Novel LIPA-Targeted Therapy for Treating Ovarian Cancer

Ovarian cancer (OCa) is the most lethal form of gynecologic cancer, and the tumor heterogeneities at the molecular, cellular, and tissue levels fuel tumor resistance to standard therapies and pose a substantial clinical challenge. Here, we tested the hypothesis that the heightened basal endoplasmic reticulum stress (ERS) observed in OCa represents an exploitable vulnerability and may overcome tumor heterogeneity. Our recent studies identified LIPA as a novel target to induce ERS in cancer cells using the small molecule ERX-41. However, the role of LIPA and theutility of ERX-41 to treat OCa remain unknown. Expression analysis using the TNMplot web tool, TCGA data sets, and immunohistochemistry analysis using a tumor tissue array showed that LIPA is highly expressed in OCa tissues, compared to normal tissues. ERX-41 treatment significantly reduced the cell viability and colony formation ability and promoted the apoptosis of OCa cells. Mechanistic studies revealed a robust and consistent induction of ERS markers, including CHOP, elF2α, PERK, and ATF4, upon ERX-41 treatment. In xenograft and PDX studies, ERX-41 treatment resulted in a significant reduction in tumor growth. Collectively, our results suggest that ERX-41 is a novel therapeutic agent that targets the LIPA with a unique mechanism of ERS induction, which could be exploited to treat heterogeneity in OCa.

The LIFR Inhibitor EC359 Effectively Targets Type II Endometrial Cancer by Blocking LIF/LIFR Oncogenic Signaling

Endometrial cancer (ECa) is the most common female gynecologic cancer. When comparing the two histological subtypes of endometrial cancer, Type II tumors are biologically more aggressive and have a worse prognosis than Type I tumors. Current treatments for Type II tumors are ineffective, and new targeted therapies are urgently needed. LIFR and its ligand, LIF, have been shown to play a critical role in the progression of multiple solid cancers and therapy resistance. The role of LIF/LIFR in the progression of Type II ECa, on the other hand, is unknown. We investigated the role of LIF/LIFR signaling in Type II ECa and tested the efficacy of EC359, a novel small-molecule LIFR inhibitor, against Type II ECa. The analysis of tumor databases has uncovered a correlation between diminished survival rates and increased expression of leukemia inhibitory factor (LIF), suggesting a potential connection between altered LIF expression and unfavorable overall survival in Type II ECa. The results obtained from cell viability and colony formation assays demonstrated a significant decrease in the growth of Type II ECa LIFR knockdown cells in comparison to vector control cells. Furthermore, in both primary and established Type II ECa cells, pharmacological inhibition of the LIF/LIFR axis with EC359 markedly decreased cell viability, long-term cell survival, and invasion, and promoted apoptosis. Additionally, EC359 treatment reduced the activation of pathways driven by LIF/LIFR, such as AKT, mTOR, and STAT3. Tumor progression was markedly inhibited by EC359 treatment in two different patient-derived xenograft models in vivo and patient-derived organoids ex vivo. Collectively, these results suggest LIFR inhibitor EC359 as a possible new small-molecule therapeutics for the management of Type II ECa.

The RNA Demethylase ALKBH5 Maintains Endoplasmic Reticulum Homeostasis by Regulating UPR, Autophagy, and Mitochondrial Function

Eukaryotic cells maintain cellular fitness by employing well-coordinated and evolutionarily conserved processes that negotiate stress induced by internal or external environments. These processes include the unfolded protein response, autophagy, endoplasmic reticulum-associated degradation (ERAD) of unfolded proteins and altered mitochondrial functions that together constitute the ER stress response. Here, we show that the RNA demethylase ALKBH5 regulates the crosstalk among these processes to maintain normal ER function. We demonstrate that ALKBH5 regulates ER homeostasis by controlling the expression of ER lipid raft associated 1 (ERLIN1), which binds to the activated inositol 1, 4, 5,-triphosphate receptor and facilitates its degradation via ERAD to maintain the calcium flux between the ER and mitochondria. Using functional studies and electron microscopy, we show that ALKBH5-ERLIN-IP3R-dependent calcium signaling modulates the activity of AMP kinase, and consequently, mitochondrial biogenesis. Thus, these findings reveal that ALKBH5 serves an important role in maintaining ER homeostasis and cellular fitness.

Abstract 3528: ALKBH5 promotes cancer growth by regulating ER homeostasis via UPR, autophagy, and mitochondrial function

Background: N6-methyladenosine (m6A) RNA methylation is a dynamic reversible epitranscriptomic modification that includes methyl transferases (writes m6A), demethylases (erases m6A) and reader proteins, which proofreads m6A marks of a specific site of transcripts. Recent studies have suggested that RNA methylation affects several fundamental cellular and molecular functions including mRNA splicing, stability, export, stem cell fate, circadian rhythms, DNA repair and cell survival. The objective of this study is to establish the mechanisms by which RNA demethylase ALKBH5 (AlkB homolog 5) facilitates tumor growth and progression.

Methods: To establish the significance of RNA methylation in children’s cancers, we performed siRNA screen targeting m6A writers, erasers, and readers in osteosarcoma (OS). We used several OS cell lines including 143B, MG63, SaOS2, U2OS and multiple patient derived OS cell lines. Mechanistic studies were conducted using ALKBH5 KO and knockdown cells and by measuring the status of Autophagy and UPR associated proteins using Western blot analysis, confocal and electron microscopy.

Results: Our results revealed that depletion of ALKBH5, a demethylase that erases the m6A mark from the target gene, altered the autophagy in OS cells. Interestingly, we found that level of LC3, which is the universal marker for autophagy, was significantly increased in OS cells. RNA seq analysis showed that depletion of ALKBH5 significantly altered several autophagy related genes in the OS cells. To better understand the molecular mechanism by which ALKBH5 regulates autophagy, we investigated the Endoplasmic Reticulum (ER) stress-induced Unfolded Protein Response (UPR) pathway, which is a known activator of autophagy. We discovered that ER stress induced UPR signaling pathway is highly activated in ALKBH5 depleted cancer cells. Further, mechanistic studies suggested that ALKBH5 promoted ER homeostasis by controlling the expression of ER lipid raft associated 1 (ERLIN1), which binds to the activated inositol 1, 4, 5,-triphosphate receptor and facilitates its degradation via ERAD to maintain calcium flux between ER and mitochondria. Using functional studies and electron microscopy, we show that ALKBH5-ERLIN1-IP3R-dependent calcium signaling modulates the activity of AMP kinase, and consequently mitochondrial biogenesis. These findings thus reveal that ALKBH5 serves an important role in maintaining ER homeostasis and cellular fitness.

Conclusion: These findings provide novel insight into how m6A may promote cancer cell growth by regulating the crosstalk among ER signaling, UPR, autophagy, and mitochondrial function. Our study is the first to show that RNA methylation plays an important role in osteosarcoma by regulating autophagy via UPR.

Citation Format: Panneerdoss Subbarayalu, Daisy Medina, Pooja Yadav, Santosh Timilsina, Kunal Baxi, Ratna Vadlamudi, Yidong Chen, Manjeet Rao. ALKBH5 promotes cancer growth by regulating ER homeostasis via UPR, autophagy, and mitochondrial function. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3528.

The antidepressant imipramine inhibits breast cancer growth by targeting estrogen receptor signaling and DNA repair events

Aberrant activities of various cell cycle and DNA repair proteins promote cancer growth and progression and render them resistant to therapies. Here, we demonstrate that the anti-depressant imipramine blocks growth of triple-negative (TNBC) and estrogen receptor-positive (ER+) breast cancers by inducing cell cycle arrest and by blocking heightened homologous recombination (HR) and non-homologous end joining-mediated (NHEJ) DNA repair activities. Our results reveal that imipramine inhibits the expression of several cell cycle- and DNA repair-associated proteins including E2F1, CDK1, Cyclin D1, and RAD51. In addition, we show that imipramine inhibits the growth of ER + breast cancers by inhibiting the estrogen receptor- α (ER-α) signaling. Our studies in preclinical mouse models and ex vivo explants from breast cancer patients show that imipramine sensitizes TNBC to the PARP inhibitor olaparib and endocrine resistant ER + breast cancer to anti-estrogens. Our studies suggest that repurposing imipramine could enhance routine care for breast cancer patients. Based on these results, we designed an ongoing clinical trial, where we are testing the efficacy of imipramine for treating patients with triple-negative and estrogen receptor-positive breast cancer. Since aberrant DNA repair activity is used by many cancers to survive and become resistant to therapy, imipramine could be used alone and/or with currently used drugs for treating many aggressive cancers.

M6A RNA Methylation Regulates Histone Ubiquitination to Support Cancer Growth and Progression

Osteosarcoma is the most common malignancy of the bone, yet the survival for osteosarcoma patients is virtually unchanged over the past 30 years. This is principally because development of new therapies is hampered by a lack of recurrent mutations that can be targeted in osteosarcoma. Here, we report that epigenetic changes via mRNA methylation holds great promise to better understand the mechanisms of osteosarcoma growth and to develop targeted therapeutics. In osteosarcoma patients, the RNA demethylase ALKBH5 was amplified and higher expression correlated with copy number changes. ALKBH5 was critical for promoting osteosarcoma growth and metastasis, yet it was dispensable for normal cell survival. Me-RIP-seq analysis and functional studies showed that ALKBH5 mediates its pro-tumorigenic function by regulating m6A levels of histone deubiquitinase USP22 and the ubiquitin ligase RNF40. ALKBH5-mediated m6A deficiency in osteosarcoma led to increased expression of USP22 and RNF40 that resulted in inhibition of histone H2A monoubiquitination and induction of key pro-tumorigenic genes, consequently driving unchecked cell cycle progression, incessant replication and DNA repair. RNF40, which is historically known to ubiquitinate H2B, inhibited H2A ubiquitination in cancer by interacting with and affecting the stability of DDB1-CUL4-based ubiquitin E3 ligase complex. Taken together, this study directly links increased activity of ALKBH5 with dysregulation of USP22/RNF40 and histone ubiquitination in cancers. More broadly, these results suggest that m6A RNA methylation works in concert with other epigenetic mechanisms to control cancer growth.

Concordant Androgen-Regulated Expression of Divergent Rhox5 Promoters in Sertoli Cells

Concordant transcriptional regulation can generate multiple gene products that collaborate to achieve a common goal. Here we report a case of concordant transcriptional regulation that instead drives a single protein to be produced in the same cell type from divergent promoters. This gene product-the RHOX5 homeobox transcription factor-is translated from 2 different mRNAs with different 5' untranslated regions (UTRs) transcribed from alternative promoters. Despite the fact that these 2 promoters-the proximal promoter (Pp) and the distal promoter (Pd)-exhibit different patterns of tissue-specific activity, share no obvious sequence identity, and depend on distinct transcription factors for expression, they exhibit a remarkably similar expression pattern in the testes. In particular, both depend on androgen signaling for expression in the testes, where they are specifically expressed in Sertoli cells and have a similar stage-specific expression pattern during the seminiferous epithelial cycle. We report evidence for 3 mechanisms that collaborate to drive concordant Pp/Pd expression. First, both promoters have an intrinsic ability to respond to androgen receptor and androgen. Second, the Pp acts as an enhancer to promote androgen-dependent transcription from the Pd. Third, Pd transcription is positively autoregulated by the RHOX5 protein, which is first produced developmentally from the Pp. Together, our data support a model in which the Rhox5 homeobox gene evolved multiple mechanisms to activate both of its promoters in Sertoli cells to produce Rhox5 in an androgen-dependent manner during different phases of spermatogenesis.

Abstract PS19-14: Matrin3 inhibits breast cancer growth by suppressing microtubule nucleation protein MZT2B

Despite improvement in overall survival, many patients with breast cancers still succumb to this disease. Identification of new biomarkers and safe therapeutic targets are urgently needed to improve the overall clinical outcome of breast cancer patients. Our studies discovered a RNA binding protein, MATRIN3 (MATR3), as a novel tumor suppressor. MATR3 is expressed at a significantly reduced levels in breast tumors. MATR3 inhibited short and long-term viability as well as migration and invasion of breast cancer cells. Further, MATR3 overexpression suppressed tumor growth, while its depletion induced tumor growth in orthotopic mouse tumor models. RNA seq and RNA immunoprecipitation analyses revealed that MATR3 binds and directly regulates the expression of several microtubule-associated proteins. Mechanistic studies identified MZT2B, a mitotic spindle organizing protein as a down stream effector of MATR3. MZT2B knockdown or knockout using CRISPR-CAS9 resulted in significantly decreased short and long term viability as well as reduced migration and invasion of breast cancer cells. Notably, MZT2B overexpression rescued the inhibitory effect of MATR3 overexpression on breast cancer growth. Furthermore, MATR3 overexpression downregulated expression of key microtubule nucleation protein complex including γ-tubulin and γ-tubulin ring complex protein (TUBGCP). Our data suggest that MATR3 inhibits breast cancer growth and progression by inhibiting MZT2B and consequently microtubule nucleation in breast cancers.

Citation Format: Panneerdoss Subbarayalu, Subapriya Rajamanickam, Suryavathi Viswanadhapalli, Fuyang Li, Vijay Eedunuri, Pooja Yadav, Esha Reddy, Santosh Timilsina, Saif SR Nirzhor, Benjamin C Onyeagucha, Li-Ju Wang, Yu-Chiao Chiu, Tabrez Mohammad, Nourhan Abdelfattah, Nicholas Dybdal-Hargreaves, Yidong Chen, Ratna Vadlamudi, Manjeet Rao. Matrin3 inhibits breast cancer growth by suppressing microtubule nucleation protein MZT2B [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS19-14.

Abstract PS17-25: Repurposing anti-depressant imipramine for treating breast cancers

About 1 in 8 women will develop invasive breast cancer during their life time and more than 41,000 women die every year in the United States alone. Most of these deaths are attributed to relapse, distant metastasis and therapy resistance. For example, despite initial response to therapy, a significant proportion of ER+ BCs become therapy resistant and progress to incurable metastases. Similarly, TNBCs, which is highly aggressive and are more likely to occur in Hispanic and black women, have higher propensity to relapse and contribute to disproportionate number of deaths. Unfortunately, the patients who do survive, have reduced quality of life due to the chemotherapy-associated toxicity. One mechanism that helps BCs to survive and become therapy-resistant is their unique ability to keep repairing their DNA. The aim of this study was to identify and test whether any FDA-approved non-cancer drug/s can block DNA repair ability and consequently growth of BC cells. Treatment of BC cells with a set of FDA approved drugs showed that antidepressants imipramine can inhibit the BC cell growth. Imipramine treatment significantly reduced the short and long-term viability of TNBC and ER+ breast cancer cells. Further, imipramine treatment inhibited the migration and invasion of breast cancer cells. Systemic delivery of imipramine suppressed the breast cancer cells growth in orthotopic mouse xenograft model. Our results revealed that imipramine treatment induced G1/S cell cycle arrest and apoptosis in breast cancer cells. Importantly, imipramine blocked the DNA repair capacity of BC cells by inhibiting the expression of DNA repair proteins including FOXM1 and RAAD51. Notably, imipramine treatment improved the efficacy of the PARP inhibitor “olapraib” in TNBC and sensitized the tamoxifen response in tamoxifen resistant ER+ breast cancer cells. Our results suggest that imipramine can be used as a single or therapeutic adjuvant for treating therapy sensitive and therapy resistant breast cancers. Based on these results, we are currently conducting a clinical trial to test the therapeutic efficacy of imipramine for treating breast cancer patients (https://www.cancer.gov/about-cancer/treatment/clinical-trials/search/v?id=NCI-2017 01937&r=1).

Citation Format: Santosh Timilsina, Subapriya Rajamanickam, Arhan Rao, Panneerdoss Subbarayalu, Ismail Jatoi, Yidong Chen, Ratna Vadlamudi, Virginia G Kaklamani, Manjeet Rao. Repurposing anti-depressant imipramine for treating breast cancers [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-25.

Abstract 5838: RNA methylation regulates autophagy via unfolded protein response in cancers

N6-methyladenosine (m6A) RNA methylation is a dynamic, reversible and most abundant epitranscriptomic modification found on mRNA and long-non coding RNAs. M6A is regulated by methyl transferases (writes m6A), demethylases (erases m6A) and read by specific RNA binding proteins known as m6A readers that can modulate the fate of specific transcript. Recent studies have suggested that RNA methylation affects several fundamental cellular and molecular functions including mRNA splicing, stability, export, stem cell fate, circadian rhythms, DNA repair and cell survival. In addition, we and others have shown that RNA methylation plays an important role in tumor growth and progression. Here, we discovered that m6A may regulate tumorigenesis by regulating autophagy in cancer cells. Our results revealed that altering the levels of m6A methylation led to increased levels of LC3, which is a universal marker for autophagy. In addition, autophagy initiation protein ULK1 and other autophagy complex proteins including ATG5, ATG12, ATG16L1, and LAMP1 levels were significantly increased in cells with altered m6A methylation. Importantly, we discovered that change in m6A levels by altering the RNA demethylase protein induced the unfolded protein response (UPR) pathway, which is a known activator of autophagy. To understand the molecular mechanism of autophagy induction, we looked into three branches of UPR pathways and discovered that protein kinase RNA like kinase (PERK) UPR signaling pathway is highly activated in ALKBH5 depleted cancer cells and might regulate autophagy induction and cancer cell survival. In conclusion, our study is the first investigation to show that RNA methylation plays an important role in cancer growth by regulating autophagy via UPR.

Citation Format: Panneerdoss Subbarayalu, Pooja Yadav, Manjeet Rao. RNA methylation regulates autophagy via unfolded protein response in cancers [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 5838.

Abstract 4274: RNA methylation regulates osteosarcoma growth and progression via autophagy

Osteosarcoma (OS) is the most common primary bone tumor and third most common cancer in children/teens, after lymphomas and brain tumors. OS is treated by surgery and multi-modal chemotherapy. Even though this treatment regimen has improved the 5-year survival rate to 60-70%, once osteosarcoma metastasize to lung and other bones, the survival is significantly reduced. Moreover, the quality of life for patients who do survive is often substantially reduced due to the toxicity associated with the chemotherapy. Since several decades, there hasn’t been any improvement in the osteosarcoma treatment outcome. Therefore, it is important to understand the molecular mechanism of osteosarcoma growth and metastasis and an urgent need to develop effective drug, which can be safe and effective for treating OS patients. We discovered that RNA methylation may regulate OS growth and progression by affecting autophagy. Our studies revealed that RNA demethylase AlkB homolog 5 (ALKBH5) supports OS viability, migration and invasion as well as tumor growth. We discovered several autophagy related genes were significantly altered in ALKBH5-silenced OS cells compared to scrambled control. Importantly, levels of LC3, which is a universal marker for monitoring autophagy, was significantly increased in ALKBH5 depleted OS cells. Furthermore, we found that autophagy initiation complex protein ULK1 level was drastically increased in ALKBH5-silenced cells when compared to scrambled control. To further establish the role of autophagy in osteosarcomogenesis, we treated OS cells with chloroquine, which is a well-known autophagy inhibitor and is currently being investigated for treating adult cancers in clinical trials. Interestingly, silencing of ALKBH5 significantly improved the efficacy of chloroquine as revealed by drastically reduced viability and invasive ability of OS cells. In conclusion, our study is first to shows that RNA methylation plays a critical role osteosarcoma growth and progression by regulating autophagy.

Citation Format: Panneerdoss Subbarayalu, Pooja Yadav, Manjeet Rao. RNA methylation regulates osteosarcoma growth and progression via autophagy [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 4274.

Abstract 4146: N6Methyladenosine RNA demethylase ALKBH5 as a novel therapeutic target for osteosarcoma

Osteosarcoma (OS) is the most prevalent primary bone malignancy that affects children and young adults. Despite several years of research, survival outcome of OS patients has not improved in last three decades. OS is treated with multi-modal chemotherapy, which is highly toxic and does not work well for metastatic and chemo-resistant tumors. Currently there is no FDA approved drug that can serve as an alternative to chemotherapy, warranting an urgent need to find more efficacious and targeted therapeutics for OS. Here, we report that RNA demethylase AlkB Homolog 5 (ALKBH5) may serve as a novel therapeutic adjuvant for treating OS. N6 Methyladenosine (m6 A) is the most common internal mRNA modification, which is modulated by the multi-component RNA methyltransferase complex, RNA demethylase (ALKBH5) and m6A readers . We show that ALKBH5 is amplified in sarcomas and its expression is highly elevated in osteosarcoma patients. We demonstrate that silencing of ALKBH5 inhibits the OS growth and migration without affecting the viability of normal human fetal osteoblast cells. Our results reveal that ALKBH5 depletion impairs the cell cycle progression and induces apoptosis in OS cells. Interestingly, we demonstrate that reduction in ALKBH5 levels suppresses the DNA damage repair capacity of osteosarcoma cells rendering them sensitive to DNA damaging agent like Doxorubicin. Using DR-GFP reporter-based homologous recombination (HR) assay, we show that ALKBH5 depletion leads to reduced HR-mediated DNA repair capacity of osteosarcoma cells. Supporting this, we observed significantly reduced expression of several genes that are known to play critical roles in cell cycle progression and DNA damage repair. In summary, this study shows that ALKBH5 is a critical regulator of OS growth and chemosensitivity. Approaches aimed at silencing ALKBH5 can be potentially used to inhibit osteosarcoma growth and progression as well as sensitize osteosarcoma cells to DNA damaging agents.

Citation Format: Pooja Yadav, Panneerdoss Subbarayalu, Nourhan Abdelfattah, Vijay K. Eedunuri, Yidong Chen, Manjeet K. Rao. N6Methyladenosine RNA demethylase ALKBH5 as a novel therapeutic target for osteosarcoma [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 4146.

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.

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.

Abstract 1116: Targeting replication stress by carbazole blue- A novel strategy to treat triple negative breast cancers

Background: Triple-negative breast cancers (TNBC) are the most aggressive forms of breast cancer and almost 60% of patients with TNBCs develop chemo-resistance, leading to recurrence, poor prognosis and poor survival. TNBCs have been reported to have high levels of replication stress, which plays pivotal role in genomic instability, and therapy resistance. Targeting replication stress is an emerging approach for better TNBC treatment. Here, we evaluated the anticancer efficacy of carbazole blue (CB), a synthetic analogue of carbazole that we recently synthesized on TNBC cells growth and progression.

Experimental Design: The effect of CB on breast cancer growth was assessed in vitro as well as in orthotopic mouse xenograft and PDX-models of breast cancer. In addition, the therapeutic efficacy and safety of CB was determined in long term toxicity studies in mice and also in ex-vivo explants from breast cancer patients. The mechanism of action of CB was evaluated by performing gene expression, cell cycle, apoptosis and DNA repair studies as well as proteins involved in the above mentioned mechanisms.

Results: Our results demonstrated that CB inhibits short and long term viability of TNBC cells in a dose dependent manner without affecting normal mammary epithelial cells. We show that the systemic delivery of CB using nanoparticle-based delivery approach suppressed breast cancer growth without inducing toxicity in preclinical and PDX mouse models of triple negative breast cancer. Our long term toxicity studies reveled that CB treatment did not induce any toxicity in Balb/c mice. Using ex-vivo explants from breast cancer patients, we demonstrated that CB modulated breast cancer growth. Consistent with that, our results revealed that CB treatment induced G1/S cell cycle arrest and apoptosis in TNBCs. Interestingly, our gene expression analysis revealed that CB modulates expression and activity of several genes known to be involved in DNA replication and DNA repair machinery.

Conclusions: Our results for the first time showed the CB can serve as a novel and potent therapeutic agent for treating breast cancer in general and TNBC in particular. These findings highlight the potential of CB to be applied as a safe regimen for treating breast cancer patients. 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: Subapriya Rajamanickam, Kaitlyn Bates, Santosh Timilsina, JunHyoung Park, Benjamin Onyeagucha, Panneerdoss Subbarayalu, Nourhan Abdelfattah, Kwang Hwa Jung, Edward Favours, Tabrez A. Mohammad, Hung-I Harry Chen, Benny A. Kaipparettu, Yidong Chen, Jack L. Arbiser, Manjeet K Rao. Targeting replication stress by carbazole blue- A novel strategy to treat triple negative breast cancers [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 1116. doi:10.1158/1538-7445.AM2017-1116

Abstract 3343: RNA demethylase alkbh5 supports breast cancer growth and progression

N6-methyladenosine (m6A) is one of the most prevalent internal modifications in eukaryotic messenger RNA. This dynamic and reversible modification is installed by methyltransferase complex consisting of three subunits: Methyltransferase-like protein 3 (METTL3), Methyltransferase-like protein 14 (METTL14) and Wilms tumor 1-associating protein (WTAP), and erased by two independent demethylases, Fat mass and obesity associated protein (FTO) and AlkB homolog 5 (ALKBH5). RNA demthylase ALKBH5 has been reported to play vital roles in several biological processes. However, very little is known about the role of ALKBH5 in cancer in general and breast tumorigenesis in particular. In this study, we report that ALKBH5 promotes breast cancer growth and progression. Using in vitro and in vivo models, we show that silencing of ALKBH5 inhibits breast cancer growth and invasion. Importantly, our studies reveal that ALKBH5 mediates its pro-tumorigenic function by regulating several microtubule associated genes including KIF2C, PLK1, MAPRE1 and RCC2 that are critical for spindle formation or assembly during mitotic progression. Interestingly, ALKBH5 target genes KIF2C and MAPRE1 are highly expressed in breast cancer patients and their higher expression is strongly correlated with lower survival of breast cancer patients. We believe that an optimal level of RNA methylation of key target genes is critical for normal cell cycle progression and any alteration in the levels of RNA methylation may alter activity or expression of these genes resulting in unabated cell proliferation.

Citation Format: Vijay Kumar Eedunuri, Panneerdoss Subbarayalu, Subhapriya Rajamanickam, Abdelfattah Nourhan, Benjamin C. Onyeagucha, Santosh Timilsina, Pooja Yadav, Manjeet K. Rao. RNA demethylase alkbh5 supports breast cancer growth and progression [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 3343. doi:10.1158/1538-7445.AM2017-3343

Abstract 5440: miRNAs as novel therapeutic adjuvants for improving the efficacy of vincristine and radiation therapy in treating medulloblastoma

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Despite recent improvements in the overall survival, only a modest percentage of patients survive Myc-driven high-risk MB. The quality of life for surviving patients is substantially reduced due to the devastating and often irreversible side effects of radiation and chemotherapy. Recently, in a large unbiased genomic screen, we uncovered a group of microRNAs (miRNAs) capable of meditating drug sensitivity in c-myc amplified high-risk MB. Our functional screen of ~1900 miRNAs identified miR-584-5p as a potent candidate that uniquely sensitizes high-risk MB to radiation as well as vincristine (VCR) (20 to 25-fold dose reduction), an anti-mitotic agent routinely administered alongside radiation and in combination with other chemotherapeutic drugs to treat medulloblastoma patients. Our studies revealed that miR-584 might act as a potent tumor suppressor as it inhibited MB growth in vivo as well as migration and invasion of c-myc amplified MB. We show that miR-584 overexpression results in defective mitosis leading to mitotic catastrophe, apoptosis, DNA damage and G2-M cell-cycle arrest in high-risk MB cells without affecting normal neural stem cell growth. Notably, we discovered that miR-584 directly regulates the expression and activity of genes including histone deacetylase 1 (HDAC1), and eukaryotic translation initiation factor 4e family member 3 (EIF4E3) that are known to play important roles in microtubule dynamics, metaphase-anaphase transition and radio-resistance. Moreover, silencing either of these two target genes resulted in significant inhibition of MB growth and enhanced sensitivity to VCR and ionizing radiation. Overexpressing miR-584 or silencing either HDAC1 or EIF4E3 also inhibited the MB stem cell proliferation and self-renewal. We report that while miR-584-5p is predominantly expressed in normal brain and cerebellum, its expression is significantly reduced in MB patient derived xenografts (PDXs). In contrast to miR-584, EIF4E3 and HDAC1 were found to be overexpressed in medulloblastoma patients. These findings are highly significant, unexpected and innovative as this miRNA and its target genes are the first to be shown to affect the therapeutic efficacy of VCR and radiation in c-myc amplified high-risk medulloblastoma.

Citation Format: Nourhan Abdelfattah, Subapriya Rajamanickam, Panneerdoss Subbarayalu, Santosh Timilsina, Benjamin Onyeagucha, Yidong Chen, Manjeet Rao. miRNAs as novel therapeutic adjuvants for improving the efficacy of vincristine and radiation therapy in treating medulloblastoma [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 5440. doi:10.1158/1538-7445.AM2017-5440

Abstract B01: MicroRNAs as novel therapeutic adjuvants to treat high-risk medulloblastoma

Medulloblastoma is the most common malignant brain tumor in children, accounting for 18% of newly diagnosed brain tumors and 10% of all children cancer-related deaths. Despite improvement in the 5-year survival rate of medulloblastoma in recent years, only a small percentage of patients survive high-risk metastatic disease. The quality of life for those who do survive is often substantially reduced due to the toxicity associated with radiation and chemotherapy. Vincristine is a microtubule-destabilizing antimitotic drug, which is routinely administered in higher dosages to both high and average risk medulloblastoma patients. As a result, these patients suffer from devastating neurotoxic effects that include but not limited to: sensorimotor and autonomic neuropathy, hearing loss, mononeuropathy, and seizures. Using high-throughput microRNA mimic library screens, we identified a group of microRNAs that may improve the efficacy of vincristine against c-MYC amplified medulloblastoma as well as re-sensitize vincristine-resistant medulloblastoma. Our findings revealed that these microRNAs may act as tumor suppressors since their overexpression inhibited colony formation, migration and invasion ability of medulloblastoma cells. Furthermore, these microRNAs suppressed stem cell renewal/proliferation of c-MYC amplified medulloblastoma cells. Expression analysis, gene enrichment analysis and target prediction algorithms revealed that these microRNAs exert their vincristine sensitizing and tumor suppressor effect by targeting genes involved in microtubule organization, cell cycle regulation, DNA damage repair and mRNA translation. One of our most interesting targets is EIF4E3, which is a translation initiation factor. Our preliminary findings indicate that EIF4E3 may regulate medulloblastoma cell growth, progression and vincristine sensitivity by modulating c-MYC translation. Further experiments are underway to test the potential of candidate miRNA and EIF4E3 as vincristine sensitizer in vivo. In conclusion, this study may identify novel factors that have potential not only to decrease the current therapeutic dose of vincristine and therefore eliminate its side effects, but also have potential to multiply the efficacy of lower doses in order to overcome hard to treat high-risk tumors.

Citation Format: Nourhan Abdelfattah, Panneerdoss Subbarayalu, Benjamin Onyeagucha, Subapriya Rajamanickam, Hung-I Harry Chen, Manjeet Rao. MicroRNAs as novel therapeutic adjuvants to treat high-risk medulloblastoma.. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr B01.

Abstract P4-07-06: Imipramine Blue - A safe and potent therapeutic regimen that suppresses breast cancer growth and progression by targeting DNA damage surveillance pathway

Despite improvement in overall survival of breast cancer patients, many women don't survive this disease. Moreover, the quality of life for patients who do survive is often substantially reduced due to the toxicity associated with the chemotherapy. Here, we report that imipramine blue (IB), a novel analogue of anti-depressant imipramine that we recently synthesized, may serve as a safe and potent therapeutic agent for treating breast cancers. We show that IB reduced cell growth, migration and invasion of breast cancer cells. Systemic delivery of IB using nanoparticle-based drug delivery approach suppressed breast cancer growth and metastasis without inducing any toxicity in pre-clinical orthotropic mouse models. Notably, using ex-vivo model of tumor explants from breast cancer patients, we demonstrated that IB inhibited breast cancer growth without affecting normal mammary epithelial cell proliferation. Furthermore, IB improved the sensitivity of breast cancer cells to chemotherapy drugs paclitaxel and doxorubicin. Our results revealed that IB mediated its anti-tumor effect by targeting genes involved in cell cycle progression, microtubule dynamics and DNA damage surveillance pathway including Forkhead Box M1 (FOXM1), stathmin1, S-phase kinase-associated protein 2 (Skp2) and XRCC3, which we show to be highly expressed in breast cancer patients. Importantly, we demonstrated that IB inhibited breast cancer cell's ability to repair DNA strand breaks by impairing homologous recombination events. These findings highlight the potential of IB to be used as a potent therapeutic regimen for treating breast cancer patients. Since IB-1 is derived from a FDA approved drug it has potential to be rapidly translated to the clinic.

Citation Format: Rajamanickam S, Subbarayalu P, Timilsina S, Gorthi A, Drake MT, Chen Y, Vadlamudi R, Bishop AJR, Arbiser JL, Rao MK. Imipramine Blue - A safe and potent therapeutic regimen that suppresses breast cancer growth and progression by targeting DNA damage surveillance pathway. [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 P4-07-06.

Abstract 1787: Imipramine blue: a novel NOX inhibitor as potent therapeutic agent to treat triple-negative breast cancers

Breast cancer is the most common cancer in women and the second leading cause of cancer death in US. Triple-negative breast cancers (TNBC) are the most aggressive forms of breast cancer. Almost 60% of patients with TNBCs develop chemo-resistance, leading to early relapse and shorter survival. The family of NADPH oxidases (NOX) enzymes is more abundant source of reactive oxygen species, which generally over expressed in a wide range of cancers including breast cancer. Over expression of NOX family of proteins in the tumor cells and stroma results in the activation of several intracellular pathways that promotes neoplastic transformation. Moreover, NOX is an important metabolic enzyme that plays a critical role in supporting increased glycolysis in cancer cells by generating NAD+, a substrate for one of the key glycolytic reactions. The constitutive upregulation of glycolysis is thought to confer significant growth advantage to cancer cells leading to uncontrolled proliferation and increased invasion. This is especially true for TNBC that shows a strong association with the Warburg effect. Herein we evaluated first time the role of imipramine blue (IB), a NOX inhibitor and a derivative of the FDA approved antidepressant imipramine in TNBC cells growth and progression. Our results demonstrated that imipramine blue inhibits TNBC, MDA-MB-231, MDA-MB-468 and Bt-549 cells growth without affecting normal mammary epithelial (MCF-10A) cells. Notably, our studies revealed that imipramine blue targets multiple NOX family members, which are highly expressed in breast tumors when compared to adjacent normal tissue. Imipramine blue treatment also reduced migration and invasion and inhibited the self-renewal capability of MDA-MB-231 cells. Importantly, imipramine blue treatment significantly reduced experimental lung metastasis of MDA-MB-231 cells in athymic nude mice without induce apparent toxicity. Our gene microarray results further showed that IB treatment significantly altered an array of genes, including FOXM1, Aurora kinase A (AURAK) and Polo-like kinase 1 (PLK1), which play important roles in cancer growth and progression as well as in mediating sensitivity/resistance of paclitaxel (PTX), a chemotherapy drug that is routinely used as a first line treatment for breast cancer patients. Taken together, our findings propose NOX inhibitor imipramine blue as a novel therapeutic agent with less toxicity to treat triple negative breast cancers.

Citation Format: Subapriya Rajamanickam, Panneerdoss Subbarayalu, Santhosh Timilsina, Michael T. Drake, Zhenze Zhao, Hung I Harry Chen, Yidong Chen, Jack L. Arbiser, Manjeet K K. Rao. Imipramine blue: a novel NOX inhibitor as potent therapeutic agent to treat triple-negative breast cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1787. doi:10.1158/1538-7445.AM2015-1787

Abstract P4-05-09: Matrin 3: A novel micro-tubule associated RNA binding protein that acts as a potent tumor suppressor

Microtubules are highly dynamic components of the cytoskeleton that play an important role in a wide range of cellular processes including cell division, cell motility and intracellular transport. Increasing evidence suggests that alterations in microtubule dynamics are critical for cancer growth and metastasis. Microtubule associated proteins (MAPs) regulate microtubule dynamics and consequently can affect sensitivity of cancer cells to microtubule targeting drugs. We discovered a novel microtubule associated protein "Matrin 3 (MATR3)" that is known to bind to RNA and play a critical role in RNA transport and RNA stabilization. Immunofluorescence analyses revealed that although MATR3 is predominantly a nuclear protein, it translocates to the cytoplasm and interacts with microtubules when breast cancer cells are treated with paclitaxel. We show that MATR3 associates with stabilized microtubules and it mediates microtubule polymerization in a taxol-dependent manner. Interestingly, our results reveal that MATR3 acts as a effective tumor suppressor as it inhibits breast cancer colony formation, migration and invasion of breast cancer cells in addition to suppressing breast tumor growth in vivo. Analysis of breast cancer samples showed a significantly lower expression of MATR3 when compared to normal adjacent tissues. Our results indicate the possibility that MATR3 mediates its tumor suppressor function by binding and regulating proteins that are known to affect microtubule dynamics. We believe that nuclear-cytoplasmic shuttling of MATR3 is critical for stability of key proteins that might regulate paclitaxel-dependent microtubule dynamics and subsequently cellular effects in cancer cells.

Citation Format: Panneerdoss Subbarayalu, Subapriya Rajamanickam, Suryavathi Viswanadhapalli, Nicholas Dybdal-Hargreaves, Santosh Timilsina, Sanjay Bansal, Hima Bansal, Tabrez Mohammad, Yidong Chen, John C Herr, Susan L Mooberry, Manjeet K Rao. Matrin 3: A novel micro-tubule associated RNA binding protein that acts as a potent tumor suppressor [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-05-09.