Androgen receptor, PARP signaling, and tumor microenvironment: the 'perfect triad' in prostate cancer?

Aberrations in the homologous recombination repair (HRR) pathway in prostate cancer (PCa) provide a unique opportunity to develop therapeutic strategies that take advantage of the reduced tumor ability to repair DNA damage. Poly-ADP-ribose polymerase (PARP) inhibitors (PARPi) have been shown to prolong the survival of PCa patients with HRR defects, particularly in those with Breast Cancer type 1 susceptibility protein/Breast Cancer type 2 susceptibility protein alterations. To expand the benefit of PARPi to patients without detectable HRR alterations, multiple preclinical and clinical studies are addressing potential synergies between PARPi and androgen receptor signaling inhibitors, and these strategies are also being evaluated in combination with other drugs such as immune checkpoint inhibitors. However, the effectiveness of these combining therapies could be hindered by multiple mechanisms of resistance, including also the role played by the immunosuppressive tumor microenvironment. In this review, we summarize the use of PARPi in PCa and the potential synergies with different molecular pathways. However, numerous unanswered questions remain, including the identification of the patient population that could benefit most from PARPi, determining whether to use PARPi as monotherapy or in combination, and finding the optimal timing of PARPi, expanding the use of genomic tests, and optimizing combination therapies.

Randomized Phase II Study Evaluating the Addition of Pembrolizumab to Radium-223 in Metastatic Castration-resistant Prostate Cancer

The checkpoint immunotherapeutic pembrolizumab induces responses in a small minority of patients with metastatic castration-resistant prostate cancer (mCRPC). Radium-223 (R223) may increase immunogenicity of bone metastases and increase pembrolizumab (P) activity. In a randomized phase II study, we assessed the effect of R223+P compared with R223 on tumor immune infiltration, safety, and clinical outcomes in patients with mCRPC. The primary endpoint was differences in CD4+ and CD8+ T-cell infiltrate in 8-week versus baseline bone metastasis biopsies; secondary endpoints were safety, radiographic progression-free survival (rPFS), and overall survival (OS). Of the 42 treated patients (29 R223+P, 13 R223), 18 R223+P and 8 R223 patients had evaluable paired tumor biopsies. Median fold-change of CD4+ T cells was -0.7 (range: -9.3 to 4.7) with R223+P and 0.1 (-11.1 to 3.7) with R223 (P = 0.66); for CD8+ T cells, median fold-change was -0.6 (-7.4 to 5.3) with R223+P and -1.3 (-3.1 to 4.8) with R223 (P = 0.66). Median rPFS and OS was 6.1 (95% confidence interval: 2.7-11.0) and 16.9 months [12.7-not reached (NR)], respectively, with R223+P and 5.7 (2.6-NR) and 16.0 (9.0-NR), respectively, with R223. Although R223+P was well tolerated with no unexpected toxicity, the combination did not improve efficacy. High-dimensional flow cytometry demonstrated minimal immune modulation with R223, whereas R223+P induced CTLA-4 expression on circulating CD4+ T cells. Clinical responders possessed lower circulating frequencies of Ki67+ T and myeloid cells at baseline and higher circulating frequencies of TIM-3+ T and myeloid cells by week 9. Although R223+P did not induce T-cell infiltration into the tumor microenvironment, exhaustion of induced peripheral T-cell immune responses may dampen the combination's clinical activity.

Practical Guidance on Establishing a Molecular Testing Pathway for Alterations in Homologous Recombination Repair Genes in Clinical Practice for Patients with Metastatic Prostate Cancer

CONTEXT

Prostate cancer is a molecularly heterogeneous disease that is amenable to diagnostic testing to identify patients potentially eligible for personalised treatments inform familial risk and provide relevant information about potential prognosis. Several guidelines support the integration of genomic testing in a shared decision-making framework so that both health care professionals (HCPs) and patients are involved in determining the best treatment approach.

OBJECTIVE

To review current guidelines on molecular diagnostic testing for homologous recombination repair (HRR) gene alterations in patients with metastatic prostate cancer, with the aim of providing practical considerations for effective guideline implementation and establishment of an appropriate pathway for molecular diagnostic testing.

EVIDENCE ACQUISITION

We undertook a nonsystematic narrative review of the literature using PubMed to identify current guidelines and recommendations on molecular diagnostic testing for BRCA and/or homologous recombination repair gene alterations (HRRm) in patients with prostate cancer. In addition, selected articles that included BRCA/HRRm testing in clinical trials in metastatic castration-resistant prostate cancer and real-world evidence were also evaluated. Websites for relevant societies were reviewed for molecular diagnostic guidelines not published on PubMed.

EVIDENCE SYNTHESIS

Our review of guidelines published by several international societies that include molecular testing in prostate cancer identified variations in molecular testing approaches. The review of testing approaches used in clinical trials and real-world settings also highlighted several aspects that require improvement. Therefore, we compiled practical guidance for establishing an appropriate BRCA/HRR mutation testing pathway.

CONCLUSIONS

While there are several challenges to molecular testing and interpretation of test results that require enhancement, a multidisciplinary team approach will empower HCPs and their institutions to improve on or initiate their own molecular testing pathways. This in turn will lead to improvements in management strategies for patients with metastatic prostate cancer, for whom better treatment outcomes is a significant unmet need.

PATIENT SUMMARY

Establishing a molecular testing pathway in clinical practice for patients with metastatic castration-resistant prostate cancer will lead to fairer and more equal access to personalised treatments. This should lead to better outcomes, particularly for patients whose disease has spread to other areas of the body.

Primary Results of Patients with Genitourinary Malignancies Presented at a Molecular Tumor Board

INTRODUCTION

Personalized medicine poses great opportunities and challenges. While the therapeutic landscape markedly expands, descriptions about status, clinical implementation and real-world benefits of precision oncology and molecular tumor boards (MTB) remain sparse, particularly in the field of genitourinary (GU) cancer. Hence, this study characterized urological MTB cases to better understand the potential role of MTB in uro-oncology.

METHODS

We analyzed patients with complete data sets being reviewed at an MTB from January 2019 to October 2022, focusing on results of molecular analysis and treatment recommendations.

RESULTS

We evaluated 102 patients with GU cancer with a mean patient age of 61.7 years. Prostate cancer (PCa) was the most frequent entity with 52.9% (54/102), followed by bladder cancer (18.6%, 19/102) and renal cell carcinoma (14.7%, 15/102). On average, case presentation at MTB took place 54.9 months after initial diagnosis and after 2.7 previous lines of therapy. During the study period, 49.0% (50/102) of patients deceased. Additional MTB-based treatment recommendations were achieved in a majority of 68.6% (70/102) of patients, with a recommendation for targeted therapy in 64.3% (45/70) of these patients. Only 6.7% (3/45) of patients - due to different reasons - received the recommended MTB-based therapy though, with 33% (1/3) of patients reaching disease control. Throughout the MTB study period, GU cancer case presentations and treatment recommendations increased, while the time interval between initial presentation and final therapy recommendation were decreasing over time.

CONCLUSION

Presentation of uro-oncological patients at the MTB is a highly valuable measure for clinical decision-making. Prospectively, earlier presentation of patients at the MTB and changing legislative issues regarding comprehensive molecular testing and targeted treatment approval might further improve patients' benefits from comprehensive molecular diagnostics.

PARP Inhibitors in the Treatment of Prostate Cancer: From Scientific Rationale to Clinical Development

Prostate cancer (PC) treatment has reached a milestone with the introduction of poly(ADP-ribose) polymerase (PARP) inhibitors. PARP inhibitors (PARPi) induce breaks in single-stranded and/or double-stranded DNA, resulting in synthetic lethality in cancer cells lacking functional homologous recombination genes. Around 20% to 25% of patients with metastatic castration-resistant prostate cancer harbor mutations in DNA damage repair genes, either somatic or germline. The success of PARPi in these patients has prompted studies exploring its potential in tumors classified as "BRCAness," which refers to tumors without germline BRCA1 or BRCA2 mutations. Additionally, there is a proposed connection between androgen receptor signaling and synthetic lethality of PARPi. The inclusion of genetic mutation tests in the treatment algorithm for PC is a significant step towards precision and personalized medicine, marking a first in the field. The objectives of this review encompass understanding the mechanism of action of PARPi in both monotherapy and combination therapy, exploring patient selection criteria, discussing pivotal studies that led to its approval, and offering future prospects. However, numerous unanswered questions remain, including the identification of the patient population that could benefit most from PARPi, determining whether to use PARPi as monotherapy or in combination, and finding the optimal timing of PARPi administration in advanced or localized disease. To address these questions, several ongoing clinical trials are being conducted.

DNA Damage Response and Mismatch Repair Gene Defects in Advanced and Metastatic Prostate Cancer

Alterations in DNA damage response (DDR) and related genes are present in up to 25% of advanced prostate cancers (PCa). Most frequently altered genes are involved in the homologous recombination repair, the Fanconi anemia, and the mismatch repair pathways, and their deficiencies lead to a highly heterogeneous spectrum of DDR-deficient phenotypes. More than half of these alterations concern non- BRCA DDR genes. From a therapeutic perspective, poly-ADP-ribose polymerase inhibitors have demonstrated robust clinical efficacy in tumors with BRCA2 and BRCA1 alterations. Mismatch repair-deficient PCa, and a subset of CDK12-deficient PCa, are vulnerable to immune checkpoint inhibitors. Emerging data point to the efficacy of ATR inhibitors in PCa with ATM deficiencies. Still, therapeutic implications are insufficiently clarified for most of the non- BRCA DDR alterations, and no successful targeted treatment options have been established.

Cardioprotective Effects of PARP Inhibitors: A Re-Analysis of a Meta-Analysis and a Real-Word Data Analysis Using the FAERS Database

Objective: This study aimed to assess the potential of PARP inhibitors to prevent cardiotoxicity. Methods: First, a re-analysis and update of a previously published study was conducted. Additional searches were conducted of the PubMed and Cochrane Central Register of Controlled Trials databases on 2 June 2023. After the selection process, the pooled odds ratio (OR) for cardiac adverse events (AEs) was calculated. Second, the FAERS database was examined for 10 frequently co-administered anticancer agents. The reporting odds ratio (ROR) was calculated based on the occurrence of cardiac AEs depending on the co-administration of PARP inhibitors. Results: Seven studies were selected for the meta-analysis. Although not statistically significant, co-administration of PARP inhibitors with chemotherapy/bevacizumab decreased the risk of cardiac AEs (Peto OR = 0.61; p = 0.36), while co-administration with antiandrogens increased the risk of cardiac AEs (Peto OR = 1.83; p = 0.18). A total of 19 cases of cardiac AEs were reported with co-administration of PARP inhibitors in the FAERS database. Co-administration of PARP inhibitors with chemotherapy/bevacizumab significantly decreased the risk of cardiac AEs (ROR = 0.352; 95% confidence interval (CI), 0.194-0.637). On the other hand, for antiandrogens co-administered with PARP inhibitors, the ROR was 3.496 (95% CI, 1.539-7.942). The ROR for immune checkpoint inhibitors co-administered with PARP inhibitors was 0.606 (95% CI, 0.151-2.432), indicating a non-significant effect on cardiac AEs. Conclusion: This study reports that PARP inhibitors show cardioprotective effects when used with conventional anticancer agents.

Hematological Toxicity of PARP Inhibitors in Metastatic Prostate Cancer Patients with Mutations of BRCA or HRR Genes: A Systematic Review and Safety Meta-analysis

BACKGROUND

PARP inhibitors (PARPis) are effective treatment options for patients with metastatic castration-resistant prostate cancer (mCRPC) as single agents or in combination with androgen receptor-targeted agents (ARTA). However, a clinically relevant adverse effect of these agents is hematological toxicity, a typical class adverse event (AE), which can lead to treatment modifications and discontinuations.

OBJECTIVE

We aimed to analyze the risk of hematological AEs, including anemia, neutropenia, and thrombocytopenia secondary to PARPi treatments in mCRPC.

PATIENTS AND METHODS

This systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. We systematically searched the PubMed, EMBASE, and Cochrane databases, the American Society of Clinical Oncology (ASCO), and the European Society of Medical Oncology (ESMO) meeting abstracts for clinical trials concerning the use of PARPis, both as single agents and in combination, in patients with mCRPC. The search deadline was 30 June, 2023. We analyzed the pooled incidence of all grades of and ≥ G3 anemia, neutropenia, and thrombocytopenia. We subsequently calculated risk ratios (RRs) for all grades of and ≥ G3 AEs of PARPis versus non-PARPis from randomized clinical trials (RCTs).

RESULTS

Eleven phase 2/3 trials with olaparib, niraparib, rucaparib, and talazoparib administered as single agents or combined with ARTA were selected. Anemia was the most common all grades (38.6%) and ≥ G3 AE (24.9%). In the analysis of relative risk, six RCTs were included. The administration of PARPis significantly increased the risk of developing all grades of anemia (RR = 2.44), neutropenia (RR = 3.15), and thrombocytopenia (RR = 4.66) compared with non-PARPis. Similarly, a significant increase in the risk of ≥ G3 anemia (RR = 5.73) and thrombocytopenia (RR = 5.44), and a not significant increased risk of neutropenia (RR = 3.41), were detected.

CONCLUSIONS

In mCRPC, PARPis increase the risk of hematological toxicity compared with other treatments, both as single agents or combined with ARTA (high-quality evidence). Clinicians should be aware of this risk and the correct management, especially with the expected increased PARPis use in mCRPC.

Stereotactic Body Radiation Therapy and Abiraterone Acetate for Patients Affected by Oligometastatic Castrate-Resistant Prostate Cancer: A Randomized Phase II Trial (ARTO)

PURPOSE

ARTO (ClinicalTrials.gov identifier: NCT03449719) is a multicenter, phase II randomized clinical trial testing the benefit of adding stereotactic body radiation therapy (SBRT) to abiraterone acetate and prednisone (AAP) in patients with oligometastatic castrate-resistant prostate cancer (CRPC).

MATERIALS AND METHODS

All patients were affected by oligometastatic CRPC as defined as three or less nonvisceral metastatic lesions. Patients were randomly assigned 1:1 to receive either AAP alone (control arm) or AAP with concomitant SBRT to all the sites of disease (experimental arm). Primary end point was the rate of biochemical response (BR), defined as a prostate-specific antigen (PSA) decrease ≥50% from baseline measured at 6 months from treatment start. Complete BR (CBR), defined as PSA < 0.2 ng/mL at 6 months from treatment, and progression-free survival (PFS) were secondary end points.

RESULTS

One hundred and fifty-seven patients were enrolled between January 2019 and September 2022. BR was detected in 79.6% of patients (92% v 68.3% in the experimental v control arm, respectively), with an odds ratio (OR) of 5.34 (95% CI, 2.05 to 13.88; P = .001) in favor of the experimental arm. CBR was detected in 38.8% of patients (56% v 23.2% in the experimental v control arm, respectively), with an OR of 4.22 (95% CI, 2.12 to 8.38; P < .001). SBRT yielded a significant PFS improvement, with a hazard ratio for progression of 0.35 (95% CI, 0.21 to 0.57; P < .001) in the experimental versus control arm.

CONCLUSION

The trial reached its primary end point of biochemical control and PFS, suggesting a clinical advantage for SBRT in addition to first-line AAP treatment in patients with metastatic castration-resistant prostate cancer.

Personalized medicine for metastatic prostate cancer: The paradigm of PARP inhibitors

Despite remarkable progress in the last decade, metastatic prostate cancer (mPCa) remains incurable. The approval of PARP inhibitors (PARPis) represents a milestone in this field, which definitively enters the era of precision medicine, as mPCa is often enriched for defects of homologous recombination repair genes. PARPis are now used as single agents for patients with metastatic castration-resistant PCa. Moreover, combinations of PARPis plus androgen-receptor targeted agents and immune checkpoint inhibitors, and earlier applications of PARPis in the metastatic hormone-sensitive PCa are under evaluation, representing the possible upcoming applications of these agents. Mechanisms of sensitization and resistance have been only partially elucidated. In our review, we summarize the current clinical evidence regarding PARPis in mPCa and the future directions of these targeted agents.

Pembrolizumab in mCRPC - Combination therapies as breakthrough to success?

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICIs) have shown promising antitumor activity in various malignant diseases. This narrative review provides an update on ongoing clinical studies investigating the only FDA-approved ICI programmed death receptor 1 (PD-1) inhibitor pembrolizumab in mono- and combination therapy in patients with metastatic castration-resistant prostate cancer (mCRPC).

RECENT FINDINGS

Although most clinical trials investigating pembrolizumab as mono- or combinational therapy did not meet their primary endpoints, there exist subgroups of patients that demonstrate impressive responses rates justifying further investigation of ICI in prostate cancer. Beside combination of pembrolizumab with approved mCRPC agents, innovative approaches, like combining pembrolizumab with radioligands, deoxyribonucleic acid vaccines or innovative immunotherapeutic agents (i.e., ONC-392, AMG160, BXCL701) are ongoing exerting promising preliminary findings.

SUMMARY

ICI monotherapy seems to be effective in a small biomarker-preselected population, however, there is evidence that especially novel ICI combination approaches can improve patient survival, which could ultimately refocus and revolutionize the treatment of mCRPC.

A Meta-Analysis of Randomized Clinical Trials Assessing the Efficacy of PARP Inhibitors in Metastatic Castration-Resistant Prostate Cancer

Prostate cancer ranks as the second most common malignancy in males. Prostate cancer progressing on androgen deprivation therapy (ADT) is castration-resistant prostate cancer (CRPC). Poly-ADP ribose polymerase (PARP) inhibitors (PARPis) have been at the forefront of the treatment of CRPC. We aim to better characterize the progression-free survival (PFS) and overall survival (OS) in metastatic CRPC patients treated with PARPis. A systemic review search was conducted using National Clinical Trial (NCT), PubMed, Embase, Scopus, and Central Cochrane Registry. The improvement in overall survival was statistically significant, favoring PARPis (hazard ratio (HR) 0.855; 95% confidence interval (CI) 0.752-0.974; p = 0.018). The improvement in progression-free survival was also statistically significant, with results favoring PARPis (HR 0.626; 95%CI 0.566-0.692; p = 0.000). In a subgroup analysis, similar results were observed where the efficacy of PARPis was evaluated in a subgroup of patients without homologous recombination repair (HRR) gene mutation, which showed improvement in PFS favoring PARPis (HR 0.747; 95%CI 0.0.637-0.877; p = 0.000). Our meta-analysis of seven RCTs showed that PARPis significantly increased PFS and OS when used with or without antihormonal agents like abiraterone or enzalutamide.

A new wave of innovations within the DNA damage response

Genome instability has been identified as one of the enabling hallmarks in cancer. DNA damage response (DDR) network is responsible for maintenance of genome integrity in cells. As cancer cells frequently carry DDR gene deficiencies or suffer from replicative stress, targeting DDR processes could induce excessive DNA damages (or unrepaired DNA) that eventually lead to cell death. Poly (ADP-ribose) polymerase (PARP) inhibitors have brought impressive benefit to patients with breast cancer gene (BRCA) mutation or homologous recombination deficiency (HRD), which proves the concept of synthetic lethality in cancer treatment. Moreover, the other two scenarios of DDR inhibitor application, replication stress and combination with chemo- or radio- therapy, are under active clinical exploration. In this review, we revisited the progress of DDR targeting therapy beyond the launched first-generation PARP inhibitors. Next generation PARP1 selective inhibitors, which could maintain the efficacy while mitigating side effects, may diversify the application scenarios of PARP inhibitor in clinic. Albeit with unavoidable on-mechanism toxicities, several small molecules targeting DNA damage checkpoints (gatekeepers) have shown great promise in preliminary clinical results, which may warrant further evaluations. In addition, inhibitors for other DNA repair pathways (caretakers) are also under active preclinical or clinical development. With these progresses and efforts, we envision that a new wave of innovations within DDR has come of age.

Niraparib plus abiraterone acetate with prednisone in patients with metastatic castration-resistant prostate cancer and homologous recombination repair gene alterations: second interim analysis of the randomized phase III MAGNITUDE trial

BACKGROUND

Patients with metastatic castration-resistant prostate cancer (mCRPC) and BRCA alterations have poor outcomes. MAGNITUDE found patients with homologous recombination repair gene alterations (HRR+), particularly BRCA1/2, benefit from first-line therapy with niraparib plus abiraterone acetate and prednisone (AAP). Here we report longer follow-up from the second prespecified interim analysis (IA2).

PATIENTS AND METHODS

Patients with mCRPC were prospectively identified as HRR+ with/without BRCA1/2 alterations and randomized 1 : 1 to niraparib (200 mg orally) plus AAP (1000 mg/10 mg orally) or placebo plus AAP. At IA2, secondary endpoints [time to symptomatic progression, time to initiation of cytotoxic chemotherapy, overall survival (OS)] were assessed.

RESULTS

Overall, 212 HRR+ patients received niraparib plus AAP (BRCA1/2 subgroup, n = 113). At IA2 with 24.8 months of median follow-up in the BRCA1/2 subgroup, niraparib plus AAP significantly prolonged radiographic progression-free survival {rPFS; blinded independent central review; median rPFS 19.5 versus 10.9 months; hazard ratio (HR) = 0.55 [95% confidence interval (CI) 0.39-0.78]; nominal P = 0.0007} consistent with the first prespecified interim analysis. rPFS was also prolonged in the total HRR+ population [HR = 0.76 (95% CI 0.60-0.97); nominal P = 0.0280; median follow-up 26.8 months]. Improvements in time to symptomatic progression and time to initiation of cytotoxic chemotherapy were observed with niraparib plus AAP. In the BRCA1/2 subgroup, the analysis of OS with niraparib plus AAP demonstrated an HR of 0.88 (95% CI 0.58-1.34; nominal P = 0.5505); the prespecified inverse probability censoring weighting analysis of OS, accounting for imbalances in subsequent use of poly adenosine diphosphate-ribose polymerase inhibitors and other life-prolonging therapies, demonstrated an HR of 0.54 (95% CI 0.33-0.90; nominal P = 0.0181). No new safety signals were observed.

CONCLUSIONS

MAGNITUDE, enrolling the largest BRCA1/2 cohort in first-line mCRPC to date, demonstrated improved rPFS and other clinically relevant outcomes with niraparib plus AAP in patients with BRCA1/2-altered mCRPC, emphasizing the importance of identifying this molecular subset of patients.

Rucaparib for the Treatment of Metastatic Castration-resistant Prostate Cancer Associated with a DNA Damage Repair Gene Alteration: Final Results from the Phase 2 TRITON2 Study

BACKGROUND

Initial TRITON2 (NCT02952534) results demonstrated the efficacy of rucaparib 600 mg BID in patients with metastatic castration-resistant prostate cancer (mCRPC) associated with a BRCA1 or BRCA2 (BRCA) or other DNA damage repair (DDR) gene alteration.

OBJECTIVE

To present the final data from TRITON2.

DESIGN, SETTING, AND PARTICIPANTS

TRITON2 enrolled patients with mCRPC who had progressed on one or two lines of next-generation androgen receptor-directed therapy and one taxane-based chemotherapy.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary endpoint was objective response rate (ORR; as per the modified Response Evaluation Criteria in Solid Tumor Version 1.1/Prostate Cancer Clinical Trials Working Group 3 criteria in patients with measurable disease by independent radiology review [IRR]); prostate-specific antigen (PSA) response rate (≥50% decrease from baseline [PSA50]) was a key secondary endpoint.

RESULTS AND LIMITATIONS

As of July 27, 2021 (study closure), TRITON2 had enrolled 277 patients, grouped by mutated gene: BRCA (n = 172), ATM (n = 59), CDK12 (n = 15), CHEK2 (n = 7), PALB2 (n = 11), or other DDR gene (Other; n = 13). ORR by IRR was 46% (37/81) in the BRCA subgroup (95% confidence interval [CI], 35-57%), 100% (4/4) in the PALB2 subgroup (95% CI, 40-100%), and 25% (3/12) in the Other subgroup (95% CI, 5.5-57%). No patients within the ATM, CDK12, or CHEK2 subgroups had an objective response by IRR. PSA50 response rates (95% CI) in the BRCA, PALB2, ATM, CDK12, CHEK2, and Other subgroups were 53% (46-61%), 55% (23-83%), 3.4% (0.4-12), 6.7% (0.2-32%), 14% (0.4-58%), and 23% (5.0-54%), respectively.

CONCLUSIONS

The final TRITON2 results confirm the clinical benefit and manageable safety profile of rucaparib in patients with mCRPC, including those with an alteration in BRCA or select non-BRCA DDR gene.

PATIENT SUMMARY

Almost half of TRITON2 patients with BRCA-mutated metastatic castration-resistant prostate cancer had a complete or partial tumor size reduction with rucaparib; clinical benefits were also observed with other DNA damage repair gene alterations.

Risk of thromboembolic events in patients with metastatic solid tumors treated with PARP inhibitors: A systematic review and meta-analysis of phase 3 randomized controlled trials

BACKGROUND AND SCOPE

Poly(ADP-ribose) polymerase inhibitors (PARPi) have revolutionized cancer treatment in recent years. These drugs present a favorable safety profile, even though the potential risk of thromboembolic events (TEs) during their use has not been addressed yet. In addition, PARPi have been involved in an active scientific debate regarding non-oncologic indications, particularly during the Coronavirus Disease 2019 pandemic, including potential anti-thromboembolic effect.

METHODS

To clarify whether patients treated with PARPi for metastatic solid tumors are either at increased or decreased risk of TEs, we conducted a systematic review of the literature and meta-analysis, including all phase 3 randomized controlled trials (RCTs) which investigated PARPi in this setting. Search was conducted through Medline, EMBASE, Pubmed, SCOPUS and Google Scholar in February 2023, including the proceedings of the principal oncology meetings of the last 10 years, with no time restriction. For each included study, frequencies of TEs in experimental and control arm were collected.

RESULTS

Our search identified 2,369 reports, of which 20 were lastly selected. A total of 4,946 patients were included, across 12 different RCTs. The meta-analysis did not demonstrate either an increased or a reduced risk in TEs in patients treated with PARPi for metastatic disease (OR 1.50, range: 1.00-2.24; 95% CI; P = 0.050), with low heterogeneity and low publication bias.

CONCLUSION

Although our research did not confirm either increased or decreased risk of TEs for PARPi use, no safety alerts emerged. Thromboembolic risk assessment models should always be integrated in daily clinical routine, to identify high-risk patients.

Parp Inhibitors and Radiotherapy: A New Combination for Prostate Cancer (Systematic Review)

PARPi, in combination with ionizing radiation, has demonstrated the ability to enhance cellular radiosensitivity in different tumors. The rationale is that the exposure to radiation leads to both physical and biochemical damage to DNA, prompting cells to initiate three primary mechanisms for DNA repair. Two double-stranded DNA breaks (DSB) repair pathways: (1) non-homologous end-joining (NHEJ) and (2) homologous recombination (HR); and (3) a single-stranded DNA break (SSB) repair pathway (base excision repair, BER). In this scenario, PARPi can serve as radiosensitizers by leveraging the BER pathway. This mechanism heightens the likelihood of replication forks collapsing, consequently leading to the formation of persistent DSBs. Together, the combination of PARPi and radiotherapy is a potent oncological strategy. This combination has proven its efficacy in different tumors. However, in prostate cancer, there are only preclinical studies to support it and, recently, an ongoing clinical trial. The objective of this paper is to perform a review of the current evidence regarding the use of PARPi and radiotherapy (RT) in PCa and to give future insight on this topic.

Metastatic Castration-Resistant Prostate Cancer: Insights on Current Therapy and Promising Experimental Drugs

The therapeutic landscape of metastatic hormone sensitive and metastatic castration-resistant prostate cancer (mCRPC) is rapidly changing. We reviewed the current treatment options for mCRPC, with insights on new available therapeutic strategies. Chemotherapy with docetaxel or cabazitaxel (for patients progressing on docetaxel), as well as treatment with androgen receptor axis targeted therapies, and Radium-223 are well-established treatment options for patients with mCRPC. The advent of theragnostic in prostate cancer established Lutetium-177 (177Lu)-PSMA-617 as a new standard of care for PSMA-positive mCRPC previously treated with ARAT and taxane-based chemotherapy. Olaparib, a poly-ADP-ribose polymerase (PARP) inhibitor, is approved for selected patients with mCRPC progressed on ARATs and in combination with abiraterone acetate as first-line treatment for mCRPC. Immunotherapy showed limited efficacy in unselected patients with mCRPC and novel immunotherapy strategies need to be explored. The search for biomarkers is a growing field of interest in mCRPC, and predictive biomarkers are needed to support the choice of treatment and the development of tailored strategies.

Roles of the PARP Inhibitor in BRCA1 and BRCA2 Pathogenic Mutated Metastatic Prostate Cancer: Direct Functions and Modification of the Tumor Microenvironment

Cancer cells frequently exhibit defects in DNA damage repair (DDR), leading to genomic instability. Mutations in DDR genes or epigenetic alterations leading to the downregulation of DDR genes can result in increased dependency on other DDR pathways. Therefore, DDR pathways could be a treatment target for various cancers. In fact, polyadenosine diphosphatase ribose polymerase (PARP) inhibitors, such as olaparib (Lynparza^®), have shown remarkable therapeutic efficacy against BRCA1/2-mutant cancers through synthetic lethality. Recent genomic analytical advancements have revealed that BRCA1/BRCA2 pathogenic variants are the most frequent mutations among DDR genes in prostate cancer. Currently, the PROfound randomized controlled trial is investigating the efficacy of a PARP inhibitor, olaparib (Lynparza^®), in patients with metastatic castration-resistant prostate cancer (mCRPC). The efficacy of the drug is promising, especially in patients with BRCA1/BRCA2 pathogenic variants, even if they are in the advanced stage of the disease. However, olaparib (Lynparza^®) is not effective in all BRCA1/2 mutant prostate cancer patients and inactivation of DDR genes elicits genomic instability, leading to alterations in multiple genes, which eventually leads to drug resistance. In this review, we summarize PARP inhibitors' basic and clinical mechanisms of action against prostate cancer cells and discuss their effects on the tumor microenvironment.

Molecular testing of DNA damage response pathways in prostate cancer patients

PURPOSE OF REVIEW

Personalizing prostate cancer therapy requires germline and tumor molecular tests that predict who will respond to specific treatments and who may not. The review covers molecular testing of DNA damage response pathways, the first biomarker-driven precision target with clinical utility for treatment selection in patients with castration resistant prostate cancer (CRPC).

RECENT FINDINGS

Recurrent somatic and germline variants cause deficiency of the mismatch repair (MMR) or homologous recombination (HR) pathways in about a quarter of CRPC patients. In prospective clinical trials, patients with deleterious variants in the MMR pathway more frequently experience a therapeutic response to immune checkpoint inhibitors (ICI). Similarly, somatic and germline events affecting HR predict response to poly(ADP) ribose polymerase inhibitor (PARPi) therapy. Molecular testing of these pathways currently involves assaying for loss of function variants in individual genes and for the genome-wide consequences of repair deficiency.

SUMMARY

DNA damage response pathways are the first major area of molecular genetic testing in CRPC settings and offer insights into this new paradigm. Our hope is that eventually an arsenal of molecularly-guided therapies will be developed across many pathways to enable precision medicine options for most men with prostate cancer.

Docetaxel versus abiraterone for metastatic hormone-sensitive prostate cancer with focus on efficacy of sequential therapy

PURPOSE

We aimed to assess the oncologic efficacy of combining docetaxel (DOC) versus abiraterone (ABI) with androgen deprivation therapy (ADT) in patients with high-risk metastatic hormone-sensitive prostate cancer (mHSPC), with a focus on the efficacy of sequential therapy, in a real-world clinical practice setting.

METHODS

The records of 336 patients who harbored de novo high-risk mHSPC, based on the LATITUDE criteria, and had received ADT with either DOC (n = 109) or ABI (n = 227) were retrospectively analyzed. Overall survival (OS), cancer-specific survival (CSS), progression-free survival (PFS), including time to castration-resistant prostate cancer (CRPC), time to 2nd-line progression (PFS2), and 2nd- and 3rd-line PFS, were compared. We used one-to-two propensity score matching to minimize the confounders. The differential efficacy of 2nd-line therapy based on agents in each arm was evaluated using the unmatched cohort as an additional interest.

RESULTS

After propensity score matching, 86 patients treated with DOC + ADT and 172 with ABI + ADT were available for analyses. The 3-year OS and CSS for DOC versus ABI were 76.2% versus 75.1% (p = 0.8) and 78.2% versus 78.6% (p = 1), respectively. There was no difference in the median PFS2 (49 vs. 43 months, p = 0.39), while the median time to CRPC in patients treated with ABI was significantly longer compared to those treated with DOC (42 vs. 22 months; p = 0.006). The median 2nd-line PFS (14 vs. 4 months, p < 0.001) and 3rd-line PFS (4 vs. 2 months, p = 0.012) were significantly better in the DOC group than in the ABI group. Among the unmatched cohort, after ABI for mHSPC, the median 2nd-line PFS did not differ between the patients treated with DOC and those treated with enzalutamide as 2nd-line therapy (both 3 months, p = 0.8).

CONCLUSIONS

ADT with DOC or ABI has comparable oncologic outcomes in terms of OS, CSS, and PFS2 in patients with de novo high-risk mHSPC. Compared to DOC, ABI resulted in longer time to CRPC but worse 2nd and 3rd-line PFS. Further studies are needed to clarify the optimal sequence of therapy in the upfront intensive treatment era.

Advances in PARP Inhibitors for Prostate Cancer

Poly-adenosine diphosphate-ribose polymerase plays an essential role in cell function by regulating apoptosis, genomic stability and DNA repair. PARPi is a promising drug class that has gained significant traction in the last decade with good outcomes in different cancers. Several trials have sought to test its effectiveness in metastatic castration resistant prostate cancer (mCRPC). We conducted a comprehensive literature review to evaluate the current role of PARPi in this setting. To this effect, we conducted queries in the PubMed, Embase and Cochrane databases. We reviewed and compared all major contemporary publications on the topic. In particular, recent phase II and III studies have also demonstrated the benefits of olaparib, rucaparib, niraparib, talazoparib in CRPC. Drug effectiveness has been assessed through radiological progression or overall response. Given the notion of synthetic lethality and potential synergy with other oncological therapies, several trials are looking to integrate PARPi in combined therapies. There remains ongoing controversy on the need for genetic screening prior to treatment initiation as well as the optimal patient population, which would benefit most from PARPi. PARPi is an important asset in the oncological arsenal for mCRPC. New combinations with PARPi may improve outcomes in earlier phases of prostate cancer.

Major adverse cardiac events and cardiovascular toxicity with PARP inhibitors-based therapy for solid tumors: a systematic review and safety meta-analysis

BACKGROUND

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) provided significant antitumor activity in various tumors, mainly carrying deleterious mutations of BRCA1/BRCA2 genes. Only few data are available regarding the cardiac and vascular safety profile of this drug class. We carried out a meta-analysis for assessing the incidence and relative risk (RR) of major adverse cardiovascular events (MACEs), hypertension, and thromboembolic events in patients with solid tumors treated with PARPi-based therapy.

METHODS

Prospective studies were identified by searching the Medline/PubMed, Cochrane Library, and ASCO Meeting abstracts. Data extraction was conducted according to the Preferred Reporting Items for Systematic review and Meta-Analyses (PRISMA) statement. Combined odds ratios (ORs), RRs, and 95% confidence intervals (CIs) were calculated using fixed- or random-effects methods, depending on studies heterogeneity. RevMan software for meta-analysis (v.5.2.3) was used to carry out statistical analyses.

RESULTS

Thirty-two studies were selected for the final analysis. The incidence of PARPi-related MACEs of any and high grade was 5.0% and 0.9%, respectively, compared with 3.6% and 0.9% in the control arms, corresponding to a significant increased risk of MACEs of any grade (Peto OR 1.62; P = 0.0009) but not of high grade (P = 0.49). The incidence of hypertension of any grade and high grade was 17.5% and 6.0% with PARPi, respectively, compared with 12.6% and 4.4% in the controls. Treatment with PARPi significantly increased the risk of hypertension of any grade (random-effects, RR = 1.53; P = 0.03) but not of high grade (random-effects, RR = 1.47; P = 0.09) compared with controls. Finally, PARPi-based therapies significantly increased the risk of thromboembolic events of any grade (Peto OR = 1.49, P = 0.004) and not of high grade (Peto OR = 1.31; P = 0.13) compared with controls.

CONCLUSIONS

PARPi-based therapy is associated with a significantly increased risk of MACEs, hypertension, and thromboembolic events of any grade compared with controls. The lack of a significant increased risk of high-grade events together with the absolute low incidence of these adverse events led not to consider routine cardiovascular monitoring as recommended in asymptomatic patients.

Rucaparib or Physician's Choice in Metastatic Prostate Cancer

BACKGROUND

In a phase 2 study, rucaparib, an inhibitor of poly(ADP-ribose) polymerase (PARP), showed a high level of activity in patients who had metastatic, castration-resistant prostate cancer associated with a deleterious BRCA alteration. Data are needed to confirm and expand on the findings of the phase 2 study.

METHODS

In this randomized, controlled, phase 3 trial, we enrolled patients who had metastatic, castration-resistant prostate cancer with a BRCA1, BRCA2, or ATM alteration and who had disease progression after treatment with a second-generation androgen-receptor pathway inhibitor (ARPI). We randomly assigned the patients in a 2:1 ratio to receive oral rucaparib (600 mg twice daily) or a physician's choice control (docetaxel or a second-generation ARPI [abiraterone acetate or enzalutamide]). The primary outcome was the median duration of imaging-based progression-free survival according to independent review.

RESULTS

Of the 4855 patients who had undergone prescreening or screening, 270 were assigned to receive rucaparib and 135 to receive a control medication (intention-to-treat population); in the two groups, 201 patients and 101 patients, respectively, had a BRCA alteration. At 62 months, the duration of imaging-based progression-free survival was significantly longer in the rucaparib group than in the control group, both in the BRCA subgroup (median, 11.2 months and 6.4 months, respectively; hazard ratio, 0.50; 95% confidence interval [CI], 0.36 to 0.69) and in the intention-to-treat group (median, 10.2 months and 6.4 months, respectively; hazard ratio, 0.61; 95% CI, 0.47 to 0.80; P<0.001 for both comparisons). In an exploratory analysis in the ATM subgroup, the median duration of imaging-based progression-free survival was 8.1 months in the rucaparib group and 6.8 months in the control group (hazard ratio, 0.95; 95% CI, 0.59 to 1.52). The most frequent adverse events with rucaparib were fatigue and nausea.

CONCLUSIONS

The duration of imaging-based progression-free survival was significantly longer with rucaparib than with a control medication among patients who had metastatic, castration-resistant prostate cancer with a BRCA alteration. (Funded by Clovis Oncology; TRITON3 ClinicalTrials.gov number, NCT02975934.).

[New treatment approaches for and ongoing trials in metastatic hormone-sensitive prostate cancer]

BACKGROUND

For many years, therapy for metastatic hormone-sensitive prostate cancer (mHSPC) was dominated by monotherapy using androgen deprivation therapy (ADT). With the demonstration of survival benefit with intensified systemic therapy from the CHAARTED and STAMPEDE trials, this has fundamentally changed. We analyzed the phase III trials that led to the change in therapy in mHSPC. In addition, we summarized ongoing trials in mHSPC.

OBJECTIVES

The ongoing studies and current data on systemic therapy in mHSPC were analyzed.

RESULTS

Monotherapy with ADT is no longer considered the standard therapy for mHSPC. Combination therapy with ADT and novel androgen receptor targeting agents (ARTAs: abiraterone, apalutamide, enzalutamide) is now the established standard option. The added value of further intensification of therapy was demonstrated in the first trials of triple therapy with ADT + docetaxel + darolutamide or abiraterone in mHSPC. Current studies are also investigating new forms of therapy. Lutetium177-PSMA radioligand therapy is an established standard in metastatic castration-resistant prostate cancer (mCRPC) and is currently being evaluated in combination with ADT + ARTA in mHSPC. The use of PARP inhibitors (PARPi) have been established in mCRPC. Current studies are showing early evidence of benefit from novel combination therapies of PARPi + ARTA, which represent a further expansion of the therapeutic landscape. Experimental therapies are testing another combination, such as an AKT inhibitor with ARTA in patients with PTEN (phosphatase and tensin homolog) loss. Based on the proof of principle in mCRPC, this combination is now being evaluated in earlier stage mHSPC. Other experimental therapies in clinical testing include inhibitors of cyclin dependent kinases (CDK).

CONCLUSIONS

Combination therapies are the current standard of care for mHSPC, with the combination of ADT + ARTA dominating. Preliminary results underline the importance of further intensification of therapy by means of triple therapy. However, novel combinations with radioligand therapy or PARP inhibitors are also promising in the treatment of mHSPC. Preliminary results show the principle efficacy of AKT inhibitors in patients with PTEN loss, which similar to therapy with CDK4/6 inhibitors still have to prove their clinical relevance in randomized trials.

DNA repair deficiency as circulating biomarker in prostate cancer

Deleterious aberrations in DNA repair genes are actionable in approximately 25% of metastatic castration-resistant prostate cancers (mCRPC) patients. Homology recombination repair (HRR) is the DNA damage repair (DDR) mechanism most frequently altered in prostate cancer; of note BRCA2 is the most frequently altered DDR gene in this tumor. Poly ADP-ribose polymerase inhibitors showed antitumor activity with a improvement in overall survival in mCRPC carrying somatic and/or germline alterations of HHR. Germline mutations are tested on peripheral blood samples using DNA extracted from peripheral blood leukocytes, while the somatic alterations are assessed by extracting DNA from a tumor tissue sample. However, each of these genetic tests have some limitations: the somatic tests are related to the sample availability and tumor heterogeneity, while the germline testing are mainly related to the inability to detect somatic HRR mutations. Therefore, the liquid biopsy, a non-invasive and easily repeatable test compared to tissue test, could identified somatic mutation detected on the circulating tumor DNA (ctDNA) extracted from a plasma. This approach should better represent the heterogeneity of the tumor compared to the primary biopsy and maybe helpful in monitoring the onset of potential mutations involved in treatment resistance. Furthermore, ctDNA may inform about timing and potential cooperation of multiple driver genes aberration guiding the treatment options in patients with mCRPC. However, the clinical use of ctDNA test in prostate cancer compared to blood and tissue testing are currently very limited. In this review, we summarize the current therapeutic indications in prostate cancer patients with DDR deficiency, the recommendation for germline and somatic-genomic testing in advanced PC and the advantages of the use liquid biopsy in clinical routine for mCRPC.

Mechanisms of Prostate Cancer Cells Survival and Their Therapeutic Targeting

Prostate cancer (PCa) is today the second most common cancer in the world, with almost 400,000 deaths annually. Multiple factors are involved in the etiology of PCa, such as older age, genetic mutations, ethnicity, diet, or inflammation. Modern treatment of PCa involves radical surgical treatment or radiation therapy in the stages when the tumor is limited to the prostate. When metastases develop, the standard procedure is androgen deprivation therapy, which aims to reduce the level of circulating testosterone, which is achieved by surgical or medical castration. However, when the level of testosterone decreases to the castration level, the tumor cells adapt to the new conditions through different mechanisms, which enable their unhindered growth and survival, despite the therapy. New knowledge about the biology of the so-called of castration-resistant PCa and the way it adapts to therapy will enable the development of new drugs, whose goal is to prolong the survival of patients with this stage of the disease, which will be discussed in this review.

Olaparib in Patients With Metastatic Prostate Cancer With BRCA1/2 Mutation: Results From the TAPUR Study

PURPOSE

The TAPUR Study is a phase II basket trial that aims to evaluate activity of approved targeted agents in patients with advanced cancers with potentially actionable genomic variants. Data from a cohort of patients with metastatic castrate-resistant prostate cancer (mCRPC) and BRCA1/2 mutations treated with olaparib are reported.

METHODS

Eligible patients with measurable mCRPC were matched to treatment according to protocol-specified genomic matching rules. Patients had no remaining standard treatment options, Eastern Cooperative Oncology Group performance status 0-2, and adequate organ function. Simon's two-stage design was used with a primary end point of disease control, defined as objective response or stable disease of at least 16-week duration. Secondary end points include radiographic progression-free survival, overall survival, duration of response, duration of stable disease, and safety.

RESULTS

Thirty patients with mCRPC with BRCA1/2 mutations were treated with olaparib. The disease control rate was 69% (95% CI, 51 to 81), and the objective response rate was 58% (95% CI, 37 to 77). The median radiographic progression-free survival and the median overall survival were 38.4 (95% CI, 16.3 to 52.1) weeks and 76.4 (95% CI, 49.3 to 106.0) weeks, respectively. Six of 30 (20%) patients experienced grade 3-4 adverse or serious adverse events including anemia, aspiration, decreased WBC count, and fatigue.

CONCLUSION

Olaparib has antitumor activity in patients with mCRPC with BRCA1/2 mutations and warrants further study to determine how to best integrate it into the standard treatment of patients with BRCA1/2-mutated prostate cancer.

Exploring new frontiers in prostate cancer research: Report from the 2022 Coffey-Holden prostate cancer academy meeting

INTRODUCTION

The 2022 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, "Exploring New Frontiers in Prostate Cancer Research," was held from June 23 to 26, 2022, at the University of California, Los Angeles, Luskin Conference Center, in Los Angeles, CA.

METHODS

The CHPCA Meeting is an annual discussion-oriented scientific conference organized by the Prostate Cancer Foundation, that focuses on emerging and next-step topics deemed critical for making the next major advances in prostate cancer research and clinical care. The 2022 CHPCA Meeting included 35 talks over 10 sessions and was attended by 73 academic investigators.

RESULTS

Major topic areas discussed at the meeting included: prostate cancer diversity and disparities, the impact of social determinants on research and patient outcomes, leveraging real-world and retrospective data, development of artificial intelligence biomarkers, androgen receptor (AR) signaling biology and new strategies for targeting AR, features of homologous recombination deficient prostate cancer, and future directions in immunotherapy and nuclear theranostics.

DISCUSSION

This article summarizes the scientific presentations from the 2022 CHPCA Meeting, with the goal that dissemination of this knowledge will contribute to furthering global prostate cancer research efforts.

Review of Toxicities of PARP Inhibitors in Metastatic Castrate Resistant Prostate Cancer

There is emerging evidence for the use of poly (ADP-ribose) polymerase inhibitors (PARPi) in patients with mCRPC with patients harboring germline or somatic mutations deriving clinical benefit. However, the toxicity profile of PARPi in mCRPC is not well established. In March 2022 a literature search was conducted across 4 databases - Medline, PubMed, Cochrane Library and Embase. In total, 14 relevant studies were identified cumulating in 2066 patients that were treated with PARPi. The overall ORR to PARPi alone or in combination with other therapy was 37% (246/666). In 5trials that investigated PARPi alone, the ORR was 39% (141/361). Treatment emergent adverse events (TEAEs) of any grade were reported in 96% (1034/1080) in PARPi treatment arms. TEAEs of grade >= 3 were reported in 57% (611/1080). 45% (457/1006) experienced treatment interruption whilst 31% (310/989) required dose reductions. 11% (114/1006) of patients had their treatment discontinued directly as the result of toxicity associated with the trial medications. The most common hematological toxicity was anemia, reported in 490/1160 (42%) patients. and lowered white blood cell count were the next 2most common toxicities, reported in 186/655 (28%) and 133/729 (18%) respectively. The 3most common non-hematological toxicities reported were nausea, fatigue and anorexia reported in 440/1013 (43%), 340/1013 (34%) and 274/1013 (27%) patients respectively. Overall, TRAEs associated with individual PARPi are still emerging with hematological toxicities being most apparent. Further toxicities will be informed from future clinical trials to allow improved treatment selection, education and management of toxicities in prostate cancer.

Preclinical patient-derived modeling of castration-resistant prostate cancer facilitates individualized assessment of homologous recombination repair deficient disease

The use of mutation analysis of homologous recombination repair (HRR) genes to estimate PARP-inhibition response may miss a larger proportion of responding patients. Here, we provide preclinical models for castration-resistant prostate cancer (CRPC) that can be used to functionally predict HRR defects. In vitro, CRPC LNCaP sublines revealed an HRR defect and enhanced sensitivity to olaparib and cisplatin due to impaired RAD51 expression and recruitment. Ex vivo-induced castration-resistant tumor slice cultures or tumor slice cultures derived directly from CRPC patients showed increased olaparib- or cisplatin-associated enhancement of residual radiation-induced γH2AX/53BP1 foci. We established patient-derived tumor organoids (PDOs) from CRPC patients. These PDOs are morphologically similar to their primary tumors and genetically clustered with prostate cancer but not with normal prostate or other tumor entities. Using these PDOs, we functionally confirmed the enhanced sensitivity of CRPC patients to olaparib and cisplatin. Moreover, olaparib but not cisplatin significantly decreased the migration rate in CRPC cells. Collectively, we present robust patient-derived preclinical models for CRPC that recapitulate the features of their primary tumors and enable individualized drug screening, allowing translation of treatment sensitivities into tailored clinical therapy recommendations.

Metastatic Prostate Cancer-A Review of Current Treatment Options and Promising New Approaches

Androgen deprivation therapy (ADT) alone has been the standard of care for many years in men with metastatic prostate cancer. Due to the limited survival under this monotherapy, many new treatment options have been developed in the last few years. Regarding hormone-sensitive prostate cancer, combination therapies of two or three agents of ADT, androgen receptor signaling inhibitors (ARSI) and chemotherapy have been established and led to a significant benefit in overall survival. Additionally, in patients with metastatic castration-resistant prostate cancer, there are many new therapeutic approaches. Chemotherapy alone has been the standard of care in this situation. In the last years, some new therapeutic options have been developed, which led to an improved survival after progression under chemotherapy. These therapies include ARSI, PARP inhibitors and Lu-PSMA radioligand therapy. The use of a bispecific T-cell engager (BiTE) in this setting is a new promising therapeutic approach, which has not been established as standard of care yet. The role of immunotherapy in prostate cancer is still under investigation. Overall, many new treatment options make prostate cancer therapy a challenging and promising field.

Phase I Study of Niraparib in Combination with Radium-223 for the Treatment of Metastatic Castrate-Resistant Prostate Cancer

PURPOSE

To identify the safety of niraparib, a PARP inhibitor, in combination with Radium-223 for the treatment of metastatic castrate-resistant prostate cancer (mCRPC) in men without known BRCA mutations.

PATIENTS AND METHODS

Men with progressive mCPRC following ≥1 line of androgen receptor (AR)-targeted therapy and bone metastases but no documented BRCA-1 or BRCA-2 alterations or bulky visceral disease were included. Niraparib dose was escalated in combination with standard dosing of Radium-223 using a time-to-event continual reassessment method. The highest dose level with a DLT probability <20% was defined as MTD. Secondary endpoints included PSA change and progression-free survival. Exploratory analyses included assessing DNA mutations found in ctDNA as well as gene expression changes assessed in whole blood samples.

RESULTS

Thirty patients were treated with niraparib and radium-223: 13 patients received 100 mg, 12 received 200 mg, and 5 patients received 300 mg of niraparib. There were six DLT events: two (13%) for neutropenia, two (13%) for thrombocytopenia, whereas fatigue and nausea each occurred once (3%). Anemia (2/13%) and neutropenia (2/13%) were the most common grade 3 adverse events. For patients with prior chemotherapy exposure, the MTD was 100 mg, whereas the MTD for chemotherapy naïve patients was 200 mg. Whole blood gene expression of PAX5 and CD19 was higher in responders and ARG-1, IL2R, and FLT3 expression was higher in nonresponders.

CONCLUSIONS

Combining niraparib with Radium-223 in patients with mCRPC was safe; however, further studies incorporating biomarkers will better elucidate the role of combinations of PARP inhibitors with DNA damaging and other agents.

Development of PARP Inhibitors in Targeting Castration-Resistant Prostate Cancer

Prostate cancer is a genetically heterogenous disease and a subset of prostate tumors harbor alterations in DNA damage and repair (DDR) genes. Prostate tumor DDR gene alterations can arise via germline or somatic events and are enriched in high-grade and advanced disease. Alterations in genes in the homologous recombination (HR) repair pathway are associated with sensitivity to PARP inhibition in breast and ovarian cancer, and data from recently completed randomized trials also demonstrate benefit of PARP inhibitor therapy in patients with advanced metastatic castration-resistant prostate cancer (mCRPC) and tumor HR gene alterations. PARP inhibitors have been investigated in first-line mCRPC in biomarker-selected and unselected populations, and are currently under study in earlier disease states in patients with DDR gene alterations. This chapter focuses on the current state of PARP inhibitor development in prostate cancer with particular emphasis on biomarkers and combination therapy approaches.

Paradigm change in urological, gynaecological and breast cancer management: A new practice-changing data from ASCO 2022 annual meeting

Changing medical practice has been a constant process based on many scientific findings for years. In the oncology community, the American Society of Clinical Oncology (ASCO), one of the major annual conferences, presented the latest updates on practice-changing in cancer. At the recent meeting of 2022, held this year on June 2-6, researchers presented essential findings in urological, gynecological, and breast cancer management. In urological cancer, olaparib + abiraterone was demonstrated thru the PROpel trial to benefit in first-line treatment mCRPC regardless of the HRR stratification factor, along with the adjuvant therapy everolimus, for fully resected RCC in the EVEREST trial. In gynecological cancer, tisotumab vedotin demonstrated a potential role in improving clinical outcomes in 1st line r/mCC thru InnovaTV-205. In breast cancer, trastuzumab deruxtecan showed significant benefit for redefined human epidermal growth factors receptor 2 status in HER2 low BC patients, where current targeted-HER2 therapies are ineffective in the DESTINY-BREAST 04 study. The use of Immuno-based combinations in the medical management of TNBC patients has been supported thru several recent studies, showing positive results and outcomes, as demonstrated by the expert's opinions in Rizzo et al. research papers. In this article, we resumed the different renowned and what we considered intriguing to review studies presented during these three long sessions at the ASCO 2022 meeting.

The Prognostic Significance of Homologous Recombination Repair Pathway Alterations in Metastatic Hormone Sensitive Prostate Cancer

INTRODUCTION

The homologous recombination repair (HRR) pathway is a frequently mutated pathway in advanced prostate cancer. The clinical course of patients with HRR gene alterations who have metastatic hormone sensitive prostate cancer (mHSPC) has not been fully characterized. Here, we examine the outcomes of men with mHSPC with HRR alterations.

METHODS

We conducted a single-center retrospective analysis of men with mHSPC who underwent next generation sequencing. The primary objective was to assess the time from diagnosis of mHSPC to metastatic castrate resistance prostate cancer (mCRPC) in patients with pathogenic HRR alterations compared to individuals lacking these alterations. Key secondary objectives included time to mCRPC in prespecified cohorts, PSA response, and overall survival.

RESULTS

151 men with mHSPC were identified for the study. 24% (N = 37) had pathogenic HRR gene alterations detected with the most common alterations found in BRCA2 (n = 15), ATM (n = 10), and CDK12 (n = 7). Time to mCRPC was significantly decreased in patients with HRR gene alterations versus those without such alterations (12.7 vs. 16.1 months, HR 1.95, P = .02). In multivariate analysis, the effect of HRR gene alterations on time to CRPC remained significant when adjusting for age, mHSPC therapy, the volume of disease, the presence of visceral metastases, and PSA (adjusted HR 1.69, P = .02). Stratified by specific HRR gene alteration, patients with BRCA2 or CDK12 had significantly decreased time to mCRPC compared to other HRR alterations.

CONCLUSION

HRR gene alterations are associated with the worse outcomes in mHSPC with significantly shorter time to mCRPC. Given the established role of Poly (ADP-ribose) Polymerase (PARP) inhibitors in mCRPC, these data highlight an opportunity to examine PARP inhibitors earlier in the clinical course for prostate cancer patients. Ongoing prospective studies will further validate the role of PARP inhibitors in mHSPC patients.

Molecular Genetics of Prostate Cancer and Role of Genomic Testing

Prostate cancer (PCa) is characterized by profound genomic heterogeneity. Recent advances in personalized treatment entail an increasing need of genomic profiling. For localized PCa, gene expression assays can support clinical decisions regarding active surveillance and adjuvant treatment. In metastatic PCa, homologous recombination deficiency, microsatellite instability-high (MSI-H), and CDK12 deficiency constitute main actionable alterations. Alterations in DNA repair genes confer variable sensitivities to poly(ADP-ribose)polymerase inhibitors, and the use of genomic instability assays as predictive biomarker is still incipient. MSI can be assessed by immunohistochemistry To date there is a lack of consensus as to testing standards.

Treatment Landscape for Patients with Castration-Resistant Prostate Cancer: Patient Selection and Unmet Clinical Needs

Metastatic castration resistant prostate cancer (CRPC) is an inevitably fatal disease. However, in recent years, several treatments have been shown to improve the outcome of CRPC patients both in the non-metastatic (nmCRPC) as well as the metastatic setting (mCRPC). In nmCRPC patients with a PSA doubling time <10 months, the addition of enzalutamide, apalutamide and darolutamide to androgen deprivation therapy (ADT) compared to ADT alone resulted in improved metastases free (MFS) and overall survival (OS). For mCRPC patients, several treatment options have been shown to be effective: two taxane based chemotherapies (docetaxel and cabazitaxel), two androgen-receptor pathway inhibitors (ARPI) (abiraterone and enzalutamide), two radiopharmaceutical agents (radium 223 and 177Lutetium-PSMA-617), one immunotherapy treatment (sipuleucel-T) and two poly ADP-ribose polymerase (PARP) inhibitors (olaparib and rucaparib). Pembrolizumab is US Food and Drug Administration (FDA) approved in all MSI high solid tumors, although a very small proportion of prostate cancer patients harboring this characteristic will benefit. Despite having a broad variety of treatments available, there are still several unmet clinical needs for CRPC. The objective of this review was to describe the therapeutic landscape in CRPC patients, to identify criteria for selecting patients for specific treatments currently available, and to address the current challenges in this setting.

Emerging hormonal agents for the treatment of prostate cancer

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Development of Olaparib-Resistance Prostate Cancer Cell Lines to Identify Mechanisms Associated with Acquired Resistance

Simple Summary

PARP inhibitors (PARPi; olaparib) are presently in clinical trials for advanced prostate cancer (PC). Resistance mechanisms are not fully understood in PC compared to ovarian and breast cancers. Our study aimed to identify new molecular mechanisms that affect acquired olaparib-resistance. We developed new resistant PC cell line models derived from original PC cell lines. We identified that DNA repair, autophagy, and the Rho-associated coiled-coil containing protein kinase 2 (ROCK2) could be potential targets to reverse the acquired olaparib-resistance.

Abstract

Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) were initially deployed to target breast and ovarian tumors with mutations in DNA damage response genes. Recently, PARPi have been shown to be beneficial in the treatment of prostate cancer (PC) patients having exhausted conventional therapeutics. Despite demonstrating promising response rates, all patients treated with PARPi eventually develop resistance. However, PARPi resistance in PC is not well understood, and further studies are required to understand PARPi resistance in PC to propose strategies to circumvent resistance. Methods: Starting from well-established olaparib-sensitive PC cell lines (LNCaP, C4-2B and DU145), we derived olaparib-resistant (OR) PC cell lines and performed a microarray analysis. Results: The olaparib IC50 values of OR cell lines increased significantly as compared to the parental cell lines. Gene expression analyses revealed that different pathways, including DNA repair, cell cycle regulation and autophagy, were affected by acquired resistance. A total of 195 and 87 genes were significantly upregulated and downregulated, respectively, in all three OR cell lines compared to their parental counterparts. Among these genes, we selected BRCC3, ROCK2 and ATG2B for validation. We showed that ROCK2 expression, basal autophagy and homologous recombination (HR) efficiency were increased in all OR cell lines. Conclusions: Our study provides a new in vitro model to study PARPi resistance in PC and suggests new possible targets to reverse resistance and prolong the benefits of PARPi treatment.

Emerging Biomarker-Guided Therapies in Prostate Cancer

Prostate cancer remains one of the leading causes of cancer death in men worldwide. In the past decade, several new treatments for advanced prostate cancer have been approved. With a wide variety of available drugs, including cytotoxic agents, androgen receptor axis-targeted therapies, and alpha-emitting radiation therapy, identifying their optimal sequencing remains a challenge. Progress in the understanding of the biology of prostate cancer has provided an opportunity for a more refined and personalized treatment selection process. With the advancement of molecular sequencing techniques, genomic precision through the identification of potential treatment targets and predictive biomarkers has been rapidly evolving. In this review, we discussed biomarker-driven treatments for advanced prostate cancer. First, we presented predictive biomarkers for established, global standard treatments for advanced diseases, such as chemotherapy and androgen receptor axis-targeted agents. We also discussed targeted agents with recent approval for special populations, such as poly ADP ribose polymerase (PARP) inhibitors in patients with metastatic castrate-resistant prostate cancer with homologous recombination repair-deficient tumors, pembrolizumab in patients with high levels of microsatellite instability or high tumor mutational burden, and prostate-specific membrane antigen (PSMA) directed radioligand theragnostic treatment for PSMA expressing tumors. Additionally, we discussed evolving treatments, such as cancer vaccines, chimeric antigen receptor T-cells (CAR-T), Bispecific T-cell engagers (BiTEs), other targeted agents such as AKT inhibitors, and various combination treatments. In summary, advances in molecular genetics have begun to propel personalized medicine forward in the management of advanced prostate cancer, allowing for a more precise, biomarker-driven treatment selection with the goal of improving overall efficacy.

PARP Inhibitors: A New Horizon for Patients with Prostate Cancer

The introduction of PARP inhibitors (PARPi) in prostate cancer is a milestone and provides a pathway to hope in fighting this disease. It is the first time that drugs, based on the concept of synthetic lethality, have been approved for prostate cancer. In addition, it is also the first time that genetic mutation tests have been included in the therapeutic algorithm of this disease, representing a significant step forward for precision and personalized treatment of prostate cancer. The objectives of this review are: (1) understanding the mechanism of action of PARPi in monotherapy and combinations; (2) gaining insights on patient selection for PARPi; (3) exposing the pivotal studies that have allowed its approval, and; (4) offering an overview of the ongoing trials. Nevertheless, many unsolved questions remain, such as the number of patients who could potentially benefit from PARPi, whether to use PARPi in monotherapy or in combination, and when is the best time to use them in advanced or localized disease. To answer these and other questions, many clinical trials are underway. Some of them have recently demonstrated promising results that may favor the introduction of new combinations in metastatic castration-resistant prostate cancer.

Prospective assessment of AR splice variant and multi-biomarker expression on circulating tumor cells of mCRPC patients undergoing androgen receptor targeted agents: interim analysis of PRIMERA trial (NCT04188275)

Circulating tumor cells detection and ARV7 expression are associated with worse clinical outcomes in metastatic Castration-Resistant Prostate Cancer (mCRPC) undergoing Androgen Receptor Targeted Agents. ARFL, PSMA and PSA may help to refine prognostic models. In our institution, a prospective observational trial testing CTC detection in mCPRC undergoing I line ARTA therapy terminated the planned enrollment in 2020. Here, we present a pre-planned interim analysis with 18 months of median follow-up. RT-qPCR was used to determine the CTC expression of PSA, PSMA, AR and ARV7 before starting ARTA. PSA-drop, Progression-Free and Overall Survival (PFS and OS) and their correlation with CTC detection were reported. Forty-four patients were included. CTC were detected in 43.2% of patients, of whom 8.94% expressed PSA, 15.78% showed ARV7, 63.15% and 73.68% displayed ARFL and PSMA, respectively. Biochemical response was significantly improved in CTC + vs CTC- patients, with median PSA-drop of 18.5 vs 2.5 ng/ml (p = 0.03). After a median follow-up of 18 months, 50% of patients progressed. PFS was significantly longer in CTC- patients (NR vs 16 months). Eight (18.2%) patients died, a non-significant trend in terms of OS was detected in favor of CTC- patients (NR vs 29 months, p = 0.05). AR, PSA and PSMA expression in CTC + had no significant impact on PSA-drop, PFS or OS. PRIMERA-trial confirmed the CTC detection predictive importance in mCRPC patients.

PARP Inhibition, a New Therapeutic Avenue in Patients with Prostate Cancer

Up to 25% of patients with metastatic prostate cancer present with germline or somatic DNA damage repair alterations, some of which are associated with aggressive disease and poor outcomes. New data have brought poly(ADP-ribose) polymerase (PARP) inhibitors into sharp focus in the treatment of metastatic castrate-resistant prostate cancer (mCRPC). Olaparib improved survival after at least one new hormonal therapy (NHT) in a cohort of patients harboring BRCA1, BRCA2 or ATM mutations in the PROfound trial, while rucaparib, talazoparib and niraparib demonstrated compelling activity in phase II trials. While patients with prostate cancer and BRCA1 or BRCA2 mutations may derive greatest benefit of PARP inhibition, the magnitude of benefit seems much lower in the context of most other homologous recombination gene mutations. Several PARP inhibitors are currently developed in combination with conventional therapy, including chemotherapy, NHT, and alpha-particle emitters, at different disease stages. Herein, we review the rationale for PARP inhibition in patients with prostate cancer, discuss the impact of PARP inhibitors on outcomes, and explore underlying challenges for future developments.