mCRPC Tumors Research Articles

Preclinical Characterization of ARX517, a Site-specific Stable PSMA-Targeted Antibody Drug Conjugate for Treatment of Metastatic Castration-Resistant Prostate Cancer.

Metastatic castration-resistant prostate cancer (mCRPC) is an advanced disease in which patients ultimately fail standard of care androgen-deprivation therapies and exhibit poor survival rates. The prostate-specific membrane antigen (PSMA) has been validated as a mCRPC tumor antigen with over-expression in tumors and low expression in healthy tissues. Using our proprietary technology for incorporating synthetic amino acids (SAAs) into proteins at selected sites, we have developed ARX517, an antibody drug conjugate (ADC) which is composed of a humanized anti-PSMA antibody site-specifically conjugated to a tubulin inhibitor at a drug-to-antibody ratio of 2. After binding PSMA, ARX517 is internalized and catabolized, leading to cytotoxic payload delivery and apoptosis. To minimize premature payload release and maximize delivery to tumor cells, ARX517 employs a non-cleavable PEG linker and stable oxime conjugation enabled via SAA protein incorporation to ensure its overall stability. In vitro studies demonstrate that ARX517 selectively induces cytotoxicity of PSMA-expressing tumor cell lines. ARX517 exhibited a long terminal half-life and high serum exposure in mice, and dose-dependent anti-tumor activity in both enzalutamide-sensitive and -resistant CDX and PDX prostate cancer models. Repeat dose toxicokinetic studies in non-human primates demonstrated ARX517 was tolerated at exposures well above therapeutic exposures in mouse pharmacology studies, indicating a wide therapeutic index. In summary, ARX517 inhibited tumor growth in diverse mCRPC models, demonstrated a tolerable safety profile in monkeys, and had a wide therapeutic index based on preclinical exposure data. Based on the encouraging preclinical data, ARX517 is currently being evaluated in a Phase 1 clinical trial ([NCT04662580]).

Genomic and transcriptomic features of androgen receptor signaling inhibitor resistance in metastatic castration-resistant prostate cancer.

BACKGROUNDAndrogen receptor signaling inhibitors (ARSIs) have improved outcomes for patients with metastatic castration-resistant prostate cancer (mCRPC), but their clinical benefit is limited by treatment resistance.METHODSTo investigate the mechanisms of ARSI resistance, we analyzed the whole-genome (n = 45) and transcriptome (n = 31) sequencing data generated from paired metastatic biopsies obtained before initiation of first-line ARSI therapy for mCRPC and after radiographic disease progression. We investigated the effects of genetic and pharmacologic modulation of SSTR1 in 22Rv1 cells, a representative mCRPC cell line.RESULTSWe confirmed the predominant role of tumor genetic alterations converging on augmenting androgen receptor (AR) signaling and the increased transcriptional heterogeneity and lineage plasticity during the emergence of ARSI resistance. We further identified amplifications involving a putative enhancer downstream of the AR and transcriptional downregulation of SSTR1, encoding somatostatin receptor 1, in ARSI-resistant tumors. We found that patients with SSTR1-low mCRPC tumors derived less benefit from subsequent ARSI therapy in a retrospective cohort. We showed that SSTR1 was antiproliferative in 22Rv1 cells and that the FDA-approved drug pasireotide suppressed 22Rv1 cell proliferation.CONCLUSIONOur findings expand the knowledge of ARSI resistance and point out actionable next steps, exemplified by potentially targeting SSTR1, to improve patient outcomes.FUNDINGNational Cancer Institute (NCI), NIH; Prostate Cancer Foundation; Conquer Cancer, American Society of Clinical Oncology Foundation; UCSF Benioff Initiative for Prostate Cancer Research; Netherlands Cancer Institute.

Computational Modeling to Identify Drugs Targeting Metastatic Castration-Resistant Prostate Cancer Characterized by Heightened Glycolysis.

Metastatic castration-resistant prostate cancer (mCRPC) remains a deadly disease due to a lack of efficacious treatments. The reprogramming of cancer metabolism toward elevated glycolysis is a hallmark of mCRPC. Our goal is to identify therapeutics specifically associated with high glycolysis. Here, we established a computational framework to identify new pharmacological agents for mCRPC with heightened glycolysis activity under a tumor microenvironment, followed by in vitro validation. First, using our established computational tool, OncoPredict, we imputed the likelihood of drug responses to approximately 1900 agents in each mCRPC tumor from two large clinical patient cohorts. We selected drugs with predicted sensitivity highly correlated with glycolysis scores. In total, 77 drugs predicted to be more sensitive in high glycolysis mCRPC tumors were identified. These drugs represent diverse mechanisms of action. Three of the candidates, ivermectin, CNF2024, and P276-00, were selected for subsequent vitro validation based on the highest measured drug responses associated with glycolysis/OXPHOS in pan-cancer cell lines. By decreasing the input glucose level in culture media to mimic the mCRPC tumor microenvironments, we induced a high-glycolysis condition in PC3 cells and validated the projected higher sensitivity of all three drugs under this condition (p < 0.0001 for all drugs). For biomarker discovery, ivermectin and P276-00 were predicted to be more sensitive to mCRPC tumors with low androgen receptor activities and high glycolysis activities (AR(low)Gly(high)). In addition, we integrated a protein-protein interaction network and topological methods to identify biomarkers for these drug candidates. EEF1B2 and CCNA2 were identified as key biomarkers for ivermectin and CNF2024, respectively, through multiple independent biomarker nomination pipelines. In conclusion, this study offers new efficacious therapeutics beyond traditional androgen-deprivation therapies by precisely targeting mCRPC with high glycolysis.

Abstract CT138: Evaluating nivolumab (nivo) plus ipilimumab (ipi) in patients with metastatic castration-resistant prostate cancer (mCRPC): Clinical and translational results from the AMADEUS prostate expansion cohort

Abstract Background: Immune checkpoint inhibitors (ICIs) have transformed cancer treatment, offering durable responses for some patients. However, response to ICIs remains limited for many solid tumors, including metastatic castration-resistant prostate cancer (mCRPC). The AMADEUS primary cohort (NCT03651271) and CheckMate 650 (NCT02985957) trials demonstrated promising durable antitumor responses in a subset of mCRPC patients treated with nivo in combination with ipi at 1 mg/kg or 3 mg/kg, respectively. The AMADEUS prostate expansion cohort was initiated to evaluate the safety and efficacy of a higher ipi dose (5 mg/kg) in combination with nivo. Methods: This open-label, multicenter cohort enrolled mCRPC patients with no restriction on the number of prior treatments. The first 10 patients with &amp;lt; 15% tumoral CD8 T cells were randomized 1:1 to receive either ipi at 3 mg/kg (ipi3) or 5 mg/kg (ipi5) IV Q6W for up to 2 doses. In addition, all patients received nivo 1 mg/kg IV Q3W for 4 doses, followed by nivo 480 mg IV Q4W until PD or intolerable toxicity. After a safety pause, 10 additional patients were enrolled to the ipi5 arm. Co-primary endpoints were DCR (CR, PR, or SD ≥ 6 months) and conversion of tumor %CD8 T cells from low (&amp;lt; 15%) to high (≥ 15%). Baseline and on-treatment tumor and blood samples were analyzed for multi-omic biomarkers. This cohort was not powered for formal statistical analysis. Results: DCR was 20% in both ipi3 (N=1/5) and ipi5 (N=3/15) arms. In patients with an on-treatment biopsy, CD8 conversion from low to high occurred in 33% (1/3) of patients in ipi3 and 13% (1/8) in ipi5. However, 50% (4/8) of patients in ipi5 had on-treatment CD8 ≥ 14.8%. Baseline CD8 T cell frequencies and CD8 conversion were not associated with disease control or PSA reduction. The frequency and severity of AEs was consistent with the known safety profile of ipi/nivo, although more patient in ipi5 discontinued treatment owing to an AE (33% vs 0% in ipi3). Both arms showed increased activated (ICOS+, CD38+) and proliferating (Ki67+) CD4 T cells, CD8 T cells, Tregs, inflammatory cytokines (IFNg), chemokines (CXCL9, CXCL10), and soluble PD-1 in circulation. Conclusions: Across both arms, ipi/nivo induced clinical responses and increased %CD8 in a subset of “cold” mCRPC tumors with low CD8 cells. Additionally, the safety profile of ipi 5 mg/kg combined with nivo was consistent with previous trials that tested lower doses of ipi. Further translational analyses may inform which mCRPC patients could benefit from immunotherapy treatment. Trial registration: ClinicalTrials.gov (NCT03651271) Citation Format: Apostolia M. Tsimberidou, Alexandra Drakaki, Danny N. Khalil, Kwame Okrah, Mike Schachter, Shikha Gautam, Diane M. Da Silva, Farah A. Alayli, Christine N. Spencer, Wai Chin Foo, Matthew Adamow, Phillip Wong, Justin Fairchild, Jamie Arnott, Ute Dugan, Silvia Boffo, Lisa Salvador, Christopher R. Cabanski, Sumit K. Subudhi, Padmanee Sharma. Evaluating nivolumab (nivo) plus ipilimumab (ipi) in patients with metastatic castration-resistant prostate cancer (mCRPC): Clinical and translational results from the AMADEUS prostate expansion cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT138.

Abstract 6356: Novel antibody targeting tumor NKG2D ligand MIC: Preclinical studies and clinical development plan for mCRPC

Abstract In response to genomic insults and DNA double-strand breaks, the stressed epithelial cells express the MHC I-chain related molecule (MIC) on the surface as a byproduct of activating the ATM pathway. The MIC molecule itself has no known impact on tumor survival or growth. In the context of immune microenvironment, tumor cell surface MIC can activate NK cells and co-stimulate CD8 T cells by engaging in the activating receptor NKG2D to hinder the early tumorigenesis. However, in established malignancies, in particular metastatic diseases, tumor cells shed surface MIC to release the soluble form MIC (sMIC). It has been well demonstrated that, in contrary to cell surface MIC, sMIC is highly immune suppressive by disturbing NK cell homeostasis and repolarizing NK cells function, impairing antigen-specific CD8 T cell function by downmodulating NKG2D expression and CD3z expression, and facilitating immune suppression of MDSCs and TAMs in tumor microenvironment. We have demonstrated that MIC is prevalently expressed by prostate tumor cells and significantly upregulated in mCRPC tumors. We have shown significantly elevated levels of serum sMIC in prostate cancer patients with metastatic diseases. We have developed a novel class of clinical candidate monoclonal antibody huB10G5 that can target both sMIC and surface MIC to re-invigorate both NK and CD8 T cell function and inhibit MDSCs and TAMs in preclinical models. The huB10G5 has an acceptable safety profile and is currently completing CMC for IND enabling. We hypothesize that huB10G5 is a novel immune therapeutic reagent for mCRPC patients. To test our hypothesis, we first conducted serial studies of the clinical candidate huB10G5 in pre-clinical models of prostate cancers. We found that huB10G5 can effectively induce 100% long-term tumor complete regression (CR) as low as 1.0 mg/KG. These animals are fully protected from tumor re-challenge. The anti-tumor effect is mediated by the combined action of NK and CD8 T cells. With the support of our pre-clinical efficacy and safety data, we have planned to initiate Phase I clinical trial with huB10G5 for mCRPC patients in 2024. Citation Format: Jennifer Donglan Wu, Jeff Sosman, Masha Kocherginsky, Anthony Serritella, Maha Hussian, David J. Vanderweele. Novel antibody targeting tumor NKG2D ligand MIC: Preclinical studies and clinical development plan for mCRPC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6356.

Abstract C034: Understanding the role of PARP activity in prostate cancer

Abstract Prostate cancer (PCa) is the second most fatal cancer in men in the United States. African American men have an incidence and death rate two times higher than that of European American men. The androgen receptor (AR) is the primary pro-oncogenic transcription factor responsible for PCa emergence and progression. AR directed therapies including androgen deprivation (ADT), direct receptor antagonism and inhibition of androgen synthesis are the current standard of care for advanced PCa. Adaptive resistance to anti-androgen therapy can occur resulting in castration-resistant prostate cancer (mCRPC). mCRPC remains universally fatal with no curative treatment options, which highlights the need for new treatment regimes. Poly (ADP-ribose) polymerase 1 (PARP-1) inhibitors are approved to treat mCRPC tumors that have homologous recombination (HR) mutations. PARP-1 is an enzyme that recruits DNA damage repair enzymes. PARP-1 enzymatic activity is elevated in mCRPC patient tumors compared to primary tumors. PARP1 enzymatic activity has been implicated in driving pro-survival mechanisms through recruitment of DNA-damage repair enzymes and regulation of oncogenic transcription factors, including AR. Although increased PARP activity has been associated with driving cancer cell survival, the mechanisms and consequences of elevated PARP activity in PCa remains an area to be further explored. The biologically relevant doses of five PARPi were established in regular and steroid depleted growth conditions in CRPC models. PARP enzymatic activity was assessed by immunoblotting for changes in PARlyation, revealing that PARP protein remains stable, while enzymatic activity is attenuated upon challenge with PARPi. Transcriptomic analysis will assess changes in gene expression programs that are associated with inhibition of PARP enzymatic activity as it relates to key oncogenic pathways in PCa. It will be imperative to gain a deeper understanding of how PARP-1 manipulation modulates pro-oncogenic transcriptional networks to better inform clinical response. Patient derived explants (PDEs) from patients with distinct racial backgrounds will be used to examine differential PARPi responses as it relates to race. This will serve to unravel the mechanisms attributed to the increased lethality of PCa observed in African American populations. Collectively, these studies and future studies for this project will further establish the impact of PARP on PCa gene expression programs and provide resources for future studies exploring PARP in PCa. Further, they may help elucidate mechanisms to address PCa racial disparities. Citation Format: Moriah Cunningham, Latese Evans, Salome Tchotorlishvili, Jasibel Vasquez Gonzalez, Candice Bizzaro, Tessa Mulders, Matthew Schiewer. Understanding the role of PARP activity in prostate cancer [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr C034.

Abstract B012: Genomic and epigenomic drivers of double-negative metastatic prostate cancer

Abstract Systemic targeted therapy in prostate cancer is primarily focused on ablating androgen receptor (AR) signaling. Androgen deprivation therapy and second-generation AR-targeted therapy selectively favor the development of treatment-resistant subtypes of metastatic castration-resistant prostate cancer (mCRPC), defined by whether the tumor expresses either AR or neuroendocrine (NE) markers. Among the subtypes of mCRPC, the molecular drivers of double-negative (AR-/NE-) mCRPC are poorly defined. In this study, we comprehensively characterize genomic and epigenomic features of treatment-emergent mCRPC subtypes in 210 tumors by integrating matched RNA sequencing, whole-genome sequencing, and whole-genome bisulfite sequencing. We show that AR-/NE- tumors exhibit a clinically and molecularly distinct phenotype. Patients with AR-/NE- mCRPC tumors have the shortest survival, and these tumors preferentially harbor amplification of the chromatin remodeler CHD7 and loss of PTEN. We demonstrate that methylation changes in CHD7 candidate enhancers are linked to elevated CHD7 expression in AR-/NE+ tumors. Moreover, we use genome-wide methylation analysis to nominate the Krüppel-like factor gene KLF5 as a driver of the AR-/NE- phenotype and link its activity to loss of the tumor suppressor RB1. These observations reveal the aggressiveness of the AR-/NE- tumors and elucidate genomic and epigenomic drivers of mCRPC subtypes, which may facilitate the identification of novel therapeutic targets in this highly aggressive disease. Citation Format: Arian Lundberg, Meng Zhang, Rahul R. Aggarwal, Haolong Li, Li Zhang, Adam Foye, Martin Sjöström, Jonathan Chou, Kevin Chang, Thaidy Moreno-Rodriguez, Raunak Shrestha, Avi Baskin, Xiaolin Zhu, Alana S. Weinstein, Noah Younger, Joshi J. Alumkal, Tomasz M. Beer, Kim N. Chi, Christopher P. Evans, Martin Gleave, Primo N. Lara, Robert E. Reiter, Matthew B. Rettig, Owen N. Witte, Alexander W. Wyatt, Felix Y. Feng, Eric J. Small, David A. Quigley. Genomic and epigenomic drivers of double-negative metastatic prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B012.

Abstract LB298: Molecular phenotype classification of metastatic prostate cancer by cell-free DNA methylation analysis

Abstract Introduction: Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease which can be classified into clinically relevant subtypes based on the expression of transcription factors (TF), such as the androgen receptor (AR) and neuroendocrine markers. Neuroendocrine prostate cancer (NEPC), characterized by gain of stem-like and neuroendocrine features and lack of AR expression is a clinically aggressive variant. Due to the absence of adequate biomarkers, NEPC is usually detected at a very advanced stage. There is mounting evidence that molecular subtype changes seen in NEPC are enforced by widespread epigenetic alterations, in particular DNA methylation changes. In this study, we aim to devise a novel DNA methylation-based assay for molecular subtyping and disease monitoring from cell-free DNA (cfDNA). Methods: We analyzed genome wide methylation patterns in 60 prostate cancer patient-derived xenograft (PDX) and 133 mCRPC tumors using array- and sequencing-based assays. We integrated DNA methylation with TF cistrome data to determine the landscape of methylation alterations at key lineage TF binding sites (TFBS). A linear regression model was trained on low-pass Enzymatic Methyl-Seq (EM-seq) cfDNA data derived from PDXs to identify molecular subtype specific DNA methylation changes at these TFBS. The model performance was optimized with in silico admixture experiments. This model was then used to discern tumor molecular phenotypes from cfDNA in three independent cohorts of mCRPC patients using low-pass whole genome bisulfite sequencing and EM-seq. Results: We observed a strong association between TFBS methylation and TF expression. For lineage specific TFs such as AR and ASCL1, we identified core sets of TFBSs whose differential methylation allowed for accurate assay-independent molecular subtype classification in tumor tissues. Applying an optimized quantitative model to mCRPC patients who underwent comprehensive tissue sampling by rapid autopsy we observed perfect subtype prediction from both tissue samples and cfDNA (AUC=1). A similar analytical performance was observed in additional clinical mCRPC cohorts with cfDNA. Conclusions: We show that methylation patterns at TFBSs can determine TF activity and can be used to classify molecular subtypes from both tumor tissue and cfDNA. For prostate cancer, we demonstrate that this approach can accurately detect NEPC by cost-effective low-pass EM-seq. More broadly, this study provides a novel analysis framework for robustly assessing molecular tumor phenotypes in cfDNA with applications in solid and liquid tumor diagnostics. Citation Format: Mohamed Adil, Brian Hanratty, Pallabi Mustafi, Ilsa Coleman, Radhika Patel, Anna-Lisa Doebley, Robert Patton, Eden Cruikshank, Patricia Galipeau, Ruth Dumpit, Martine Roudier, Jin-Yih Low, Navonil De Sarkar, Robert Montgomery, Eva Corey, Colm Morrissey, Peter Nelson, Gavin Ha, Michael Haffner. Molecular phenotype classification of metastatic prostate cancer by cell-free DNA methylation analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB298.

Effect of Janus kinase (JAK) signaling inhibition on lineage plasticity and drug sensitivity in castrate resistant prostate cancer.

227 Background: Despite the remarkable successes of targeted cancer therapies, certain cancers, including lung, breast, and prostate cancer and melanoma, invariably become resistant to therapy. One mechanism of secondary resistance—lineage plasticity—arises when cells alter their identity and transition into aggressive states. In the case of prostate cancer, cells can acquire a neuroendocrine histology. This is often associated with a loss of tumor suppressor genes, such as TP53, RB1, and PTEN. However, while these genomic events initiate plasticity, tumor progression is not always associated with successive genomic alterations. This, in essence, not only poses a clinical challenge, but also confronts us with a wide-open biological question—what are the molecular underpinnings of lineage plasticity, and importantly, can the process be reversed? Methods: To study the temporal evolution of lineage plasticity and its relationship to androgen receptor signaling inhibitor (ARSI) resistance, we utilized genetically engineered mouse models (GEMMs) and murine organoids that were deleted for Tp53, Rb1, and/or Pten. Single cell RNA analyses were utilized to dissect which genes and pathways were up-regulated and most associated with the progression of plasticity. Plasticity-associated genes and pathways were perturbed using FDA-approved inhibitors or genetic editing tools. The presence of these pathways was confirmed in a subset of metastatic index lesions obtained by radiologically guided biopsies and as visualized by metabolic imaging. Furthermore, relevant findings were functionally validated in human tumor derived organoids (“tumoroids”). Results: Using GEMMs and organoid models, we found the lineage plasticity depended on increased Janus Kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Pharmacologic inhibition using FDA–approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafinitib), or through genetic knockdown, demonstrated increased androgen receptor (AR) signaling and restored ARSI sensitivity. These findings were further validated in a subset of ARSI-insensitive human tumoroids. By performing single cell RNA sequencing on mCRPC tumors biopsies, the presence of highly plastic JAK/STAT- and FGFR-high cells were confirmed, with implications for stratifying patients for clinical trials. Conclusions: JAK/STAT and FGFR signaling pathways promote lineage plasticity and result in complete insensitivity to androgen receptor signaling inhibitors (ARSIs). FDA-approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafitinib) synergize to reverse lineage plasticity and restore ARSI sensitivity.

Integrative molecular analyses define correlates of high B7-H3 expression in metastatic castrate-resistant prostate cancer

B7-H3 (CD276) is an immune checkpoint overexpressed in prostate cancer with minimal expression in normal tissues and associated with poor prognosis, making it an excellent therapy target. We interrogated B7-H3 expression and its regulation in metastatic castration-resistant prostate cancer (mCRPC). We found greater expression of B7-H3 transcript relative to other immunotherapy targets (CTLA-4, PD-L1/2), including in tumors that lacked expression of prostate-specific membrane antigen (PSMA). Enzalutamide-resistant mCRPC cells demonstrated increased amounts of B7-H3, and this was associated with resistance signaling pathways. Using a machine-learning algorithm, the gene network of B7-H3 was strongly correlated with androgen receptor (AR) and AR co-factor (HOXB13, FOXA1) networks. In mCRPC samples, the B7-H3 promoter and distal enhancer regions exhibited enhanced transcriptional activity and were directly bound by AR and its co-factors. Altogether, our study characterizes molecular profiles and epigenetic regulation of B7-H3-expressing mCRPC tumors, which informs optimal precision-oncology approaches for mCRPC patients.

Deregulation of Cholesterol Homeostasis by a Nuclear Hormone Receptor Crosstalk in Advanced Prostate Cancer.

Simple SummaryMetastatic castration-resistant prostate cancer (mCRPC) is one of the leading causes of cancer-related death. mCRPC tumors feature high intratumoral cholesterol levels. Our current study shows that the nuclear receptor RORγ plays crucial roles in the aberrant cholesterol homeostasis of mCRPC. RORγ simultaneously stimulates cholesterol biosynthesis and suppresses cholesterol efflux programs through a RORγ and LXR crosstalk. Our study also demonstrated that RORγ antagonists alone or in combination with cholesterol-lowering drug statins are effective in inhibiting mCRPC cell and tumor growth. Our findings revealed a mechanism underlying the elevated cholesterol levels in mCRPC and suggested a potential therapeutic strategy for mCRPC patients.Metastatic castration-resistant prostate cancer (mCRPC) features high intratumoral cholesterol levels, due to aberrant regulation of cholesterol homeostasis. However, the underlying mechanisms are still poorly understood. The retinoid acid receptor-related orphan receptor gamma (RORγ), an attractive therapeutic target for cancer and autoimmune diseases, is strongly implicated in prostate cancer progression. We demonstrate in this study that in mCRPC cells and tumors, RORγ plays a crucial role in deregulation of cholesterol homeostasis. First, we found that RORγ activates the expression of key cholesterol biosynthesis proteins, including HMGCS1, HMGCR, and SQLE. Interestingly, we also found that RORγ inhibition induces cholesterol efflux gene program including ABCA1, ABCG1 and ApoA1. Our further studies revealed that liver X receptors (LXRα and LXRβ), the master regulators of cholesterol efflux pathway, mediate the function of RORγ in repression of cholesterol efflux. Finally, we demonstrated that RORγ antagonist in combination with statins has synergistic effect in killing mCRPC cells through blocking statin-induced feedback induction of cholesterol biosynthesis program and that the combination treatment also elicits stronger anti-tumor effects than either alone. Altogether, our work revealed that in mCRPC, RORγ contributes to aberrant cholesterol homeostasis by induction of cholesterol biosynthesis program and suppression of cholesterol efflux genes. Our findings support a therapeutic strategy of targeting RORγ alone or in combination with statin for effective treatment of mCRPC.

Therapeutic Implications for Intrinsic Phenotype Classification of Metastatic Castration-Resistant Prostate Cancer.

To determine whether metastatic castration-resistant prostate cancers (mCRPC) partition into molecular phenotypes corresponding to intrinsic differentiation states and ascertain whether these subtypes exhibit specific druggable features and associate with treatment outcomes. We used RNAseq, digital spatial profiling, and histological assessments from metastatic biopsies and patient-derived xenografts to segregate mCRPCs into subtypes defined by the PAM50 breast cancer classification algorithm. Subtype associations with treatment responses in preclinical models and patients were determined. Using the PAM50 algorithm, we partitioned 270 mCRPC tumors into LumA (42%), LumB (24%), and Basal (34%) subtypes with classification largely driven by proliferation rates and androgen receptor (AR) activity. Most neuroendocrine tumors classified as Basal. Pathways enriched in the LumA subtype include TGFß and NOTCH signaling. LumB subtype tumors were notable for elevated MYC activity. Basal subtype tumors exhibited elevated IL6-STAT3 signaling and features of adult stem cell states. In patients where multiple tumors were evaluated, the majority had concordant PAM50 subtype determination, though a subset exhibited marked inter- and intratumor heterogeneity, including divergent classifications between primary and metastatic sites. In preclinical models, LumA subtype tumors were highly responsive to androgen deprivation and docetaxel chemotherapy whereas Basal tumors were largely resistant. In clinical cohorts patients with Basal subtype tumors demonstrated a shorter time on treatment with AR signaling inhibitors and docetaxel relative to patients with luminal subtypes. Subtyping of mCRPC based on cell differentiation states has potential clinical utility for identifying patients with divergent expression of treatment targets and responses to systemic therapy.

Somatic driver mutation prevalence in 1844 prostate cancers identifies ZNRF3 loss as a predictor of metastatic relapse

Driver gene mutations that are more prevalent in metastatic, castration-resistant prostate cancer (mCRPC) than localized disease represent candidate prognostic biomarkers. We analyze 1,844 localized (1,289) or mCRPC (555) tumors and quantify the prevalence of 113 somatic driver single nucleotide variants (SNVs), copy number aberrations (CNAs), and structural variants (SVs) in each state. One-third are significantly more prevalent in mCRPC than expected while a quarter are less prevalent. Mutations in AR and its enhancer are more prevalent in mCRPC, as are those in TP53, MYC, ZNRF3 and PRKDC. ZNRF3 loss is associated with decreased ZNRF3 mRNA abundance, WNT, cell cycle & PRC1/2 activity, and genomic instability. ZNRF3 loss, RNA downregulation and hypermethylation are prognostic of metastasis and overall survival, independent of clinical and pathologic indices. These data demonstrate a strategy for identifying biomarkers of localized cancer aggression, with ZNRF3 loss as a predictor of metastasis in prostate cancer.

620P MGC018, an anti-B7-H3 antibody-drug conjugate (ADC), in patients with advanced solid tumors: Preliminary results of phase I cohort expansion

MGC018 is an investigational ADC with a duocarmycin payload linked to an anti-B7-H3 monoclonal antibody. B7-H3 is expressed on multiple solid tumors with limited normal tissue expression. It is hypothesized that MGC018 may exert activity against B7-H3-expressing tumors with an acceptable safety profile. Phase I dose escalation was completed with two dose-limiting toxicities: one neutropenia grade 4 and one grade 3 fatigue of 72 hrs. There was 1 confirmed partial response in a melanoma patient, and 5/9 patients with 50% prostate-specific antigen (PSA) reduction in metastatic castration resistant prostate cancer (mCRPC). The cohort expansion characterizes safety and preliminary efficacy with the recommended phase II dose of 3 mg/kg IV every 3 weeks. Patients with advanced mCRPC, non-small cell lung cancer (NSCLC), triple-negative breast cancer (TNBC), squamous cell carcinoma of the head and neck (SCCHN), and melanoma are eligible for enrollment. Response is evaluated per RECIST v1.1 for all participants. mCRPC tumor response and PSA are evaluated using Prostate Cancer Working Group 2 criteria. The cohort expansion enrolled and dosed 49/80 patients as of May 3, 2021. mCRPC n=26/40, NSCLC, n=16/20, and TNBC n=7/20. At least 1 treatment emergent adverse event occurred in 43 patients (87.7%); the most common (≥10%) were neutropenia/neutrophil count decreased, fatigue, asthenia, palmar plantar erythrodysesthesia, and headache. Febrile neutropenia was not reported. Of 13 mCRPC patients with measurable disease, six were not yet evaluable, and seven had first 9-week imaging. Of the seven, four had reductions in target lesion sums of 13%, 21%, 27%, and 35% (unconfirmed partial response); 12 of the 13 remain on treatment. There are 11/22 evaluable patients with ≥50% PSA reduction. Results to date have demonstrated a manageable safety profile with evidence of clinical activity by PSA and tumor responses in mCRPC. Enrollment is ongoing in advanced mCRPC, NSCLC, TNBC, SCCHN, and melanoma. Updated data will be provided.

Abstract 3197: Transcriptional characterization of immunological features observed in localized and metastatic prostate cancer

Abstract Objectives: There is a paucity of data describing the immunologic subtypes of prostate cancer, and the features that contribute to them, in either the localized or metastatic disease setting. The objective of our effort was to utilize publicly available datasets in both disease settings to better understand the prevalence of immunologic subtypes within each disease setting and to explore biological mechanisms that may regulate them. Methods: Publicly available datasets utilized were The Cancer Genome Atlas (TCGA), for localized disease, and Stand Up To Cancer (SU2C), for metastatic disease. Evaluating a pan-cancer unsupervised clustering analysis of over 5000 tumors in TCGA with 20 biologically distinct immune related transcriptional signatures we identified sample classes with distinct profiles. The expression level of signatures within each sample class was taken as a composite score to identify the immunological characteristics of individual tumors. This characterization was then applied to the SU2C dataset to interrogate 444 mCRPC tumors. Results: The results of the pan-cancer analysis identified 4 individual sample classes; hot, cold, and 2 altered phenotypes. Of the two altered phenotypes identified, one represented only prostate cancer samples, and was the focus of our investigation in this study. The TCGA dataset showed, 60% cold, 12% hot, and 28% altered. A transcriptional signature representing Macrophage Colony Stimulating Factor 1 (CSF-1) response showed positive correlation with effector cells(CD4 &amp; CD8), while it showed a negative correlation with suppressive cell(Tregs &amp; MDSCs) highlighting the potential for positive immune modulation through this pathway. The SU2C dataset showed, 83% cold, 6% hot, and 11% altered. Cancer testis antigens (CTAs) were expressed at a higher level in SU2C compared to TCGA. We also observed positive correlation between the expression of CTAs and immune suppressive mechanisms and a negative correlation with inflammation. These observations were unique to the metastatic disease setting suggesting a role of CTA expression and increased immune suppressive environment in mCRPC. Conclusions: Through characterization of publicly available datasets, TCGA &amp; SU2C, we were able to define frequencies and characteristics of hot, cold, and altered immune subtypes within different disease settings in prostate cancer. Further validation of unique subtypes and mechanisms identified in this study in larger cohorts would be required to understand the true biological impact of these observations. Citation Format: Justin Lucas, Clemente Aguilar, Michael Gormley, Shibu Thomas, Natalie Hutnick, John Loffredo. Transcriptional characterization of immunological features observed in localized and metastatic prostate 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 3197.

Using real-world outcomes to evaluate the predictive power of tissue-assessed genomic biomarkers for taxane versus novel hormonal therapy (NHT) outcomes in metastatic castration-resistant prostate cancer (mCRPC).

5054 Background: No established genomic biomarkers exist for guiding treatment decisions between novel hormonal therapy (NHT) vs taxane chemotherapy in mCRPC. However, specific alterations in AR have been associated to decreased responsiveness to NHT in this setting. Leveraging routine comprehensive genomic profiling (CGP) testing of mCRPC tissue samples, we hypothesized that patients (pts) with AR amplification ( ARamp) would have better outcomes on taxanes over NHT. Methods: Pts were selected from Flatiron Health (FH)-Foundation Medicine (FMI) clinico-genomic database (CGDB), a nationwide deidentified electronic health record database linked to CGP. Data originated from approximately 280 US cancer clinics (̃800 sites). CGP results (including analysis of AR and 15 other genomic biomarkers) were obtained from mCRPC tumor tissue collected up to 180 days before or 30 days after initiation of new systemic therapy between 1/1/11 - 6/30/20, and linked to PSA response, time to next therapy (TTNT) and overall survival (OS). Multivariable treatment interaction models were adjusted for drug assignment imbalances (line of therapy, prior NHT or taxane use, PSA, alkaline phosphatase, hemoglobin, albumin, years to CRPC, biopsy site) using inverse probability of treatment weighting via propensity scores. Results: Among 5754 evaluable mCRPC lines of therapy, 180 receiving NHT and 179 receiving taxanes met inclusion criteria, 359 total from 308 unique patients. Pts with ARamp vs no ARamp on NHT had worse PSA response (median +57.3% vs. -31.4%, p = 0.002), TTNT (HR: 2.03, p &lt; 0.001), and OS (HR: 2.28, p &lt; 0.001), but had no difference in outcomes on taxanes. Multivariable interaction Cox models found ARamp independently associated to better TTNT on taxanes vs. NHT (HR: 0.48, p = 0.010), similar to pts with RB1 alterations (HR: 0.46, p = 0.027). Consistent treatment interactions were seen with OS for ARamp (HR: 0.53, p = 0.025) and RB1 (HR: 0.32, p = 0.024). While CDK12 was not predictive, it independently associated with worse OS overall (HR: 2.25, p = 0.0011). In the 55 pts who received NHT followed by taxane immediately after, ARamp pre-NHT was associated with better TTNT on the subsequent taxane than on the initial NHT (HR: 0.40, p = 0.028). Of these, 33 had PSA responses evaluable, and ARamp pre-NHT was significantly associated with better PSA decline on the subsequent taxane, despite disadvantage of first progressing on NHT (OR: 10.9, p = 0.021). Conclusions: Genomic biomarkers routinely identified with CGP such as ARamp may aid in identifying mCRPC pts who are to obtain greater benefit from taxane chemotherapy instead of NHT. Prospective efforts are needed to further validate the utility of CGP for assisting treatment decisions for mCRPC patients.

Genomic landscape of CDK12 mutated metastatic castrate-resistant prostate cancer (mCRPC).

165 Background: Identifying prostate cancer patients likely to benefit from immune checkpoint inhibitors (ICPI) remains an unmet need. Specific loss-of-function genomic alterations (GA) in CDK12 are associated with focal tandem duplications linked to fusion-induced production of neoantigens and are a promising candidate biomarker for ICPI. Using comprehensive genomic profiling (CGP) we compared the GA landscape of CDK12 altered (CDK12mut+) and unaltered (CDK12mut-) tumors. Methods: 4,918 mCRPC tumors were sequenced using a hybrid capture-based FDA-approved CGP assay. Tumor mutational burden (TMB) was determined on 0.8 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 95 loci. PD-L1 expression was determined by IHC (Dako 22C3) with low tumor cell positive staining -49% and high staining ≥50% expression. Results: Overall, 315 (6.4%) of the mCRPC cases were CDK12mut+ (Table). CDKmut+ cases had significantly fewer GA in TMPRSS2: ERG (P &lt; .0001), TP53 (P &lt; .0001), PTEN (P &lt; .0001), ATM (P = .001), PIK3CA (P = .003), RB1 (P = .02), BRCA2 (P &lt; .0001) and APC (P = .002). CDK12mut+ cases featured higher frequencies only in CCND1 (P &lt; .0001), BRAF (P = .007) and ERBB2 (P &lt; .001) as well as in cell cycle regulatory genes including MDM2/4 (P &lt; .0001), CDK4 (P &lt; .0001) and CDK6 (P = .002). CDK12mut+ cases featured more frequent MSI-H status (P = .007), significantly higher median TMB (P &lt; .001) and more frequent low positive (1-49% staining) PD-L1 expression (P = .02). High (≥50%) PD-L1 expression was rarely identified in either cohort. Conclusions: CDK12mut+ mCRPC demonstrates a unique genomic profile with significant differences compared with CDK12mut- mCRPC. Lower frequencies of GA associated with homologous recombination defect and mTOR pathway may impact the use of platinum agents, as well as PARPi and PIK3CA/Akt/mTOR inhibitors. Opportunities for targeted therapies for BRAF and ERBB2 driven mCRPC may be enriched in the CDK12mut+ tumors and raise the possibility of combination therapy strategies although the numbers of patients are small and validation is needed. The slightly higher MSI High status, median TMB and PD-L1 staining may be associated with additional benefit from ICPI and warrants further prospective investigation. [Table: see text]

Could Harnessing Natural Killer Cell Activity Be a Promising Therapy for Prostate Cancer?

Harnessing natural killer (NK) cell activity, either endogenous NK or NK-cell-based therapy, is in the forefront development for many tumor types. There are compelling clinical evidence demonstrating the significant relevance of loss of NK cell activity with prostate cancer (PCa) disease progression to the lethal phenotype, metastatic castration-resistant PCa (mCRPC). Given that mCRPC is generally regarded as a "cold" tumor and has only elicited marginal response to immune checkpoint blockade therapy to revive CD8 T cell activity, NK cell targeted therapy may present a viable opportunity not only to directly target mCRPC and also to "fire up" the cold mCRPC tumor. However, current efforts on harnessing NK cell activity for treating mCRPC is very limited with only one open NK-cell-based clinical trial. This minireview will present the clinical significance of NK cell activity in controlling metastatic PCa and provide perspectives on harnessing NK cell activity for treating mCRPC.

Taxane-induced Attenuation of the CXCR2/BCL-2 Axis Sensitizes Prostate Cancer to Platinum-based Treatment

BackgroundTaxanes are the most active chemotherapy agents in metastatic castration-resistant prostate cancer (mCRPC) patients; yet, resistance occurs almost invariably, representing an important clinical challenge. Taxane-platinum combinations have shown clinical benefit in a subset of patients, but the mechanistic basis and biomarkers remain elusive. ObjectiveTo identify mechanisms and response indicators for the antitumor efficacy of taxane-platinum combinations in mCRPC. Design, setting, and participantsTranscriptomic data from a publicly available mCRPC dataset of taxane-exposed and taxane-naïve patients were analyzed to identify response indicators and emerging vulnerabilities. Functional and preclinical validation was performed in taxane-resistant mCRPC cell lines and genetically engineered mouse models (GEMMs). InterventionMetastatic CRPC cells were treated with docetaxel, cisplatin, carboplatin, the CXCR2 antagonist SB265610, and the BCL-2 inhibitor venetoclax. Gain and loss of function in culture of CXCR2 and BCL-2 were achieved by overexpression or siRNA silencing. Preclinical assays in GEMM mice tested the antitumor efficacy of taxane-platinum combinations. Outcome measurements and statistical analysisProliferation, apoptosis, and colony assays measured drug activity in vitro. Preclinical endpoints in mice included growth, survival, and histopathology. Changes in CXCR2, BCL-2, and chemokines were analyzed by reverse transcriptase quantitative polymerase chain reaction and Western blot. Human expression data were analyzed using Gene Set Enrichment Analysis, hierarchical clustering, and correlation studies. GraphPad Prism software and R-studio were used for statistical and data analyses. Results and limitationsTranscriptomic data from taxane-exposed human mCRPC tumors correlate with a marked negative enrichment of apoptosis and inflammatory response pathways accompanied by a marked downregulation of CXCR2 and BCL-2. Mechanistically, we show that docetaxel inhibits CXCR2 and that BCL-2 downregulation occurs as a downstream effect. Further, we demonstrated in experimental models that the sensitivity to cisplatin is dependent on CXCR2 and BCL-2, and that targeting them sensitizes prostate cancer (PC) cells to cisplatin. In vivo taxane-platinum combinations are highly synergistic, and previous exposure to taxanes sensitizes mCRPC tumors to second-line cisplatin treatment. ConclusionsThe hitherto unappreciated attenuation of the CXCR2/BCL-2 axis in taxane-treated mCRPC patients is an acquired vulnerability with potential predictive activity for platinum-based treatments. Patient summaryA subset of patients with aggressive and therapy-resistant prostate cancer benefits from taxane-platinum combination chemotherapy; however, we lack the mechanistic understanding of how that synergistic effect occurs. Here, using patient data and preclinical models, we found that taxanes reduce cancer cell escape mechanisms to chemotherapy-induced cell death, hence making these cells more vulnerable to additional platinum treatment.

Copy Number Loss of 17q22 Is Associated with Enzalutamide Resistance and Poor Prognosis in Metastatic Castration-Resistant Prostate Cancer.

The purpose of this study was to measure genomic changes that emerge with enzalutamide treatment using analyses of whole-genome sequencing and RNA sequencing. One hundred and one tumors from men with metastatic castration-resistant prostate cancer (mCRPC) who had not been treated with enzalutamide (n = 64) or who had enzalutamide-resistant mCRPC (n = 37) underwent whole genome sequencing. Ninety-nine of these tumors also underwent RNA sequencing. We analyzed the genomes and transcriptomes of these mCRPC tumors. Copy number loss was more common than gain in enzalutamide-resistant tumors. Specially, we identified 124 protein-coding genes that were more commonly lost in enzalutamide-resistant samples. These 124 genes included eight putative tumor suppressors located at nine distinct genomic regions. We demonstrated that focal deletion of the 17q22 locus that includes RNF43 and SRSF1 was not present in any patient with enzalutamide-naïve mCRPC but was present in 16% (6/37) of patients with enzalutamide-resistant mCRPC. 17q22 loss was associated with lower RNF43 and SRSF1 expression and poor overall survival from time of biopsy [median overall survival of 19.3 months in 17q22 intact vs. 8.9 months in 17q22 loss, HR, 3.44 95% confidence interval (CI), 1.338-8.867, log-rank P = 0.006]. Finally, 17q22 loss was linked with activation of several targetable factors, including CDK1/2, Akt, and PLK1, demonstrating the potential therapeutic relevance of 17q22 loss in mCRPC. Copy number loss is common in enzalutamide-resistant tumors. Focal deletion of chromosome 17q22 defines a previously unappreciated molecular subset of enzalutamide-resistant mCRPC associated with poor clinical outcome.