Androgen Signaling Inhibitors Research Articles

A Modular Trial of Androgen Signaling Inhibitor Combinations Testing a Risk-Adapted Strategy in Patients with Metastatic Castration-Resistant Prostate Cancer.

To determine the efficacy and safety of risk-adapted combinations of androgen signaling inhibitors and inform disease classifiers for metastatic castration-resistant prostate cancers (mCRPC). In a modular, randomized phase II trial, 192 men were treated with 8 weeks of abiraterone acetate, prednisone and apalutamide (AAPA; Module 1), then allocated to Modules 2 or 3 based on Satisfactory (≥50% PSA decline from baseline and <5 CTC/7.5 mL) versus Unsatisfactory status. Men in the former were randomized to continue AAPA alone (Module 2A) or with ipilimumab (Module 2B). Men in the latter had carboplatin+cabazitaxel added to AAPA (Module 3). Optional baseline biopsies were subject to correlative studies. Median overall survival (from allocation) was 46.4 (95% CI 39.2, 68.2), 41.4 (95% CI 33.3, 49.9) and 18.7 (95% CI 14.3, 26.3) months in Modules 2A (n=64), 2B (n=64) and 3 (n=59) respectively. Toxicities were within expectations. Of 192 eligible patients, 154 (80.2%) underwent pre-treatment metastatic biopsies. The aggressive variant prostate cancer molecular profile (defects in ≥2 of p53, RB1, and PTEN) was associated with Unsatisfactory status. Exploratory analyses suggested SPP1+ and IGFBP2+ macrophages, druggable myeloid cell markers, and germline pathogenic mutations were enriched in the Unsatisfactory group. Adding ipilimumab to AAPA did not improve outcomes in men with androgen responsive mCRPC. Despite the addition of carboplatin+cabazitaxel, men in the Unsatisfactory group had shortened survivals. Adaptive designs can enrich for biologically and clinically relevant disease subgroups, to contribute to the development of marker-informed, risk-adapted therapy strategies in men with prostate cancer.

Creatine supplementation and resistance training to preserve muscle mass and attenuate cancer progression (CREATINE-52): a protocol for a double-blind randomized controlled trial

BackgroundMuscle mass is important for metastatic prostate cancer survival and quality of life (QoL). The backbone of treatment for men with metastatic castration sensitive prostate cancer (mCSPC) is androgen deprivation therapy (ADT) with an androgen signaling inhibitor. ADT is an effective cancer treatment, but it facilitates significant declines in muscle mass and adverse health outcomes important to mCSPC survivors, such as fatigue, and reductions in physical function, independence, insulin sensitivity, and QoL. In non-metastatic CSPC survivors, resistance training (RT) preserves muscle mass and improves these related health outcomes, but the biggest barrier to RT in CSPC survivors of all stages is fatigue. Creatine monohydrate supplementation coupled with RT (Cr + RT) may address this barrier since creatine plays a critical role in energy metabolism. Cr + RT in cancer-free older adults and other clinical populations improves muscle mass and related health outcomes. Evidence also suggests that creatine supplementation can complement cancer treatment. Thus, Cr + RT is a strategy that addresses gaps in survivorship needs of people with mCSPC. The purpose of this parallel, double-blind randomized controlled trial is to test the effects of 52-weeks of Cr + RT compared with placebo (PLA) and RT (PLA + RT) on muscle mass, other related health outcomes, and markers of cancer progression.MethodsWe will carry out this trial with our team’s established, effective, home-based, telehealth RT program in 200 mCSPC survivors receiving ADT, and evaluate outcomes at baseline, 24-, and 52-weeks. RT will occur twice weekly with elastic resistance bands, and an established creatine supplementation protocol will be used for supplementation delivery. Our approach addresses a major facilitator to RT in mCSPC survivors, a home-based RT program, while utilizing a supervised model for safety.DiscussionFindings will improve delivery of comprehensive survivorship care by providing a multicomponent, patient-centered lifestyle strategy to preserve muscle mass, improve health outcomes, and complement cancer treatment (NCT06112990).

Abstract 3266: Plk1 promotes Pdcd4 degradation to enhance enzalutamide resistance in prostate cancer

Abstract The androgen receptor (AR) signaling pathway plays critical role in the development of prostate cancer (PCa), including castration-resistant prostate cancer (CRPC). As a result, androgen signaling inhibitors (ASIs) like abiraterone and enzalutamide (ENZ) have emerged as the first-line treatment for CRPC. Nevertheless, the limited success of ASIs underscores the urgency of developing new approaches for managing CRPC patients who have become unresponsive to ASIs. Programmed cell death 4 (Pdcd4) is a tumor suppressor, which is frequently down-regulated during PCa progression. It has been shown that reduced Pdcd4 expression promotes both AR-dependent and AR-independent growth in PCa. In this study, we found that down-regulation of Pdcd4 led to acquisition of ENZ resistance in PCa. We also observed that down-regulation of Pdcd4 resulted in activation of mTORC2 activity. Additionally, knockdown of Rictor, a component of mTORC2 complex, enhanced sensitivity to ENZ treatment in PCa. These findings suggested that activation of mTORC2 due to Pdcd4 loss contributes to ASI resistance in PCa. To understand how Pdcd4 is down-regulated in the PCa, we identified that polo-like kinase (Plk1) phosphorylated Pdcd4 at Ser239. Phosphorylation of Pdcd4 by Plk1 led to ubiquitin-mediated proteasomal degradation of Pdcd4. Over-expression of the phosphomimic Pdcd4(S239D) in 22Rv1 cells promoted tumor cell growth in cultured cells and mice. Taken together, our data suggest that targeting Plk1/Pdcd4/mTORC2 signaling axis holds promise as a strategy to overcome ENZ resistance in PCa. Citation Format: Qing Wang, Qiongsi Zhang, Yanquan Zhang, Xiaoqi Liu, Hsin-Sheng Yang. Plk1 promotes Pdcd4 degradation to enhance enzalutamide resistance in prostate cancer [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 3266.

Abstract 1725: Role of PRMT5 in neuroendocrine prostate cancer development

Abstract Background: Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer responsible for an estimated 20-30% of castration resistant prostate cancer (CRPC) deaths. While NEPC can arise de novo, the majority of these cases emerge as treatment-induced NEPC (tNEPC). Our data establish PRMT5:MEP50 as a key epigenetic regulator in NEPC and provide a potential predictive biomarker for tNEPC. Methods: Here we generated an in vitro cell culture model and mouse model to mimic the clinical conditions in androgen signaling inhibitor (ASI) or androgen deprivation treatment (ADT) We developed an in vitro cell culture and in vivo model to mimic the clinical conditions in enzalutamide-resistant prostate cancer. Regulation and role of protein arginine methyltransferase 5 (PRMT5) and its cofactor methylosome protein 50 (MEP50) were determined by treating cells and mice tumors with doxycycline inducible-shRNAs and catalytic inhibitors followed by analysis of cell viability, neurite growth, and effects on neuroendocrine related gene transcription. Pro-NEPC development effects were analyzed by immunofluorescence, immunohistochemical analysis, and western blot. PRMT5:MEP50-dependent methyltransferase activity was further validated by observing histone deposition levels via western blot and ChIP-qPCR. For clinical correlation, PRMT5 and MEP50 expression levels were comprehensively analyzed in both CRPC and NEPC patient prostate tissue samples. Results: Our clinical and computational analyses have identified increased expression of PRMT5:MEP50 in NEPC. Overexpression of PRMT5 and MEP50 in prostate cancer cells is sufficient to induce neuroendocrine differentiation (NED) in prostate cancer cells. Gene depletion of PRMT5 and MEP50 prevented the NE phenotype induced by androgen receptor inhibition and resensitized the prostate cancer cells to ASI/ADT. PRMT5 and MEP50 facilitate chromatin modulation through the dimethylation of H4R3, which is highly correlated with the NED phenotype. Moreover, overexpression of PRMT5 and MEP50 in mouse prostate induces NEPC development, and gene downregulation can prevent NED in a xenograft mouse model. Elevated PRMT5 and MEP50 correlated with increased recurrence in prostate cancer patients receiving ADT and their recurrence probability after the treatment. Conclusion: Our data establish PRMT5:MEP50 as a key epigenetic regulator in NEPC and provide a potential predictive biomarker for tNEPC. Citation Format: Hye Seung Nam, Xuehong Deng, Chang-Deng Hu. Role of PRMT5 in neuroendocrine prostate cancer development [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 1725.

Ligand-gated ion channels as potential biomarkers for ADT-mediated cognitive decline in prostate cancer patients.

Men with prostate cancer are at increased risk of developing cognitive decline by the use of second-generation androgen signaling inhibitors. To date, reliable and sensitive biomarkers that could distinguish men at high risk of cognitive dysfunction under androgen deprivation therapy (ADT) have not been characterized. We used high-throughput transcriptional profiling utilizing human prostate cancer cell culture models mimicking ADT, biomarker selection using minimal common oncology data elements-cytoscape, and bioinformatic analyses employing Advaita® iPathwayGuide and DisGeNET for identification of disease-related gene associations. Validation analysis of genes was performed on brain neuronal and glial cells by quantitative real-time polymerase chain reaction assay. Our systematic analysis of androgen deprivation-associated genes involved multiple biological processes, including neuroactive ligand-receptor interaction, axon guidance, cytokine-cytokine receptor interaction, and metabolic and cancer signaling pathways. Genes associated with neuroreceptor ligand interaction, including gamma-aminobutyric acid (GABA) A and B receptors and nuclear core proteins, were identified as top upstream regulators. Functional enrichment and protein-protein interaction network analysis highlighted the role of ligand-gated ion channels (LGICs) and their receptors in cognitive dysfunction. Gene-disease association assigned forgetfulness, intellectual disability, visuospatial deficit, bipolar disorder, and other neurocognitive impairment with upregulation of type-1 angiotensin II receptor, brain-derived neurotrophic factor, GABA type B receptor subunit 2 (GABBR2), GABRA3, GABRA5, GABRB1, glycine receptor beta, glutamate ionotropic receptor N-methyl-D-aspartate receptor (NMDA) type subunit 1, glutamate ionotropic receptor NMDA type subunit 2D, 5-hydroxytryptamine receptor 1D, interferon beta 1, and nuclear receptor subfamily 3 group C member 1 as top differentially expressed genes. Validation studies of brain glial cells, neurons, and patients on ADT demonstrated the association of these genes with cognitive decline. Our findings highlight LGICs as potential biomarkers for ADT-mediated cognitive decline. Further validation of these biomarkers may lead to future practical clinical use.

Real-world experience on tolerability and safety of relugolix combined with androgen signaling inhibitors in patients with advanced prostate cancer.

85 Background: Relugolix is the first oral GNRH antagonist approved by the FDA in 2021 for the treatment of advanced prostate cancer (PCa). Approval was based on HERO study, which showed a rapid and sustained testosterone suppression superior to that of Leuprolide coupled with a significantly shorter time to eugonad state after discontinuation. Relugolix was associated with a 54% lower risk of major adverse cardiovascular events as compared with Leuprolide. There is very little data available regarding the tolerability safety of Relugolix in combination Enhanced Androgen Signaling Inhibitors (ASI). Here we provide real world experience on the combination of Relugolix and ASIs in patients(pts) with advanced PCa, focusing on safety, tolerability and pharmacodynamic outcome measures. Methods: Houston Methodist Genitourinary Oncology records were reviewed for identification of pts treated with combination Relugolix plus ASI for at least 1 month, from 09/21 to 07/23. Data collected included pts’ baseline and tumor characteristics, cardiovascular and metabolic comorbidities concomitant medication. We recorded Adverse Events, potential Drug Drug Interaction (DDI) and Testosterone (T) and PSA decline. Results: We report 152 advanced hormone-naive PCa pts with median age of 71 (range 48-96). 81% were White or/and Hispanic, 17 % black, 2 % Asian. Majority (90%) had at least 1 cardiovascular risk factor; hypertension (72%), hyperlipidemia (52%), obesity (41 %), diabetes mellitus (26%), coronary artery disease (30%) and atrial fibrillation (13%). ASIs combined with Relugolix included: Darolutamide (78%), Abiraterone (14%), Apalutamide (7%) and Enzalutamide (1%). All but one pt were compliant (99%). Median treatment exposure is 8 months (range 1 -21). All pts had baseline Testosterone &gt;150ng/dL. All pts reached castrate T levels and 90% of patients achieved a T &lt; 20 ng/dL. 55% pts reached PSA &lt;0.1 at median of 4ms, 75% PSA decline &gt; 90% and 91% PSA decline ≥50%. 7% pts discontinued Relugolix due to adverse events. Three pts (2%) had a major adverse cardiovascular event, including one sudden death, one with congestive heart failure, and one with myocardial infarction. Two pts (1%) reported grade 3 fatigue. G3 LFT elevations recorded in 2 pts (1%). No clinical signals of DDI reported. Conclusions: This is the first large original report of the combination of Relugolix with ASIs in real world practice. The combination has a favorable safety and tolerability profile with no new safety concerns. No new DDI concerns were raised. These findings in combination with pharmacodynamic outcome measures of T / PSA support the use of Relugolix in combination with ASIs as standard of care in advanced PCa.

Days spent with healthcare contact by patients with metastatic castrate-resistant prostate cancer in the last year of life.

100 Background: Days spent with healthcare contact while pursuing cancer treatment (i.e., “time toxicity”) may be particularly relevant when life expectancy is most limited. Patients with metastatic castrate resistant prostate cancer (mCRPC) ultimately choose whether to pursue further cancer directed therapies or receive supportive care and reduce expected healthcare contact. We sought to define the evolution of time toxicity over the last year of life in patients with mCRPC. Methods: Contact days, defined as any day with healthcare contact outside the home, were retrospectively assessed and categorized (e.g., infusion, ER visit) in 96 patients at an academic cancer center. The primary objective was to compare contact days in the 90-day period between 12 and 9 months prior to date of death (“first quarter”) and the 90-day period prior to death (“last quarter”) using the Wilcoxon signed rank test. Additional exploratory analyses were performed evaluating the association between clinicodemographic variables and systemic treatments received. Results: There were higher median [IQR] total contact days in the last quarter (6 [2,17]) compared to the first quarter (4 [3,6], p &lt; 0.01), driven by ER visits and hospitalizations. Compared to patients off treatment/supportive care (4 [3,4]) in the first quarter, chemotherapy (5 [4,6], p = 0.02) and radiotherapeutics (5 [4,9], p = 0.03) were associated with greater contact days, but androgen signaling inhibitors were not (3 [2,5], p = 0.20). However, there were no significant differences in contact days between any treatment vs non-treatment in the last quarter. Non-White patients (n = 27) and those without higher education (n = 30) had more contact days in the last quarter (9 [2,19], p &lt; 0.01 for both). Patients who enrolled on hospice 7 days (n = 11) or 30 days (n = 39) before date of death had more contact days in the last quarter than those with earlier enrollment (23 [7,28], p &lt; 0.01; 13 [4,24], p &lt; 0.01 respectively). Conclusions: Healthcare contact was higher in the last 3 months of life due to increased number of days with inpatient level of care. Further studies to define healthcare exposure and time toxicity of mCRPC treatments are warranted to inform patient expectations towards the end-of-life. [Table: see text]

Association of inherited steroidogenic genotype with body composition changes after androgen signaling inhibition (ASI) in men with biochemical recurrent (BCR), hormone-sensitive prostate cancer (HSPC).

Association of inherited steroidogenic genotype with body composition changes after androgen signaling inhibition (ASI) in men with biochemical recurrent (BCR), hormone-sensitive prostate cancer (HSPC).

Monitoring Glucocorticoid Receptor in Plasma-derived Extracellular Vesicles as a Marker of Resistance to Androgen Receptor Signaling Inhibition in Prostate Cancer.

Longitudinal monitoring of GR expression in plasma-derived EVs from patients with prostate cancer treated with androgen signaling inhibitors facilitates early detection of acquisition of resistance to androgen receptor signaling inhibition in individual patients.

Impact of germline DNA repair gene variants on prognosis and treatment of men with advanced prostate cancer

The clinical importance of germline variants in DNA repair genes (DRGs) is becoming increasingly recognized, but their impact on advanced prostate cancer prognosis remains unclear. A cohort of 221 newly diagnosed metastatic castration-resistant prostate cancer (mCRPC) patients were screened for pathogenic germline variants in 114 DRGs. The primary endpoint was progression-free survival (PFS) on first-line androgen signaling inhibitor (ARSI) treatment for mCRPC. Secondary endpoints were time to mCRPC progression on initial androgen deprivation therapy (ADT) and overall survival (OS). Twenty-seven patients (12.2%) carried a germline DRG variant. DRG carrier status was independently associated with shorter PFS on first-line ARSI [HR 1.72 (1.06–2.81), P = 0.029]. At initiation of ADT, DRG carrier status was independently associated with shorter progression time to mCRPC [HR 1.56, (1.02–2.39), P = 0.04] and shorter OS [HR 1.99, (1.12–3.52), P = 0.02]. Investigating the contributions of individual germline DRG variants on PFS and OS revealed CHEK2 variants to have little effect. Furthermore, prior taxane treatment was associated with worse PFS on first-line ARSI for DRG carriers excluding CHEK2 (P = 0.0001), but not for noncarriers. In conclusion, germline DRG carrier status holds independent prognostic value for predicting advanced prostate cancer patient outcomes and may potentially inform on optimal treatment sequencing already at the hormone-sensitive stage.

Cell Plasticity in a Mouse Model of Benign Prostate Hyperplasia Drives Amplification of Androgen-Independent Epithelial Cell Populations Sensitive to Antioxidant Therapy

Benign prostate hyperplasia (BPH) is caused by the nonmalignant enlargement of the transition zone of the prostate gland, leading to lower urinary tract symptoms. Although current medical treatments are unsatisfactory in many patients, the limited understanding of the mechanisms driving disease progression prevents the development of alternative therapeutic strategies. The probasin-prolactin (Pb-PRL) transgenic mouse recapitulates many histopathological features of human BPH. Herein, these alterations parallel urodynamic disturbance reminiscent of lower urinary tract symptoms. Single-cell RNA-sequencing analysis of Pb-PRL mouse prostates revealed that their epithelium mainly includes low-androgen signaling cell populations analogous to Club/Hillock cells enriched in the aged human prostate. These intermediate cells are predicted to result from the reprogramming of androgen-dependent luminal cells. Pb-PRL mouse prostates exhibited increased vulnerability to oxidative stress due to reduction of antioxidant enzyme expression. One-month treatment of Pb-PRL mice with anethole trithione (ATT), a specific inhibitor of mitochondrial ROS production, reduced prostate weight and voiding frequency. In human BPH-1 epithelial cells, ATT decreased mitochondrial metabolism, cell proliferation, and stemness features. ATT prevented the growth of organoids generated by sorted Pb-PRL basal and LSCmed cells, the two major BPH-associated, androgen-independent epithelial cell compartments. Taken together, these results support cell plasticity as a driver of BPH progression and therapeutic resistance to androgen signaling inhibition, and identify antioxidant therapy as a promising treatment of BPH.

Role of androgen signaling in androgen receptor-positive extramammary Paget's disease: Establishment of organoids and their biological analysis as a novel therapeutic target

BackgroundExtramammary Paget’s disease (EMPD) is a rare intraepithelial adenocarcinoma that mainly affects the anogenital and axillary regions. Although its etiology has not been fully elucidated, there is evidence that androgen receptors (AR) are expressed in most cases of EMPD. However, the role of androgen signaling in the pathogenesis of EMPD remains unclear. ObjectiveTo evaluate the role of androgen signaling in tumor growth of AR-positive EMPD. MethodsPatient-derived organoids were established and cultured from two AR-positive EMPD patients: one man and one woman. Cultured organoids were treated with androgen agonists and/or antagonists, then subjected to analysis of changes in organoid proliferation, as well as changes in androgen signaling pathway-specific genes. ResultsOrganoid cultures were established from each EMPD sample. These organoids were immunohistologically and genetically identical to the original tumor. For each organoid sample, viable cell number increased in response to androgen exposure. The mRNA level of Fkbp5, a known AR target gene, increased in a concentration-dependent manner in organoids exposed to the synthetic androgen R1881. Conversely, the AR inhibitor darolutamide suppressed the viable cell number in a concentration-dependent manner. The mRNA expression levels of MKI67 and Fkbp5 were also suppressed by darolutamide. ConclusionOur results indicate that androgen signaling is a key pathway involved in the growth of AR-positive EMPD. Therefore, androgen signaling inhibition may be a novel treatment option for EMPD patients who require systemic therapy.

Impact of androgen receptor alterations on cell-free DNA genomic profiling on survival outcomes in metastatic castration-resistant prostate cancer.

Androgen receptor (AR) gene alterations, as detected by circulating tumor cell-free DNA (cfDNA) genomic profiling, have been shown to emerge after a variable duration of androgen signaling inhibition. AR alterations were associated with inferior outcomes on treatment with androgen receptor pathway inhibitors (ARPI) in the first line metastatic castration-resistant prostate cancer (mCRPC) setting in a phase 2 trial. Here in, we assessed the impact of these AR alterations on survival outcomes in a real-world patient population of mCRPC experiencing disease progression on an ARPI. In this IRB-approved retrospective study, consecutively seen patients with a confirmed diagnosis of mCRPC, with disease progression on a treatment with ARPIs in the first line mCRPC setting, with no prior exposure to an ARPI in the castration sensitive setting, and with available cfDNA profiling from a CLIA certified laboratory were included. Patients were categorized based on AR status: wild-type (ARwt ) or alteration-positive (AR+ ). The objective was to correlate overall survival (OS) after disease progression on the first-line ARPI with the presence or absence of AR alterations. Kaplan-Meier and Cox Regression Tests were used as implemented in R-Studio (v.4.2). A total of 137 mCRPC patients were eligible: 69 with ARwt versus 68 with AR+ . The median OS posttreatment with the first ARPI was significantly higher for ARwt than AR+ patients (30.1 vs. 15.2 mos; p < 0.001). Of 108 patients who received a subsequent line of therapy, 63 received an alternate ARPI (AR+ 39 vs. 24 ARwt ), while 20 received a taxane-based therapy (11 AR+ vs. 9 ARwt ). Among patients receiving an alternate ARPI, AR+ had numerically shorter OS (16.8 vs. 30.4 mos, p = 0.1). Among patients receiving taxane-based regimens, the OS was not significantly different between AR+ and ARwt (14.5 vs. 10.1 mos, p = 0.18). In this real-world study, mCRPC patients with AR alterations on cfDNA had inferior OS after disease progression on the first ARPI, compared to those who did not, and may impact outcomes on a subsequent ARPI but not on subsequent taxane-based therapy received. By providing survival estimates for patients with or without AR alterations, our data may aid in patient counseling, prognostication, treatment decision, and for designing future clinical trials in this setting.

Glucocorticoid receptor-induced non-muscle caldesmon regulates metastasis in castration-resistant prostate cancer

Lethal prostate cancer (PCa) is characterized by the presence of metastases and development of resistance to therapies. Metastases form in a multi-step process enabled by dynamic cytoskeleton remodeling. An actin cytoskeleton regulating gene, CALD1, encodes a protein caldesmon (CaD). Its isoform, low-molecular-weight CaD (l-CaD), operates in non-muscle cells, supporting the function of filaments involved in force production and mechanosensing. Several factors, including glucocorticoid receptor (GR), have been identified as regulators of l-CaD in different cell types, but the regulation of l-CaD in PCa has not been defined. PCa develops resistance in response to therapeutic inhibition of androgen signaling by multiple strategies. Known strategies include androgen receptor (AR) alterations, modified steroid synthesis, and bypassing AR signaling, for example, by GR upregulation. Here, we report that in vitro downregulation of l-CaD promotes epithelial phenotype and reduces spheroid growth in 3D, which is reflected in vivo in reduced formation of metastases in zebrafish PCa xenografts. In accordance, CALD1 mRNA expression correlates with epithelial-to-mesenchymal transition (EMT) transcripts in PCa patients. We also show that CALD1 is highly co-expressed with GR in multiple PCa data sets, and GR activation upregulates l-CaD in vitro. Moreover, GR upregulation associates with increased l-CaD expression after the development of resistance to antiandrogen therapy in PCa xenograft mouse models. In summary, GR-regulated l-CaD plays a role in forming PCa metastases, being clinically relevant when antiandrogen resistance is attained by the means of bypassing AR signaling by GR upregulation.

Current Trends in Chemotherapy in the Treatment of Metastatic Prostate Cancer.

Prostate cancer is the second most common cancer among men. Despite advances in diagnosis and management, prostate cancer led to more than 300,000 deaths globally in 2020. Chemotherapy is a cornerstone of therapy for advanced prostate cancer and can prolong survival of patients with both castration-sensitive and castration-resistant disease. Herein, we present a comprehensive review of the data supporting implementation of chemotherapy in the modern treatment of advanced prostate cancer, with special attention to the use of chemotherapy for aggressive variant prostate cancer (e.g., neuroendocrine prostate cancer) and the combination of chemotherapy with androgen signaling inhibitors. As the field of prostate cancer research continues to rapidly evolve yielding novel agents and treatment modalities, chemotherapy continues to play an essential role in prolonging the survival of patients with advanced and metastatic prostate cancer.

Downregulation of EZH2 inhibits epithelial-mesenchymal transition in enzalutamide-resistant prostate cancer.

Androgen signaling inhibitors (ASI) have been approved for treatment of metastatic castration-resistant prostate cancer (mCRPC). However, the limited success of ASI in clinic justifies an urgent need to identify new targets and develop novel approaches for treatment. EZH2 significantly increases in prostate cancer (PCa). Little is understood, however, regarding the roles of EZH2 in Enzalutamide-resistant (EnzR) mCRPC. We firstly investigated the levels of EZH2 and the altered pathways in public database which was comprised with primary and metastatic PCa patient tumors. To elucidate the roles of EZH2 in mCRPC, we manipulated EZH2 in EnzR PCa cell lines to examine epithelial-mesenchymal transition (EMT). To dissect the underlying mechanisms, we measured the transcription levels of EMT-associated transcription factors (TFs). We found that EZH2 was highly expressed in mCRPC than that of primary PCa tumors and that EnzR PCa cells gained more EMT characteristics than those of enzalutamide-sensitive counterparts. Further, loss of EZH2-induced inhibition of EMT is independent of polycomb repressive complex 2 (PRC2). Mechanistically, downregulation of EZH2 inhibits transcription of EMT-associated TFs by repressing formation of H3K4me3 to the promotor regions of the TFs. We identified the novel roles of EZH2 in EnzR mCRPC. EnzR PCa gains more EMT properties than that of enzalutamide-sensitive PCa. Loss of EZH2-assocaited inhibition of EMT is PRC2 independent. Downregulation of EZH2 suppresses EMT by impairing formation of H3K4me3 at the promotor regions, thus repressing expression of EMT-associated TFs.

Abstract PR003: Convergent evolution in DNA repair-deficient mCRPC in response to targeted therapy

Abstract BACKGROUND: Distinct metastatic prostate cancer lesions within the same patient can show a range of responses to targeted therapy. These variations in response present a challenge for the interpretation of predictive biomarkers derived from a single lesion. The influence of tumor evolution on how lesions respond to Androgen Signaling Inhibitor (ASI) or PARP inhibitor therapy has been difficulty to study, because few autopsy studies have been performed in heavily treated patients with DNA repair defects. METHODS: In this study, we analyzed an autopsy cohort of 54 tumors from six men with DNA repair-deficient metastatic prostate cancer using whole genome, exome, and targeted DNA sequencing as well as RNA-sequencing. Observations were validated in an independent cohort of 135 mCRPC biopsies with whole genome and transcriptome sequencing. To automate the analysis of mutations conferring resistance to PARP inhibitor therapy, we developed a tool (AARDVARK) that detects and annotates PARP inhibitor resistance mutations. RESULTS: Patients harboring germline inactivation of the DNA repair gene BRCA2 showed consistent BRCA2 biallelic inactivation, while somatic BRCA2 inactivation was not always associated with biallelic deletion and genomic scars of DNA repair inactivation. AARDVARK identified numerous identical resistance mutations in physically distinct tumors in the same individual, consistent with dissemination of these mutations prior to later targeted therapy. We identified DNA structural variations linked to extra-chromosomal DNA (ecDNA) in 52% of mCRPC biopsies, and ecDNA amplified an oncogene 28% of the time. Extensive heterogeneity of structural variants was present at the Androgen Receptor locus, which was the most frequent target of ecDNA amplification (15% of tumors). Cyclins CCND1 and CCNE1 were amplified in 3% of cases, and a long tail of oncogenes were also targeted. Phylogenetic analysis was consistent with AR amplification by ecDNA in response to both androgen deprivation therapy and second-generation ASI. The presence of ecDNA was significantly associated with overall genomic instability, aneuploidy, whole genome doubling, chromothripsis, and with inactivating PTEN alterations. CONCLUSIONS: This study demonstrated that mCRPC lesions continue to evolve on therapy, and their varied responses can be influenced by shared genetic backgrounds. Oncogene amplification by ecDNA is common in mCRPC, particularly at the AR locus, and is linked to genomic instability. Alterations conferring resistance to ASI and PARP inhibitor therapy can be present in individual lesions before metastatic dissemination, and the evolutionary history of tumors plays an important role in their tumor response to targeted therapy. Citation Format: Thaidy Moreno, Meng Zhang, Arian Lundberg, Raunak Shrestha, Martin Sjöström, Anu Pasam, Adam Foye, Anna Trigos, Felix Feng, Shahneen Sandhu, David A. Quigley. Convergent evolution in DNA repair-deficient mCRPC in response to targeted therapy [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 PR003.

Abstract A024: Glucocorticoid receptor-induced non-muscle caldesmon regulates growth and metastasis in castration-resistant prostate cancer

Abstract Lethal prostate cancer (PCa) is characterized by the presence of metastases and the development of resistance to therapies. Metastases form in a multi-step process enabled by dynamic cytoskeleton remodeling. An actin cytoskeleton regulating gene, CALD1, encodes a protein caldesmon (CaD). Its isoform, low-molecular-weight CaD (l-CaD), operates in non-muscle cells, supporting the function of filaments involved in force production and mechanosensing. Several factors, including glucocorticoid receptor (GR), have been identified as regulators of l-CaD in different cell types, but the regulation of l-CaD in PCa has not been defined. PCa develops resistance in response to therapeutic inhibition of androgen signaling by multiple strategies. Known strategies include androgen receptor (AR) alterations, modified steroid synthesis, and bypassing AR signaling, for example, by GR upregulation. The goal of our study was to characterize the potential role of l-CaD in PCa metastases and antiandrogen therapy resistance. In this study, we extracted co-expression data of l-CaD from the largest public PCa patient data sets and identified the common transcripts between the sets. The common co-expression hits were used to recognize biological processes associated with l-CaD in the PCa context. Next, we used in vitro techniques, including 3D culture, cell viability assays, immunofluorescence staining, and Western blotting, to study the role of l-CaD in PCa with a focus on cancer hallmarks and the recognized associated biological processes. Finally, we used in vivo zebrafish and mouse xenograft models to verify the findings observed in silico in PCa patient data and in vitro in PC3, DU145, and VCaP cell lines. Here, we report that in vitro downregulation of l-CaD promotes the epithelial phenotype and reduces the spheroid growth in 3D, which is reflected in vivo in the reduced formation of metastases in a zebrafish PCa xenograft model. In accordance, CALD1 mRNA expression correlates with epithelial-to-mesenchymal transition transcripts in PCa patients. We also show that CALD1 is highly co-expressed with GR in multiple PCa data sets and that GR activation upregulates l-CaD in vitro. Moreover, GR upregulation associates with increased l-CaD expression after the development of resistance to antiandrogen therapy in PCa xenograft mouse models. In summary, GR-regulated l-CaD plays a role in forming PCa metastases, being clinically relevant when antiandrogen resistance is attained by the means of bypassing AR signaling by GR upregulation. Citation Format: Verneri Virtanen, Kreetta Paunu, Antti Kukkula, Saana Niva, Ylva Junila, Mervi Toriseva, Terhi Jokilehto, Sari Mäkelä, Riikka Huhtaniemi, Matti Poutanen, Ilkka Paatero, Maria Sundvall. Glucocorticoid receptor-induced non-muscle caldesmon regulates growth and metastasis in castration-resistant 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 A024.

Treatment and survival of de novo metastatic hormone sensitive prostate cancer among African American US Veterans.

5079 Background: Combinations of androgen deprivation therapy (ADT) plus docetaxel (DOC) or androgen signaling inhibitors (ASIs: abiraterone, enzalutamide, etc.) have revolutionized treatment of metastatic hormone sensitive prostate cancer (mHSPC), particularly for high volume disease. However, little is known about the use of and outcomes of combination therapy in African Americans (AA) with de novo mHSPC, due to their lack of representation in clinical studies. This study evaluates the patient characteristics, treatment, and survival in a cohort of US veterans with mHSPC with equal access to treatment under the Veterans Affairs Health System (VA). Methods: Veterans with mHSPC were identified from 2014-2022 in the VA using the initial pathological diagnosis of prostate cancer with SEER stage ‘distant’ and first ADT initiated within 1 month prior and 3 months after diagnosis. Therapies including DOC or ASIs were collected if initiated from 1 month prior to 4 months after ADT. Additional information at the time of diagnosis was collected including Prostate Specific Antigen (PSA), race from VA enrollment, and Charlson Comorbidity Index (CCI). Median survival was obtained for each group and stratified by PSA level &gt;100 ng/mL. Chi-square and ANOVA testing were used differences in survival (OS) were assessed by log-rank testing. Results: 4,248 veterans with de novo mHSPC were identified, 1138 (26.8%) were AA and 3110 (73.2%) white. Black veterans were younger (70.8 vs. 74.8, p&lt;0.001) and had higher median PSA (183 vs. 86.3, p&lt;0.001) with similar mean CCI (4.4 vs. 4.4, p=0.78). AA veterans were likely to have a PSA &gt;100 ng/mL at diagnosis (61.6% vs. 46.1%, p&lt;0.001) and to receive combination therapy than white veterans (36.8% vs. 32.7%, p=0.01). The median OS among AA and white veterans was similar (32.5 months vs. 32.1, p=0.75). In 2,120 veterans with PSA&gt;100 ng/mL (a surrogate for higher volume disease), AA veterans were more likely to receive combination therapy (39.5% vs. 32.9%, p=0.003) without differences in survival in AA veterans compared to white (31.0 vs. 26.9 months, p=0.18). Conclusions: In an equal access health care system, AA veterans had similar survival to white veterans despite having double the PSA levels, reflecting higher risk disease. AA presented 4 years younger and are likely treated with doublet therapy. The differences in the age of onset and burden of disease highlight persistent differences in populations with mHSPC. Further investigations to understand environmental, social, and tumor factors are warranted to explain these disparities. [Table: see text]

Sequential metastasis-directed therapy (MDT) for oligometastatic prostate cancer (Oligo PCa) assessed by PET-based imaging.

5032 Background: Prostate specific membrane antigen (PSMA) and F-18-Fluciclovine PET imaging have high sensitivity for the detection of prostate cancer (PCa) metastases. MDT with stereotactic body radiation therapy (SBRT) to PET-detected Oligo PCa has been shown to improve progression free survival (PFS) and delay androgen deprivation therapy (ADT). However, in those patients (pts) who ultimately develop oligoprogressive disease following MDT, the utility of subsequent courses of MDT has not been well defined. Methods: A single institution retrospective review was undertaken to describe outcomes following ≥2 courses of PET-guided SBRT in pts with Oligo PCa. Pts included in this analysis had undergone initial SBRT for ≤5 PCa lesions detected on PSMA or Fluciclovine PET, and subsequently underwent ≥1 additional course of SBRT at progression. Baseline data collected included stage, PSA level, Gleason Score, tracer type, and concurrent systemic therapy. Endpoints collected for each SBRT course included PSA decline ≥50% (PSA50), PFS, and systemic therapy change free survival (RxFS) (initiation of ADT, or for pts already on ADT, addition of an androgen signaling inhibitor). Association of factors with PFS after SBRT2 were analyzed using multivariable Cox proportional-hazards models. Results: 34 pts underwent ≥2 courses of MDT (SBRT1, SBRT2). At SBRT2, progression was identified by PSMA-PET in 26 (77%) pts, and by Fluciclovine-PET in 8 (23%). With SBRT2, 18 (53%) had a concurrent systemic therapy change; 10 (29%) did not receive any systemic therapy. 12 pts subsequently underwent SBRT3. Progression was detected by PSMA PET in 9 (75%) and Fluciclovine PET in 3 (25%). Clinical outcomes are summarized in the table. In the multivariable analysis, predictors associated with PFS following SBRT2 were 1) PSA decline at SBRT1 (HR 1.10, 95% CI 1.05-1.16, P&lt;0.001) and 2) PSA doubling time (PSADT) &lt; 12 months at the time of SBRT2 (HR 11.52, 95% CI 1.36-97.38, P 0.025). Overall, from SBRT1 to last follow-up (median 25.2 months), 23 (68%) pts remained ADT-free (14 after SBRT2; 9 after SBRT3). Conclusions: Serial MDT for Oligo PCa detected on PSMA or Fluciclovine PET is feasible and results in PSA declines, independent of change in systemic therapy. There is a persistent but diminishing benefit of MDT over successive courses. Overall, 2/3 of pts were able to postpone the use of ADT. PSA decline at SBRT1 and PSADT at SBRT2 may be biomarkers for SBRT2 benefit. Despite the retrospective nature of this study and cohort heterogeneity, these data provide a rationale for serial SBRT in Oligo PCA, and the need for larger, prospective studies of this strategy. [Table: see text]