Second-generation Antiandrogen Therapy Research Articles

Abstract 6205: Identify drugs for metastatic castration-resistance prostate cancer (mCRPC) patients with high glycolytic activity through in silico approach

Abstract Prostate cancer (PC) remains a prominent cause of cancer-related mortality among men in the United States. A significant factor contributing to the mortality of PC patients is the development of resistance to second-generation antiandrogen therapies, particularly androgen receptor-signaling inhibitors (ARSI), which is pronounced in patients with late-stage PC, metastatic castration-resistance prostate cancer (mCRPC). Therefore, there is an urgent need for novel therapeutics beyond AR signaling inhibition for patients with mCRPC. One of the key drivers of resistance to ARSI and a critical feature of CRPC is cancer metabolism reprogramming to elevated glycolysis. However, the current research on finding drugs to impede high-glycolytic tumor growth is hurdled by a resistance raised from metabolic plasticity. The aim of this research is to quickly repurpose existing drugs for inhibiting high-glycolytic mCRPC growth while proactively circumstancing resistance from metabolic plasticity through computational approaches. To do this, we imputed a large number of drug responses in patients with mCRPC using a computational algorithm (OncoPredict), identified drugs that were projected to show higher sensitivity in high-glycolytic tumors, and performed in vitro validation. Furthermore, to maximize drug efficacy, we identified biomarkers for drug candidates. By implementing this computational pipeline, we identified a number of drugs with various mechanisms of action that show higher efficacy in mCRPC with high glycolysis. Furthermore, we successfully validated the efficacy of these nominated drug candidates including an anti-parasitic agent, an HSP90 inhibitor, and a CDK inhibitor. These drug candidates exhibited superior tumor growth inhibition in in vitro models of high glycolysis-induced advanced PC. In conclusion, this study introduces an innovative in silico approach to unveil the existing drugs’ unknown potential for the treatment of patients with mCRPC. Our findings hold promise for development of effective therapeutics for combating this challenging disease. Citation Format: Mei-Chi Su, Adam M. Lee, R. Stephanie Huang. Identify drugs for metastatic castration-resistance prostate cancer (mCRPC) patients with high glycolytic activity through in silico approach [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 6205.

Identification of a Predictive Genomic Biomarker for Prostate Directed Therapy in Synchronous Low-Volume Metastatic Castration Sensitive Prostate Cancer.

Standard of care management for metastatic castration sensitive prostate cancer (mCSPC) includes androgen deprivation therapy (ADT) with docetaxel or second-generation anti-androgen therapy. Recently, randomized data has demonstrated radiotherapy to the prostate is associated with an improvement in overall survival among patients with low-volume metastatic disease. Tumor genomics represents an additional dimension to understand the clinical trajectory of patients with mCSPC. Herein we aim to evaluate a high-risk genomic signature for its ability to predict response to prostate directed therapy (PDT). We performed a single institution retrospective review of men with low-volume mCSPC who underwent next-generation sequencing of their tumor. Patients were classified according to the presence of high-risk (HiRi) mutation including pathogenic mutations in either TP53, ATM, BRCA1/2, or Rb1. Our primary endpoint was to determine the effect of PDT on overall survival (OS) in patients with and without a HiRi mutation. Survival analysis was performed with the Kaplan-Meier method compared with log-rank test and multivariable cox regression. Interaction between HiRi mutation and PDT was evaluated. A total of 101 patients with synchronous low-volume CSPC were included in our analysis with a median follow-up of 44 months. Approximately half of patients were found to have a HiRi pathogenic mutation (48.5%) with TP53 mutations accounting for 75.5% of HiRi mutations. On multivariable cox regression PDT was associated with improvement in OS (HR = 0.37, 95% CI 0.16-0.88; p = 0.03). When stratified by presence of HiRi mutation, PDT was not associated with any clinical outcome. Patients with HiRi mutations demonstrated a median OS of 73 vs 66.8 months (p = 0.28) for no PDT and PDT, respectively. Conversely, patients without a HiRi mutation demonstrated a significant improvement in median OS of 60 vs 105.3 months (p<0.01) for no PDT and PDT, respectively. The p-value for interaction for OS between PDT and HiRi mutation was statistically significant (p<0.01). Here we have identified a high-risk genomic biomarker that appears predictive for response to PDT in men with synchronous low-volume mCSPC. Further work validating these results with prospective randomized data is warranted.

Clinical Experience with [225Ac]Ac-PSMA Treatment in Patients with [177Lu]Lu-PSMA-Refractory Metastatic Castration-Resistant Prostate Cancer.

For patients with advanced-stage metastatic castration-resistant prostate cancer (mCRPC) who do not respond to [177Lu]Lu-PSMA therapy, there are limited treatment options. Clinical results obtained with [225Ac]Ac-PSMA are promising. We retrospectively analyzed the outcomes of patients treated with [225Ac]Ac-PSMA between December 2018 and October 2022. Methods: We evaluated the treatment results of 23 patients (mean age, 70.3 ± 8.8 y) with mCRPC who were refractory to treatment with [177Lu]Lu-PSMA (2-9 cycles). The safety profile was assessed according to Common Technology Criteria for Adverse Events version 5.0. Treatment efficacy was assessed using prostate-specific membrane antigen PET progression criteria and prostate-specific antigen (PSA) response according to Prostate Cancer Working Group 2 criteria after the first cycle of [225Ac]Ac-PSMA treatment. Results: All patients received androgen-deprivation therapy, whereas 22 (96%) and 19 (83%) patients received chemotherapy and second-generation antiandrogen therapy, respectively. One patient received 4 cycles, 2 received 3 cycles, 8 received 2 cycles, and 12 received 1 cycle of [225Ac]Ac-PSMA. The median interval between cycles was 13 wk (range, 8-28 wk). [225Ac]Ac-PSMA was administered with a mean activity of 7.6 MBq (range, 6.2-10.0 MBq) in each cycle. Patients were at an advanced stage of disease, and tumor burden was very high. Although the best PSA response was observed in 5 patients (26%) after [225Ac]Ac-PSMA treatment, there was at least some level of decline in PSA observed in 11 patients (58%; n = 19). Treatment response was assessed in patients who underwent [68Ga]Ga-PSMA PET/CT imaging. After the first cycle of treatment (n = 18), 50% of patients (n = 9) showed disease progression according to prostate-specific membrane antigen PET progression criteria, and the disease control rate was calculated to be 50%. Median progression-free survival was 3.1 mo, and median overall survival was 7.7 mo. Grade 3 hematologic toxicity occurred in 1 patient, and grade 3 nephrotoxicity was observed in another patient. Parotid SUVmax decreased by 33%, although all patients complained of dry mouth before treatment. Conclusion: We observed that [225Ac]Ac-PSMA therapy was safe and showed potential even in cases with advanced-stage mCRPC in which all other treatment options were completed.

Identification of a Predictive Genomic Biomarker for Prostate-directed Therapy in Synchronous Low-volume Metastatic Castration-sensitive Prostate Cancer

BackgroundStandard of care management for synchronous metastatic castration-sensitive prostate cancer (mCSPC) includes androgen deprivation therapy with a second-generation antiandrogen therapy and/or docetaxel. Recently, randomized data have demonstrated that prostate-directed therapy (PDT) is associated with an improvement in overall survival (OS) among patients with low-volume metastatic disease. Tumor genomics represents an additional dimension to define the clinical trajectory of patients with mCSPC. ObjectiveTo evaluate a high-risk (HiRi) genomic signature to predict the benefit from PDT. Design, setting, and participantsWe performed a single-institution retrospective review of men with synchronous low-volume mCSPC who underwent DNA panel sequencing of their tumor. Patients were classified according to the presence of HiRi mutation including pathogenic mutations in TP53, ATM, BRCA1, BRCA2, or Rb1. Outcome measurements and statistical analysisThe primary endpoint was to determine the effect of PDT on OS in patients with and without a HiRi mutation. A survival analysis was performed with the Kaplan-Meier method compared with log-rank test and multivariable Cox regression. The interaction between HiRi mutation and PDT was evaluated. Results and limitationsA total of 101 patients with synchronous low-volume CSPC were included with a median follow-up of 44 mo. Approximately half of patients were found to have a HiRi pathogenic mutation (49%). Patients with HiRi mutations demonstrated median OS of 73 versus 66.8 mo (p = 0.3) for no PDT versus PDT. Conversely, patients without a HiRi mutation demonstrated a significant improvement in OS of 60 versus 105.3 mo (p < 0.001) for no PDT versus PDT. The p value for interaction for OS between PDT and HiRi mutation was statistically significant (p < 0.001). Limitations include the retrospective nature of the study. ConclusionsHere, we have identified a HiRi genomic biomarker that appears predictive for the lack of benefit from PDT in men with synchronous low-volume mCSPC. Further work validating these results is warranted. Patient summaryIn this report, we evaluated a high-risk genomic biomarker to predict the benefit from prostate-directed therapy for men with synchronous low-volume metastatic castration-sensitive prostate cancer. We found that men without a high-risk mutation appear to experience a greater clinical benefit from prostate-directed therapy than those with a high-risk mutation.

A phase 1/2 study of REGN4336, a PSMAxCD3 bispecific antibody, alone and in combination with cemiplimab in patients with metastatic castration-resistant prostate cancer.

TPS284 Background: Prostate cancer is the leading cause of new cancer diagnoses and the second most common cause of cancer-related death in American men. Prognosis is especially poor for men with metastatic castration resistant prostate cancer (mCRPC). Prostate-specific membrane antigen (PSMA) is highly expressed on malignant prostate tissue but shows limited expression on normal tissue. As such, PSMA is an excellent research target for treatment of mCRPC. REGN4336 is a PSMAxCD3 bispecific antibody designed to facilitate T-cell–mediated killing of PSMA-expressing tumor cells. In preclinical models, REGN4336 demonstrated strong PSMA-dependent antitumor activity that was dose-dependent. Preclinical data also support clinical research into the combination of REGN4336 with cemiplimab (anti–programmed cell death-1) for treating mCRPC. Methods: This is an open-label, Phase 1/2, first-in-human, multicenter dose-escalation study with dose expansion evaluating safety, tolerability, pharmacokinetics (PK), and antitumor activity of REGN4336 administered subcutaneously alone and in combination with intravenous cemiplimab in patients with mCRPC (NCT05125016). Patients must have received at least two prior lines of systemic therapy approved for metastatic and/or castration-resistant disease including a second-generation anti-androgen therapy. In Module 1, REGN4336 as monotherapy is administered weekly but may be extended to once every 3 weeks following identification of the minimal pharmacologically active dose. In Module 2, REGN4336 will be administered in combination with cemiplimab (350 mg) once every 3 weeks after a 4-week REGN4336 monotherapy lead-in cycle. Study therapies are administered until disease progression, intolerable adverse events, withdrawal of consent, or a study withdrawal criterion is met. The primary objectives in dose escalation are to evaluate the safety, tolerability, PK, and recommended phase 2 dosing regimen (RP2DR) of REGN4336 alone and in-combination with cemiplimab. Expansion cohort(s) will be enrolled once RP2DRs have been determined. During the expansion phase, the primary objective is to assess clinical activity, as measured by objective response rate with REGN4336 alone or in combination with cemiplimab per modified Prostate Cancer Working Group 3 criteria. At selected sites, PSMA positron emission tomography/computed tomography scans will be performed at predefined timepoints on study. This study is currently open to enrollment. Clinical trial information: NCT03088540 .

A phase 1/2 study of REGN4336, a PSMAxCD3 bispecific antibody, alone and in combination with cemiplimab in patients with metastatic castration-resistant prostate cancer.

TPS5105 Background: Prostate cancer is the leading cause of new cancer diagnoses and the second most common cause of cancer-related death in American men. Prognosis is especially poor for men with metastatic castration resistant prostate cancer (mCRPC). Prostate-specific membrane antigen (PSMA) is highly expressed on malignant prostate tissue but shows limited expression on normal tissue. As such, PSMA is an excellent research target for treatment of mCRPC. REGN4336 is a PSMAxCD3 bispecific antibody designed to facilitate T-cell–mediated killing of PSMA-expressing tumor cells. In preclinical models, REGN4336 demonstrated strong PSMA-dependent antitumor activity that was dose-dependent. Preclinical data also support clinical research into the combination of REGN4336 with cemiplimab (anti–programmed cell death-1) for treating mCRPC. Methods: This is an open-label, Phase 1/2, first-in-human, multicenter dose-escalation study with dose expansion evaluating safety, tolerability, pharmacokinetics (PK), and antitumor activity of REGN4336 administered subcutaneously alone and in combination with intravenous cemiplimab in patients with mCRPC (NCT05125016). Patients must have received at least two prior lines of systemic therapy approved for metastatic and/or castration-resistant disease including a second-generation anti-androgen therapy. In this study, REGN4336 as monotherapy is administered weekly but may be extended to once every 3 weeks following identification of the minimal pharmacologically active dose. REGN4336 in combination with cemiplimab (350 mg) will be administered once every 3 weeks after a 4-week REGN4336 monotherapy lead-in cycle. Study therapies are administered until disease progression, intolerable adverse events, withdrawal of consent, or study withdrawal criterion is met. The primary objectives in dose escalation are to evaluate the safety, tolerability, PK, and recommended phase 2 dosing regimen (RP2DR) of REGN4336 alone and in-combination with cemiplimab. Expansion cohort(s) will be enrolled once RP2DRs have been determined. During the expansion phase, the primary objective is to assess clinical activity, as measured by objective response rate with REGN4336 alone or in combination with cemiplimab per modified Prostate Cancer Working Group 3 criteria. At selected sites, PSMA positron emission tomography/computed tomography scans will be performed at predefined timepoints on study. This study is currently open to enrollment. Clinical trial information: NCT03088540.

Mechanisms of Resistance to Second-Generation Antiandrogen Therapy for Prostate Cancer: Actual Knowledge and Perspectives.

Prostate cancer therapy for locally advanced and metastatic diseases includes androgen deprivation therapy (ADT). Second-generation antiandrogens have a role in castration-resistant prostate cancer. Nevertheless, some patients do not respond to this therapy, and eventually all the patients became resistant. This is due to modifications to intracellular signaling pathways, genomic alteration, cytokines production, metabolic switches, constitutional receptor activation, overexpression of some proteins, and regulation of gene expression. The aim of this review is to define the most important mechanisms that drive this resistance and the newest discoveries in this field, specifically for enzalutamide and abiraterone, with potential implications for future therapeutic targets. Furthermore, apalutamide and darolutamide share some resistance mechanisms with abiraterone and enzalutamide and could be useful in some resistance settings.

SU086, an inhibitor of HSP90, impairs glycolysis and represents a treatment strategy for advanced prostate cancer

SummaryAmong men, prostate cancer is the second leading cause of cancer-associated mortality, with advanced disease remaining a major clinical challenge. We describe a small molecule, SU086, as a therapeutic strategy for advanced prostate cancer. We demonstrate that SU086 inhibits the growth of prostate cancer cells in vitro, cell-line and patient-derived xenografts in vivo, and ex vivo prostate cancer patient specimens. Furthermore, SU086 in combination with standard of care second-generation anti-androgen therapies displays increased impairment of prostate cancer cell and tumor growth in vitro and in vivo. Cellular thermal shift assay reveals that SU086 binds to heat shock protein 90 (HSP90) and leads to a decrease in HSP90 levels. Proteomic profiling demonstrates that SU086 binds to and decreases HSP90. Metabolomic profiling reveals that SU086 leads to perturbation of glycolysis. Our study identifies SU086 as a treatment for advanced prostate cancer as a single agent or when combined with second-generation anti-androgens.

A phase I/II study of REGN5678 (Anti-PSMAxCD28, a costimulatory bispecific antibody) with cemiplimab (anti–PD-1) in patients with metastatic castration-resistant prostate cancer.

TPS174 Background: Bispecific antibodies (bsAbs) are emerging as a protein-based therapeutic strategy for directing T-cell-mediated cytotoxicity in a tumor antigen-specific manner, typically by binding to both tumor antigen and the CD3 receptor on T-cells. REGN5678 is a human IgG4-based, first-in-class costimulatory bsAb designed to target prostate tumors by bridging prostate specific membrane antigen expressing tumor cells with the costimulatory receptor, CD28, on T-cells, and providing amplified T-cell receptor-CD3 complex-mediated T-cell activation within the tumor through the activation of CD28 signaling. At the tumor site, REGN5678 may synergize with PD-1 inhibitors. In mouse models, REGN5678 in combination with a PD-1 antibody has improved anti-tumor activity compared with either therapy alone (Waite JC et al. Sci Transl Med. 2020:12;549). Methods: This is an open label, Phase I/II, first-in-human study evaluating safety, tolerability, pharmacokinetics (PK), and anti-tumor activity of REGN5678 alone and in combination with cemiplimab in patients with metastatic castration resistant prostate cancer (mCRPC) who progressed after prior therapy (NCT03972657). For inclusion, patients must have received at least two prior lines of systemic therapy (in addition to androgen deprivation therapy) approved for metastatic and/or castration-resistant disease including a second-generation anti-androgen therapy. REGN5678 is administered weekly; cemiplimab (350 mg) is administered once every 3 weeks. During dose escalation, a 3-week safety lead-in of REGN5678 monotherapy will be administered prior to addition of cemiplimab. Study therapies are administered until disease progression, intolerable adverse events, withdrawal of consent, or study withdrawal criterion is met. The primary objectives in dose escalation are to evaluate safety, tolerability, and PK of REGN5678 alone and in combination with cemiplimab. Expansion cohort(s) will be enrolled once a maximum-tolerated REGN5678/cemiplimab dose is reached, or if a recommended Phase 2 dose or doses have been determined. During the expansion phase, the primary objective is to assess clinical activity, as measured by objective response rate of REGN5678 in combination with cemiplimab per modified Prostate Cancer Working Group 3 criteria. At selected sites, prostate-specific membrane antigen PET/CT scans are performed at baseline and select time points on study. This study is currently open to enrollment. Clinical trial information: NCT03972657.

SU086, a New Inhibitor of HSP90, Impairs Glycolysis and Represents a New Treatment Strategy for Advanced Prostate Cancer

Among men, prostate cancer is the second leading cause of cancer-associated mortality, with advanced disease remaining a major clinical challenge. We describe a small molecule, SU086, as a new therapeutic strategy for advanced prostate cancer. We demonstrate that SU086 inhibits the growth of prostate cancer cells in vitro, cell line and patient-derived xenografts in vivo, and ex vivo prostate cancer patient specimens. Furthermore, SU086 in combination with standard of care second-generation anti-androgen therapies displayed increased impairment of prostate cancer cell and tumor growth in vitro and in vivo. Cellular thermal shift assay (CETSA) revealed that SU086 binds to heat shock protein 90 (HSP90) and leads to a decrease in HSP90 levels. Proteomic and metabolomic profiling further revealed that the SU086 decreases HSP90 and leads to perturbation of glycolysis. Our study identifies SU086 as a new treatment for advanced prostate cancer as a single agent or when combined with second-generation anti-androgens.

Steroid Sulfatase Stimulates Intracrine Androgen Synthesis and is a Therapeutic Target for Advanced Prostate Cancer.

Most patients with prostate cancer receiving enzalutamide or abiraterone develop resistance. Clinical evidence indicates that serum levels of dehydroepiandrosterone sulfate (DHEAS) and biologically active DHEA remain in the high range despite antiandrogen treatment. The conversion of DHEAS into DHEA by steroid sulfatase (STS) may contribute to sustained intracrine androgen synthesis. Here, we determine the contribution of STS to treatment resistance and explore the potential of targeting STS to overcome resistance in prostate cancer. STS expression was examined in patients and cell lines. In vitro, STS activity and expression were modulated using STS-specific siRNA or novel STS inhibitors (STSi). Cell growth, colony formation, androgen production, and gene expression were examined. RNA-sequencing analysis was conducted on VCaP cells treated with STSi. Mice were treated with STSis with or without enzalutamide to determine their effects in vivo. STS is overexpressed in patients with castration-resistant prostate cancer (CRPC) and resistant cells. STS overexpression increases intracrine androgen synthesis, cell proliferation, and confers resistance to enzalutamide and abiraterone. Inhibition of STS using siRNA suppresses prostate cancer cell growth. Targeting STS activity using STSi inhibits STS activity, suppresses androgen receptor transcriptional activity, and reduces the growth of resistant C4-2B and VCaP prostate cancer cells. STSis significantly suppress resistant VCaP tumor growth, decrease serum PSA levels, and enhance enzalutamide treatment in vitro and in vivo. These studies suggest that STS drives intracrine androgen synthesis and prostate cancer proliferation. Targeting STS represents a therapeutic strategy to treat CRPC and improve second-generation antiandrogen therapy.

Blood-based gene expression signature associated with metastatic castrate-resistant prostate cancer patient response to abiraterone plus prednisone or enzalutamide.

Precision medicine approaches for managing patients with metastatic castrate-resistant prostate cancer (mCRPC) are lacking. Non-invasive approaches for molecular monitoring of disease are urgently needed, especially for patients suffering from bone metastases for whom tissue biopsy is challenging. Here we utilized baseline blood samples to identify mCRPC patients most likely to benefit from abiraterone plus prednisone (AAP) or enzalutamide. Baseline blood samples were collected for circulating tumor cell (CTC) enumeration and qPCR-based gene expression analysis from 51 men with mCRPC beginning treatment with abiraterone or enzalutamide. Of 51 patients (median age 68 years [51-82]), 22 received AAP (abiraterone 1000 mg/day plus prednisone 10 mg/day) and 29 received enzalutamide (160 mg/day). The cohort was randomly divided into training (n = 37) and test (n = 14) sets. Baseline clinical variables (Gleason score, PSA, testosterone, and hemoglobin), CTC count, and qPCR-based gene expression data for 141 genes/isoforms in CTC-enriched blood were analyzed with respect to overall survival (OS). Genes with expression most associated with OS included MSLN, ARG2, FGF8, KLK3, ESRP2, NPR3, CCND1, and WNT5A. Using a Cox-elastic net model for our test set, the 8-gene expression signature had a c-index of 0.87(95% CI [0.80, 0.94]) and was more strongly associated with OS than clinical variables or CTC count alone, or a combination of the three variables. For patients with a low-risk vs. high-risk gene expression signature, median OS was not reached vs. 18 months, respectively (HR 5.32 [1.91-14.80], p = 0.001). For the subset of 41 patients for whom progression-free survival (PFS) data was available, the median PFS for patients with a low-risk vs high-risk gene expression signature was 20 vs. 5 months, respectively (HR 2.95 [1.46-5.98], p = 0.003). If validated in a larger prospective study, this test may predict patients most likely to benefit from second-generation antiandrogen therapy.

Second-Generation Antiandrogen Therapy Radiosensitizes Prostate Cancer Regardless of Castration State through Inhibition of DNA Double Strand Break Repair.

Simple SummaryThe combination of RT and the first generation AR blockers to improve the outcome in prostate cancer remain a matter of controversial debate in clinical trials. In the current study we aim to investigate the effect of three FDA approved second-generation antiandrogens (abiraterone acetate, apalutamide and enzalutamide), as more potent inhibitors of the AR signaling, on the cytotoxicity of RT in pre-clinical models. In vitro and ex vivo analyses revealed a strong radiosensitising effect for the second-generation antiandrogens, regardless of the castration state. The first-generation AR-blocker bicalutamide failed to show any radiosensitising effect. The radiosensitising effect of the second-generation antiandrogens was attributed to the inhibition of DSB repair. Together, we provide a proof-of-principle pre-clinical evidence to rationalize the clinical use of the second-generation antiandrogens to enhance the effect of IR as a potential strategy to improve the outcomes of PCa patients with localized disease who undergo ablative RT.(1) Background: The combination of the first-generation antiandrogens and radiotherapy (RT) has been studied extensively in the clinical setting of prostate cancer (PCa). Here, we evaluated the potential radiosensitizing effect of the second-generation antiandrogens abiraterone acetate, apalutamide and enzalutamide. (2) Methods: Cell proliferation and agarose-colony forming assay were used to measure the effect on survival. Double strand break repair efficiency was monitored using immunofluorescence staining of γH2AX/53BP1. (3) Results: We report retrospectively a minor benefit for PCa patients received first-generation androgen blockers and RT compared to patients treated with RT alone. Combining either of the second-generation antiandrogens and 2Gy suppressed cell growth and increased doubling time significantly more than 2Gy alone, in both hormone-responsive LNCaP and castration-resistant C4-2B cells. These findings were recapitulated in resistant sub-clones to (i) hormone ablation (LNCaP-abl), (ii) abiraterone acetate (LNCaP-abi), (iii) apalutamide (LNCaP-ARN509), (iv) enzalutamide (C4-2B-ENZA), and in castration-resistant 22-RV1 cells. This radiosensitization effect was not observable using the first-generation antiandrogen bicalutamide. Inhibition of DNA DSB repair was found to contribute to the radiosensitization effect of second-generation antiandrogens, as demonstrated by a significant increase in residual γH2AX and 53BP1 foci numbers at 24h post-IR. DSB repair inhibition was further demonstrated in 22 patient-derived tumor slice cultures treated with abiraterone acetate before ex-vivo irradiation with 2Gy. (4) Conclusion: Together, these data show that second-generation antiandrogens can enhance radiosensitivity in PCa through DSB repair inhibition, regardless of their hormonal status. Translated into clinical practice, our results may help to find additional strategies to improve the effectiveness of RT in localized PCa, paving the way for a clinical trial.

Targeting RET Kinase in Neuroendocrine Prostate Cancer.

The increased treatment of metastatic castration-resistant prostate cancer (mCRPC) with second-generation antiandrogen therapies (ADT) has coincided with a greater incidence of lethal, aggressive variant prostate cancer (AVPC) tumors that have lost dependence on androgen receptor (AR) signaling. These AR-independent tumors may also transdifferentiate to express neuroendocrine lineage markers and are termed neuroendocrine prostate cancer (NEPC). Recent evidence suggests kinase signaling may be an important driver of NEPC. To identify targetable kinases in NEPC, we performed global phosphoproteomics comparing several AR-independent to AR-dependent prostate cancer cell lines and identified multiple altered signaling pathways, including enrichment of RET kinase activity in the AR-independent cell lines. Clinical NEPC patient samples and NEPC patient-derived xenografts displayed upregulated RET transcript and RET pathway activity. Genetic knockdown or pharmacologic inhibition of RET kinase in multiple mouse and human models of NEPC dramatically reduced tumor growth and decreased cell viability. Our results suggest that targeting RET in NEPC tumors with high RET expression could be an effective treatment option. Currently, there are limited treatment options for patients with aggressive neuroendocrine prostate cancer and none are curative. IMPLICATIONS: Identification of aberrantly expressed RET kinase as a driver of tumor growth in multiple models of NEPC provides a significant rationale for testing the clinical application of RET inhibitors in patients with AVPC.

Tumor Microenvironment-Derived NRG1 Promotes Antiandrogen Resistance in Prostate Cancer

SUMMARYDespite the development of second-generation antiandrogens, acquired resistance to hormone therapy remains a major challenge in treating advanced prostate cancer. We find that cancer-associated fibroblasts (CAFs) can promote antiandrogen resistance in mouse models and in prostate organoid cultures. We identify neuregulin 1 (NRG1) in CAF supernatant, which promotes resistance in tumor cells through activation of HER3. Pharmacological blockade of the NRG1/HER3 axis using clinical-grade blocking antibodies re-sensitizes tumors to hormone deprivation in vitro and in vivo. Furthermore, patients with castration-resistant prostate cancer with increased tumor NRG1 activity have an inferior response to second-generation antiandrogen therapy. This work reveals a paracrine mechanism of antiandrogen resistance in prostate cancer amenable to clinical testing using available targeted therapies.

Systemic Management for Nonmetastatic Castration-resistant Prostate Cancer: A Systematic Review and Network Meta-Analysis.

To indirectly compare the efficacy and safety of systemic therapies used for patients with nonmetastatic castration-resistant prostate cancer (nmCRPC). The relevant randomized controlled trials were retrieved from PubMed and the Cochrane Library. Network meta-analyses were used to compare multiple drugs simultaneously for the outcomes of nmCRPC. Direct evidence in trials and indirect evidence across trials were combined by the network meta-analyses to estimate the treatment efficiency. Eight studies were included in our research. For prostate-specific antigen progression-free survival, the rate of progression was significantly decreased following apalutamide, enzalutamide, bicalutamide+dutasteride, and bicalutamide treatment compared with placebo. Compared with placebo treatment, metastases-free survival was significantly increased in patients who received apalutamide (hazard ratio [HR]: 0.28, 95% confidence interval [CI]: 0.23-0.35), enzalutamide (HR: 0.29, 95% CI: 0.24-0.35), and darolutamide (HR: 0.42, 95% CI: 0.35-0.50). Direct comparison showed significant survival benefits in patients who received second-generation anti-androgen therapy (apalutamide, enzalutamide, and darolutamide: HR: 0.74, 95% CI: 0.61-0.91) compared with patients who received placebo. With respect to metastases-free survival, based on SUCRA analysis, there was 80% and 78% probability that apalutamide and enzalutamide were preferred treatment, while darolutamide was likely to be second-best choice. Compared with placebo, all agents were not associated with significantly higher likelihood of serious adverse events and grade 3 to 4 adverse events. Our outcomes support equivalent efficacy and similar risk of adverse effects between apalutamide, enzalutamide, and darolutamide, supporting the use of these antiandrogen agents in high-risk of progression nmCRPC.

Deubiquitination in prostate cancer progression: role of USP22.

Prostate cancer (PCa) is the leading cause of cancer death in men. With more therapeutic modalities available, the overall survival in PCa has increased significantly in recent years. Patients with relapses after advanced secondgeneration anti-androgen therapy however, often show poor disease prognosis. This group of patients often die from cancer-related complicacies. Multiple approaches have been taken to understand disease recurrence and to correlate the gene expression profile. In one such study, an 11-gene signature was identified to be associated with PCa recurrence and poor survival. Amongst them, a specific deubiquitinase called ubiquitin-specific peptidase 22 (USP22) was selectively and progressively overexpressed with PCa progression. Subsequently, it was shown to regulate androgen receptors and Myc, the two most important regulators of PCa progression. Furthermore, USP22 has been shown to be associated with the development of therapy resistant PCa. Inhibiting USP22 was also found to be therapeutically advantageous, especially in clinically challenging and advanced PCa. This review provides an update of USP22 related functions and challenges associated with PCa research and explains why targeting this axis is beneficial for PCa relapse cases.

Second-Generation Antiandrogens: From Discovery to Standard of Care in Castration Resistant Prostate Cancer.

Prostate cancer is the most commonly diagnosed cancer affecting men in the United States. The prostate is a hormone-dependent gland in which androgen hormones testosterone and dihydrotestosterone bind to and activate the androgen receptor, initiating nuclear translocation of androgen receptor and a subsequent signaling cascade. Due to the androgen dependency of the prostate, androgen deprivation therapies have emerged as first line treatment for aggressive prostate cancer. Such therapies are effective until the point at which prostate cancer, through a variety of mechanisms including but not limited to generation of ligand-independent androgen receptor splice variants, or intratumoral androgen production, overcome hormone deprivation. These cancers are androgen ablation resistant, clinically termed castration resistant prostate cancer (CRPC) and remain incurable. First-generation antiandrogens established androgen receptor blockade as a therapeutic strategy, but these therapies do not completely block androgen receptor activity. Efficacy and potency have been improved by the development of second-generation antiandrogen therapies, which remain the standard of care for patients with CRPC. Four second-generation anti-androgens are currently approved by the Food and Drug Administration (FDA); abiraterone acetate, enzalutamide, and recently approved apalutamide and darolutamide. This review is intended to provide a thorough overview of FDA approved second-generation antiandrogen discovery, treatment application, strategies for combination therapy to overcome resistance, and an insight for the potential future approaches for therapeutic inhibition of androgen receptor.

Loss of Notch1 Activity Inhibits Prostate Cancer Growth and Metastasis and Sensitizes Prostate Cancer Cells to Antiandrogen Therapies.

Prostate cancer remains among the leading causes of cancer-related deaths in men. Patients with aggressive disease typically undergo hormone deprivation therapy. Although treatment is initially very successful, these men commonly progress to lethal, castration-resistant prostate cancer (CRPC) in 2 to 3 years. Standard therapies for CRPC include second-generation antiandrogens, which prolong patient lifespan by only several months. It is imperative to advance our understanding of the mechanisms leading to resistance to identify new therapies for aggressive prostate cancer. This study identifies Notch1 as a therapeutic target in prostate cancer. Loss of NOTCH1 in aggressive prostate cancer cells decreases proliferation, invasion, and tumorsphere formation. Therapeutic inhibition of Notch1 activity with gamma secretase inhibitors RO4929097 or DAPT in prostate cancer cells further results in decreased proliferative abilities. Loss of NOTCH1 and treatment of immunocompromised mice bearing prostate cancer xenografts with RO4929097 display significantly impaired tumor growth. Loss of NOTCH1 additionally decreased metastatic potential of prostate cancer cells in invasion assays in vitro as well as in vivo experiments. Moreover, treatment with gamma secretase inhibitors or NOTCH1 gene deletion synergized with antiandrogen therapies, enzalutamide or abiraterone, to decrease the growth of prostate cancer cells. Combination of gamma secretase inhibitors with abiraterone significantly inhibited cell migration and invasion, while combination with enzalutamide reversed enzalutamide-induced migration and invasion. These collective findings suggest loss of NOTCH1 delays growth of CRPC and inhibits metastasis, and inhibition of Notch1 activation in conjunction with second-generation antiandrogen therapies could delay growth and progression of prostate cancer.

Testosterone levels and androgen receptor copy number variations in castration-resistant prostate cancer treated with abiraterone or enzalutamide.

Our study aims to investigate the association between copy number of the androgen receptor (AR) and testosterone levels in metastatic castration-resistant prostate cancer (mCRPC) treated with second-generation antiandrogen therapies. We retrospectively collected data from mCRPC treated with abiraterone acetate and enzalutamide. Serum testosterone levels were collected at baseline, at 3 months since the start of therapy and at disease progression. A cohort of cases treated with docetaxel was also used to evaluate the impact of testosterone levels. Patients treated with abiraterone with AR copy number aberrations and basal testosterone levels below 0.09 nmol/L had worse progression-free survival (PFS) compared to patients with no AR copy number abnormalities (8.5 vs 2.9 months, P = 0.005). No relevant differences were observed in the enzalutamide group with a PFS of 3.9 months (no AR gain) vs 2.7 months ( AR gain, P = 0.004) for patients with below 0.09 nmol/L testosterone levels. Similar results are obtained for univariate analysis for overall survival (OS). The negative prognostic role of AR copy number gain in OS for both treatment groups (25.5 vs 10.6 months, P = 0.0002 for abiraterone and 14.1 vs 8.3 months, P = 0.031 for enzalutamide) was confirmed, and it was recognized the negative prognostic impact of testosteronemia below 0.09 only for patients treated with enzalutamide (8.8 vs 42.8 months, P = 0.016). On multivariate analysis for patients treated with abiraterone, low testosterone levels below 0.09 and plasma AR gain were significantly associated with worse PFS and OS. These data are confirmed in the enzalutamide group for PFS. Testosterone levels and the AR copy number alterations were considered as independent prognostic factors. The results of this study show that serum testosteronemia associated with changes in copy number of AR gene could represent a noninvasive biomarker useful to identify a subgroup of patients with worse prognosis that can benefit less from second-generation antiandrogen therapies in the mCRPC setting.