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

Combining PARP Inhibitors and Androgen Receptor Signalling Inhibitors in Metastatic Prostate Cancer: A Quantitative Synthesis and Meta-analysis

CONTEXT

PARP inhibitors (PARPi) are established treatments for metastatic castration-resistant prostate cancer (mCRPC) with homologous recombination repair (HRR) deficiency after androgen receptor signalling inhibitor (ARSI) failure. New PARPi + ARSI combinations have been tested in all comers, although their clinical relevance in HRR-proficient tumours remains uncertain.

OBJECTIVE

To quantitatively synthesise evidence from randomised trials assessing the efficacy and safety of PARPi + ARSI combinations for first-line treatment of mCRPC.

EVIDENCE ACQUISITION

We searched the PubMed, EMBASE, SCOPUS, and Cochrane Library databases up to February 28, 2023. Randomised controlled trials (RCTs) comparing PARPi + ARSI versus placebo + ARSI for first-line treatment of mCRPC were eligible. Two reviewers independently performed screening and data extraction and assessed the risk of bias, while a third reviewer evaluated the eligibility criteria.

EVIDENCE SYNTHESIS

Overall, three phase 3 RCTs were included in the systematic review: PROPEL, MAGNITUDE, and TALAPRO-2. A total of 2601 patients with mCRPC were enrolled. Two of these trials (PROPEL and TALAPRO-2) assessed the radiographic progression-free survival benefit of PARPi + ARSI for first-line treatment of mCRPC, independent of HRR status. The pooled hazard ratio was 0.62 (95% confidence interval 0.53-0.72). The pooled hazard ratio for overall survival was 0.84 (95% confidence interval 0.72-0.98), indicating a 16% reduction in the risk of death among patients who received the combination.

CONCLUSIONS

Results from this meta-analysis support the use of ARSI + PARPi combinations in biomarker-unselected mCRPC. However, such combinations might be less clinically relevant in HRR-proficient cancers, especially considering the change in treatment landscape for mCRPC.

PATIENT SUMMARY

We looked at outcomes from trials testing combinations of two classes of drugs (PARP inhibitors and ARSI) in advanced prostate cancer. We found that these combinations seem to work regardless of gene mutations identified as biomarkers of response to PARP inhibitors when used on their own.

Molecular heterogeneity in prostate cancer and the role of targeted therapy

Data collected from large-scale studies has shown that the incidence of prostate cancer globally is on the rise, which could be attributed to an overall increase in lifespan. So, the question is how has modern science with all its new technologies and clinical breakthroughs mitigated or managed this disease? The answer is not a simple one as prostate cancer exhibits various subtypes, each with its unique characteristics or signatures which creates challenges in treatment. To understand the complexity of prostate cancer these signatures must be deciphered. Molecular studies of prostate cancer samples have identified certain genetic and epigenetic alterations, which are instrumental in tumorigenesis. Some of these candidates include the androgen receptor (AR), various oncogenes, tumor suppressor genes, and the tumor microenvironment, which serve as major drivers that lead to cancer progression. These aberrant genes and their products can give an insight into prostate cancer development and progression by acting as potent markers to guide future therapeutic approaches. Thus, understanding the complexity of prostate cancer is crucial for targeting specific markers and tailoring treatments accordingly.

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.

Synthetic Lethality by Co-Inhibition of Androgen Receptor and Polyadenosine Diphosphate-Ribose in Metastatic Prostate Cancer

Androgen receptor pathway inhibitors (ARPI) and polyadenosine diphosphate-ribose inhibitors (PARPi) are part of the standard of care in patients with metastatic castration-resistant prostate cancer (mCRPC). There is biological evidence that the association of ARPI and PARPi could have a synergistic effect; therefore, several ongoing clinical trials are investigating the efficacy of this combination with preliminary results that are not perfectly concordant in identifying patients who can obtain the most benefit from this therapeutic option. The purpose of this review is to describe the PARPi mechanisms of action and to analyze the biological mechanisms behind the interplay between the androgen receptor and the PARPi system to better understand the rationale of the ARPI + PARPi combinations. Furthermore, we will summarize the preliminary results of the ongoing studies on these combinations, trying to understand in which patients to apply. Finally, we will discuss the clinical implications of this combination and its possible future perspectives.

Hematological Toxicities with PARP Inhibitors in Prostate Cancer: A Systematic Review and Meta-Analysis of Phase II/III Randomized Controlled Trials

BACKGROUND

Poly ADP-ribose polymerase inhibitors (PARPis) are an important class of therapeutics for metastatic castration-resistant prostate cancer (mCRPC). Unlike hormone-based treatments for mCRPC, PARPis are not without drug-related hematological adverse events.

OBJECTIVE

To review the evidence on hematological toxicities, including anemia, thrombocytopenia, and neutropenia from PARPis in prostate cancer.

STUDY METHODOLOGY

A systematic review and meta-analysis using the PRISMA guidelines was performed for phase II and III randomized controlled trials (RCTs) of PARPis in prostate cancer. PubMed, Embase, and Ovid All EBM reviews-Cochrane were queried from inception to 9 June 2023. The Mantel-Haenszel method was used to report risk ratios (RR) and 95% confidence intervals (CI) for all-grade and high-grade anemia, thrombocytopenia, and neutropenia toxicities.

RESULTS

The systematic review retrieved eight phase II and III RCTs; specifically, eight were included in the anemia, five in the all-grade thrombocytopenia and neutropenia, and four in the high-grade thrombocytopenia and neutropenia outcomes. Compared to a placebo and/or other non-PARPi treatments, PARPi use was associated with an increased risk of all-grade anemia (RR, 3.37; 95% CI, 2.37-4.79; p < 0.00001), thrombocytopenia (RR, 4.54; 95% CI, 1.97-10.44; p = 0.0004), and neutropenia (RR, 3.11; 95% CI, 1.60-6.03; p = 0.0008). High-grade anemia (RR, 6.94; 95% CI, 4.06-11.86; p < 0.00001) and thrombocytopenia (RR, 5.52; 95% CI, 2.80-10.88; p < 0.00001) were also associated with an increased risk, while high-grade neutropenia (RR, 3.63; 95% CI, 0.77-17.23; p = 0.10) showed no significant association. Subgroup stratification analyses showed differences in various all-grade and high-grade toxicities.

CONCLUSION

PARPis were associated with an increased risk of hematological AEs. Future studies with more pooled RCTs will enhance this understanding and continue to inform patient-physician shared decision-making. Future studies may also have a role in improving the current management strategies for these AEs.

Safety of PARP inhibitors as maintenance therapy in ovarian cancer

INTRODUCTION

Antiangiogenic agents and poly(ADP-ribose) polymerase inhibitors (PARP-Is) have improved the outcome of patients suffering from ovarian cancer. However, as they are associated with many adverse events (AEs), it is important to be aware of their safety and toxicity profiles.

AREAS COVERED

We reviewed PARP-I therapeutical indications, mechanism of action, metabolism, and interactions. We reported on all major and minor AEs that have emerged from clinical trials (SOLO1, PRIMA, PAOLA1, ATHENA, SOLO2, NOVA, ARIEL3, NORA), their follow-ups, meta-analyses, and real-world studies, particularly hematologic toxicities and their management, and secondary malignancies (myelodysplastic syndrome and acute myeloid leukemia). We also addressed gastrointestinal, neurological, respiratory, hepatic, and renal toxicity and the use of PARP-Is in older, pregnant, and lactating patients. No specific research strategy in terms of keywords, inclusive dates and databases was used.

EXPERT OPINION

PARP-Is benefits largely outweigh the risks associated with potential AEs. Randomized controlled trials produced strong good, quality data, but they enrolled a selected population and failed to capture rare events. More pharmacovigilance data and real-life studies on a larger and more heterogeneous sample are needed to understand PARP-Is differences and to clarify the incidence of late AEs to balance the risk/benefit ratio.