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

Empowering PARP inhibition through rational combination: Mechanisms of PARP inhibitors and combinations with a focus on the treatment of metastatic castration-resistant prostate cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors have revolutionized the treatment of many cancers. Metastatic castration-resistant prostate cancer (mCRPC) is an area where PARP inhibitors are intensively studied; the efficacy with PARP inhibitor monotherapy in patients with homologous recombination repair mutations following novel hormonal therapy have prompted the investigation of combination therapy, with adding an androgen receptor pathway inhibitor (ARPI) being one focus of research. Data on PARP inhibitor monotherapy and combination therapy for mCRPC are accumulating, and it is important to navigate through the complex data to inform treatment decision. Here we review the mechanisms of action of PARP inhibitors, their pharmacological properties, the synergistic activity of PARP inhibitors plus other drug classes, and the clinical evidence on monotherapy and combination therapy in patients with mCRPC. We propose key considerations in the selection of agents and treatment sequence for mCRPC, such as efficacy, toxicity profiles, biomarkers, and interactions with concomitant medications.

Heterogeneity of the Treatment Effect with PARP Inhibitors in Metastatic Castration-resistant Prostate Cancer: A Living Interactive Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE

Selection of patients harboring mutations in homologous recombination repair (HRR) genes for treatment with a PARP inhibitor (PARPi) is challenging in metastatic castration-resistant prostate cancer (mCRPC). To gain further insight, we quantitatively assessed the differential efficacy of PARPi therapy among patients with mCRPC and different HRR gene mutations.

METHODS

This living meta-analysis (LMA) was conducted using the Living Interactive Evidence synthesis framework. We included clinical trials assessing PARPi as monotherapy in pretreated mCRPC or in combination with an androgen receptor pathway inhibitor (ARPI) in treatment-naïve patients. Random-effects meta-analyses were performed for a priori subgroups stratified by HRR status, BRCA status, and each gene.

KEY FINDINGS AND LIMITATIONS

This first report for our LMA includes 13 trials (4278 patients). Among patients with pretreated mCRPC receiving PARPi monotherapy, the tumor response rate per 100 person-months was numerically higher for patients with BRCA2 (50% prostate-specific antigen response [PSA50%] 3.3; objective response rate [ORR] 3.3), BRCA1 (PSA50% 1.2; ORR 2.0), or PALB2 (PSA50% 3.3; ORR 1.4) alterations than for patients with ATM (PSA50% 0.4; ORR 0.3), CDK12 (PSA50% 0.2; ORR 0.2), or CHEK2 (PSA50% 1.0; ORR 0.7) alterations. Among patients receiving PARPi + ARPI, a significant radiographic progression-free survival benefit was observed in those with BRCA (hazard ratio [HR] 0.28, 95% confidence interval [CI] 0.13-0.62) or CDK12 (HR 0.58, 95% CI 0.35-0.95) alterations, but not in patients with PALB2 (HR 0.53, 95% CI 0.21-1.32), ATM (HR 0.93, 95% CI 0.57-1.53), or CHEK2 (HR 0.92, 95% CI 0.53-1.61) alterations. An overall survival benefit was observed for patients with BRCA alterations (HR 0.47, 95% CI 0.31-0.71) after adjustment for crossover and subsequent therapy, but not for patients with PALB2 (HR 0.33, 95% CI 0.10-1.16), ATM (HR 0.97, 95% CI 0.57-1.67), CDK12 (HR 0.80, 95% CI 0.36-1.78), or CHEK2 (HR 0.81, 95% CI 0.37-1.75) alterations.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Our LMA delivers information on the effect of PARPi therapy in relation to specific gene alterations in mCRPC via an interactive web platform. The evidence suggests the greatest PARPi benefit in patients with BRCA alterations, a strong signal of benefit in patients with PALB2 or CDK12 alterations, and no benefit in patients with ATM or CHEK2 alterations.

Role of multi‑omics in advancing the understanding and treatment of prostate cancer (Review)

The application of multi‑omics methodologies, encompassing genomics, transcriptomics, proteomics, metabolomics and integrative genomics, has markedly enhanced the understanding of prostate cancer (PCa). These methods have facilitated the identification of molecular pathways and biomarkers crucial for the early detection, prognostic evaluation and personalized treatment of PCa. Studies using multi‑omics technologies have elucidated how alterations in gene expression and protein interactions contribute to PCa progression and treatment resistance. Furthermore, the integration of multi‑omics data has been used in the identification of novel therapeutic targets and the development of innovative treatment modalities, such as precision medicine. The evolving landscape of multi‑omics research holds promise for not only deepening the understanding of PCa biology but also for fostering the development of more effective and tailored therapeutic interventions, ultimately improving patient outcomes. The present review aims to synthesize current findings from multi‑omics studies associated with PCa and to assess their implications for the improvement of patient management and therapeutic outcomes. The insights provided may guide future research directions and clinical practices in the fight against PCa.

Targeting Poly (ADP-ribose) polymerase-1 (PARP-1) for DNA repair mechanism through QSAR-based virtual screening and MD simulation

Poly (ADP-ribose) polymerase-1 (PARP-1) is a key enzyme in the base excision repair pathway, crucial for maintaining genomic stability by repairing DNA breaks. In cancers with mutations in DNA repair genes, such as BRCA1 and BRCA2, PARP-1 activity becomes essential for tumor cell survival, making it a promising target for therapeutic intervention. This study employs QSAR modeling, virtual screening, and molecular dynamics (MD) simulations to identify potential PARP-1 inhibitors. A dataset of inhibitors was analyzed using 12 molecular fingerprint descriptors to develop robust QSAR models, with the optimal model based on the CDK descriptor achieving R2 = 0.96, Q2_CV = 0.78, and Q2_Ext = 0.80. The model was applied to virtually screen three chemical libraries-ZINC, FDA, and NPA-identifying promising candidates for PARP-1 inhibition. Molecular docking revealed that compounds ZINC13132446, Z2037280227, and NPC193377 have strong binding affinity for the PARP-1 active site. MD simulations and MM-PBSA confirmed the stability of these complexes, with Z2037280227 and NPC193377 exhibiting the most stable interactions. These results underscore the potential of targeting PARP-1 as a therapeutic strategy for cancers with homologous recombination deficiencies, including prostate, breast, and ovarian cancer, particularly in patients with DNA repair deficiencies.

Integrating machine learning driven virtual screening and molecular dynamics simulations to identify potential inhibitors targeting PARP1 against prostate cancer

Prostate cancer (PC) is one of the most common types of malignancies in men, with a noteworthy increase in newly diagnosed cases in recent years. PARP1 is a ubiquitous nuclear enzyme involved in DNA repair, nuclear transport, ribosome synthesis, and epigenetic bookmarking. In this study, a library of 9000 phytochemicals was screened, with a focus on those with high drug efficacy and potential PARP1 inhibition. Different machine learning models were generated and assessed using various statistical measures. The RF model outperformed all other models in terms of accuracy (0.9489), specificity (0.9171), and area under the curve (AUC = 0.9846). Following this, a library of 9510 phytochemicals was screened, yielding 181 compounds predicted to be active. These compounds were subsequently assessed using Lipinski's Rule of Five, yielding 40 interesting candidates. Molecular docking experiments demonstrated that compound ZINC2356684563, ZINC2356558598, and ZINC14584870, had strong affinity for the PARP1 active site. Further molecular dynamics simulations and MM-PBSA validated the stability of the ligand-protein complexes, with ZINC14584870 and ZINC43120769 demonstrating the most stable interaction, as seen by low RMSD and RMSF levels. Our findings emphasize the potential of these phytochemical inhibitors as novel therapeutic agents against PARP1 in prostate cancer treatment, paving the path for further experimental validation and clinical investigations. These results open new possibilities for developing treatments to benefit prostate cancer patients.

Efficacy and safety of PARP inhibitors in prostate cancer: An umbrella review of systematic reviews and meta-analyses

Prostate cancer is a significant cause of cancer-related deaths in men. Poly (ADP-ribose) polymerase inhibitors (PARPi) have been shown to improve progression-free survival, especially in patients with BRCA1/2 mutations and deficiencies in homologous recombination repair (HRR). We conducted systematic reviews and meta-analyses and found that PARPi, combined with androgen receptor inhibitors, significantly improved overall survival (OS) and progression-free survival (PFS) in BRCA1/2-mutant and HRR-deficient patients. PARPi therapies increased the incidence of adverse events (AEs), including fatigue, nausea, anemia, neutropenia, and thrombocytopenia. Among different PARP inhibitors, Olaparib, Talazoparib, and Rucaparib demonstrated the strongest efficacy in improving OS and PFS but were also linked to higher rates of AEs. Combination therapies with PARPi and hormonal treatments proved more effective than monotherapy, especially in genetically targeted subgroups like BRCA1/2-mutant patients. This umbrella review demonstrates that PARPi treatment significantly improves clinical outcomes, particularly in BRCA1/2-mutant and HRR-deficient mCRPC patients.

A pan-tumor review of the role of poly(adenosine diphosphate ribose) polymerase inhibitors

Poly(adenosine diphosphate ribose) polymerase (PARP) inhibitors, such as olaparib, talazoparib, rucaparib, and niraparib, comprise a therapeutic class that targets PARP proteins involved in DNA repair. Cancer cells with homologous recombination repair defects, particularly BRCA alterations, display enhanced sensitivity to these agents because of synthetic lethality induced by PARP inhibitors. These agents have significantly improved survival outcomes across various malignancies, initially gaining regulatory approval in ovarian cancer and subsequently in breast, pancreatic, and prostate cancers in different indications. This review offers a comprehensive clinical overview of PARP inhibitor approvals, emphasizing their efficacy across different cancers based on landmark phase 3 clinical trials.

Ancestry-Specific DNA Damage Repair Gene Mutations and Prostate Cancer

This review is intended to reflect the currently available literature on both clinically significant germline mutations in DNA damage repair (DDR) genes as well as the importance of ancestral diversity in the pathogenesis of prostate cancer (PCa). The second most prevalent cancer worldwide in men is PCa, causing significant morbidity and mortality in its advanced stage. Emerging data highlight the substantial role of germline mutations of DDR genes in PCa pathogenesis, especially in progression to aggressive forms of the disease. Germline genetic testing is recognized as a necessary tool for efficient, individualized patient care. NCCR guidelines recommend inquiring about the family history of PCa and known germline variants and, if indicated, proceeding with germline multigene testing followed by post-test genetic counseling. Depending on the germline mutations in HR repair genes or in MMR genes, specific treatment options may provide clinical benefit. We will discuss specific germline mutations that are involved in PCa progression and prognosis in racially diverse populations.

Efficacy and Safety of Combination AKT and Androgen Receptor Signaling Inhibition in Metastatic Castration-Resistant Prostate Cancer: Systematic Review and Meta-Analysis

BACKGROUND

Metastatic castration-resistant prostate cancer (mCRPC) has a poor prognosis with current treatment options including chemotherapy and androgen receptor signaling inhibitor (ARSI) medications. Poly-ADP ribose polymerase (PARP) inhibitors alone and in combination with ARSI has recently been incorporated in management for mCRPC deficient in BRCA1/2 genes. However, downregulating androgen-receptor signaling using ARSIs can upregulate the PI3K/AKT/mTOR pathway, promoting tumor cell survival. This creates a rationale for co-targeting both these pathways. This systematic review aimed to investigate AKT inhibitors and ARSI combination therapy.

METHODS

EMBASE, MEDLINE, and Scopus were searched from database inception to July 2023. Primary outcomes included objective response rate (ORR), prostate-specific antigen (PSA) response rate, adverse events (AEs), overall survival (OS), and radiographic progression-free survival (rPFS). Quality was assessed using the risk of bias tool (ROB2) and certainty of evidence with GRADE.

RESULTS

Six clinical trials with 3 Phase I, 1 Phase II, 1 Phase III were included with 771 patients and a median age ranging from 67 years to 70 years. The pooled ORR was 30% (n = 5 studies, 95% CI, 3%-84%) and PSA response rate was 43% (n = 5 studies, 95% CI, 15%-77%). The median duration of rPFS ranged from 8.2 to 19.2 months in the intervention compared with 6.4 to 16.6 months in the placebo group. A 16% reduction in radiographic progression or death was reported in patients receiving dual therapy compared with those receiving placebo. This reduction was greater by PTEN-loss status, ranging from 23% to 61%. The median OS ranged from 15.6 to 18.9 months. No significant difference was reported in survival relative to placebo. 98.8% (767/776) of patients experienced AEs of any grade, with GRADE ≥3 AEs occurring in 65.9% (512/776) of patients. The most common AE and GRADE ≥3 AEs were diarrhoea (pooled prevalence = 70%, 95% CI, 57%-81%), and hyperglycaemia (pooled prevalence = 12%, 95% CI, 6%-20%), respectively.

CONCLUSION

Combined therapy reduced the risk of rPFS, with the response higher in PTEN-loss subgroup, with a modest but not significant increase in OS. Our AE estimates showed consistency with other studies. AEs of any grade were common with the majority experiencing at least 1 AE. (PROSPERO Registration Number: CRD420202352583).

Navigating therapeutic sequencing in the metastatic castration-resistant prostate cancer patient journey

BACKGROUND

Novel therapies for metastatic castration-resistant prostate cancer (mCRPC) have improved patient outcomes. However, there is uncertainty on the optimal selection of therapeutic agents for subsequent lines of therapy.

METHODS

We conducted a comprehensive review of published evidence from pivotal clinical trials and recent guidelines for the treatment of mCRPC. We further identify gaps in knowledge and areas for future research.

RESULTS

Key considerations to help guide treatment selection for patients with mCRPC include personal treatment history, individual clinical characteristics, symptoms, prognosis, availability of clinical trials, and other patient-specific factors. Genetic testing and prostate-specific membrane antigen-targeted imaging are important tools to evaluate candidacy for newer therapeutic options such as poly (ADP-ribose) polymerase inhibitors, alone or in combination with androgen receptor pathway inhibitors, and [177Lu]Lu-PSMA-617.

CONCLUSION

This article provides an overview of the evolving treatment landscape of mCRPC, discussing guideline-recommended treatment options and data from key clinical trials, while highlighting ongoing trials that may impact the future treatment landscape. Recommendations for optimal treatment sequencing based on individual patient factors are provided.

Olaparib Combined with Abiraterone versus Olaparib Monotherapy for Patients with Metastatic Castration-resistant Prostate Cancer Progressing after Abiraterone and Harboring DNA Damage Repair Deficiency: A Multicenter Real-world Study

BACKGROUND AND OBJECTIVE

Olaparib + abiraterone has a combined antitumor effect in metastatic castration-resistant prostate cancer (mCRPC), but the efficacy of this combination in patients with DNA damage repair (DDR)-deficient mCRPC progressing after abiraterone is unknown. Our aim was to compare the efficacy of olaparib + abiraterone versus olaparib monotherapy for patients with DDR-deficient mCRPC progressing after abiraterone.

METHODS

The study included 86 consecutive patients with DDR-deficient mCRPC progressing after abiraterone: 34 received olaparib + abiraterone, and 52 received olaparib monotherapy. DDR-deficient status was defined as the presence of a DDR gene with a pathogenic or likely pathogenic variant (DDR-PV), or with a variant of unknown significance (DDR-VUS). We assessed progression-free survival (PFS) and overall survival (OS) using the Kaplan-Meier method. Potential factors influencing PFS and OS were compared between the treatment arms using Cox proportional-hazards models. The prostate-specific antigen (PSA) response, the treatment effect across subgroups, and adverse events (AEs) were also evaluated.

KEY FINDINGS AND LIMITATIONS

Median follow-up was 9 mo. In the overall cohort, median PFS and OS were significantly longer in the combination arm than in the monotherapy arm (PFS: 6.0 vs 3.0 mo; hazard ratio [HR] 0.41, 95% confidence interval [CI] 0.25-0.67; p < 0.01; OS: 25.0 vs 12.0 mo; HR 0.30, 95% CI 0.14-0.67; p < 0.01). PSA responses were significantly higher following combination therapy versus monotherapy. Combination therapy had significantly better efficacy in the DDR-PV and DDR-VUS subgroups, and was an independent predictor of better PFS and OS. AE rates were acceptable. The retrospective nature, small sample size, and short follow-up are limitations.

CONCLUSIONS

Olaparib + abiraterone resulted in better PFS and OS than olaparib alone for patients with DDR-deficient mCRPC progressing after abiraterone. These results need to be confirmed by a large-scale prospective randomized controlled trial.

PATIENT SUMMARY

Our study shows that the drug combination of olaparib plus abiraterone improved survival over olaparib alone for patients who have mutations in genes affecting DNA repair and metastatic prostate cancer resistant to hormone therapy. The results provide evidence of a synergistic effect of the two drugs in these patients.

Combination of the PARPi and ARSi in advanced castration resistant prostate cancer: a review of the recent phase III trials

Tumors with an impaired ability to repair DNA double-strand breaks by homologous recombination, including those with alterations in breast cancer 1 and 2 (BRCA1 and BRCA2) genes, are very sensitive to blocking DNA single-strand repair by inhibition of the poly (ADP-ribose) polymerase (PARP) enzyme. This provides the basis for a synthetic deadly strategy in the treatment of different types of cancer, such as prostate cancer (PCa). The phase 3 PROfound study was the first to lead to olaparib approval in patients with metastatic castration resistant PCa (mCRPC) and BRCA genes mutations. In recent years, the benefit of combination therapy consisted of a PARP inhibitor (PARPi) plus an androgen receptor signalling inhibitor (ARSi), was evaluated as first-line treatment of mCRPC, regardless of the mutational state of genes, participating in the homologous recombination repair (HRR). This review explores the role of PARPi in PCa and analyses the data of latest clinical trials exploring the PARPi-ARSi combinations, and how these results could change our clinical practice.

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.

Poly (ADP-ribose) Polymerase Inhibitors in Patients with Metastatic Castration-Resistant Prostate Cancer: A Meta-Analysis of Randomized Controlled Trials

Context: Several recent randomized controlled trials (RCTs) have reported on the survival benefits of poly (ADP-ribose) polymerase inhibitors (PARPi) compared to standard-of-care (SOC) treatment (enzalutamide, abiraterone, or docetaxel) in patients with metastatic castration-resistant prostate cancer (mCRPC). However, there is a limited integrated analysis of high-quality evidence comparing the efficacy and safety of PARPi and SOC treatments in this context. Objective: This study aims to comprehensively analyze the survival benefits and adverse events associated with PARPi and SOC treatments through a head-to-head meta-analysis in mCRPC. Evidence acquisition: A systematic review search was conducted in PubMed, Embase, Clinical trials, and the Central Cochrane Registry in July 2023. RCTs were assessed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The systematic review was prospectively registered on PROSPERO (CRD42023441034). Evidence synthesis: A total of 8 studies, encompassing 2341 cases in the PARPi treatment arm and 1810 cases in the controlled arm, were included in the qualitative synthesis. The hazard ratio (HR) for radiographic progression-free survival (rPFS) and overall survival (OS) were 0.74 (95% CI, 0.61-0.90) and 0.89 (95% CI, 0.80-0.99), respectively, in the intention-to-treatment patients. For subgroup analysis, HRs for rPFS and OS in the BRCA-mutated subgroup were 0.39 (95% CI, 0.28-0.55) and 0.62 (95% CI, 0.38-0.99), while in the HRR-mutated subgroup, HR for rPFS was 0.57 (95% CI, 0.48-0.69) and for OS was 0.77 (95% CI, 0.64-0.93). The odds ratio (OR) for all grades of adverse events (AEs) and AEs with severity of at least grade 3 were 3.86 (95% CI, 2.53-5.90) and 2.30 (95% CI, 1.63-3.26), respectively. Conclusions: PARP inhibitors demonstrate greater effectiveness than SOC treatments in HRR/BRCA-positive patients with mCRPC. Further research is required to explore ways to reduce adverse event rates and investigate the efficacy of HRR/BRCA-negative patients.

Olaparib plus Abiraterone for Metastatic Castration-resistant Prostate Cancer: Pharmacokinetics Data from the PROpel Trial

PROpel (NCT03732820) was a positive phase 3 trial that demonstrated a clinically significant improvement in radiographic progression-free survival with olaparib plus abiraterone versus placebo plus abiraterone in first-line metastatic castration-resistant prostate cancer. For a subset of PROpel patients, steady-state concentrations of olaparib, abiraterone, and Δ4-abiraterone were measured in blood samples collected before and at several time points after dose administration. The pharmacokinetics (PK) for each drug and metabolite were evaluated to determine whether any clinically relevant drug-drug interactions between olaparib and abiraterone occurred. The results demonstrate that steady-state PK parameters for olaparib and abiraterone in PROpel were comparable with those in monotherapy trials. Abiraterone steady-state exposures were similar between treatment arms. Δ4-Abiraterone had slightly lower steady-state exposures when abiraterone was administered in combination with olaparib. These results are consistent with a previous phase 2 study, supporting the conclusion that no clinically relevant PK-based drug-drug interactions occurred when olaparib and abiraterone were given in combination at their full monotherapy doses. PATIENT SUMMARY: When drugs are administered in combination, a key consideration is whether there are any interactions between the drugs that may affect their activity. We analyzed blood concentrations of olaparib and abiraterone in a subset of patients with prostate cancer from the PROpel trial to determine if there were interactions between these two drugs. We found that there was no significant effect on the profile of either drug when they were given together at the same doses used when each drug is given individually.

Double trouble for prostate cancer: synergistic action of AR blockade and PARPi in non-HRR mutated patients

Prostate cancer (PCa) is the most common cancer in men worldwide. Despite better and more intensive treatment options in earlier disease stages, a large subset of patients still progress to metastatic castration-resistant PCa (mCRPC). Recently, poly-(ADP-ribose)-polymerase (PARP)-inhibitors have been introduced in this setting. The TALAPRO-2 and PROpel trials both showed a marked benefit of PARPi in combination with an androgen receptor signaling inhibitor (ARSI), compared with an ARSI alone in both the homologous recombination repair (HRR)-mutated, as well as in the HRR-non-mutated subgroup. In this review, we present a comprehensive overview of how maximal AR-blockade via an ARSI in combination with a PARPi has a synergistic effect at the molecular level, leading to synthetic lethality in both HRR-mutated and HRR-non-mutated PCa patients. PARP2 is known to be a cofactor of the AR complex, needed for decompacting the chromatin and start of transcription of AR target genes (including HRR genes). The inhibition of PARP thus reinforces the effect of an ARSI. The deep androgen deprivation caused by combining androgen deprivation therapy (ADT) with an ARSI, induces an HRR-like deficient state, often referred to as "BRCA-ness". Further, PARPi will prevent the repair of single-strand DNA breaks, leading to the accumulation of DNA double-strand breaks (DSBs). Due to the induced HRR-deficient state, DSBs cannot be repaired, leading to apoptosis.