ZNF397 Deficiency Triggers TET2-driven Lineage Plasticity and AR-Targeted Therapy Resistance in Prostate Cancer

Cancer cells exhibit phenotypical plasticity and epigenetic reprogramming, which allows them to evade lineage-dependent targeted treatments by adopting lineage plasticity. The underlying mechanisms by which cancer cells exploit the epigenetic regulatory machinery to acquire lineage plasticity and therapy resistance remain poorly understood. We identified Zinc Finger Protein 397 (ZNF397) as a bona fide coactivator of the androgen receptor (AR), essential for the transcriptional program governing AR-driven luminal lineage. ZNF397 deficiency facilitates the transition of cancer cell from an AR-driven luminal lineage to a Ten-Eleven Translocation 2 (TET2)-driven lineage plastic state, ultimately promoting resistance to therapies inhibiting AR signaling. Intriguingly, our findings indicate that a TET2 inhibitor can eliminate the resistance to AR targeted therapies in ZNF397-deficient tumors. These insights uncover a novel mechanism through which prostate cancer acquires lineage plasticity via epigenetic rewiring and offer promising implications for clinical interventions designed to overcome therapy resistance dictated by lineage plasticity.

Evaluating physiochemical properties of FDA-approved orally administered drugs

INTRODUCTION

Analyses of orally administered FDA-approved drugs from 1990 to 1993 enabled the identification of a set of physiochemical properties known as Lipinski's Rule of Five (Ro5). The original Ro5 and extended versions still remain the reference criteria for drug development programs. Since many bioactive compounds do not conform to the Ro5, we validated the relevance of and adherence to these rulesets in a contemporary cohort of FDA-approved drugs.

AREAS COVERED

The authors noted that a significant proportion of FDA-approved orally administered parent compounds from 2011 to 2022 deviate from the original Ro5 criteria (~38%) or the Ro5 with extensions (~53%). They then evaluated if a contemporary Ro5 criteria (cRo5) could be devised to better predict oral bioavailability. Furthermore, they discuss many case studies showcasing the need for and benefit of increasing the size of certain compounds and cover several evolving strategies for improving oral bioavailability.

EXPERT OPINION

Despite many revisions to the Ro5, the authors find that no single proposed physiochemical rule has universal concordance with absolute oral bioavailability. Innovations in drug delivery and formulation have dramatically expanded the range of physicochemical properties and the chemical diversity for oral administration.

UBE2J1 is the E2 ubiquitin-conjugating enzyme regulating androgen receptor degradation and antiandrogen resistance

Prostate cancer (PCa) is primarily driven by aberrant Androgen Receptor (AR) signaling. Although there has been substantial advancement in antiandrogen therapies, resistance to these treatments remains a significant obstacle, often marked by continuous or enhanced AR signaling in resistant tumors. While the dysregulation of the ubiquitination-based protein degradation process is instrumental in the accumulation of oncogenic proteins, including AR, the molecular mechanism of ubiquitination-driven AR degradation remains largely undefined. We identified UBE2J1 as the critical E2 ubiquitin-conjugating enzyme responsible for guiding AR ubiquitination and eventual degradation. The absence of UBE2J1, found in 5-15% of PCa patients, results in disrupted AR ubiquitination and degradation. This disruption leads to an accumulation of AR proteins, promoting resistance to antiandrogen treatments. By employing a ubiquitination-based AR degrader to adeptly restore AR ubiquitination, we reestablished AR degradation and inhibited the proliferation of antiandrogen-resistant PCa tumors. These findings underscore the fundamental role of UBE2J1 in AR degradation and illuminate an uncharted mechanism through which PCa maintains heightened AR protein levels, fostering resistance to antiandrogen therapies.

Transposable Elements Are Co-opted as Oncogenic Regulatory Elements by Lineage-Specific Transcription Factors in Prostate Cancer

Transposable elements hold regulatory functions that impact cell fate determination by controlling gene expression. However, little is known about the transcriptional machinery engaged at transposable elements in pluripotent and mature versus oncogenic cell states. Through positional analysis over repetitive DNA sequences of H3K27ac chromatin immunoprecipitation sequencing data from 32 normal cell states, we report pluripotent/stem and mature cell state-specific "regulatory transposable elements." Pluripotent/stem elements are binding sites for pluripotency factors (e.g., NANOG, SOX2, OCT4). Mature cell elements are docking sites for lineage-specific transcription factors, including AR and FOXA1 in prostate epithelium. Expanding the analysis to prostate tumors, we identify a subset of regulatory transposable elements shared with pluripotent/stem cells, including Tigger3a. Using chromatin editing technology, we show how such elements promote prostate cancer growth by regulating AR transcriptional activity. Collectively, our results suggest that oncogenesis arises from lineage-specific transcription factors hijacking pluripotent/stem cell regulatory transposable elements.

SIGNIFICANCE

We show that oncogenesis relies on co-opting transposable elements from pluripotent stem cells as regulatory elements altering the recruitment of lineage-specific transcription factors. We further discover how co-option is dependent on active chromatin states with important implications for developing treatment options against drivers of oncogenesis across the repetitive DNA. This article is featured in Selected Articles from This Issue, p. 2293.

Riluzole Suppresses Growth and Enhances Response to Endocrine Therapy in ER+ Breast Cancer

Background

Resistance to endocrine therapy in estrogen receptor-positive (ER+) breast cancer remains a significant clinical problem. Riluzole is FDA-approved for the treatment of amyotrophic lateral sclerosis. A benzothiazole-based glutamate release inhibitor with several context-dependent mechanism(s) of action, riluzole has shown antitumor activity in multiple malignancies, including melanoma, glioblastoma, and breast cancer. We previously reported that the acquisition of tamoxifen resistance in a cellular model of invasive lobular breast cancer is accompanied by the upregulation of GRM mRNA expression and growth inhibition by riluzole.

Methods

We tested the ability of riluzole to reduce cell growth, alone and in combination with endocrine therapy, in a diverse set of ER+ invasive ductal and lobular breast cancer-derived cell lines, primary breast tumor explant cultures, and the estrogen-independent, ESR1-mutated invasive lobular breast cancer patient-derived xenograft model HCI-013EI.

Results

Single-agent riluzole suppressed the growth of ER+ invasive ductal and lobular breast cancer cell lines in vitro, inducing a histologic subtype-associated cell cycle arrest (G0-G1 for ductal, G2-M for lobular). Riluzole induced apoptosis and ferroptosis and reduced phosphorylation of multiple prosurvival signaling molecules, including Akt/mTOR, CREB, and Fak/Src family kinases. Riluzole, in combination with either fulvestrant or 4-hydroxytamoxifen, additively suppressed ER+ breast cancer cell growth in vitro. Single-agent riluzole significantly inhibited HCI-013EI patient-derived xenograft growth in vivo, and the combination of riluzole plus fulvestrant significantly reduced proliferation in ex vivo primary breast tumor explant cultures.

Conclusion

Riluzole may offer therapeutic benefits in diverse ER+ breast cancers, including lobular breast cancer.

Critical role of antioxidant programs in enzalutamide-resistant prostate cancer

Therapy resistance to second-generation androgen receptor (AR) antagonists, such as enzalutamide, is common in patients with advanced prostate cancer (PCa). To understand the metabolic alterations involved in enzalutamide resistance, we performed metabolomic, transcriptomic, and cistromic analyses of enzalutamide-sensitive and -resistant PCa cells, xenografts, patient-derived organoids, patient-derived explants, and tumors. We noted dramatically higher basal and inducible levels of reactive oxygen species (ROS) in enzalutamide-resistant PCa and castration-resistant PCa (CRPC), in comparison to enzalutamide-sensitive PCa cells or primary therapy-naive tumors respectively. Unbiased metabolomic evaluation identified that glutamine metabolism was consistently upregulated in enzalutamide-resistant PCa cells and CRPC tumors. Stable isotope tracing studies suggest that this enhanced glutamine metabolism drives an antioxidant program that allows these cells to tolerate higher basal levels of ROS. Inhibition of glutamine metabolism with either a small-molecule glutaminase inhibitor or genetic knockout of glutaminase enhanced ROS levels, and blocked the growth of enzalutamide-resistant PCa. The critical role of compensatory antioxidant pathways in maintaining enzalutamide-resistant PCa cells was validated by targeting another antioxidant program driver, ferredoxin 1. Taken together, our data identify a metabolic need to maintain antioxidant programs and a potentially targetable metabolic vulnerability in enzalutamide-resistant PCa.

Abstract 3986: Novel LIPA targeted therapy for treating ovarian cancer

BACKGROUND: Ovarian cancer (OCa) is the deadliest of all gynecologic cancers in the United States. Currently approved therapies have improved OCa survival for clinically localized disease, however, the majority (~90%) of patients with high-grade serous OCa (HGSOC) experience relapse with incurable metastases. There is a dire need for new therapeutic approaches. We hypothesized that the high basal endoplasmic reticulum stress (ERS) in OCa represents a critical and targetable vulnerability and may overcome the tumor heterogeneity. The objective of this project is to exploit increased ERS in ovarian cancer cells by engaging the novel target LIPA using the unique compound ERX-41.

METHODS: The utility of ERX-41 as a new therapy was evaluated using MTT and CellTiter-Glo Cell Viability Assays. We used multiple established and patient derived OCa cell lines. The effect of ERX-41 on the Cell viability of patient-derived organoids (PDO) was measured using CellTiter-Glo 3D Assay. Long term effects of ERX-41 on cell survival were measured using colony formation assays. Apoptosis was measured using Annexin V and Caspase-Glo® 3/7 Assays. Cell cycle analysis was analyzed by Flow Cytometry. Mechanistic studies were done using LIPA knockout (KO) cells, RT-qPCR, and western blotting. Status of LIPA in OCa was determined using TNMplot database. In vivo efficacy of ERX-41 was tested using both cell line derived (CDX) and patient derived (PDXs) xenografts.

RESULTS: TNM plot results showed that LIPA is highly expressed in OCa tumors compared to normal tissues and LIPA expression correlated with clinical grade. Kaplan-Meier plotter analyses of TCGA data revealed that LIPA expression is negatively correlated with overall survival in OCa patients. MTT and CellTitre-Glo assay results showed that ERX-41 significantly reduced the cell viability of both established and primary OCa cells, and PDO’s with an IC50 of ~500nM. ERX-41 treatment also significantly reduced the cell survival, increased S-phase arrest, and promoted apoptosis of OCa cells. A time course study revealed a robust and consistent induction of ERS markers (CHOP and sXBP1) in OCa cells by ERX-41 within 4h. Western blotting analyses also confirmed increased expression of ERS markers including CHOP, elF2α, PERK, and ATF4 upon ERX-41 treatment confirming that ERX-41 induces ERS. In xenograft studies, ERX-41 treatment resulted in ~66% reduction of tumor volume measured by Xenogen-IVIS. Further, in studies using PDX tumors, treatment with ERX-41 resulted in a significant reduction (~60%) of tumor volume and tumor weight.

CONCLUSION: Collectively, our results suggest that ERX-41 is a novel therapeutic agent that targets the LIPA with a unique mechanism of action and implicate ERX-41 binding to LIPA induces ER stress, and apoptosis of OCa cells. Further molecular characterization of how ERX-41 binding to LIPA induces ER stress in OCa cells is ongoing.

Citation Format: Alexia B. Collier, Suryavathi Viswanadhapalli, Tae-Kyung Lee, Kara Kassees, Karla Parra, Gaurav Sharma, Tanner Reese, Michael Hsieh, Xihui Liu, Xue Yang, Behnam Ebrahimi, Uday P. Pratap, Rahul Gopalam, Chia Yuan Chen, Scott Terry Elmore, Gangadhara Reddy Sareddy, Edward R. Kost, Jung-Mo Ahn, Ganesh V. Raj, Ratna K. Vadlamudi. Novel LIPA targeted therapy for treating ovarian cancer. [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 3986.

Abstract 2405: Delineating molecular vulnerabilities of ATM mutant prostate cancers

Background: Mutations in DNA Damage Response (DDR) genes, including Ataxia, Telangiectasia, Mutated (ATM), are common in advanced castration-resistant prostate cancers (CRPCs). Poly (ADP-ribose) polymerase (PARP) inhibitors are approved in DDR mutant CRPCs, but demonstrate limited clinical efficacy in CRPCs with ATM mutations. In this project, we sought to specifically define the impact of ATM loss on DDR pathways in CRPC, with the goal of identifying alternate therapeutic vulnerabilities.

Methods: ATM-KO CRPC cell lines were generated via CRISPR-Cas9 mediated knockout. ATM loss and abolishment of downstream ATM kinase activity was confirmed via western blot. We performed an unbiased phospho-proteomic evaluation of DDR pathways in parental and ATM-KO cells after ionizing radiation (IR). Clonogenic survival assays were performed with either an ATR inhibitor (VX970), the selective DNA-PKcs inhibitor (M3814), or combination therapy. Kinetics of DDR protein recruitment and resolution were interrogated with immunofluorescence (IF) staining for γH2ax, 53BP1, MDC1, and Rad51 foci.

Results: ATM-KO cells were able to effectively repair DNA damage following IR, as measured by recruitment and resolution of γH2ax, 53BP1, MDC1, and Rad51 foci. Phospho-proteomic studies demonstrated that ATM-KO cells maintain canonical DDR pathways through ATR and DNA-PKcs kinase activation. Treatment of ATM-KO cells with either VX-970 or M3814 only incrementally affected DDR in ATM-KO cells compared to parental controls, as evidenced by clonogenic survival assays and maintenance of DDR foci. Importantly, combination treatment with VX-970 and M3814 prevented downstream DDR foci recruitment and radio-sensitized ATM-KO CRPC to a greater extent than parental controls. This suggested that activity of any of the trinity of kinases is sufficient to mediate DDR, and that blockade of both ATR and DNA-PKcs is required to effectively prevent DDR in ATM-KO CRPC. We then leveraged a RUVBL1 ATPase inhibitor Compound B, which significantly attenuates levels of these kinases in lung cancer cells. We confirmed that Compound B treatment attenuated ATR and DNA-PKcs protein expression and kinase activity in ATM-KO CRPC cells, and demonstrated sensitivity of ATM-KO cells to Compound B.

Conclusions: Our data demonstrates that dual targeting of ATR and DNA-PKcs is necessary in ATM-KO CRPC, as either kinase is independently capable of mediating DDR following IR. Our initial studies indicate that the RUVBL1 ATPase inhibitor Compound B may effectively block DDR in ATM-mutant CRPC, and could be utilized as a novel therapeutic strategy in this molecular subtype.

Citation Format: Mia Hofstad, Lan Yu, Andrea Woods, Zoi Sychev, Collin Gilbreath, Xiaofang Huo, Ralf Kittler, Justin M. Drake, Ganesh V. Raj. Delineating molecular vulnerabilities of ATM mutant prostate cancers [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 2405.

Abstract 4813: ERX-208 as a novel therapeutic for treating ovarian cancer by enhancing endoplasmic reticulum stress

Background: Ovarian cancer (OCa) is the deadliest of all gynecologic cancers in the United States. Despite initial response to chemotherapy, most OCa patients become chemo resistant and progress to metastatic disease. Here, we tested the hypothesis that the high basal level of endoplasmic reticulum stress (ERS) in OCa represents a critical vulnerability and drugs that further aggravate this already engaged system in OCa may exhaust its protective features and contribute to apoptosis induction. The objective of this proposal is to identify a hit compound that enhances ERS in OCa and to conduct mechanistic studies.

Methods: We synthesized a small library of >200 chemically distinct oligobenzamide analogs with maintenance of the chemical backbone but altered R groups of ERX-11. We performed the primary screening of this library to evaluate the induction of mRNA levels of two canonical ERS/UPR (unfolded protein response) genes- sXBP1 and CHOP. Biological activity of ERX-208 was validated using multiple OCa cells. Mechanistic studies were conducted using CRISPR/Cas9 KO, Western blotting, reporter gene assays, IHC and RNA-seq analysis. PK (pharmacokinetics) and toxicity studies were done using C57BL/6 mice. Cell line-derived xenografts (CDXs), patient-derived xenografts (PDXs), patient-derived explants (PDEs), and patient-derived organoids (PDO) were used for preclinical evaluation.

Results: From a screen of a curated ERX-11 derived oligobenzamide library, we identified a hit compound, ERX-208 that potently (IC50~100nM) induces ERS/UPR and apoptosis in multiple OCa cells in vitro. CRISPR KO screen identified the lysosomal acid lipase A (LIPA) protein as the critical target of ERX-208. LIPA KO abrogates response to ERX-208, while reconstitution of LIPA restores ERX-208 response. The time course studies showed a robust and consistent induction (>15-fold CHOP, and >10-fold sXBP1) by ERX-208 treatment within 24h. We confirmed induction of classic UPR components peIF2α, CHOP and LC3B using Western blotting in multiple OCa cells. Functionally, ERX-208 causes growth inhibition of OCa cells, as noted by MTT cell viability assays using 15 OCa cells with an IC50 of ~50-100nM. The activity of ERX-208 is distinct among oligobenzamides as ERX-11 has limited/no activity against OCa cells. RNA-seq analysis confirmed that ERX-208 induces significant ERS, UPR, and apoptosis. Further, ERX-208 reduced the growth of OCa PDO’s in vitro, PDEs ex vivo and CDXs and PDXs in vivo. ERX-208 treatment did not show any signs of toxicity and body weight of mice was not affected. IHC analyses showed increased activation of ERS/UPR markers such as GRP78, p-PERK and decreased proliferation measured by Ki67.

Conclusions: Collectively, our results demonstrated the utility of ERX-208 and will establish a novel therapeutic paradigm in OCa that overcomes tumor heterogeneity by targeting LIPA and enhancing ERS leading to apoptosis.

Citation Format: Suryavathi Viswanadhapalli, Tae-Kyung Lee, Kara Kassees, Gaurav Sharma, Rahul Gopalam, Karla Parra, Tanner Reese, Michael Hsieh, Uday P. Pratap, Xue Yang, Behnam Ebrahimi, Chia Yuan Chen, Scott Terry Elmore, Christian Cervantes, Zhenming Xu, Edward Kost, Gangadhara Reddy Sareddy, Rajeshwar Rao Tekmal, Jung-Mo Ann, Ganesh V. Raj, Ratna K. Vadlamudi. ERX-208 as a novel therapeutic for treating ovarian cancer by enhancing endoplasmic reticulum stress. [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 4813.

Abstract P6-10-14: Lysosomal acid lipase (LIPA) as a novel therapeutic vulnerability for treating TNBC

Background: TNBCs have the highest mortality rate among all BC subtypes. There is thus an urgent and unmet need for effective targeted therapies in TNBC. Recently we, identified a novel agent ERX-41 that showed good efficacy in treating TNBC in preclinical mouse models, however, its molecular action remain unknown. In this study, we identified LIPA as novel molecular target of ERX-41. Methods: We have used CRISPR knockout pooled library and multiple TNBC models for identifying molecular target of ERX-41. Mechanistic studies were performed using LIPA mutants, RNA-seq, Turbo-ID mapping, Mass spectrometry, Immunoprecipitation, and Western blotting. The in vivo efficacy of ERX-41 was examined using four different patient-derived xenograft (PDX) models. We evaluated LIPA protein expression in TNBC using tissue microarray (TMA). Results: To identify the molecular target of ERX-41, we performed an unbiased CRISPR–Cas9 knockout (KO) screen in MDA-MB-231 cells and the results identified LIPA as a top hit. KO of LIPA alone (which encodes lysosomal acid lipase (LAL) abrogated cytotoxic response to ERX-41. Cellular thermal shift assays confirmed that ERX-41 binds to LAL. In silico modelling and mutational studies confirmed that ERX-41 interacts with LAL through residues in its LXXLL domain and that ERX-41 ability to induce ER stress and cell death in TNBC is independent of the lipase activity of LAL. Unbiased RNA-seq studies with and without ERX-41 in parental and LIPA KO SUM-159 cells revealed induction of genes involved in ER stress and UPR response by ERX-41 in parental SUM-159 cells but not in cells with LIPA KO. Ultrastructural studies using live-cell confocal microscopy show that LIPA KO abrogated ER morphological changes at 2 and 4 h after ERX-41 treatment. Further, subcellular localization studies showed LIPA localizes to endoplasmic reticulum (ER). Unbiased proteomic approaches (TurboID and DIA mass spec) identified a core set of proteins that were both LAL binders and affected by ERX-41 treatment. GO analyses of LAL binding proteins confirmed their involvement in protein folding. Tumor micro array (TMA) analyses confirmed that >80% of primary TNBC tumors had significant and detectable LAL protein expression in contrast, normal breast tissue had lower LAL expression. ERX-41 (10 mg/kg body weight) decreased growth of four distinct TNBC patient-derived xenografts (PDXs) in vivo. Conclusions: Our results identified a new molecular target (LAL) for ERX-41 and novel mechanism of action (disruption of protein folding and induction of ER stress) that may have utility in treating patients with TNBC.

Citation Format: Suryavathi Viswanadhapalli, Xihui Liu, Uday Pratap, Gangadhara R. Sareddy, Susan T. Weintraub, Ganesh V. Raj, Jung-Mo Ahn, Ratna K. Vadlamudi. Lysosomal acid lipase (LIPA) as a novel therapeutic vulnerability for treating TNBC [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-14.

Emerging hormonal agents for the treatment of prostate cancer

INTRODUCTION

Prostate cancer is the most common solid organ malignancy in men in the United States. Until recently, treatment options for men with metastatic disease were limited and patients faced poor outcomes with minimal alternatives. The landscape of prostate cancer treatment has transformed and taken shape over the last 20 years with novel hormonal and non-hormonal therapeutics that have demonstrated significant improvement in survival. However, patients with advanced disease still face imminent progression on hormone blockade therapy.

AREAS COVERED

There is a significant market opportunity to devise novel, more potent agents for patients with hormone-resistant disease. Here we review the existing treatment options in men with advanced prostate cancer, the market opportunity within this field, goals of current research, and the novel agents under investigation, including androgen receptor degraders, testosterone synthesis pathway inhibitors, DNA-binding domain and N-terminal domain antagonists, and the combination of hormonal and non-hormonal agents.

EXPERT OPINION

Combination therapy regimens and novel agents targeting alternative binding domains of the androgen receptor are of great interest, as they may overcome resistance mechanisms and hold promise as the future of advanced prostate cancer treatment.

A first-in-class inhibitor of ER coregulator PELP1 targets ER+ breast cancer

Most patients with estrogen receptor alpha-positive breast cancers (ER+ BC) initially respond to treatment but eventually develop therapy resistance with disease progression. Overexpression of oncogenic ER coregulators, including proline, glutamic acid, and leucine-rich protein 1 (PELP1), are implicated in BC progression. The lack of small molecules that inhibits PELP1 represents a major knowledge gap. Here, using a yeast-two-hybrid screen, we identified novel peptide inhibitors of PELP1 (PIPs). Biochemical assays demonstrated that one of these peptides, PIP1, directly interacted with PELP1 to block PELP1 oncogenic functions. Computational modeling of PIP1 revealed key residues contributing to its activity and facilitated the development of a small molecule inhibitor of PELP1, SMIP34, and further analyses confirmed that SMIP34 directly bound to PELP1. In BC cells, SMIP34 reduced cell growth in a PELP1-dependent manner. SMIP34 inhibited proliferation of not only wild-type (WT) but also mutant (MT) ER+ and therapy-resistant (TR) BC cells, in part by inducing PELP1 degradation via the proteasome pathway. RNA-seq analyses showed that SMIP34 treatment altered the expression of genes associated with estrogen response, cell cycle, and apoptosis pathways. In cell line-derived and patient-derived xenografts of both WT- and MT- ER+ BC models, SMIP34 reduced proliferation and significantly suppressed tumor progression. Collectively, these results demonstrate SMIP34 as a first-in-class inhibitor of oncogenic PELP1 signaling in advanced BC.

Targeting ESR1 mutation-Induced transcriptional addiction in breast cancer with BET inhibition

Acquired mutations in the ligand-binding domain (LBD) of the gene encoding Estrogen Receptor alpha (ESR1) are a common mechanism of endocrine therapy resistance in metastatic ER-positive breast cancer patients. ESR1 Y537S mutation, in particular, is associated with development of resistance to most endocrine therapies used to treat breast cancer. Employing a high-throughput screen of nearly 1200 Federal Drug Administration (FDA)-approved drugs, we show that OTX015, a bromodomain and extraterminal domain (BET) inhibitor, is one of the top suppressors of ESR1 mutant cell growth. OTX015 was more efficacious than fulvestrant, a selective ER degrader, in inhibiting ESR1 mutant xenograft growth. When combined with abemaciclib, a CDK4/6 inhibitor, OTX015 induced more potent tumor regression than current standard-of-care treatment of abemaciclib+fulvestrant. OTX015 has preferential activity against Y537S mutant breast cancer cells and blocks their clonal selection in competition studies with wild-type cells. Thus, BET inhibition has the potential to both prevent and overcome ESR1 mutant-induced endocrine therapy resistance in breast cancer.

Targeting radioresistance and replication fork stability in prostate cancer

The bromodomain and extraterminal (BET) family of chromatin reader proteins bind to acetylated histones and regulate gene expression. The development of BET inhibitors (BETi) has expanded our knowledge of BET protein function beyond transcriptional regulation and has ushered several prostate cancer (PCa) clinical trials. However, BETi as a single agent is not associated with antitumor activity in patients with castration-resistant prostate cancer (CRPC). We hypothesized novel combinatorial strategies are likely to enhance the efficacy of BETi. By using PCa patient-derived explants and xenograft models, we show that BETi treatment enhanced the efficacy of radiation therapy (RT) and overcame radioresistance. Mechanistically, BETi potentiated the activity of RT by blocking DNA repair. We also report a synergistic relationship between BETi and topoisomerase I (TOP1) inhibitors (TOP1i). We show that the BETi OTX015 synergized with the new class of synthetic noncamptothecin TOP1i, LMP400 (indotecan), to block tumor growth in aggressive CRPC xenograft models. Mechanistically, BETi potentiated the antitumor activity of TOP1i by disrupting replication fork stability. Longitudinal analysis of patient tumors indicated that TOP1 transcript abundance increased as patients progressed from hormone-sensitive prostate cancer to CRPC. TOP1 was highly expressed in metastatic CRPC, and its expression correlated with the expression of BET family genes. These studies open new avenues for the rational combinatorial treatment of aggressive PCa.

Dose-Intensified Stereotactic Ablative Radiation for Localized Prostate Cancer

Purpose

Stereotactic ablative radiation (SAbR) has been increasingly used in prostate cancer (PCa) given its convenience and cost efficacy. Optimal doses remain poorly defined with limited prospective comparative trials and long-term safety/efficacy data at higher dose levels. We analyzed toxicity and outcomes for SAbR in men with localized PCa at escalated 45 Gy in 5 fractions.

Methods and Materials

This study retrospectively analyzed men from 2015 to 2019 with PCa who received linear-accelerator-based SAbR to 45 Gy in 5 fractions, along with perirectal hydrogel spacer, fiducial placement, and MRI-based planning. Disease control outcomes were calculated from end of treatment. Minimally important difference (MID) assessing patient-reported quality of life was defined as greater than a one-half standard deviation increase in American Urological Association (AUA) symptom score after SAbR.

Results

Two-hundred and forty-nine (249) low-, intermediate-, and high-risk PCa patients with median follow-up of 14.9 months for clinical toxicity were included. Acute urinary grade II toxicity occurred in 20.4% of patients. Acute grade II GI toxicity occurred in 7.3% of patients. For follow-up > 2 years (n = 69), late GU and GI grade ≥III toxicity occurred in 5.8% and 1.5% of patients, respectively. MID was evident in 31.8%, 23.4%, 35.8%, 37.0%, 33.3%, and 26.7% of patients at 3, 6, 12, 24, 36, and 48 months, respectively. The median follow-up for biochemical recurrence was 22.6 months with biochemical failure-free survival of 100% at 1 year (n = 226) and 98.7% for years 2 (n = 113) and 3 (n = 54).

Conclusions

SAbR for PCa at 45 Gy in 5 fractions shows an encouraging safety profile. Prospective studies with longer follow-up are warranted to establish this dose regimen as standard of care for PCa.

The central role of Sphingosine kinase 1 in the development of neuroendocrine prostate cancer (NEPC): A new targeted therapy of NEPC

Background

Neuroendocrine prostate cancer (NEPC) is often diagnosed as a sub‐type from the castration‐resistant prostate cancer (CRPC) recurred from the second generation of anti‐androgen treatment and is a rapidly progressive fatal disease. The molecular mechanisms underlying the trans‐differentiation from CRPC to NEPC are not fully characterized, which hampers the development of effective targeted therapy.

Methods

Bioinformatic analyses were conducted to determine the clinical correlation of sphingosine kinase 1 (SphK1) in CRPC progression. To investigate the transcriptional regulation SphK1 and neuroendocrine (NE) transcription factor genes, both chromosome immunoprecipitation and luciferase reporter gene assays were performed. To demonstrate the role of SphK1 in NEPC development, neurosphere assay was carried out along with several biomarkers determined by quantitative PCR and western blot. Furthermore, in vivo NEPC xenograft models and patient‐derived xenograft (PDX) model were employed to determine the effect of SphK1 inhibitors and target validation.

Results

Significant prevalence of SphK1 in NEPC development is observed from clinical datasets. SphK1 is transcriptionally repressed by androgen receptor‐RE1‐silencing transcription factor (REST) complex. Furthermore, sphingosine 1‐phosphate produced by SphK1 can modulate REST protein turnover via MAPK signaling pathway. Also, decreased REST protein levels enhance the expression of NE markers in CRPC, enabling the transition to NEPC. Finally, specific SphK1 inhibitors can effectively inhibit the growth of NEPC tumors and block the REST protein degradation in PDX.

Conclusions

SphK1 plays a central role in NEPC development, which offers a new target for this lethal cancer using clinically approved SphK1 inhibitors.

Poly-glutamine-dependent self-association as a potential mechanism for regulation of androgen receptor activity

The androgen receptor (AR) plays a central role in prostate cancer. Development of castration resistant prostate cancer (CRPC) requires androgen-independent activation of AR, which involves its large N-terminal domain (NTD) and entails extensive epigenetic changes depending in part on histone lysine demethylases (KDMs) that interact with AR. The AR-NTD is rich in low-complexity sequences, including a polyQ repeat. Longer polyQ sequences were reported to decrease transcriptional activity and to protect against prostate cancer, although they can lead to muscular atrophy. However, the molecular mechanisms underlying these observations are unclear. Using NMR spectroscopy, here we identify weak interactions between the AR-NTD and the KDM4A catalytic domain, and between the AR ligand-binding domain and a central KDM4A region that also contains low-complexity sequences. We also show that the AR-NTD can undergo liquid-liquid phase separation in vitro, with longer polyQ sequences phase separating more readily. Moreover, longer polyQ sequences hinder nuclear localization in the absence of hormone and increase the propensity for formation of AR-containing puncta in the nucleus of cells treated with dihydrotestosterone. These results lead us to hypothesize that polyQ-dependent liquid-liquid phase separation may provide a mechanism to decrease the transcriptional activity of AR, potentially opening new opportunities to design effective therapies against CRPC and muscular atrophy.

Alterations in BRCA2 as Determinants of Therapy Response in Prostate Cancer

Prostate cancer (PCa) is one of the leading causes of cancer diagnoses and cancer-related deaths in the United States. Mutations or deletions in the genes involved in the DNA damage response (DDR) are common in aggressive primary PCa (germline alterations) and further enriched in advanced therapy-resistant PCa (somatic alterations). Among the DDR genes, BRCA2 is the most commonly altered (~ 13%) in advanced therapy-resistant PCa. Patients with BRCA2-altered PCas are exquisitely sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis). Indeed, two PARPis-olaparib and rucaparib have recently gained U.S. Food & Drug Administration approval for the treatment of advanced PCas harboring a BRCA2 mutation. This review seeks to explore the role of BRCA2 in DNA damage repair, the pathogenesis and progression of BRCA2 mutant PCa, and the utility of radiation therapy, targeted therapies, and platinum-based chemotherapies for patients with BRCA2 alterations.

SAbR for High-Risk Prostate Cancer-A Prospective Multilevel MRI-Based Dose Escalation Trial

PURPOSE

Radiation dose intensification improves outcome in men with high-risk prostate cancer (HR-PCa). A prospective trial was conducted to determine safety, feasibility, and maximal tolerated dose of multilevel magnetic resonance imaging (MRI)-based 5-fraction SAbR in patients with HR-PCa.

METHODS AND MATERIALS

This phase I clinical trial enrolled patients with HR-PCa with grade group ≥4, prostate-specific antigen (PSA) ≥20 ng/mL, or radiographic ≥T3, and well-defined prostatic lesions on multiparametric MRI (mpMRI) into 4 dose-escalation cohorts. The initial cohort received 47.5 Gy to the prostate, 50 Gy to mpMRI-defined intraprostatic lesion(s), and 22.5 Gy to pelvic lymph nodes in 5 fractions. Radiation doses were escalated for pelvic nodes to 25 Gy and mpMRI lesion(s) to 52.5 Gy and then 55 Gy. Escalation was performed sequentially according to rule-based trial design with 7 to 15 patients per cohort and a 90-day observation period. All men received peri-rectal hydrogel spacer, intraprostatic fiducial placement, and 2 years of androgen deprivation. The primary endpoint was maximal tolerated dose according to a 90-day acute dose-limiting toxicity (DLT) rate <33%. DLT was defined as National Cancer Institute Common Toxicity Criteria for Adverse Events ≥grade 3 treatment-related toxicity. Secondary outcomes included acute and delayed gastrointestinal (GI)/genitourinary (GU) toxicity graded with Common Toxicity Criteria for Adverse Events.

RESULTS

Fifty-five of the 62 enrolled patients were included in the analysis. Dose was escalated through all 4 cohorts without observing any DLTs. Median overall follow-up was 18 months, with a median follow-up of 42, 24, 12, and 7.5 months for cohorts 1 to 4 respectively. Acute and late grade 2 GU toxicities were 25% and 20%, while GI were 13% and 7%, respectively. Late grade 3 GU and GI toxicities were 2% and 0%, respectively.

CONCLUSIONS

SAbR dose for HR-PCa was safely escalated with multilevel dose painting of 47.5 Gy to prostate, 55 Gy to mpMRI-defined intraprostatic lesions, and 25 Gy to pelvic nodal region in 5 fractions. Longer and ongoing follow-up will be required to assess late toxicity.

LIFR inhibition enhances the therapeutic efficacy of HDAC inhibitors in triple negative breast cancer

Histone deacetylase inhibitors (HDACi) are identified as novel therapeutic agents, however, recent clinical studies suggested that they are marginally effective in treating triple negative breast cancer (TNBC). Here, we show that first-in-class Leukemia Inhibitory Factor Receptor (LIFRα) inhibitor EC359 could enhance the therapeutic efficacy of HDACi against TNBC. We observed that both targeted knockdown of LIFR with CRISPR or treatment with EC359 enhanced the potency of four different HDACi in reducing cell viability, cell survival, and enhanced apoptosis compared to monotherapy in TNBC cells. RNA-seq studies demonstrated oncogenic/survival signaling pathways activated by HDACi were attenuated by the EC359 + HDACi therapy. Importantly, combination therapy potently inhibited the growth of TNBC patient derived explants, cell derived xenografts and patient-derived xenografts in vivo. Collectively, our results suggest that targeted inhibition of LIFR can enhance the therapeutic efficacy of HDACi in TNBC.

Abstract 1237: Preclinical evaluation of ERX-41 in triple negative breast cancer

Background: Women with triple-negative breast cancer (TNBC) have a more aggressive clinical course, with a higher propensity to metastasize and a worse outcome due to a lack of effective therapies and significant intratumoral and intertumoral heterogeneity. Development of novel therapeutic strategies represents a clear unmet need. We have developed a first-in-class compound, an oligobenzamide, ERX-41, that has anti-proliferative activity against all six molecular subtypes of TNBC.

Methods: In vitro activity of ERX-41 on TNBC cell lines was tested using CellTiter glo, MTT, and apoptosis assays. Efficacy of ERX-41 was tested using TNBC patient derived explants (PDEs) ex vivo, cell line-derived xenografts (CDXs), and patient derived xenografts (PDX) in vivo. To examine the mechanism, we conducted mass spec analyses using total lysates of TNBC cells treated with vehicle or ERX-41.

Results: ERX-41 demonstrated potent activity in both blocking proliferation and inducing apoptosis in 30 distinct cell line models of TNBC, (representing all six molecular subtypes of TNBC), with an IC50 that ranges from 50-250nM. Incubation of ERX-41 with PDEs from primary TNBC patient tumors ex vivo caused a significant reduction in proliferation indices, as measured by Ki67 staining. ERX-41 also decreased proliferation and increased apoptosis in explants from TNBC CDX and PDX tumors cultured ex vivo. Oral administration of ERX-41 (10 mg/kg/daily) was shown to be non-toxic and dramatically limited the growth of CDX tumors derived from MDA-MB-231, SUM-159 or D2A1 syngeneic tumors. Importantly, ERX-41 treatment also significantly reduced tumor progression in four TNBC PDX (PDX-1, PDX-89, PDX-96 and PDX-98) models compared to the vehicle treated control group. Our ultrastructural and molecular studies indicate that ERX-41 induces significant endoplasmic reticulum (ER) stress within TNBC cells but not in primary epithelial cells. Global mass spectrometry studies indicated that ERX-41 treatment resulted in the alteration [down regulation (265 proteins) or upregulation (218 proteins)] of 483 proteins out of ~4000 proteins quantified with two or more peptides. Reactome pathway analysis indicated that the top pathways modulated by ERX-41 included Intra-Golgi and retrograde Golgi-to-ER traffic, membrane trafficking and TP53 mediated apoptosis. ER stress induced by ERX-41 blocks de novo protein synthesis, and triggers ER-assisted degradation (ERAD) pathways, causing TNBC apoptotic cell death.

Conclusions: ERX-41 is orally bioavailable, non-toxic, and demonstrated activity in primary PDEs, CDXs and PDXs. The ability of ERX-41 to induce ER stress and apoptotic cell death in multiple types of TNBC suggests that this drug targets a fundamental weakness in TNBC cells (the high basal level of ER stress) and can effectively overcome the heterogeneity of TNBC. These studies strongly support the further clinical translation of ERX-41.

Citation Format: Suryavathi Viswanadhapalli, Xihui Liu, Shi-Hong Ma, Tae-Kyung Lee, Mengxing Li, Weiwei Tang, Junhao Liu, Xiaonan Li, Gangadhara R. Sareddy, Rajeshwar Rao Tekmal, Jung-Mo Ahn, Ratna K. Vadlamudi, Ganesh V. Raj. Preclinical evaluation of ERX-41 in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1237.

Abstract PS17-09: Development of a potent mutant-ESR1 targeted agent, ERX-245, for treating metastatic therapy-resistant breast cancer

Background: ESR1 mutations are acquired following ERα targeted therapies and are a major determinant of therapy-resistance. These ESR1 mutations maintain ESR1 signaling, albeit in a ligand-independent manner. Effective drugs targeting these mutant (MT) ERα proteins represent a significant unmet clinical need. We had previously shown that ERX-11, an ESR1-coregulator binding inhibitor, could block the function of these MT ERα proteins. In this study, we sought to leverage recently published structures of MT ERα to develop more potent analogues of ERX-11. Methods: Virtual screening of &gt;250,000 derivatives of ERX-11 was performed with simulated docking on the MT ERα to identify and design analogues of ERX-11. Several hundred analogues were synthesized and tested in vitro using multiple BC model cells that express wild type (WT) ESR1 or mutant (MT) ESR1 (Y537S or D538G). Mechanistic studies were performed using RNA-Seq, Western blotting, qRT-PCR and reporter gene assays. The in vivo efficacy of the most potent ERX-11 analogue ERX-245 was examined using xenograft, PDX and metastatic models of MT-ER driven BC. Results: From our virtual and functional screen, we identified an ERX-11 analogue, ERX-245 as the most potent hit to target MT-ERα. Docking studies modeled a better fit of ERX-245 into the ligand binding domain of both the Y537S and D538G MT-ERα. ERX-245 potently reduced (IC50 ~250 nM) the cell viability of both WT-ERα and MT-ERα driven BC cells but not ERα negative BC cells. ERX-245 significantly reduced the growth (colony formation, clonogenic and mammosphere assays) of MT-ERα BC cells. ERX-245 exhibited synergistic activity in combination with CDK4/6 inhibitors. In distinction to classic SERDs like fulvestrant (which degrade ERα with in 4h), ERX-245 treatment decreased MT-ERα protein levels over 24 hours. PK studies indicated that ERX-245 is more polar and has better solubility and pharmacokinetic properties than ERX-11. ERX-245 reduced tumor growth of subcutaneous xenograft and PDX models driven by MT-ERα as well as the proliferation of xenograft derived MT-ERα explant models. ERX-245 significantly reduced the invasive capability of MT-ERα BC cells in vitro and inhibited both the metastatic capability and growth of metastatic tumors derived from MT-ERα BC cells injected by intracardiac or intratibial routes. Conclusions: Taken together, these results indicate that ERX-245 is a potent and pharmacologically translatable analog of ERX-11, with activity against both primary and metastatic tumors driven by MT-ERα.

Citation Format: Ganesh V Raj, Suryavathi Viswanadhapalli, Karla Parra, Shihong Ma, Tae-Kyung Lee, Xihui Liu, Kara Kassees, Weiwei Tang, Junhao Liu, Zexuan Liu, Uday P Pratap, Behnam Ebrahimi, Rajeshwar Rao Tekmal, Jung-Mo Ann, Ratna K Vadlamudi. Development of a potent mutant-ESR1 targeted agent, ERX-245, for treating metastatic therapy-resistant breast cancer [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 PS17-09.

The landscape of RNA polymerase II-associated chromatin interactions in prostate cancer

Transcriptional dysregulation is a hallmark of prostate cancer (PCa). We mapped the RNA polymerase II-associated (RNA Pol II-associated) chromatin interactions in normal prostate cells and PCa cells. We discovered thousands of enhancer-promoter, enhancer-enhancer, as well as promoter-promoter chromatin interactions. These transcriptional hubs operate within the framework set by structural proteins - CTCF and cohesins - and are regulated by the cooperative action of master transcription factors, such as the androgen receptor (AR) and FOXA1. By combining analyses from metastatic castration-resistant PCa (mCRPC) specimens, we show that AR locus amplification contributes to the transcriptional upregulation of the AR gene by increasing the total number of chromatin interaction modules comprising the AR gene and its distal enhancer. We deconvoluted the transcription control modules of several PCa genes, notably the biomarker KLK3, lineage-restricted genes (KRT8, KRT18, HOXB13, FOXA1, ZBTB16), the drug target EZH2, and the oncogene MYC. By integrating clinical PCa data, we defined a germline-somatic interplay between the PCa risk allele rs684232 and the somatically acquired TMPRSS2-ERG gene fusion in the transcriptional regulation of multiple target genes - VPS53, FAM57A, and GEMIN4. Our studies implicate changes in genome organization as a critical determinant of aberrant transcriptional regulation in PCa.

Overcoming oncogene addiction in breast and prostate cancers: a comparative mechanistic overview

Prostate cancer (PCa) and breast cancer (BCa) are both hormone-dependent cancers that require the androgen receptor (AR) and estrogen receptor (ER, ESR1) for growth and proliferation, respectively. Endocrine therapies that target these nuclear receptors (NRs) provide significant clinical benefit for metastatic patients. However, these therapeutic strategies are seldom curative and therapy resistance is prevalent. Because the vast majority of therapy-resistant PCa and BCa remain dependent on the augmented activity of their primary NR driver, common mechanisms of resistance involve enhanced NR signaling through overexpression, mutation, or alternative splicing of the receptor, coregulator alterations, and increased intracrine hormonal synthesis. In addition, a significant subset of endocrine therapy-resistant tumors become independent of their primary NR and switch to alternative NR or transcriptional drivers. While these hormone-dependent cancers generally employ similar mechanisms of endocrine therapy resistance, distinct differences between the two tumor types have been observed. In this review, we compare and contrast the most frequent mechanisms of antiandrogen and antiestrogen resistance, and provide potential therapeutic strategies for targeting both advanced PCa and BCa.

Jean Wilson and His Legacy, 50 Years and Counting

OBJECTIVE

To evaluate the legacy of endocrinologist Jean Wilson, whose discovery in 1969 of 5 alpha-reductase (5AR) and description of dihydrotestosterone (DHT) as the primary hormone associated with prostatic growth ushered in a golden age of collaboration between endocrinologists, oncologists, and urologists that led to some of the critical discoveries in the understanding and treatment of prostatic pathology.

MATERIALS AND METHODS

A review of the medical literature between 1969 and 2020 was conducted and multiple authors interviewed.

RESULTS

In 1969, Gloyna and Wilson demonstrated the reduction of testosterone to DHT in the prostate. With Bruchovsky, Wilson established that DHT was the primary hormone associated with prostatic growth. Wilson went on to show that androgens are involved in every aspect of prostate development, growth, and function. Wenderoth and Wilson then showed that a 5AR inhibitor blocked the prostatic growth. Subsequently, clinical trials with therapies targeting 5AR were led by Roehrborn and McConnell. Tilley and Wilson with Marcelli and McPhaul cloned the human androgen receptor at UT Southwestern in 1989 and provided the first evidence that androgen receptor was a transcriptional factor that could regulate its own expression in prostate cancer. Androgen receptor mutations explaining the molecular basis of androgen resistance syndromes were first described by Wilson, McPhaul, et al in the early 1990s.

CONCLUSION

Basic, translational, and clinical research has played a pivotal role in our current understanding of prostatic disease. Much of this legacy is credited to Jean Wilson and the cross-pollination of world-class scientists across fields, whom he inspired.

Synthesis and fluorine-18 radiolabeling of a phospholipid as a PET imaging agent for prostate cancer

INTRODUCTION

Altered lipid metabolism and subsequent changes in cellular lipid composition have been observed in prostate cancer cells, are associated with poor clinical outcome, and are promising targets for metabolic therapies. This study reports for the first time on the synthesis of a phospholipid radiotracer based on the phospholipid 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine (PC44:12) to allow tracking of polyunsaturated lipid tumor uptake via PET imaging. This tracer may aid in the development of strategies to modulate response to therapies targeting lipid metabolism in prostate cancer.

METHODS

Lipidomics analysis of prostate tumor explants and LNCaP tumor cells were used to identify PC44:12 as a potential phospholipid candidate for radiotracer development. Synthesis of phosphocholine precursor and non-radioactive standard were optimised using click chemistry. The biodistribution of a fluorine-18 labeled analogue, N-{[4-(2-[¹⁸F]fluoroethyl)-2,3,4-triazol-1-yl]methyl}-1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine ([¹⁸F]2) was determined in LNCaP prostate tumor-bearing NOD SCID gamma mice by ex vivo biodistribution and PET imaging studies and compared to biodistribution of [¹⁸F]fluoromethylcholine.

RESULTS

[¹⁸F]2 was produced with a decay-corrected yield of 17.8 ± 3.7% and an average radiochemical purity of 97.00 ± 0.89% (n = 6). Molar activity was 85.1 ± 3.45 GBq/μmol (2300 ± 93 mCi/μmol) and the total synthesis time was 2 h. Ex vivo biodistribution data demonstrated high liver uptake (41.1 ± 9.2%ID/g) and high splenic uptake (10.9 ± 9.1%ID/g) 50 min post-injection. Ex vivo biodistribution showed low absolute tumor uptake of [¹⁸F]2 (0.8 ± 0.3%ID/g). However, dynamic PET imaging demonstrated an increase over time of the relative tumor-to-muscle ratio with a peak of 2.8 ± 0.5 reached 1 h post-injection. In contrast, dynamic PET of [¹⁸F]fluoromethylcholine demonstrated no increase in tumor-to-muscle ratios due to an increase in both tumor and muscle over time. Absolute uptake of [¹⁸F]fluoromethylcholine was higher and peaked at 60 min post injection (2.25 ± 0.29%ID/g) compared to [¹⁸F]2 (1.44 ± 0.06%ID/g) during the 1 h dynamic scan period.

CONCLUSIONS AND ADVANCES IN KNOWLEDGE

This study demonstrates the ability to radiolabel phospholipids and indicates the potential to monitor the in vivo distribution of phospholipids using fluorine-18 based PET.

Dynamic differences between DNA damage repair responses in primary tumors and cell lines

The study of DNA damage repair response (DDR) in prostate cancer is restricted by the limited number of prostate cancer cell lines and lack of surrogates for heterogeneity in clinical samples. Here, we sought to leverage our experience with patient derived explants (PDEs) cultured ex vivo to study dynamics of DDR in primary tumors following application of clinically relevant doses of ionizing radiation (IR) to tumor cells in their native 3-dimensional microenvironment. We compared DDR dynamics between prostate cancer cell lines, PDEs and xenograft derived explants (XDEs) following treatment with IR (2Gy) either alone or in combination with pharmacological modulators of DDR. We have shown that following treatment with 2Gy, DDR can be consistently detected in PDEs from multiple solid tumors, including prostate, kidney, testes, lung and breast, as evidenced by γ-H2AX, 53BP1, phospho-ATM and phospho-DNA-PKcs foci. By examining kinetics of resolution of IR-induced foci, we have shown that DDR in prostate PDEs (complete resolution in 8 h) is much faster than in prostate cancer cell lines (<50% resolution in 8 h). The transcriptional profile of DDR genes following 2Gy IR appears to be distinct between PDEs and cell lines. Pre-treatment with drugs targeting DDR pathways differentially alter the kinetics of DDR in the PDEs and cell lines, as evidenced by altered kinetics of foci resolution. This study highlights the utility of PDEs as a robust model system for short-term evaluation of DDR in primary solid tumors in clinically relevant microenvironment.

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IR induces distinct DNA damage repair kinetics in prostate cancer PDEs and cell lines.

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IR induces a distinct transcriptional program in prostate cancer PDE and cell lines.

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DNA-PKcs inhibition blocks IR-induced DDR in prostate cancer PDE.

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Inhibition of AR impairs NHEJ in prostate cancer PDEs.

Implementation of Germline Testing for Prostate Cancer: Philadelphia Prostate Cancer Consensus Conference 2019

PURPOSE

Germline testing (GT) is a central feature of prostate cancer (PCA) treatment, management, and hereditary cancer assessment. Critical needs include optimized multigene testing strategies that incorporate evolving genetic data, consistency in GT indications and management, and alternate genetic evaluation models that address the rising demand for genetic services.

METHODS

A multidisciplinary consensus conference that included experts, stakeholders, and national organization leaders was convened in response to current practice challenges and to develop a genetic implementation framework. Evidence review informed questions using the modified Delphi model. The final framework included criteria with strong (> 75%) agreement (Recommend) or moderate (50% to 74%) agreement (Consider).

RESULTS

Large germline panels and somatic testing were recommended for metastatic PCA. Reflex testing-initial testing of priority genes followed by expanded testing-was suggested for multiple scenarios. Metastatic disease or family history suggestive of hereditary PCA was recommended for GT. Additional family history and pathologic criteria garnered moderate consensus. Priority genes to test for metastatic disease treatment included BRCA2, BRCA1, and mismatch repair genes, with broader testing, such as ATM, for clinical trial eligibility. BRCA2 was recommended for active surveillance discussions. Screening starting at age 40 years or 10 years before the youngest PCA diagnosis in a family was recommended for BRCA2 carriers, with consideration in HOXB13, BRCA1, ATM, and mismatch repair carriers. Collaborative (point-of-care) evaluation models between health care and genetic providers was endorsed to address the genetic counseling shortage. The genetic evaluation framework included optimal pretest informed consent, post-test discussion, cascade testing, and technology-based approaches.

CONCLUSION

This multidisciplinary, consensus-driven PCA genetic implementation framework provides novel guidance to clinicians and patients tailored to the precision era. Multiple research, education, and policy needs remain of importance.

Abstract 5676: Preclinical evaluation of estrogen receptor coregulator binding inhibitor ERX-245 in breast cancer

Background: Breast cancer (BC) is the most common cancer in American women. Majority of BC (70%) is estrogen receptor alpha (ERα) positive and these tumors initially respond to ER-targeted therapy, however, acquired therapy-resistance limit the utility of ERα-targeted therapy using aromatase inhibitors and antiestrogens. Importantly, both therapy-sensitive and therapy-resistant tumors retain ESR1 signaling, via interaction with critical oncogenic coregulator proteins. We recently developed a small organic molecule, ESR1 coregulator binding inhibitor ERX-11. The objective of this study is to develop better analogues of ERX-11 using medicinal chemistry approaches.

Methods: Virtual screening of a quarter million compounds and medicinal chemistry approaches were used to design new analogues of ERX-11 and identified ERX-245 as potent analogue. Effect of ERX-245 was evaluated in vitro using multiple BC models that express wild type (WT) ERα (MCF-7, ZR-75) and BC models with acquired resistance (MCF-7-Tam, MCF-7-LTLT). Mechanistic studies were performed using RNA-Seq, Western blotting, qRT-PCR and reporter gene assays. The in vivo efficacy of ERX-245 was examined using xenograft, and xenograft-derived explant (XDEx) models.

Results: We initially performed an intensive virtual screening of a quarter million compounds and selected several candidates that showed strong binding energy to ERα. We then designed and developed several analogues of ERX-11 using modeled structural interactions. Using this approach, we identified ERX-245 as a potential lead compound for interaction with ERα. Like the parental ERX-11, ERX-245 significantly reduced the cell viability of both WT and therapy-resistant BC cells with an IC50 of 300-500 nM with minimal activity in ER-negative models such as TNBC cells. In long-term colony formation assays, ERX-245 significantly reduced the colony formation ability of both ER-WT and therapy-resistant BC cells. In ERE reporter assays, ERX-245 significantly reduced the estrogen-mediated reporter activity. ERX-245 significantly reduced the invasion of endocrine-resistant BC cells. RNA sequencing revealed unique pathways blocked by ERX-245. PK studies indicated that ERX-245 is more polar and has better solubility and pharmacokinetic properties compared to ERX-11. Treatment of ERX-245 decreased the proliferation and increased apoptosis (TUNEL staining) in xenograft derived explant (XDEx) models. ERX-245 also showed potent activity against WT-ERα and therapy-resistant xenograft models.

Conclusions: Collectively, these results suggest that the ERX-11 analogue ERX-245 has potential to therapeutically target endocrine therapy resistant BC.

Citation Format: Suryavathi Viswanadhapalli, Shihong Ma, Tae Kyung Lee, Xihui Liu, Kara Kassees, Uday P. Pratap, Junhao Liu, Weiwei Tang, Rajeshwar R. Tekmal, Jung-Mo Ahn, Ganesh V. Raj, Ratna K. Vadlamudi. Preclinical evaluation of estrogen receptor coregulator binding inhibitor ERX-245 in breast cancer [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 5676.

Mithramycin suppresses DNA damage repair via targeting androgen receptor in prostate cancer

The dependency of prostate cancer (PCa) growth on androgen receptor (AR) signaling has been harnessed to develop first-line therapies for high-risk localized and metastatic PCa treatment. However, the occurrence of aberrant expression, mutated or splice variants of AR confers resistance to androgen ablation therapy (ADT), radiotherapy or chemotherapy in AR-positive PCa. Therapeutic strategies that effectively inhibit the expression and/or transcriptional activity of full-length AR, mutated AR and AR splice variants have remained elusive. In this study, we report that mithramycin (MTM), an antineoplastic antibiotic, suppresses cell proliferation and exhibits dual inhibitory effects on expression and transcriptional activity of AR and AR splice variants. MTM blocks AR recruitment to its genomic targets by occupying AR enhancers and causes downregulation of AR target genes, which includes key DNA repair factors in DNA damage repair (DDR). We show that MTM significantly impairs DDR and enhances the effectiveness of ionizing radiation or the radiomimetic agent Bleomycin in PCa. Thus, the combination of MTM treatment with RT or radiomimetic agents, such as bleomycin, may present a novel effective therapeutic strategy for patients with high-risk, clinically localized PCa.

SAT-119 Targeting Glutamate Metabolism and Signaling in ER+, Endocrine Therapy-Resistant Breast Cancer

Estrogen receptor-positive (ER+) breast cancer is the most commonly diagnosed form of this malignancy. Aromatase inhibitors and selective estrogen receptor modulators or degraders (SERMS, SERDs) can be highly effective in treating ER+ breast cancer, but de novo and acquired resistance to these interventions is a persistent clinical problem. Endocrine therapy resistant breast cancer cells rewire their metabolism to support cellular demands associated with rapid proliferation and/or increased invasion and metastasis. An important feature of this metabolic flexibility is conversion of glutamine to glutamate, an amino acid integral to protection of cells from oxidative stress. Consistent with this, we show multiple cellular models of ER+, endocrine resistant breast cancer cells markedly increase glutamate release and upregulate expression of essential glutamine/glutamate metabolic enzymes and transporters, including the glutamate/cystine antiporter xCT, glutamate dehydrogenase (GLUD1/2), and/or the glutamine importer SLC1A5. Riluzole (RIL) is FDA-approved for the treatment of amyotrophic lateral sclerosis (ALS), and has several proposed mechanisms of action, including suppression of glutamate release and increased glutamate uptake. We show ER+, endocrine responsive and resistant breast cancer cells are growth-inhibited by RIL. This is due to an increase in cell death, particularly in endocrine resistant breast cancer cells, and cell cycle arrest. Interestingly, histologic subtype confers a different cell cycle arrest profile, with invasive ductal cancer (IDC) models arresting in G1 but invasive lobular cancer (ILC) models arresting in G2/M. Isobologram analysis of RIL plus SERMs or SERDs shows additive-to-synergistic activity in a subset of ER+ cell line models, and preliminary studies show combination activity in patient-derived explants (PDEs). Mechanistically, we tested whether signaling through metabotropic glutamate receptors (mGluRs, GRMs) and/or cystine import contribute to RIL’s growth-inhibitory phenotype. Antagonists of mGluRs/GRMs don’t phenocopy the effects of RIL, suggesting extracellular glutamate signaling through these receptors is not a key mechanism. Rescue experiments with β-mercaptoethanol to promote cystine uptake through transporters other than xCT show partial reversal of RIL-mediated cell cycle arrest in some cells, suggesting xCT may contribute to RIL-induced growth inhibition. In summary, we show RIL may be a viable addition to endocrine therapy in ER+ breast cancer. Ongoing studies will test additional mechanism(s) by which RIL may attenuate the growth of ER+ breast cancer models in vitro, including inhibition of protein kinase C and casein kinase 1 delta. We are further testing RIL efficacy alone and in combination with a SERD in primary tumors and lung metastases in a ER+ patient-derived xenograft (PDX) model.

Abstract P6-04-05: ERX-41, a novel drug to target and block mutant-ERα-coregulator driven signaling

Background: A significant proportion of breast cancers (BC) that express estrogen receptor α (ERα) will initially respond to antiestrogens or aromatase inhibitors. However, endocrine therapy resistance is common with progression to incurable metastases. A significant proportion (~39%) of therapy resistant tumors acquires ERα mutations which enables estrogen-independent constitutive interaction of ERα with coregulators, transcription and resistance to endocrine therapy. Drugs that specifically target and block mutant-ERα (MT ER)-coregulator driven signaling are urgently needed to treat therapy-resistant BC. Methods: Using an innovative strategy of oligobenzamide-based peptidomimetics (small synthetic organic molecules), we developed an estrogen receptor modulator ERX-41 that disrupt the interactions between MT ERα and critical coregulators. Effect of ERX-41 was evaluated using BC models that express wild type (WT) ERα (MCF-7, ZR-75) and BC models with acquired resistance (MCF-7-TamR, MCF-7-LTLT), and engineered models that express ERα mutations (MCF-7-MT ERα-D538G, MCF-7-MT ERα-Y537S, ZR-75-MT ERα-D538G, ZR-75-MT ERα-Y537S). Mechanistic studies were performed using RNA-Seq, Mass spectrometry, immunoprecipitation, Western blotting, RT-qPCR and reporter gene assays. The in vivo efficacy of ERX-41 was examined using xenograft, and patient-derived explant (PDEX) models. Results: ERX-41 exhibited broad and potent activity (IC50 between 50-125 nM) against both WT and MT ERα driven BC models in in vitro assays. ERX-41 had no activity against benign breast epithelial cells. Mechanistic studies confirmed that ERX-41 modulates multiple ERα functions including alterations in ERα transcription, down regulation of ERα and ERα-signaling. Using immunoprecipitation mass spectrometry (IPMS) analyses, we found that ERX-41 disrupts the interaction of ERα with a number of protein binding partners. RNA-Seq analyses of ERX-41 treated BC cells indicated upregulation of endoplasmic reticulum stress pathways. Furthermore, mechanistic studies confirmed that anti-proliferative effect of ERX-41 is directly related to its ability to induce endoplasmic reticulum stress and subsequent unfolded protein response. Treatment of ERX-41 decreased the proliferation (Ki-67 staining) and increased apoptosis (TUNEL staining) in PDEX models. ERX-41 showed potent activity against WT ERαand MTERα xenograft models but no effect on mouse liver or body weight. Histologic evaluation of these tumors showed dramatically decreased Ki-67 proliferation indices. Conclusions: Collectively, our data indicate that ERX-41 could effectively target both the WT and MT ERα driven signaling and could be clinically translated for the treatment of therapy-resistant BC. Supported by NIH grant CA223828.

Citation Format: Ratna Vadlamudi, Suryavathi Viswanadhapalli, Xihui Liu, Tae-Kyung Lee, Gangadhara R Sareddy, Shihong Ma, Mengxing Li, Ben Ho Park, Rajeshwar R Tekmal, Jung-Mo Ahn, Ganesh V. Raj. ERX-41, a novel drug to target and block mutant-ERα-coregulator driven signaling [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 P6-04-05.

RUVBL1/RUVBL2 ATPase Activity Drives PAQosome Maturation, DNA Replication and Radioresistance in Lung Cancer

RUVBL1 and RUVBL2 (collectively RUVBL1/2) are essential AAA+ ATPases that function as co-chaperones and have been implicated in cancer. Here we investigated the molecular and phenotypic role of RUVBL1/2 ATPase activity in non-small cell lung cancer (NSCLC). We find that RUVBL1/2 are overexpressed in NSCLC patient tumors, with high expression associated with poor survival. Utilizing a specific inhibitor of RUVBL1/2 ATPase activity, we show that RUVBL1/2 ATPase activity is necessary for the maturation or dissociation of the PAQosome, a large RUVBL1/2-dependent multiprotein complex. We also show that RUVBL1/2 have roles in DNA replication, as inhibition of its ATPase activity can cause S-phase arrest, which culminates in cancer cell death via replication catastrophe. While in vivo pharmacological inhibition of RUVBL1/2 results in modest antitumor activity, it synergizes with radiation in NSCLC, but not normal cells, an attractive property for future preclinical development.

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.

A Cellular Anatomy of the Normal Adult Human Prostate and Prostatic Urethra

A comprehensive cellular anatomy of normal human prostate is essential for solving the cellular origins of benign prostatic hyperplasia and prostate cancer. The tools used to analyze the contribution of individual cell types are not robust. We provide a cellular atlas of the young adult human prostate and prostatic urethra using an iterative process of single-cell RNA sequencing (scRNA-seq) and flow cytometry on ~98,000 cells taken from different anatomical regions. Immunohistochemistry with newly derived cell type-specific markers revealed the distribution of each epithelial and stromal cell type on whole mounts, revising our understanding of zonal anatomy. Based on discovered cell surface markers, flow cytometry antibody panels were designed to improve the purification of each cell type, with each gate confirmed by scRNA-seq. The molecular classification, anatomical distribution, and purification tools for each cell type in the human prostate create a powerful resource for experimental design in human prostate disease.

Using single-cell RNA sequencing, immunofluorescence, and flow cytometry, Henry et al. create a cellular anatomy of the normal human prostate and provide the tools to identify, isolate, and localize every cell type. They identify two additional epithelial cell types enriched in the prostatic urethra and proximal prostatic ducts.

DNA-Dependent Protein Kinase Drives Prostate Cancer Progression through Transcriptional Regulation of the Wnt Signaling Pathway

PURPOSE

Protein kinases are known to play a prominent role in oncogenic progression across multiple cancer subtypes, yet their role in prostate cancer progression remains underexplored. The purpose of this study was to identify kinases that drive prostate cancer progression.Experimental Design: To discover kinases that drive prostate cancer progression, we investigated the association between gene expression of all known kinases and long-term clinical outcomes in tumor samples from 545 patients with high-risk disease. We evaluated the impact of genetic and pharmacologic inhibition of the most significant kinase associated with metastatic progression in vitro and in vivo.

RESULTS

DNA-dependent protein kinase (DNAPK) was identified as the most significant kinase associated with metastatic progression in high-risk prostate cancer. Inhibition of DNAPK suppressed the growth of both AR-dependent and AR-independent prostate cancer cells. Gene set enrichment analysis nominated Wnt as the top pathway associated with DNAPK. We found that DNAPK interacts with the Wnt transcription factor LEF1 and is critical for LEF1-mediated transcription.

CONCLUSIONS

Our data show that DNAPK drives prostate cancer progression through transcriptional regulation of Wnt signaling and is an attractive therapeutic target in aggressive prostate cancer.

Abstract 26: Development of potent lead compounds in multiple tumor types

Background: We had earlier reported a novel therapeutic agent, ERX-11, that modulates estrogen receptor coregulator interactions. For lead optimization, we designed, synthesized and tested over 500 analogs of ERX-11 in multiple models of BC. We also tested this library of compounds for activity against other cancer cell lines both in vitro and in vivo and against primary tumors ex vivo.

Methods: In vitro activity was tested using Cell titer glo, MTT, and apoptosis assays.The utility of the ERX analogs in treating therapy resistant ER-positive BC was evaluated using models with acquired resistance (Tamoxifen, Letrozole), and engineered models that express ER mutations. Xenografts were used for testing the utility of ERX analogs in vivo. Primary patient tumor derived explants were used for ex vivo testing of ERX analogs.

Results: Our screening studies identified several ERX analogs with potent activity against BC cells. Subtle changes in the ERX analogs appear to have significant ramifications on both their potency against ER+ BC cell lines and against other tumors types. Some analogs like ERX-41 were more potent than ERX-11 in their ability to block the proliferation of multiple ER-positive BC cell lines (IC50 ranging from 20-200nM). Other analogs like ERX-208 showed similar activity as ERX-11 against ER-positive BC cell lines (IC50 ranging from 100-500nM) but had potent activity against ovarian cancer cell lines. Through iterative changes, we have identified leads compounds with significant activity against other cancers, including in gliomas, ovarian and pancreatic cancers. Although all these compounds were designed to better target the ligand binding pocket of ER, these active compounds do not all target ER and appear to target other proteins, including other nuclear receptors. Some compounds for example have activity in ER-negative breast cancers. In several xenograft models, including pancreatic cancer and ER-negative, the activity of the compounds have been confirmed by oral administration of the ERX analog in vivo. We have also validated the activity of these analogs in patient-derived explants cultured ex vivoin multiple tumor types.

Conclusions: From our studies to develop a more potent ERX-11 lead analog, we have identified multiple analogs with distinct activities against multiple cancers. While the intended target of these analogs was ER, our library of analogs has potent activity against both ER-positive and ER-negative tumors. In collaboration, we are pursuing further leads in multiple cancers to further delineate the mechanism of action of these various analogs.

Citation Format: Ganesh V. Raj, Xihui Liu, Dede Ekoue, Jung-Mo Ahn, Ratna Vadlamudi. Development of potent lead compounds in multiple tumor types [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 26.

Discovery of a novel long noncoding RNA overlapping the LCK gene that regulates prostate cancer cell growth

Background

Virtually all patients with metastatic prostate cancer (PCa) will relapse and develop lethal castration-resistant prostate cancer (CRPC). Long noncoding RNAs (lncRNAs) are emerging as critical regulatory elements of many cellular biological processes, and may serve as therapeutic targets for combating PCa progression. Here, we have discovered in a high-throughput RNAi screen a novel lncRNA in PCa, and assessed the oncogenic effects of this lncRNA.

Methods

Rapid amplification of cDNA ends and sequencing was utilized to identify a previously unannotated lncRNA lying within exon six and the 3’UTR of the lymphocyte-specific protein tyrosine kinase (LCK) gene. The levels of HULLK in the presence or absence of hormone and/or enzalutamide or coregulator inhibitors were measured by quantitative PCR (qPCR). The determination of HULLK transcription and localization were characterized by strand-specific qPCR and cellular fractionation followed by qPCR, respectively. The correlation between HULLK expression and prostate cancer Gleason score was analyzed by droplet digital PCR. CyQuant assays were conducted to evaluate the effects of knocking down HULLK with shRNAs or overexpressing HULLK on cell growth.

Results

In this study, a previously unannotated lncRNA lying within exon six and 3’UTR of the LCK gene was dramatically upregulated by androgen in a dose-dependent manner, and the anti-androgen enzalutamide completely blocked this hormone-induced increase. Therefore, we labeled this lncRNA “HULLK” for Hormone-Upregulated lncRNA within LCK. Binding sites for two AR coregulators p300 and Brd4 reside near the HULLK transcriptional start site (TSS), and inhibitors of these coregulators downregulated HULLK. HULLK is transcribed from the sense strand of DNA, and predominantly localizes to the cytoplasm. HULLK transcripts are not only expressed in prostate cancer cell lines, but also prostate cancer patient tissue. Remarkably, there was a significant positive correlation between HULLK expression and high-grade PCa in multiple cohorts. shRNAs targeting HULLK significantly decreased PCa cell growth. Moreover, cells overexpressing HULLK were hypersensitive to androgen stimulation.

Conclusions

HULLK is a novel lncRNA situated within the LCK gene that may serve as an oncogene in PCa. Our data enhances our understanding of lncRNA biology and may assist in the development of additional biomarkers or more effective therapeutic targets for advanced PCa.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1039-6) contains supplementary material, which is available to authorized users.

Molecular mechanisms of enzalutamide resistance in prostate cancer

An estimated 30,000 men in the United States will die of metastatic prostate cancer (PCa) each year due to the development of therapy resistance, most notably resistance to second-generation antiandrogen enzalutamide. The vast majority of PCa is driven by the androgen receptor (AR). Enzalutamide is an AR antagonist, which extends patient survival and is widely used in the clinic for the treatment of castration-resistant prostate cancer (CRPC); however, many patients will have primary or develop acquired resistance and continue to progress. Characterization of the molecular mechanisms of enzalutamide resistance provides insight into potentially efficacious therapies for enzalutamide-resistant CRPC (ER-CRPC). Understanding these mechanisms is critical for the identification of biomarkers predictive of therapy resistance and the development of therapeutic strategies to target ER-CRPC.

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.

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.

Investigational luteinizing hormone releasing hormone (LHRH) agonists and other hormonal agents in early stage clinical trials for prostate cancer

INTRODUCTION

The treatment and management of prostate cancer continues to evolve; newer classes of agents and combination therapies are being developed and some are being investigated in early phase clinical trials.

AREAS COVERED

We discuss investigational hormonal agents for the treatment of prostate cancer and focus primarily on luteinizing hormone releasing hormone (LHRH) agonists in early stage trials. We look at agents that target the hormonal axis, including anti-androgens, gonadotropins, estrogenic agents and progestogenic agents and other non-hormonal agents often used in combination with LHRH agonists. We review these candidates in the specific clinical niche in which they might find utility.

EXPERT OPINION

Of all candidate compounds being evaluated in clinical trials, very few will receive FDA approval. Few, if any of the investigational agents discussed here will be used routinely in clinical practice for treating prostate cancer. Recognizing the reasons for the failure of agents to advance to later stage trials is important. Furthermore, a thorough understanding of the mechanisms underlying prostate cancer pathogenesis, including various points in the HGPA and parallel pathways, will help identify potentially actionable targets.

Targeting the turnover of oncoproteins as a new avenue for therapeutics development in castration-resistant prostate cancer

The current therapeutic armamentarium for castration-resistant prostate cancer (CRPC) includes second-generation agents such as the Androgen Receptor (AR) inhibitor enzalutamide and the androgen synthesis inhibitor abiraterone acetate, immunotherapies like sipuleucel-T, chemotherapies including docetaxel and cabazitaxel and the radiopharmaceutical radium 223 dichloride. However, relapse of CRPC resistant to these therapeutic modalities occur rapidly. The mechanisms of resistance to these treatments are complex, including specific mutations or alternative splicing of oncogenic proteins. An alternative approach to treating CRPC may be to target the turnover of these molecular drivers of CRPC. In this review, the mechanisms by which protein stability of several oncoproteins such as AR, ERG, GR, CYP17A1 and MYC, will be discussed, as well as how these findings could be translated into novel therapeutic agents.

PARP-1 regulates DNA repair factor availability

PARP-1 holds major functions on chromatin, DNA damage repair and transcriptional regulation, both of which are relevant in the context of cancer. Here, unbiased transcriptional profiling revealed the downstream transcriptional profile of PARP-1 enzymatic activity. Further investigation of the PARP-1-regulated transcriptome and secondary strategies for assessing PARP-1 activity in patient tissues revealed that PARP-1 activity was unexpectedly enriched as a function of disease progression and was associated with poor outcome independent of DNA double-strand breaks, suggesting that enhanced PARP-1 activity may promote aggressive phenotypes. Mechanistic investigation revealed that active PARP-1 served to enhance E2F1 transcription factor activity, and specifically promoted E2F1-mediated induction of DNA repair factors involved in homologous recombination (HR). Conversely, PARP-1 inhibition reduced HR factor availability and thus acted to induce or enhance "BRCA-ness". These observations bring new understanding of PARP-1 function in cancer and have significant ramifications on predicting PARP-1 inhibitor function in the clinical setting.

IFNγ-Induced IFIT5 Promotes Epithelial-to-Mesenchymal Transition in Prostate Cancer via miRNA Processing

IFNγ, a potent cytokine known to modulate tumor immunity and tumoricidal effects, is highly elevated in patients with prostate cancer after radiation. In this study, we demonstrate that IFNγ can induce epithelial-to-mesenchymal transition (EMT) in prostate cancer cells via the JAK-STAT signaling pathway, leading to the transcription of IFN-stimulated genes (ISG) such as IFN-induced tetratricopeptide repeat 5 (IFIT5). We unveil a new function of IFIT5 complex in degrading precursor miRNAs (pre-miRNA) that includes pre-miR-363 from the miR-106a-363 cluster as well as pre-miR-101 and pre-miR-128, who share a similar 5'-end structure with pre-miR-363. These suppressive miRNAs exerted a similar function by targeting EMT transcription factors in prostate cancer cells. Depletion of IFIT5 decreased IFNγ-induced cell invasiveness in vitro and lung metastasis in vivo. IFIT5 was highly elevated in high-grade prostate cancer and its expression inversely correlated with these suppressive miRNAs. Altogether, this study unveils a prometastatic role of the IFNγ pathway via a new mechanism of action, which raises concerns about its clinical application.Significance: A unique IFIT5-XRN1 complex involved in the turnover of specific tumor suppressive microRNAs is the underlying mechanism of IFNγ-induced epithelial-to-mesenchymal transition in prostate cancer.See related commentary by Liu and Gao, p. 1032.