RNA-Based Homologous Recombination Deficiency Signature Detects Homologous Recombination Deficiency-RNA+ Patients With and Without Homologous Recombination Repair Gene Pathogenic Alterations in Men With Prostate Cancer

PURPOSE

Homologous recombination deficiency (HRD) is a well-described phenotype of some prostate cancers; however, current biomarkers for HRD are imperfect and rely on detection of single gene alterations in the homologous recombination repair (HRR) pathway, which may not capture the complexity of HRD biology. RNA signature-based methods of HRD identification present a potentially dynamic assessment of the HRD phenotype; however, its relationship with HRR gene alterations is not well characterized in prostate cancer.

METHODS

A HRD assay on the basis of an RNA signature associated with biallelic BRCA1/2 loss was applied to a retrospective cohort study of 985 men with prostate cancer analyzed on the Tempus xT platform. HRD status was defined by a binary threshold on a continuous scale.

RESULTS

In this cohort, of the 126 (13%) patients found to be HRD+ by RNA signature (HRD-RNA+), 100 (79%) had no coexisting HRR gene alteration. Among samples with biallelic BRCA1/2 loss, 78% (7/9) were classified as HRD-RNA+, while 8% (2/25) of samples with BRCA1/2 monoallelic loss were HRD-RNA+. Biallelic and monoallelic ATM loss exhibited HRD-RNA+ at a lower prevalence: 6.7% (1/15) and 7.1% (1/14), respectively, compared with HRD-RNA+ prevalence among samples without any HRR gene loss (13%; 100/782). HRD-RNA+ was associated with a significantly higher prevalence of TP53 and AR gene alterations relative to HRD-RNA- after correction for multiple comparisons, 59% versus 39% (q = 0.003) and 23% versus 12% (q = 0.024), respectively.

CONCLUSION

Use of an RNA-based HRD signature significantly expands the fraction of patients with prostate cancer who may derive benefit from poly (ADP-ribose) polymerase inhibitors (PARPis) compared with using HRR gene mutations alone. Further studies are needed to evaluate functional HRD significance and inform future usage as a predictive biomarker for PARPi selection.

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.

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.

Analysis of the Clinical Advancements for BRCA-Related Malignancies Highlights the Lack of Treatment Evidence for BRCA-Positive Male Breast Cancer

Male breast cancer (MBC) is a rare disease that accounts for less than 1% of all breast cancers and male malignancies. Despite recognised clinico-pathological and molecular differences to female breast cancer (FBC), the clinical management of MBC follows established FBC treatment strategies. Loss of function mutations in the DNA damage response genes BRCA1 and BRCA2, have been strongly implicated in the pathogenesis of MBC. While there have been extensive clinical advancements in other BRCA-related malignancies, including FBC, improvements in MBC remain stagnant. Here we present a review that highlights the lack of treatment evidence for BRCA-related MBC and the required national and global collaborative effort to address this unmet need. In doing so, we summarise the transformative clinical advancements with poly(ADP-ribose) polymerase (PARP) inhibitors in other BRCA-related cancers namely, FBC and prostate cancer.

The growing role of rucaparib in contemporary treatment of metastatic prostate cancer: a review of efficacy and guidance for side effect management

INTRODUCTION

In May 2020, the approval of rucaparib - a poly-ADP-ribose polymerase (PARP) inhibitor - in the USA marked the arrival of a new class of targeted therapeutics for a subset of metastatic castration-resistant prostate cancer patients whose tumors harbor germline or somatic BRCA1/2 gene alterations. It has now become critical for physicians to be aware of the role and nuances of management of PARP inhibitor therapies in prostate cancer.

AREAS COVERED

We focus on rucaparib's pharmacology, key clinical trials that support its current indication, the competitive landscape, and our considerations for management of adverse events. We also review the ongoing clinical trials that may expand its utility in prostate cancer in our expert opinion. Finally, we discuss the opportunities that exist for further development of this class of targeted agents in prostate cancer.

EXPERT OPINION

We believe that the time has come to develop functional assays of HRR proficiency or deficiency in order to better guide PARP inhibitor selection for patients with prostate cancer and beyond.

PARP Inhibitors as Monotherapy in Daily Practice for Advanced Prostate Cancers

Despite recent improvements in survival, metastatic castration-resistant prostate cancers (mCRPCs) remain lethal. Alterations in genes involved in the homologous recombination repair (HRR) pathway are associated with poor prognosis. Poly-ADP-ribose polymerase (PARP) inhibitors (PARPis) have demonstrated anti-tumoral effects by synthetic lethality in patients with mCRPCs harboring HRR gene alterations, in particular BRCA2. While both olaparib and rucaparib have obtained government approvals for use, the selection of eligible patients as well as the prescription of these treatments within the clinical urology community are challenging. This review proposes a brief review of the rationale and outcomes of PARPi treatment, then a pragmatic vision of PARPi use in terms of prescription and the selection of patients based on molecular screening, which can involve potential genetic counseling in the case of associated germinal alterations.

With Our Powers Combined: Exploring PARP Inhibitors and Immunotherapy

ABSTRACT

The use of poly(ADP-ribose) polymerase inhibitors and immune checkpoint inhibitor therapies has seen substantial clinical success in oncology therapeutic development. Although multiple agents within these classes have achieved regulatory approval globally-in several malignancies in early and advanced stages-drug resistance remains an issue. Building on preclinical evidence, several early trials and late-phase studies are underway. This review explores the therapeutic potential of combination poly(ADP-ribose) polymerase inhibitors and immune checkpoint inhibitor therapy in solid tumors, including the scientific and therapeutic rationale, available clinical evidence, and considerations for future trial and biomarker development across different malignancies using ovarian and other solid cancer subtypes as key examples.

Optimal Sequencing and Predictive Biomarkers in Patients with Advanced Prostate Cancer

The treatment landscape of advanced prostate cancer has completely changed during the last decades. Chemotherapy (docetaxel, cabazitaxel), androgen-receptor signaling inhibitors (ARSi) (abiraterone acetate, enzalutamide), and radium-223 have revolutionized the management of metastatic castration-resistant prostate cancer (mCRPC). Lutetium-177-PSMA-617 is also going to become another treatment option for these patients. In addition, docetaxel, abiraterone acetate, apalutamide, enzalutamide, and radiotherapy to primary tumor have demonstrated the ability to significantly prolong the survival of patients with metastatic hormone-sensitive prostate cancer (mHSPC). Finally, apalutamide, enzalutamide, and darolutamide have recently provided impactful data in patients with nonmetastatic castration-resistant disease (nmCRPC). However, which is the best treatment sequence for patients with advanced prostate cancer? This comprehensive review aims at discussing the available literature data to identify the optimal sequencing approaches in patients with prostate cancer at different disease stages. Our work also highlights the potential impact of predictive biomarkers in treatment sequencing and exploring the role of specific agents (i.e., olaparib, rucaparib, talazoparib, niraparib, and ipatasertib) in biomarker-selected populations of patients with prostate cancer (i.e., those harboring alterations in DNA damage and response genes or PTEN).

Prostate cancer and PARP inhibitors: progress and challenges

Despite survival improvements achieved over the last two decades, prostate cancer remains lethal at the metastatic castration-resistant stage (mCRPC) and new therapeutic approaches are needed. Germinal and/or somatic alterations of DNA-damage response pathway genes are found in a substantial number of patients with advanced prostate cancers, mainly of poor prognosis. Such alterations induce a dependency for single strand break reparation through the poly(adenosine diphosphate-ribose) polymerase (PARP) system, providing the rationale to develop PARP inhibitors. In solid tumors, the first demonstration of an improvement in overall survival was provided by olaparib in patients with mCRPC harboring homologous recombination repair deficiencies. Although this represents a major milestone, a number of issues relating to PARP inhibitors remain. This timely review synthesizes and discusses the rationale and development of PARP inhibitors, biomarker-based approaches associated and the future challenges related to their prescription as well as patient pathways.