) is an oestrogen receptor (ER) coregulator protein identified by our collaborative group. Work from our laboratory and others has shown that PELP1 is a scaffold protein that interacts with ERs and kinase signalling factors, as well as proteins involved in chromatin remodelling and DNA repair. Its role in mediating 17β-oestradiol (E₂ ) signalling and actions has been studied in detail in cancer cells, although only recently has attention turned to its role in the brain. In this review, we discuss the tissue, cellular and subcellular localisation of PELP1 in the brain. We also discuss recent evidence from PELP1 forebrain-specific knockout mice demonstrating a critical role of PELP1 in mediating both extranuclear and nuclear ER signalling in the brain, as well as E₂ -induced neuroprotection, anti-inflammatory effects and regulation of cognitive function. Finally, the PELP1 interactome and unique gene network regulated by PELP1 in the brain is discussed, especially because it provides new insights into PELP1 biology, protein interactions and mechanisms of action in the brain. As a whole, the findings discussed in the present review indicate that PELP1 functions as a critical ER coregulator in the brain to mediate E₂ signalling and actions.

Abstract LB-B04: Development of a first-in-class leukemia inhibitory factor (LIF)/LIFR inhibitor, EC359 for targeted therapy

Background: An IL-6 family member, leukemia inhibitory factor (LIF), is a pleotropic cytokine involved in multiple cellular signaling and pathophysiology of various malignancies including cancer. Overexpression of LIF is significantly correlated with advanced tumor stage, larger tumor size and worse relapse free survival rate. The objective of present study to develop and characterize next generation steroidal LIF/LIFR inhibitor based on our first LIF inhibitor, EC330. In this study, we optimized EC330 by synthetic modifications and generated EC359 to reduce its binding to classical steroid receptors and to improve its oral bioavailability. Material and methods: In silico docking studies were used to identify putative interaction of EC359 and LIF/LIFR receptor complex. We confirmed binding of EC359 to LIFR using surface plasmon resonance (SPR). Biophysical and biological characterization was performed by measuring cytotoxicity in various cancer cell lines and anchorage-independent colony assays. Specificity to LIF/LIFR was measured by GST pull-down assay and by SPR using commercially available recombinant proteins of LIF and LIFR. In vivo efficacy and toxicity was tested using syngeneic mice tumors and xenograft models.

Results: EC359 showed cytotoxicity in various cancer cells at low nano-molar range, blocked formation of colonies in soft agar and inhibited triple negative breast cancer (TNBC) stem cells. Physical direct-interaction was confirmed by SPR which showed EC359 binding to LIFR with an affinity of 81μM. EC359 showed cytoskeletal disruption and targeting cancer-associated fibroblasts (CAFs) through inhibition of alpha-SMA but not beta-tubulin. Blockade of LIF-LIFR interaction reduced the STAT3 phosphorylation, mTOR and further downstream signaling cascades. In vivo, EC359 treatment (1 and 5mg/kg) dose dependently reduced tumor burden in both TNBC xenograft and murine syngeneic MM51 models. Pharmacologically, EC359 exhibits a high oral bioavailability and long half-life in rats with a wide therapeutic window. Conclusions: Our findings establish EC359 as a novel LIF/LIFR targeting drug with therapeutic perspectives for patients with advanced primary tumors. LIF/LIFR targeting may result in the blockade of JAK- STAT signaling pathway as well as cancer fibroblast associated pro invasive tumor microenvironment in regular as well as therapy resistant tumors.

Citation Format: Hareesh B. Nair, Bindu Santhamma, Suryavathi Viswanadhapalli, Gangadhara R. Sareddy, Xinlei Pan, Vijaya Manthati, Ratna K. Vadlamudi, Murali Ramachandran, Klaus J. Nickisch. Development of a first-in-class leukemia inhibitory factor (LIF)/LIFR inhibitor, EC359 for targeted therapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B04.

Tamoxifen Resistance in Breast Cancer Is Regulated by the EZH2-ERα-GREB1 Transcriptional Axis

Resistance to cancer treatment can be driven by epigenetic reprogramming of specific transcriptomes in favor of the refractory phenotypes. Here we discover that tamoxifen resistance in breast cancer is driven by a regulatory axis consisting of a master transcription factor, its cofactor, and an epigenetic regulator. The oncogenic histone methyltransferase EZH2 conferred tamoxifen resistance by silencing the expression of the estrogen receptor α (ERα) cofactor GREB1. In clinical specimens, induction of DNA methylation of a particular CpG-enriched region at the GREB1 promoter negatively correlated with GREB1 levels and cell sensitivity to endocrine agents. GREB1 also ensured proper cellular reactions to different ligands by recruiting distinct sets of ERα cofactors to cis-regulatory elements, which explains the contradictory biological effects of GREB1 on breast cancer cell growth in response to estrogen or antiestrogen. In refractory cells, EZH2-dependent repression of GREB1 triggered chromatin reallocation of ERα coregulators, converting the antiestrogen into an agonist. In clinical specimens from patients receiving adjuvant tamoxifen treatment, expression levels of EZH2 and GREB1 were correlated negatively, and taken together better predicted patient responses to endocrine therapy. Overall, our work suggests a new strategy to overcome endocrine resistance in metastatic breast cancer by targeting a particular epigenetic program.Significance: This study suggests a new strategy to overcome endocrine resistance in metastatic breast cancer by targeting a particular epigenetic program defined within. Cancer Res; 78(3); 671-84. ©2017 AACR.

Novel post-transcriptional and post-translational regulation of pro-apoptotic protein BOK and anti-apoptotic protein Mcl-1 determine the fate of breast cancer cells to survive or die

Deregulation of apoptosis is central to cancer progression and a major obstacle to effective treatment. The Bcl-2 gene family members play important roles in the regulation of apoptosis and are frequently altered in cancers. One such member is pro-apoptotic protein Bcl-2-related Ovarian Killer (BOK). Despite its critical role in apoptosis, the regulation of BOK expression is poorly understood in cancers. Here, we discovered that miR-296-5p regulates BOK expression by binding to its 3'-UTR in breast cancers. Interestingly, miR-296-5p also regulates the expression of anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1), which is highly expressed in breast cancers. Our results reveal that Mcl-1 and BOK constitute a regulatory feedback loop as ectopic BOK expression induces Mcl-1, whereas silencing of Mcl-1 results in reduced BOK levels in breast cancer cells. In addition, we show that silencing of Mcl-1 but not BOK reduced the long-term growth of breast cancer cells. Silencing of both Mcl-1 and BOK rescued the effect of Mcl-1 silencing on breast cancer cell growth, suggesting that BOK is important for attenuating cell growth in the absence of Mcl-1. Depletion of BOK suppressed caspase-3 activation in the presence of paclitaxel and in turn protected cells from paclitaxel-induced apoptosis. Furthermore, we demonstrate that glycogen synthase kinase (GSK3) α/β interacts with BOK and regulates its level post-translationally in breast cancer cells. Taken together, our results suggest that fine tuning of the levels of pro-apoptotic protein BOK and anti-apoptotic protein Mcl-1 may decide the fate of cancer cells to either undergo apoptosis or proliferation.

Estrogen receptor coregulator binding modulators (ERXs) effectively target estrogen receptor positive human breast cancers

The majority of human breast cancer is estrogen receptor alpha (ER) positive. While anti-estrogens/aromatase inhibitors are initially effective, resistance to these drugs commonly develops. Therapy-resistant tumors often retain ER signaling, via interaction with critical oncogenic coregulator proteins. To address these mechanisms of resistance, we have developed a novel ER coregulator binding modulator, ERX-11. ERX-11 interacts directly with ER and blocks the interaction between a subset of coregulators with both native and mutant forms of ER. ERX-11 effectively blocks ER-mediated oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant human breast cancer cells. ERX-11 is orally bioavailable, with no overt signs of toxicity and potent activity in both murine xenograft and patient-derived breast tumor explant models. This first-in-class agent, with its novel mechanism of action of disrupting critical protein-protein interactions, overcomes the limitations of current therapies and may be clinically translatable for patients with therapy-sensitive and therapy-resistant breast cancers.

DOI:http://dx.doi.org/10.7554/eLife.26857.001

Around 70% of breast cancers in women need one or both of the female hormones (estrogen and progesterone) to grow. To treat these 'hormone-dependent' cancers, patients receive drugs that either block the production of estrogen or directly target a receptor protein that senses estrogen in the cancer cells. Unfortunately, many breast cancers develop resistance to these drugs. This resistance is often caused by genetic mutations that alter the estrogen receptor; for example, the receptor may develop the ability to interact with other proteins in the cell known as coregulators to promote tumor growth.

Developing new drugs that prevent estrogen receptors from interacting with coregulators may provide more options for treating hormone-dependent breast cancers. Here, Raj et al. developed a new small molecule named ERX-11 that is able to inhibit the growth of human breast cancer cells that are sensitive to existing drugs as well as cells that have become drug-resistant.

For the experiments, hormone-dependent breast cancer cells from humans were transplanted into mice. This procedure usually causes the mice to develop tumors, but giving the mice ERX-11 by mouth stopped estrogen receptors from interacting with coregulators and blocked the growth of tumors. Furthermore, ERX-11 does not appear to have any toxic effects on the mice, indicating that it may also be safe for humans.

The findings of Raj et al. suggest that ERX-11 is a promising new drug candidate for treating some breast cancers. The next steps are to examine the effects of ERX-11 on mice and other animals in more detail before deciding whether this molecule is suitable for clinical trials. In the longer term, molecules similar to ERX-11 could also be developed into drugs to treat other types of cancer that are also caused by abnormal interactions of coregulator proteins.

DOI:http://dx.doi.org/10.7554/eLife.26857.002

Abstract 4764: Activation of estrogen receptor beta signaling reduces stemness and promotes differentiation of glioma stem cells

Glioblastoma (GBM) are the most common and deadliest tumors of the central nervous system. GBM have poor prognosis due to tumor recurrence and resistance to current therapies. Glioma Stem Cells (GSCs) are implicated in the tumor initiation and therapy resistance of GBM. Agents that can specifically reduce stemness of GSCs are urgently needed for the effective treatment of GBM. Estrogen play a crucial role during brain development, differentiation and in neuroprotection. However, its role in promoting differentiation of GSCs remain unknown. Estrogen effects are mediated by two estrogen receptors (ESR1 and ESR2) and ESR2 functions as a tissue-specific tumor suppressor. Our recent studies discovered that GSCs preferably express ESR2 with low or undetectable levels of ESR1. The objective of this study is to test whether ESR2 agonists modulate stemness of GSCs and to determine their mechanism(s) of action. We have tested the hypothesis using GSCs isolated from established and patient derived GBM cells using stem cell markers CD133 and CD15. Knockout of ESR2 using CRISPR/Cas9 system increased the CD133 positive GSCs and overexpression of ESR2 reduces the CD133-positive population in GBM cells. Treatment of GSCs with ESR2 agonists (Liquiritigenin and LY500307) significantly inhibited the neurosphere formation, self-renewal ability and proliferation. Further ESR2 agonist treatment resulted in the loss of stemness and induction of differentiation and apoptosis of GSCs. Western blot analysis and RT-qPCR analysis revealed reduced expression of stemness markers such as Nestin and Sox-2 and increased expression of differentiation markers GFAP and tuj-1 in GSCs. RNA sequencing analysis of ESR2 agonist treated and untreated GSCs revealed modulation of pathways related to apoptosis, cell cycle, stemness and differentiation. Further, ESR2 agonists treatment significantly reduced the GSCs mediated tumor growth in orthotopic models and improved the mice overall survival. Immunohistochemical studies demonstrated that ESR2 agonists reduces the expression of proliferation of marker Ki67 and induced the apoptosis in tumors. Together, our results established ESR2 agonists liquiritigenin and LY500307 as novel therapeutic agents for elimination of GSCs. Since ESR2 agonists has good blood-brain barrier permeability and less neuronal toxicity, they can be readily transferred to clinical use with current radiation and chemotherapies, thereby providing an additional tool for enhancing survival in GBM patients.

Citation Format: Gangadhara Reddy Sareddy, Jinyou Liu, Suryavathi Viswanadhapalli, Rajeshwar R. Tekmal, Andrew Brenner, Ratna K. Vadlamudi. Activation of estrogen receptor beta signaling reduces stemness and promotes differentiation of glioma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4764. doi:10.1158/1538-7445.AM2017-4764

Abstract 5531: Significance and functions of estrogen receptor beta (ESR2) isoforms in glioblastoma

Background: Glioblastoma (GBM) are the deadliest form of primary brain neoplasms. Several lines of evidence suggest tumor suppressive role of female sex hormones on brain tumors. However, mechanisms by which estrogens mediate protection against the GBM remains unknown. GBM preferentially express estrogen receptor beta (ESR2). Emerging evidence suggests that ESR2 is expressed as multiple isoforms, (ESR2-1 to 5, with variation at the C-terminal domain); however, much of the published information is focused primarily on ESR2-1. Little is known about the expression and functions of other ESR2 isoforms in GBM. The objective of this study is to examine the expression and determine the functions of ESR2 isoforms in GBM cells.

Methods: Expression of ESR2 isoforms was profiled using 10 different patients derived and 5 established GBM cells. To study the functions of individual ESR2 isoforms in GBM cells, we have generated ESR2 knockout (ESR2-KO) cells using CRISPR/Cas9 system and then established GBM model cells expressing individual ESR2-1, 2, and 5 using lentiviral transduction in the ESR2-KO background GBM cells. IPMS analysis was used to identify binding proteins of each ESR2 isoforms. Effect of each isoform on the growth, apoptosis, cell cycle progression, migration and invasion was analyzed using established methods. Mechanistic studies were conducted using reporter gene assays, RT-qPCR and signaling analysis.

Results: RT-qPCR results demonstrated that ESR2-5 is highly expressed in majority of primary and established GBM cells compared to ESR2-1 and ESR2-2, with ESR2-4 is the least expressed. Expression of ESR2-1 but not ESR2-5 significantly reduced proliferation of GBM cells. Further, ESR2-KO cells exhibited high migratory and invasive potential compared to parental GBM cells and re-expression of ESR2-1, but not ESR2-5 resulted in reduction in migratory and invasive potential of GBM cells. ESR2-KO GBM cells exhibited decreased levels of cell cycle arrest and apoptosis proteins p27, p21 and PUMA compared to parental GBM cells and re-expression of ESR2-1 or ESR2-5 in ESR2-KO cells rescued the phenotype. IPMS studies identified several common and unique proteins that bind to each of the isoforms. Both ESR2-1 and ESR2-5 interacted with mTOR, while ESR2-5 uniquely interacted with several proteins related to DNA repair, immunomodulatory and apoptosis pathways. Overexpression of ESR2-1 reduced the activation of mTOR signaling molecules including p-mTOR, p-S6K and p-S6 in GBM cells compared to ESR2-KO cells, while ESR2-5 enhanced mTOR downstream signaling.

Conclusion: Using ESR2KO cells, we have provided genetic evidence for the role of ESR2-1 in GBM tumor suppression. Our results also discovered that ESR2-5 is highly expressed in GBMs. Unlike ESR2-1, ESR2-5 has lesser tumor suppression ability and its interactions with mTOR, DNA repair, and apoptotic pathways may have important implications in GBM progression.

Citation Format: Jinyou Liu, Gangadhara Reddy Sareddy, Mei Zhou, Suryavathi Viswanadhapalli, Andrew Brenner, Rajeshwar R. Tekmal, Ratna K. Vadlamudi. Significance and functions of estrogen receptor beta (ESR2) isoforms in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5531. doi:10.1158/1538-7445.AM2017-5531

Abstract 4148: Novel ERX-11 and CDK4/6 inhibitor combination therapy for treating therapy resistant breast cancer

BACKGROUND: The majority of the breast cancer is estrogen receptor alpha (ESR1) positive. While tamoxifen and letrozole therapies are effective, therapy resistance is common. Importantly, both therapy-sensitive and therapy-resistant tumors retain ESR1 signaling, via interaction with critical oncogenic coregulator proteins. Further, resistant tumors commonly acquire cyclin D1:CDK4/6 signaling via multiple mechanisms, cyclin D1 can independently activate ESR1 and thus contribute to estrogen independence of ESR+ tumor. Currently, CDK4/6 inhibitors in clinical trials for treating breast cancer, however, considering complex signaling interplay of estrogen and CDK axis, combination therapy of CDK inhibitor with other potent ESR1 targeted agents may have better utility and may prevent development of resistance to the CDK4/6 inhibitors. We recently developed a small organic molecule, ESR1 coregulator binding inhibitor ERX-11 (EtiraRx-11). The objective of this study is to test the utility of novel combination therapy of ERX-11 with CDK4/6 inhibitor palbociclib in treating therapy resistant cancer.

METHODS: We have utilized multiple therapy sensitive and therapy-resistant models with various genetic back grounds. We tested efficacy using both acquired resistance and engineered models that express ESR1 mutations or oncogenes. Efficacy of combination therapy was tested using established in vitro assays including, MTT, colony formation, apoptosis, and cell cycle progression. Mechanistic studies were conducted using reporter gene assays, gene expression and signaling alterations. Xenograft studies were used to determine the in vivo efficacy of the combination therapy.

RESULTS: ERX-11 effectively blocked ESR1-mediated oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant breast cancer cells. Mechansistic studies showed that ERX-11 blocks the interaction between a subset of coregulators with both native and mutant forms of ESR1. ERX-11 showed potent activity in both preclinical xenograft models and patient-derived breast tumor explant models. Co-treatment of ERX-11 with palbociclib synergistically reduced cell viability and induced apoptosis of therapy sensitive and resistant breast cancer model cells. Importantly, combination therapy of ERX-11 and the palbociclib synergistically reduced the growth and induced apoptosis of tamoxifen and letrozole resistant xenograft tumors compared to either drug alone. Mechanistic studies showed combination therapy significantly altered E2F1 and ESR1 signaling pathways and promoted apoptosis.

CONCLUSIONS: Collectively our studies have discovered a novel combinational treatment with ERX-11 and palbociclib for patients with therapy-sensitive and therapy-resistant breast cancers.

Citation Format: Suryavathi Viswanadhapalli, Gangadhara Reddy Sareddy, Shi-Hong Ma, Tae-Kyung Lee, Rajeshwar Rao Tekmal, Jung-Mo Ahn, Ganesh Raj, Ratna K. Vadlamudi. Novel ERX-11 and CDK4/6 inhibitor combination therapy for treating therapy resistant breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4148. doi:10.1158/1538-7445.AM2017-4148

Abstract P6-11-15: Pre-clinical investigation of estrogen receptor β agonists for the treatment of breast cancer

Breast Cancer is the primary cause of cancer-associated mortality worldwide, and in United States alone, more than 250,000 women are diagnosed every year. Current breast cancer treatment strategies focus on Estrogen Receptor α signaling, given that the majority of cases diagnosed are ERα positive. These treatment strategies include endocrine therapies; such as anti-estrogens or aromatase inhibitors. Although, endocrine therapy has been demonstrated to be successful and effective, therapy resistance commonly arises and results in relapse. While current endocrine therapies focus on ERα signaling, emerging studies highlight the importance of Estrogen Receptor β.Unlike ERα, ERβ has been shown to have tumor-suppressive function in various cancers, including breast cancer. Recent studies have identified, synthesized, and tested the clinical safety of ERβ-selective agonists. The objective of this study was to investigate the utility of using ERβ agonists in the treatment of breast cancer.

To investigate the utility of ERβ agonists in the treatment of breast cancer, we used in-vitro and in-vivo pre-clinical models systems. Our results demonstrated that treatment with ERβ agonists, S-Equol and LY500307, was able to inhibit the short-term and long-term growth of both endocrine therapy sensitive and resistant breast cancer cells. Progression through the cell cycle, cell migration and cell invasion was also abrogated upon treatment. In-vivo, our syngeneic tumor mouse model demonstrates a decline in tumor growth rate after treating with a combination of letrozole and ERβ agonist. Gene expression array analysis reveal that treatment with ERβ agonist elicits changes in key signaling molecules involved in cell death and cell cycle pathways. In Letrozole resistant cells, Letrozole treatment had not effect on gene expression, while LY500307 treatment resulted in the modulation of 780 genes. Interestingly, combining Letrozole with LY500307 resulted in the modulation of 966 genes, of which 417 were unique to the combination treatment. Our studies suggest that activation of ERβ signaling is a valuable strategy in the treatment of breast cancer, even in cases which have developed resistance to current endocrine therapies.

Citation Format: Samayoa C, Krishnegowda NK, Vadlamudi RK, Tekmal RR. Pre-clinical investigation of estrogen receptor β agonists for the treatment of breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-11-15.

Abstract P4-15-02: Investigating the use estrogen receptor β agonists in the prevention of breast cancer using a transgenic mouse model

Breast cancer is the most common cancer among women worldwide. In the United States, 1 in 8 women will develop breast cancer during her lifetime, and in 2016 over 240,000 new cases will be diagnosed. Incidence rates differ by geographic location, with women living in Asia having the lowest rates. However, after migrating to the U.S and adopting a western diet their rates increase. This highlights the importance of lifestyle, including diet, in modulating breast cancer risk. Soy has been previously implicated as the dietary component contributing to the reduced breast cancer rates in Asian women. Compounds that can selectively activate Estrogen Receptor β have been identified in plants, including soy. Given the tumor-suppressive properties of ERβ, it may be possible to use these agonists in the chemoprevention of breast cancer.

The objective of this study was to investigate the utility of using ERβ agonists in the prevention of breast cancer using a transgenic mouse model. MMTV-HER2/neu mice develop premalignant lesions at 4-5 months, and tumors starting at month 7 due to overexpression of the Her2/neu proto-oncogene. MMTV-HER2/neu mice were treated with 2 different ERβ agonists, S-equol or LY500307, for 3 months and evaluated for branching, hyperplasia and differential gene expression. When compared to controls, ERβ agonist-treated mice exhibited a significant decrease in branching and ductal hyperplasia, with no change in body weight. Differential gene expression analysis revealed 218 modified genes in response to S-equol treatment, and 258 genes modified by LY500307 treatment, with an overlap of 36 genes. Pathway analysis identified an enrichment for chemokines signaling pathways, particularly TNF, in the reversal of hyperbranching resulting from treatment with ERβ agonists.

Although previous studies have demonstrated crosstalk between ER's non-genomic signaling and growth factor signal transductions pathway, this is the first study to demonstrate the impact of ERβ activation on HER2/neu mediated pre-neoplastic changes. Our study suggest that ER β agonist treatment may be a valuable therapeutic option for the chemoprevention of breast cancer in women at increased risk.

Citation Format: Samayoa C, Krishnegowda NK, Vadlamudi RK, Tekmal RR. Investigating the use estrogen receptor β agonists in the prevention of breast cancer using a transgenic mouse model [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-15-02.

NADPH oxidase in brain injury and neurodegenerative disorders

Oxidative stress is a common denominator in the pathology of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, as well as in ischemic and traumatic brain injury. The brain is highly vulnerable to oxidative damage due to its high metabolic demand. However, therapies attempting to scavenge free radicals have shown little success. By shifting the focus to inhibit the generation of damaging free radicals, recent studies have identified NADPH oxidase as a major contributor to disease pathology. NADPH oxidase has the primary function to generate free radicals. In particular, there is growing evidence that the isoforms NOX1, NOX2, and NOX4 can be upregulated by a variety of neurodegenerative factors. The majority of recent studies have shown that genetic and pharmacological inhibition of NADPH oxidase enzymes are neuroprotective and able to reduce detrimental aspects of pathology following ischemic and traumatic brain injury, as well as in chronic neurodegenerative disorders. This review aims to summarize evidence supporting the role of NADPH oxidase in the pathology of these neurological disorders, explores pharmacological strategies of targeting this major oxidative stress pathway, and outlines obstacles that need to be overcome for successful translation of these therapies to the clinic.

HPIP promotes epithelial-mesenchymal transition and cisplatin resistance in ovarian cancer cells through PI3K/AKT pathway activation

PURPOSE

Hematopoietic PBX interacting protein (HPIP), a scaffold protein, is known to regulate the proliferation, migration and invasion in different cancer cell types. The aim of this study was to assess the role of HPIP in ovarian cancer cell migration, invasion and epithelial-mesenchymal transition (EMT), and to unravel the mechanism by which it regulates these processes.

METHODS

HPIP expression was assessed by immunohistochemistry of tissue microarrays containing primary ovarian tumor samples of different grades. OAW42, an ovarian carcinoma-derived cell line exhibiting a high HPIP expression, was used to study the role of HPIP in cell migration, invasion and EMT. HPIP knockdown in these cells was achieved using a small hairpin RNA (shRNA) approach. Cell migration and invasion were assessed using scratch wound and transwell invasion assays, respectively. The extent of EMT was assessed by determining the expression levels of Snail, Vimentin and E-cadherin using Western blotting. The effect of HPIP expression on AKT and MAPK activation was also investigated by Western blotting. Cell viabilities in response to cisplatin treatment were assessed using a MTT assay, whereas apoptosis was assessed by determining caspase-3 and PARP cleavage in ovarian carcinoma-derived SKOV3 cells.

RESULTS

We found that HPIP is highly expressed in high-grade primary ovarian tumors. In addition, we found that HPIP promotes the migration, invasion and EMT in OAW42 cells and induces EMT in these cells via activation of the PI3K/AKT pathway. The latter was found to lead to stabilization of the Snail protein and to repression of E-cadherin expression through inactivation of GSK-3β. We also found that HPIP expression confers cisplatin resistance to SKOV3 cells after prolonged exposure and that its subsequent knockdown decreases the viability of these cells and increases caspase-3 activation and PARP proteolysis in these cells following cisplatin treatment.

CONCLUSIONS

From these results we conclude that HPIP expression is associated with high-grade ovarian tumors and may promote their migration, invasion and EMT, a process that is associated with metastasis. In addition, we conclude that HPIP may serve as a potential therapeutic target for cisplatin resistant ovarian tumors.

Novel KDM1A inhibitors induce differentiation and apoptosis of glioma stem cells via unfolded protein response pathway

Glioma stem cells (GSCs) have a central role in glioblastoma (GBM) development and chemo/radiation resistance, and their elimination is critical for the development of efficient therapeutic strategies. Recently, we showed that lysine demethylase KDM1A is overexpressed in GBM. In the present study, we determined whether KDM1A modulates GSCs stemness and differentiation and tested the utility of two novel KDM1A-specific inhibitors (NCL-1 and NCD-38) to promote differentiation and apoptosis of GSCs. The efficacy of KDM1A targeting drugs was tested on purified GSCs isolated from established and patient-derived GBMs using both in vitro assays and in vivo orthotopic preclinical models. Our results suggested that KDM1A is highly expressed in GSCs and knockdown of KDM1A using shRNA-reduced GSCs stemness and induced the differentiation. Pharmacological inhibition of KDM1A using NCL-1 and NCD-38 significantly reduced the cell viability, neurosphere formation and induced apoptosis of GSCs with little effect on differentiated cells. In preclinical studies using orthotopic models, NCL-1 and NCD-38 significantly reduced GSCs-driven tumor progression and improved mice survival. RNA-sequencing analysis showed that KDM1A inhibitors modulate several pathways related to stemness, differentiation and apoptosis. Mechanistic studies showed that KDM1A inhibitors induce activation of the unfolded protein response (UPR) pathway. These results strongly suggest that selective targeting of KDM1A using NCL-1 and NCD-38 is a promising therapeutic strategy for elimination of GSCs.

Abstract 1163: Estrogen receptor beta (ESR2)-mediated tumor suppression of glioblastoma involves modulation of cell cycle and DNA damage response pathways

Purpose: Glioblastomas (GBM) are deadly brain tumors, have greater incidence in males than females. Epidemiological evidence supports a role of estrogen in tumor suppression. Estrogen signaling is mediated by estrogen receptor alpha (ESR1) and beta (ESR2). Our earlier studies showed that GBM preferentially express ESR2. However, mechanisms by which E2-ESR2 signaling promote suppression of GBM is poorly understood. The objective of this study is to determine the mechanisms by which ESR2 promote tumor suppression.

Experimental design: Established and patient derived primary GBM cells overexpressing or under expressing ESR2 were generated using lentiviral vectors. Three different ESR2 agonists (LY500307, Liquiritigenin, and Erb041) were used in the study and transcription changes elicited by ESR2 were profiled using RNA-seq. Cell cycle was analyzed using FACS analysis. In vivo efficacy of ESR2 agonists was tested in an orthotopic model using syngeneic murine GBM model (GL26), tumor growth was measured using bioluminescence, and survival was recorded. The synergy experiments using 119 FDA approved drugs was done using cell viability assay.

Results: ESR2 agonist treatment or ESR2 overexpression significantly reduced the viability and colony formation and induced apoptosis of various GBM cell lines with minimal effect on normal astrocytes. Further, ESR2 agonist (LY500307 5mg/kg/day) treatment significantly improved survival of GL26 tumor-bearing mice. RNA-seq studies using ESR2 overexpression or ligands treatment revealed downregulation of a number of genes involved in DNA repair, DNA damage response and cell cycle. The canonical pathways modulated by ESR2 included cell cycle, DNA damage, p53 signaling, and checkpoint regulation. In addition, pathways related to molecular mechanism of cancer, ILK signaling, Wnt signaling and glioma invasion were also altered. ESR2 agonist treatment significantly increased the percentage of cells in G2/M phase in U87, U251 and LN229 GBM cells when compared to vehicle further supporting the RNA-seq pathway analysis of cell cycle and G2/M DNA damage checkpoint regulation. Using combinational screening of 119 FDA-approved drugs combined with a low dose of ESR2 agonists (below the IC50 dose), we discovered synergism of ESR2 agonist treatment with several DNA-damaging agents. We independently validated synergy using additional ESR2 agonists with currently used chemotherapy drugs in GBM including temozolomide.

Conclusions: Our results demonstrate that ESR2 as tumor suppressor for GBM and ESR2 agonists have potential as a therapeutic agent for GBM. ERβ agonists’ ability to suppress pathways involved in DNA repair can be exploited to promote apoptosis of GBM cells.

Citation Format: Ratna K. Vadlamudi, Gangadhara Reddy Sareddy, Xiaonan Li, Jinyou Liu, Lauren Garcia, Andrew Brenner. Estrogen receptor beta (ESR2)-mediated tumor suppression of glioblastoma involves modulation of cell cycle and DNA damage response pathways. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1163.

Abstract 1123: The role of proto-oncogene PELP1 in breast cancer stem cell maintenance and therapy resistance

BACKGROUND: Cancer stem cells (CSCs) are known to evade hormonal therapy and regrowth of tumor cells from cancer stem cells is a major clinical problem. Histone methyltransferase G9a/EHMT2 plays a critical role in stem cell maintenance. Proline, glutamic acid, and leucine rich protein (PELP1) is a proto-oncogene, functions as a coregulator of nuclear receptors, and is prognostically linked to shorter breast cancer survival. Recent studies from our lab discovered that PELP1 interacts with G9a/EHMT2. The objective of this study is to develop small molecular inhibitors that block PELP1 interactions with G9a/EHMT2.

METHODS: We isolated CD44high/CD24low CSCs from three breast cancer cell lines (ZR75, MCF7, T47D) using FACS. Cells were analyzed for spheroid formation, morphological changes, immunofluorescence for differentiation markers, protein (Western) and RNA (RT-qPCR) analysis. Expression of differentiation markers K19 and K14 and stem cell markers CD133, CD44, Id1, Nestin, Musashi-1, SOX2, Notch2, and OCT1 was determined. Effect of inhibitors on the cell viability of breast cancer cells was determined using cell titer glow assays. Xenograft studies were used to determine the in vivo efficacy of the inhibitors.

RESULTS: Using yeast based genetic screen, we identified a small peptide inhibitor (PIP1) that interferes PELP1 interaction with G9/EHMT2. Utilizing Hit-Ligand interaction site with the PELP1 hot spot residues based on 3D alignment and shape, we have identified 61 potential hits from Ligand-Based screening using a 10,000 Diverse Set. Screening of these 61 potential hits using MTT based cell viability assays identified three small organic molecule inhibitors (peptidomimetics) as leads. All three peptidomimetics showed activity similar to PELP1 peptide inhibitor 1 (PIP1) in MTT assays and in biochemical assays disrupted PELP1 interaction with G9a/EHMT2. Peptidomimetic treatment inhibited the proliferation of tamoxifen and letrozole resistant cells. In mechanistic studies, we found that knockdown of PELP1 inhibited stem cell maintenance. In FACS analysis of ZR75, ZR75-PELP1 and ZR75-PELP1KD cells, the percentage of CD44high/CD24low cells correlated with PELP1 status. In mammosphere assays, PELP1 targeting peptidomimetics significantly inhibited the formation of mammospheres. Further, in self-renewal assays, peptidomimetic-treated cells had decreased self-renewal capacity. In xenograft assays using ZR-75 cells, PELP1 inhibitor significantly reduced the tumor growth.

CONCLUSIONS: Collectively, our studies have discovered an essential role for PELP1 in breast cancer stem cell maintenance and identified the PELP1-G9a/EHMT2 axis as a potential therapeutic target for reducing stemness. Further, the novel small molecule inhibitors of PELP1 could be used for therapeutic targeting of breast cancer stem cells and therapy resistance.

Citation Format: Suryavathi Viswanadhapalli, Monica Mann, Gangadhara Reddy Sareddy, Xaionan Lix, Hariprasad Vankayalapati, Ratna K. Vadlamudi. The role of proto-oncogene PELP1 in breast cancer stem cell maintenance and therapy resistance. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1123.

Abstract 860: ESR1 coregulator binding inhibitor (ECBI): a novel agent for treating hormone therapy-resistant breast cancer

Background: Estrogen contribute to the progression of breast cancer via estrogen receptor 1 (ESR1) and current therapies involve either antiestrogens (AE) or aromatase inhibitors (AI). However, most patients develop resistance to these drugs. In resistant tumors, activation of ESR1 in the absence of ligand or mutations in ESR1 allow interaction between the ESR1 and coregulators leading to sustained ESR1 signaling and proliferation. Here we, developed a novel ESR1 coregulator binding inhibitor (ECBI) that targets persistent ESR1 signaling that commonly occur in therapy resistant breast tumors.

Methods: Using rational design, we synthesized and evaluated a small organic molecule (ECBI) that mimics the ESR1 coregulator nuclear receptor box motif. Mechanistic studies were conducted using reporter gene assays, RT-qPCR., ChIP, and RNA-Seq analysis. Xenografts and patient derived tumors were used for preclinical evaluation and toxicity.

Results: In estrogen induced proliferation assays using several ESR1+ve model cells, ECBI significantly inhibited growth and promoted apoptosis. Importantly, ECBI showed little or no activity on ESR1 negative cells. Further, ECBI also reduced the proliferation of several ESR1 positive hormonal therapy resistant cells. Mechanistic studies showed that ECBI interacts with ESR1, efficiently blocks ESR1 interactions with coregulators and reduces the ESR1 driven ERE reporter gene activity. Further, ECBI directly interacted with mutant-ESR1 with high affinity and significantly inhibited mutant-ESR1 driven oncogenic activity. RNA sequencing analysis revealed that ECBI blocks multiple ESR1 driven pathways, likely representing the ability of a single ECBI compound to block multiple ESR1-coregulator interactions. Treatment of ESR1-positive and therapy resistant as well as syngeneic xenograft tumors with ECBI (10 mg/kg/day/oral) significantly reduced the tumor volume compared to control. Using human primary breast tissue ex vivo cultures, we have provided evidence that ECBI has potential to dramatically reduce proliferation of human breast tumors.

Conclusions: The ECBI is a novel agent that targets ESR1 with a unique mechanism of action. ECBI has distinct pharmacologic advantages of oral bioavailability, in vivo stability, and is associated with minimal systemic side effects. Remarkably, ECBI block both native and mutant forms of ESR1 and have activity against therapy resistant breast cancer cell proliferation both in vitro and in vivo and against primary human tumor tissues ex vivo. This first-in-class agent with its novel mechanism of action overcomes the limitations of current therapies.

Citation Format: Ratna K. Vadlamudi, Gangadhara Reddy Sareddy, Suryavathi Viswanadhapalli, Tae-Kyung Lee, Shi-Hong Ma, Wan Ru Lee, Monica Mann, Samaya Rajeshwari Krishnan, Vijay Gonugunta, Yang Liu, Douglas W. Strand, Rajeshwar Rao Tekmal, Jung-Mo Ahn, Ganesh V. Raj. ESR1 coregulator binding inhibitor (ECBI): a novel agent for treating hormone therapy-resistant breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 860.

Abstract 1820: Investigating the role of estrogen receptor β agonists in the prevention and treatment of breast cancer

Breast Cancer is the primary cause of cancer-associated mortality worldwide. In the United States alone, more than 250,000 women are diagnosed every year. Asian women have the lowest incidence rates. However, their rates increase to those of the US within one generation after migration. Suggesting that diet and lifestyle are major contributing factors in breast cancer risk. Since Asian women consume high amount of soy when compared to other populations, perhaps compounds found in soy may have a protective effect that is lost once they adopt a western diet.

Recent studies have identified plant-derived compounds from soy and licorice that activate Estrogen Receptor β. Unlike previous ERβ agonists, these novel compounds are selective for ERβ and have been tested for safety in clinical trials.

Current breast cancer treatment strategies focus on Estrogen Receptor α signaling, given that the majority of cases diagnosed are ERα positive. These treatment strategies include endocrine therapies; such as anti-estrogens or aromatase inhibitors. However, in the last decade, the importance of ERβ has emerged. Unlike ERα, ERβ has been shown to have tumor-suppressive function in various cancers, including breast cancer.

The objective of this study was to investigate the utility of using ERβ agonists in the prevention and treatment on breast cancer. To investigate the significance of ERβ activation in the prevention of breast cancer, we used an immunocompetent transgenic mouse model of breast cancer. Specifically, HER2/neu overexpressing mice develop premalignant lesions at 4-5 months and tumors starting at month 7. HER2/neu mice were treated with ERβ agonists for 3 months and subsequently mammary glands were analyzed using whole mount and IHC. When compared to controls, ERβ agonist treated mice showed a decrease in branching and ductal hyperplasia, with no change in body weight. These results suggest that ER β agonist treatment is chemopreventive and provided protection against premalignant lesion in the mammary gland.

To investigate the utility of ERβ agonists in the treatment of breast cancer, we used in-vitro and in-vivo models systems. Our results demonstrated that treatment with the agonists was able to inhibit the short-term and long-term growth of the breast cancer cell lines; MCF7aro and LTLT which represent post-menopausal breast cancer and letrozole resistant cells, respectively. In addition to growth inhibition, treatment with ERβ agonists also decreased cell migration and invasion. In addition to activating ERβ, we also found that the agonists are also able to increase the expression of ERβ without increasing ERα levels. Our studies also demonstrated that treatment with ERβ agonists modulated key signaling molecules involved in cell death and cell cycle. Our studies suggest that activation of ERβ signaling is a valuable strategy in the treatment and chemoprevention of breast cancer.

Citation Format: Cathy Samayoa, Naveen K. Krishnegowda, Ratna K. Vadlamudi, Rajeshwar R. Tekmal. Investigating the role of estrogen receptor β agonists in the prevention and treatment of breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1820.

Selective Estrogen Receptor β Agonist LY500307 as a Novel Therapeutic Agent for Glioblastoma

Glioblastomas (GBM), deadly brain tumors, have greater incidence in males than females. Epidemiological evidence supports a tumor suppressive role of estrogen; however, estrogen as a potential therapy for GBM is limited due to safety concerns. Since GBM express ERβ, a second receptor for estrogen, targeting ERβ with a selective agonist may be a potential novel GBM therapy. In the present study, we examined the therapeutic effect of the selective synthetic ERβ agonist LY500307 using in vitro and in vivo GBM models. Treatment with LY500307 significantly reduced the proliferation of GBM cells with no activity on normal astrocytes in vitro. ERβ agonists promoted apoptosis of GBM cells, and mechanistic studies using RNA sequencing revealed that LY500307 modulated several pathways related to apoptosis, cell cycle, and DNA damage response. Further, LY500307 sensitized GBM cells to several FDA-approved chemotherapeutic drugs including cisplatin, lomustine and temozolomide. LY500307 treatment significantly reduced the in vivo tumor growth and promoted apoptosis of GBM tumors in an orthotopic model and improved the overall survival of tumor-bearing mice in the GL26 syngeneic glioma model. Our results demonstrate that LY500307 has potential as a therapeutic agent for GBM.

Abstract B08: ESR1 coregulator binding site inhibitors (ECBIs) as novel therapeutics to target hormone therapy-resistant breast cancer

Estrogens contribute to the progression of breast cancer via estrogen receptor 1 (ESR1) and current therapies involve either antiestrogens (AE) or aromatase inhibitors (AI). However, most patients develop resistance to these drugs. Critically, therapy-resistant tumors retain ESR1-signaling. Mechanisms of therapy resistance involve the activation of ESR1 in the absence of ligand or mutations in ESR1 that allow interaction between the ESR1 and coregulators leading to sustained ESR1 signaling and proliferation. For patients with therapy-resistant breast cancers, there is a critical unmet need for novel agents to disrupt ESR1 signaling by blocking ESR1 interactions with its coregulators.

Methods: Using rational design, we synthesized and evaluated a small organic molecule (ESR1 coregulator binding inhibitor, ECBI) that mimics the ESR1 coregulator nuclear receptor box motif. Using in vitro cell proliferation and apoptosis assays, we tested the effect of ECBI on several breast cancer cells and therapy-resistant model cells. Mechanistic studies were conducted using established biochemical assays, reporter gene assays, RTqPCR and RNASeq analysis. Gene differential expression lists were analyzed using Ingenuity Pathway Analysis (IPA). ESR1+ve (MCF7 and ZR75) xenografts were used for preclinical evaluation and toxicity. The efficacy of ECBI was tested using an ex vivo cultures of freshly extirpated prrimary human breast tissues.

Results: In estrogen induced proliferation assays using several ESR1+ve model cells, we found that ECBI inhibit growth (IC50=300-500 nM). Importantly, ECBI showed little or no activity on ESR1 negative cells. Further, ECBI also reduced the proliferation of several ESR1 positive hormonal therapy resistant cells, directly interacted with MT-ESR1 with high affinity and significantly inhibited MT-ESR1 driven oncogenic activity. Mechanistic studies showed that ECBI interacts with ESR1, efficiently blocks ESR1 interactions with coregulators and reduces the ESR1 reporter gene activity. RNA sequencing analysis revealed that ECBI blocks multiple ESR1 driven pathways, likely representing the ability of a single ECBI compound to block multiple ESR1-coregulator interactions. Treatment of ESR1-positive xenograft tumors with ECBI (10 mg/Kg/oral) reduced tumor volume by 67% compared to control. Further, ECBI also significantly reduced the proliferation of coregulator-overexpressed breast cancer cells in xenograft model. Using human primary breast tissue ex vivo cultures, we have provided evidence that ECBI has potential to dramatically reduce proliferation of human breast tumor cells.

Conclusions: The ECBI is a novel agent that targets ESR1 with a unique mechanism of action. ECBI has distinct pharmacologic advantages of oral bioavailability, in vivo stability, and is associated with minimal systemic side effects. Remarkably, ECBIs block both native and mutant forms of ESR1 and have activity against therapy resistant breast cancer cell proliferation both in vitro and in vivo and against primary human tissues ex vivo. Thus development of ECBI represents a quantum leap in therapies to target ESR1

Citation Format: Ratna K. Vadlamudi, Gangadhara Reddy Sareddy, Suryavathi Viswanadhapalli, Tae-Kyung Lee, Shi-Hong Ma, Wan Ru Lee, Monica Mann, Samaya Rajeshwari Krishnan, Vijay Gonugunta, Douglas W. Strand, Rajeshwar Rao Tekmal, JungMo Ahn, Ganesh V. Raj. ESR1 coregulator binding site inhibitors (ECBIs) as novel therapeutics to target hormone therapy-resistant breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B08.

Inhibition of FoxM1-Mediated DNA Repair by Imipramine Blue Suppresses Breast Cancer Growth and Metastasis

PURPOSE

The approaches aimed at inhibiting the ability of cancer cells to repair DNA strand breaks have emerged as promising targets for treating cancers. Here, we assessed the potential of imipramine blue (IB), a novel analogue of antidepressant imipramine, to suppress breast cancer growth and metastasis by inhibiting the ability of breast cancer cells to repair DNA strand breaks by homologous recombination (HR).

EXPERIMENTAL DESIGN

The effect of IB on breast cancer growth and metastasis was assessed in vitro as well as in preclinical mouse models. Besides, the therapeutic efficacy and safety of IB was determined in ex vivo explants from breast cancer patients. The mechanism of action of IB was evaluated by performing gene-expression, drug-protein interaction, cell-cycle, and DNA repair studies.

RESULTS

We show that the systemic delivery of IB using nanoparticle-based delivery approach suppressed breast cancer growth and metastasis without inducing toxicity in preclinical mouse models. Using ex vivo explants from breast cancer patients, we demonstrated that IB inhibited breast cancer growth without affecting normal mammary epithelial cells. Furthermore, our mechanistic studies revealed that IB may interact and inhibit the activity of proto-oncogene FoxM1 and associated signaling that play critical roles in HR-mediated DNA repair.

CONCLUSIONS

These findings highlight the potential of IB to be applied as a safe regimen for treating breast cancer patients. Given that FoxM1 is an established therapeutic target for several cancers, the identification of a compound that inhibits FoxM1- and FoxM1-mediated DNA repair has immense translational potential for treating many aggressive cancers. Clin Cancer Res; 22(14); 3524-36. ©2016 AACR.

Abstract S3-04: ESR1 coregulator binding inhibitor (ECBI) as a novel therapeutic to target hormone therapy resistant metastatic breast cancer

BACKGROUND: Estrogen contribute to the progression of breast cancer via estrogen receptor 1 (ESR1) and current therapies involve either antiestrogens or aromatase inhibitors. However, most patients develop resistance to these drugs. Critically, therapy-resistant tumors retain ESR1-signaling. Mechanisms of therapy resistance involve the activation of ESR1 in the absence of ligand or mutations in ESR1 that allow interaction between the ESR1 and coregulators leading to sustained ESR1 signaling and proliferation. For patients with therapy-resistant breast cancers, there is a critical unmet need for novel agents to disrupt ESR1 signaling by blocking ESR1 interactions with its coregulators.

METHODS: Using rational design, we synthesized and evaluated a small organic molecule (ESR1 coregulator binding inhibitor, ECBI) that mimics the ESR1 coregulator nuclear receptor box motif. Using in vitro cell proliferation and apoptosis assays, we tested the effect of ECBI on several breast cancer and therapy-resistant model cells. Mechanistic studies were conducted using established biochemical assays, reporter gene assays, RT-qPCR and RNA-Seq analysis. Differentially expressed genes were analyzed using Ingenuity Pathway Analysis (IPA). ESR1 positive (MCF7 and ZR75) xenografts were used for preclinical evaluation and toxicity. The efficacy of ECBI was tested using ex vivo cultures of freshly extirpated primary human breast tissues.

RESULTS: In estrogen induced proliferation assays using several ESR1 positive model cells, ECBI significantly inhibited growth and promoted apoptosis. Importantly, ECBI showed little or no activity on ESR1 negative cells. Further, ECBI also reduced the proliferation of several ESR1 positive hormonal therapy resistant cells. Mechanistic studies showed that ECBI interacts with ESR1, efficiently blocks ESR1 interactions with coregulators and reduces the ESR1 driven ERE reporter gene activity. Further, ECBI directly interacted with mutant-ESR1 with high affinity and significantly inhibited mutant-ESR1 driven oncogenic activity. RNA sequencing analysis revealed that ECBI blocks multiple ESR1 driven pathways, likely representing the ability of a single ECBI compound to block multiple ESR1-coregulator interactions. Treatment of ESR1-positive xenograft tumors with ECBI (10 mg/kg/day/oral) significantly reduced the tumor volume compared to control. Further, ECBI also significantly reduced the tumor growth of coregulator-overexpressed breast cancer cells in xenograft model. Using human primary breast tissue ex vivo cultures, we have provided evidence that ECBI has potential to dramatically reduce proliferation of human breast tumors.

CONCLUSIONS: The ECBI is a novel agent that targets ESR1 with a unique mechanism of action. ECBI has distinct pharmacologic advantages of oral bioavailability, in vivo stability, and is associated with minimal systemic side effects. Remarkably, ECBI block both native and mutant forms of ESR1 and have activity against therapy resistant breast cancer cell proliferation both in vitro and in vivo and against primary human tumor tissues ex vivo. Thus development of ECBI represents a quantum leap in therapies to target ESR1.

Citation Format: Vadlamudi RK, Sareddy GR, Viswanadhapalli S, Lee T-K, Ma S-H, Lee WR, Mann M, Krishnan SR, Gonugunta V, Strand DW, Tekmal RR, Ahn J-M, Raj GV. ESR1 coregulator binding inhibitor (ECBI) as a novel therapeutic to target hormone therapy resistant metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S3-04.

Abstract P1-06-09: Proto-oncogene PELP1 signaling regulates breast cancer stem cells via G9a/EHMT2

BACKGROUND: Evolving evidence suggests that cancer stem cells (CSCs) evade hormonal therapy and therapy resistance occurs due to regrowth of tumor cells from cancer stem cells that escaped hormonal therapy or remained in the body after tumor resection. Recent studies suggest that estrogen stimulates breast cancer stem-cells and G9a/EHMT2 plays a critical role in stem cell maintenance. Proline, glutamic acid, and leucine rich protein (PELP1) is a proto-oncogene that functions as a critical coregulator of several nuclear receptors and other transcription factors. PELP1 is commonly overexpressed in hormone-related cancers, and is prognostically linked to shorter breast cancer survival. Recent studies from our lab discovered PELP1 interacts with G9a/EHMT2. However, it remains unknown whether PELP1-G9a signaling plays a role in breast cancer stem cell proliferation. The objective of this study is to develop small molecular inhibitors that block G9a/EHMT2 interactions and to test their utility.

METHODS: We isolated CD44high/CD24low CSCs from three breast cancer cell lines (ZR75, MCF7, T47D) using FACS. To test the effect of PELP1 inhibitors on CSCs, we cultured CSCs in SFM in the presence or absence of PELP1 inhibitors for a period of 7-10 days. Cells were analyzed for spheroid formation, morphological changes, immunofluorescence for differentiation markers, protein (Western) and RNA (RT-qPCR) analysis. Expression of differentiation markers K19 and K14 and stem cell markers CD133, CD44, Id1, Nestin, Musashi-1, SOX2, Notch2, and OCT1 was determined.

RESULTS: Using mapping studies, we identified a small peptide inhibitor (PIP1) that interferes PELP1 interaction with G9/EHMT2. Utilizing Hit-Ligand interaction site with the PELP1 hot spot residues based on 3D alignment and shape, we have identified 61 potential hits from Ligand-Based screening using a 10,000 Diverse Set. Screening of these 61 potential hits using MTT based cell viability assays identified three small organic molecule inhibitors (peptidomimetics) as leads. All three peptidomimetics (#20, #29, #34) showed activity similar to PELP1 peptide inhibitor 1 (PIP1) in assays using three different breast cancer cell lines. Further, PELP1 targeting peptidomimetic disrupted PELP1 interaction with G9a/EHMT2. Peptidomimetic treatment inhibited the proliferation of tamoxifen therapy resistant cells. In mechanistic studies, we found that knockdown of PELP1 inhibited stem cell maintenance. In FACS analysis of ZR75, ZR75-PELP1 and ZR75-PELP1KD cells, the percentage of CD44high/CD24low cells correlated with PELP1 status. Accordingly, in mammosphere formation assays, PELP1 targeting peptidomimetic significantly inhibited the formation of mammospheres and the size of the mammospheres was also substantially decreased. Further, in self-renewal assays, peptidomimetic-treated cells had decreased self-renewal capacity.

CONCLUSIONS: Collectively, our studies have discovered an essential role for PELP1 in breast cancer stem cell maintenance and identified the PELP1- G9a/EHMT2 axis as a potential therapeutic target for reducing stemness. Further, the novel small molecule inhibitors of PELP1 could be used for therapeutic targeting of breast cancer stem cells and therapy resistance.

Citation Format: Viswanadhapalli S, Mann M, Sareddy GR, Xaionan L, Vankayalapati H, Brann D, Vadlamudi RK. Proto-oncogene PELP1 signaling regulates breast cancer stem cells via G9a/EHMT2. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-06-09.