Dual roles of PARP-1 promote cancer growth and progression

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.

A bioactive fraction from the leaves of Ceiba pentandra (L.) Gaertn. exhibits antiproliferative activity via cell cycle arrest at the G1/S checkpoint and initiation of apoptosis via poly [ADP-ribose] polymerase 1 (PARP1) cleavage in HeLa cells

ETHNOPHARMACOLOGICAL RELEVANCE

Ceibapentandra (L.) Gaertn. (Malvaceae) has been used in Africa traditionally to manage a variety of illnesses, including cancer. The hydroethanolic extract of the leaves of C. pentandra has been shown to possess antiproliferative activity. However, the fractionation of antiproliferative bioactive constituents from the leaves of C. pentandra and the determination of the mechanisms of action of such bioactive constituents remain unexplored.

AIM OF THE STUDY

This work sought to fractionate the extract of C. pentandra leaves, establish the antiproliferative activity of the fractionated constituents, and determine the active constituents' possible mechanisms of action.

MATERIAL AND METHODS

Chromatographic techniques were used to fractionate bioactive constituents from C. pentandra leaves. The fractionated constituents were evaluated for their antiproliferative activity against four cancer cell lines (viz hepatocellular carcinoma, colorectal adenocarcinoma, cervical carcinoma, and mammary adenocarcinoma) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT)-based assay. The possible mechanisms of action of the active constituent, Fraction A (IsoA), were also determined via western blot analysis.

RESULTS

Six constituents were fractionated from the leaves of C. pentandra. Among the six constituents, IsoA stood out for its remarkable antiproliferative activity across the four cancer cell lines, with hepatocellular carcinoma (HepG2) cells being the most affected. With half-maximal inhibitory concentration (IC50) values ranging from 6.4±1.2 μg/mL to 19.2±3.4 μg/mL, IsoA demonstrated great potential in inhibiting cancer cell proliferation. Notably, IsoA's mechanisms of action involve critical molecular targets associated with cell cycle regulation and apoptosis. It significantly increased the levels of phosphorylated cyclin-dependent kinase 2 (Cdk2 pTyr15), a key regulator of cell cycle arrest, and cleaved poly [ADP-ribose] polymerase 1 (PARP1), a hallmark of apoptosis initiation. These findings underscore the therapeutic potential of IsoA in cancer treatment.

CONCLUSIONS

IsoA demonstrated highly promising in vitro antiproliferative activity by effectively arresting the cell cycle at the G1/S checkpoint, halting cancer cell proliferation. Additionally, IsoA induced programmed cell death (apoptosis) through mechanisms such as PARP1 cleavage, highlighting its potential as a candidate for cancer therapy.

Combination niraparib and abiraterone for HRR-altered metastatic castration-resistant prostate cancer

Metastatic prostate cancer remains incurable. Though significant progress has been made in the field, the search for agents that improve outcomes for patients is ongoing. Several clinical trials have explored the benefit of combining PARP inhibitors (PARPi) with androgen receptor pathway inhibitors (ARPIs) for metastatic castrate resistant prostate cancer (mCRPC), especially those cancers with alterations in homologous recombination repair (HRR) genes. Niraparib, a highly selective inhibitor of PARP1 and PARP2, has been shown to confer a radiographic progression-free survival benefit in the treatment of mCRPC with HRR-associated gene alterations, particularly BRCA1 and BRCA2 (BRCA1/2), when combined with abiraterone acetate plus prednisolone (AAP). This combination has recently been approved in the USA, Canada and Europe for patients with mCRPC and a BRCA1/2 gene mutation. This review summarizes the evidence with regards to the pharmacologic activity and clinical efficacy of niraparib with a specific focus on its efficacy in combination with AAP in mCRPC patients with HRR alterations.

Acute BRCAness Induction and AR Signaling Blockage through CDK12/7/9 Degradation Enhances PARP Inhibitor Sensitivity in Prostate Cancer

Current treatments for advanced prostate cancer (PCa) primarily target the androgen receptor (AR) pathway. However, the emergence of castration-resistant prostate cancer (CRPC) and resistance to AR pathway inhibitors (APSIs) remains ongoing challenges. Here, we present BSJ-5-63, a novel proteolysis-targeting chimera (PROTAC) targeting cyclin-dependent kinases (CDKs) CDK12, CDK7, and CDK9, offering a multi-pronged approach to CRPC therapy. BSJ-5-63 degrades CDK12, diminishing BRCA1 and BRCA2 expression and inducing a sustained "BRCAness" state. This sensitizes cancer cells to PARP inhibitors (PARPis) regardless of their homologous recombination repair (HRR) status. Furthermore, CDK7 and CDK9 degradation attenuates AR signaling, enhancing its therapeutic efficacy. Preclinical studies, including both in vitro and in vivo CRPC models, demonstrate that BSJ-5-63 exerts potent anti-tumor activity in both AR-positive and AR-negative setting. This study introduces BSJ-5-63 as a promising therapeutic agent that addresses both DNA repair and AR signaling mechanisms, with potential benefits for a board patient population.

AR coactivators, CBP/p300, are critical mediators of DNA repair in prostate cancer

Castration resistant prostate cancer (CRPC) remains an incurable disease stage with ineffective treatments options. Here, the androgen receptor (AR) coactivators CBP/p300, which are histone acetyltransferases, were identified as critical mediators of DNA damage repair (DDR) to potentially enhance therapeutic targeting of CRPC. Key findings demonstrate that CBP/p300 expression increases with disease progression and selects for poor prognosis in metastatic disease. CBP/p300 bromodomain inhibition enhances response to standard of care therapeutics. Functional studies, CBP/p300 cistrome mapping, and transcriptome in CRPC revealed that CBP/p300 regulates DDR. Further mechanistic investigation showed that CBP/p300 attenuation via therapeutic targeting and genomic knockdown decreases homologous recombination (HR) factors in vitro, in vivo, and in human prostate cancer (PCa) tumors ex vivo. Similarly, CBP/p300 expression in human prostate tissue correlates with HR factors. Lastly, targeting CBP/p300 impacts HR-mediate repair and patient outcome. Collectively, these studies identify CBP/p300 as drivers of PCa tumorigenesis and lay the groundwork to optimize therapeutic strategies for advanced PCa via CBP/p300 inhibition, potentially in combination with AR-directed and DDR therapies.

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.

Abiraterone, Olaparib, or Abiraterone + Olaparib in First-Line Metastatic Castration-Resistant Prostate Cancer with DNA Repair Defects (BRCAAway)

PURPOSE

Deleterious germline/somatic homologous recombination repair mutations (HRRm) are present in ∼25% of patients with metastatic castration-resistant prostate cancer (mCRPC). Preclinically, poly(ADP-ribose) polymerase (PARP) inhibition demonstrated synergism with androgen receptor pathway (ARP)-targeted therapy. This trial evaluated the efficacy of ARP inhibitor versus PARP inhibitor versus their combination as first-line therapy in patients with mCRPC with HRRms.

PATIENTS AND METHODS

BRCAAway is a biomarker preselected, randomized, phase 2 trial. Patients with BRCA1/2 and/or ATM alterations were randomized 1:1:1 to Arm1: abiraterone (1,000 mg)/prednisone (5 mg BID) (Abi/pred), Arm2: olaparib (300 mg BID) (Ola), or Arm3: abiraterone/prednisone + olaparib (Abi/pred + Ola). Single-agent arms could cross over at progression. Exploratory Arm4 patients with other HRRms received olaparib alone. The primary endpoint was progression-free survival (PFS), and secondary endpoints were objective response, PSA response, and safety.

RESULTS

Sixty-one of 165 eligible patients had BRCA1/2 or ATM mutations: median age: 67 (IQR, 62-73) years. Mutations: BRCA1 n = 3, BRCA2 n = 46, ATM n = 11, and multiple n = 1; 33 germline and 28 somatic mutations. Median PFS [95% confidence interval (CI)]: Abi/pred, 8.6 months (m; 2.9, 17), Ola, 14 m (8.4, 20), and Abi/pred + Ola, 39 m [22, not reached (NR)]. There were no G4/5 adverse events; 8/19 patients on Abi/pred treatment crossed over to Ola, and 8/21 vice versa. Median PFS (95% CI) from crossover: Ola-after-Abi/pred, 8.3 m (5.5, 15) and Abi/pred-after-Ola, 7.2 m (2.8, NR). Median PFS (95% CI) from randomization: Ola-after-Abi/pred, 16 m (7.8, 25) and Abi/pred-after-Ola, 16 m (11, NR). Seventeen of 165 patients with other HRRms received olaparib: median PFS (95% CI): 5.5 m (2, 11).

CONCLUSIONS

In patients with mCRPC with BRCA1/2 or ATM HRRm, Abi/pred + Ola was well tolerated and demonstrated longer PFS versus either agent alone or sequentially.

Combination of PARP Inhibitors and Androgen Receptor Pathway Inhibitors in Metastatic Castration-Resistant Prostate Cancer

Despite recent advances in the treatment of metastatic prostate cancer, progression to a castration-resistant state remains inevitable for most and prognosis is limited. Genetic testing for homologous recombination repair pathway alterations is recommended for all patients with advanced prostate cancer given that a mutation is present in up to 25% of cases. Poly(ADP-ribose) polymerase (PARPis) are now approved for use in patients with metastatic castration-resistant prostate cancer who have progressed on an androgen receptor pathway inhibitor (ARPI) and harbour a germline or somatic homologous recombination repair mutation. Preclinical data support a synergistic effect with an ARPI and PARPi, and various ARPI-PARPi combinations have therefore been explored in phase III clinical trials. Despite heterogeneous findings, a clear hierarchy of benefit is evident, with patients harbouring a BRCA mutation deriving the greatest magnitude of benefit, followed by any homologous recombination repair mutation. The benefit in homologous recombination repair-proficient cohort is less clear, and questions remain about whether ARPI-PARPi combination therapy should be offered to patients without a homologous recombination repair mutation. With ARPIs now considered standard-of-care for metastatic hormone-sensitive prostate cancer, ARPI-PARPi combination therapy is currently being explored earlier in the treatment paradigm. The purpose of this review is to discuss the rationale behind ARPI-PARPi combination therapy, summarise the results of key clinical trials, and discuss clinical considerations and future perspectives.

Acetylated KHSRP impairs DNA-damage-response-related mRNA decay and facilitates prostate cancer tumorigenesis

Androgen-regulated DNA damage response (DDR) is one of the essential mechanisms in prostate cancer (PCa), a hormone-sensitive disease. The heterogeneous nuclear ribonucleoprotein K (hnRNPK)-homology splicing regulatory protein known as far upstream element-binding protein 2 (KHSRP) is an RNA-binding protein that can attach to AU-rich elements in the 3' untranslated region (3'-UTR) of messenger RNAs (mRNAs) to mediate mRNA decay and emerges as a critical regulator in the DDR to preserve genome integrity. Nevertheless, how KHSRP responds to androgen-regulated DDR in PCa development remains unclear. This study found that androgen can significantly induce acetylation of KHSRP, which intrinsically drives tumor growth in xenografted mice. Moreover, enhanced KHSRP acetylation upon androgen stimuli impedes KHSRP-regulated DDR gene expression, as seen by analyzing RNA sequencing (RNA-seq) and Gene Set Enrichment Analysis (GSEA) datasets. Additionally, NAD-dependent protein deacetylase sirtuin-7 (SIRT7) is a promising deacetylase of KHSRP, and androgen stimuli impairs its interaction with KHSRP to sustain the increased KHSRP acetylation level in PCa. We first report the acetylation of KHSRP induced by androgen, which interrupts the KHSRP-regulated mRNA decay of the DDR-related genes to promote the tumorigenesis of PCa. This study provides insight into KHSRP biology and potential therapeutic strategies for PCa treatment, particularly that of castration-resistant PCa.

Veliparib exerts protective effects in intracerebral hemorrhage mice by inhibiting the inflammatory response and accelerating hematoma resolution

Poly (ADP-ribose) polymerase (PARP) inhibitors have potent anti-inflammatory effects, including the suppression of brain microglial activation. Veliparib, a well-known PARP1/2 inhibitor, exhibits particularly high brain penetration, but its effects on stroke outcome is unknown. Here, the effects of veliparib on the short-term outcome of intracerebral hemorrhage (ICH), the most lethal type of stroke, were investigated. Collagenase-induced mice ICH model was applied, and the T2-weighted magnetic resonance imaging was performed to evaluate lesion volume. Motor function and hematoma volume were also measured. We further performed immunofluorescence, enzyme linked immunosorbent assay, flow cytometry, and blood-brain barrier assessment to explore the potential mechanisms. Our results demonstrated veliparib reduced the ICH lesion volume dose-dependently and at a dosage of 5 mg/kg, veliparib significantly improved mouse motor function and promoted hematoma resolution at days 3 and 7 post-ICH. Veliparib inhibited glial activation and downregulated the production of pro-inflammatory cytokines. Veliparib significantly decreased microglia counts and inhibited peripheral immune cell infiltration into the brain on day 3 after ICH. Veliparib improved blood-brain barrier integrity at day 3 after ICH. These findings demonstrate that veliparib improves ICH outcome by inhibiting inflammatory responses and may represent a promising novel therapy for ICH.

Leveraging PARP-1/2 to Target Distant Metastasis

Poly (ADP-Ribose) Polymerase (PARP) inhibitors have changed the outcomes and therapeutic strategy for several cancer types. As a targeted therapeutic mainly for patients with BRCA1/2 mutations, PARP inhibitors have commonly been exploited for their capacity to prevent DNA repair. In this review, we discuss the multifaceted roles of PARP-1 and PARP-2 beyond DNA repair, including the impact of PARP-1 on chemokine signalling, immune modulation, and transcriptional regulation of gene expression, particularly in the contexts of angiogenesis and epithelial-to-mesenchymal transition (EMT). We evaluate the pre-clinical role of PARP inhibitors, either as single-agent or combination therapies, to block the metastatic process. Efficacy of PARP inhibitors was demonstrated via DNA repair-dependent and independent mechanisms, including DNA damage, cell migration, invasion, initial colonization at the metastatic site, osteoclastogenesis, and micrometastasis formation. Finally, we summarize the recent clinical advancements of PARP inhibitors in the prevention and progression of distant metastases, with a particular focus on specific metastatic sites and PARP-1 selective inhibitors. Overall, PARP inhibitors have demonstrated great potential in inhibiting the metastatic process, pointing the way for greater use in early cancer settings.

Therapeutic targeting of PARP with immunotherapy in acute myeloid leukemia

Targeting the poly (ADP-ribose) polymerase (PARP) protein has shown therapeutic efficacy in cancers with homologous recombination (HR) deficiency due to BRCA mutations. Only small fraction of acute myeloid leukemia (AML) cells carry BRCA mutations, hence the antitumor efficacy of PARP inhibitors (PARPi) against this malignancy is predicted to be limited; however, recent preclinical studies have demonstrated that PARPi monotherapy has modest efficacy in AML, while in combination with cytotoxic chemotherapy it has remarkable synergistic antitumor effects. Immunotherapy has revolutionized therapeutics in cancer treatment, and PARPi creates an ideal microenvironment for combination therapy with immunomodulatory agents by promoting tumor mutation burden. In this review, we summarize the role of PARP proteins in DNA damage response (DDR) pathways, and discuss recent preclinical studies using synthetic lethal modalities to treat AML. We also review the immunomodulatory effects of PARPi in AML preclinical models and propose future directions for therapy in AML, including combined targeting of the DDR and tumor immune microenvironment; such combination regimens will likely benefit patients with AML undergoing PARPi-mediated cancer therapy.

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.

Cancer organoids 2.0: modelling the complexity of the tumour immune microenvironment

The development of neoplasia involves a complex and continuous interplay between malignantly transformed cells and the tumour microenvironment (TME). Cancer immunotherapies targeting the immune TME have been increasingly validated in clinical trials but response rates vary substantially between tumour histologies and are often transient, idiosyncratic and confounded by resistance. Faithful experimental models of the patient-specific tumour immune microenvironment, capable of recapitulating tumour biology and immunotherapy effects, would greatly improve patient selection, target identification and definition of resistance mechanisms for immuno-oncology therapeutics. In this Review, we discuss currently available and rapidly evolving 3D tumour organoid models that capture important immune features of the TME. We highlight diverse opportunities for organoid-based investigations of tumour immunity, drug development and precision medicine.

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.

Recent advances in c-Met-based dual inhibitors in the treatment of cancers

The cellular-mesenchymal epithelial transition factor (c-Met) is a receptor tyrosine kinase (RTK) located on the 7q31 locus encoding the Met proto-oncogene and plays a critical role in regulating cell proliferation, metastasis, differentiation, and apoptosis through various signaling pathways. However, its aberrant activation and overexpression have been implicated in many human cancers. Therefore, c-Met is a promising target for cancer treatment. However, the anticancer effect of selective single-targeted drugs is limited due to the complexity of the signaling system and the involvement of different proteins and enzymes. After inhibiting one pathway, signal molecules can be transmitted through other pathways, resulting in poor efficacy of single-targeted drug therapy. Dual inhibitors that simultaneously block c-Met and another factor can significantly improve efficacy and overcome some of the shortcomings of single-target inhibitors, including drug resistance. In this review, We introduced c-Met kinase and the synergism between c-Met and other anti-tumor targets, then dual-target inhibitors based on c-Met for the treatment of cancers were summarized and their design concepts and structure-activity relationships (SARs) were discussed elaborately, providing a valuable insight for the further development of novel c-Met-based dual inhibitors.

New target therapies in prostate cancer: from radioligand therapy, to PARP-inhibitors and immunotherapy

Prostate cancer (PCa) remains a significant global health challenge, particularly in its advanced stages. Despite progress in early detection and treatment, PCa is the second most common cancer diagnosis among men. This review aims to provide an overview of current therapeutic approaches and innovations in PCa management, focusing on the latest advancements and ongoing challenges. We conducted a narrative review of clinical trials and research studies, focusing on PARP inhibitors (PARPis), phosphoinositide 3 kinase-protein kinase B inhibitors, immunotherapy, and radioligand therapies (RLTs). Data was sourced from major clinical trial databases and peer-reviewed journals. Androgen deprivation therapy and androgen-receptor pathway inhibitors remain foundational in managing castration-sensitive and early-stage castration-resistant PCa (CRPC). PARPi's, such as olaparib and rucaparib, have emerged as vital treatments for metastatic CRPC with homologous recombination repair gene mutations, highlighting the importance of personalized medicine. Immune checkpoint inhibitors (ICIs) have shown clinical benefit limited to specific subgroups of PCa, demonstrating significant improvement in efficacy in patients with microsatellite instability/mismatch repair or cyclin-dependent kinase 12 alteration, highlighting the importance of focusing ongoing research on identifying and characterizing these subgroups to maximize the clinical benefits of ICIs. RLTs have shown effectiveness in treating mCRPC. Different alpha emitters (like [225Ac]PSMA) and beta emitters compounds (like [177Lu]PSMA) impact treatment differently due to their energy transfer characteristics. Clinical trials like VISION and TheraP have demonstrated positive outcomes with RLT, particularly [177Lu]PSMA-617, leading to FDA approval. Ongoing trials and future perspectives explore the potential of [225Ac]PSMA, aiming to improve outcomes for patients with mCRPC. The landscape of PCa treatment is evolving, with significant advancements in both established and novel therapies. The combination of hormonal therapies, chemotherapy, PARPis, immunotherapy, and RLTs, guided by genetic and molecular insights, opens new possibilities for personalized treatment.

Therapeutic biomarkers in metastatic castration-resistant prostate cancer: does the state matter?

The treatment of metastatic castration-resistant prostate cancer (mCRPC) has been fundamentally transformed by our greater understanding of its complex biological mechanisms and its entrance into the era of precision oncology. A broad aim is to use the extreme heterogeneity of mCRPC by matching already approved or new targeted therapies to the correct tumor genotype. To achieve this, tumor DNA must be obtained, sequenced, and correctly interpreted, with individual aberrations explored for their druggability, taking into account the hierarchy of driving molecular pathways. Although tumor tissue sequencing is the gold standard, tumor tissue can be challenging to obtain, and a biopsy from one metastatic site or primary tumor may not provide an accurate representation of the current genetic underpinning. Sequencing of circulating tumor DNA (ctDNA) might catalyze precision oncology in mCRPC, as it enables real-time observation of genomic changes in tumors and allows for monitoring of treatment response and identification of resistance mechanisms. Moreover, ctDNA can be used to identify mutations that may not be detected in solitary metastatic lesions and can provide a more in-depth understanding of inter- and intra-tumor heterogeneity. Finally, ctDNA abundance can serve as a prognostic biomarker in patients with mCRPC.The androgen receptor (AR)-axis is a well-established therapeutical target for prostate cancer, and through ctDNA sequencing, insights have been obtained in (temporal) resistance mechanisms that develop through castration resistance. New third-generation AR-axis inhibitors are being developed to overcome some of these resistance mechanisms. The druggability of defects in the DNA damage repair machinery has impacted the treatment landscape of mCRPC in recent years. For patients with deleterious gene aberrations in genes linked to homologous recombination, particularly BRCA1 or BRCA2, PARP inhibitors have shown efficacy compared to the standard of care armamentarium, but platinum-based chemotherapy may be equally effective. A hierarchy exists in genes associated with homologous recombination, where, besides the canonical genes in this pathway, not every other gene aberration predicts the same likelihood of response. Moreover, evidence is emerging on cross-resistance between therapies such as PARP inhibitors, platinum-based chemotherapy and even radioligand therapy that target this genotype. Mismatch repair-deficient patients can experience a beneficial response to immune checkpoint inhibitors. Activation of other cellular signaling pathways such as PI3K, cell cycle, and MAPK have shown limited success with monotherapy, but there is potential in co-targeting these pathways with combination therapy, either already witnessed or anticipated. This review outlines precision medicine in mCRPC, zooming in on the role of ctDNA, to identify genomic biomarkers that may be used to tailor molecularly targeted therapies. The most common druggable pathways and outcomes of therapies matched to these pathways are discussed.

Homologous Recombination Repair Deficiency in Metastatic Prostate Cancer: New Therapeutic Opportunities

More than 20% of metastatic prostate cancer carries genomic defects involving DNA damage repair pathways, mainly in homologous recombination repair-related genes. The recent approval of olaparib has paved the way to precision medicine for the treatment of metastatic prostate cancer with PARP inhibitors in this subset of patients, especially in the case of BRCA1 or BRCA2 pathogenic/likely pathogenic variants. In face of this new therapeutic opportunity, many issues remain unsolved. This narrative review aims to describe the relationship between homologous recombination repair deficiency and prostate cancer, the techniques used to determine homologous recombination repair status in prostate cancer, the crosstalk between homologous recombination repair and the androgen receptor pathway, the current evidence on PARP inhibitors activity in metastatic prostate cancer also in homologous recombination repair-proficient tumors, as well as emerging mechanisms of resistance to PARP inhibitors. The possibility of combination therapies including a PARP inhibitor is an attractive option, and more robust data are awaited from ongoing phase II and phase III trials outlined in this manuscript.

PARP-ish: Gaps in Molecular Understanding and Clinical Trials Targeting PARP Exacerbate Racial Disparities in Prostate Cancer

PARP is a nuclear enzyme with a major function in the DNA damage response. PARP inhibitors (PARPi) have been developed for treating tumors harboring homologous recombination repair (HRR) defects that lead to a dependency on PARP. There are currently three PARPi approved for use in advanced prostate cancer (PCa), and several others are in clinical trials for this disease. Recent clinical trial results have reported differential efficacy based on the specific PARPi utilized as well as patient race. There is a racial disparity in PCa, where African American (AA) males are twice as likely to develop and die from the disease compared to European American (EA) males. Despite the disparity, there continues to be a lack of diversity in clinical trial cohorts for PCa. In this review, PARP nuclear functions, inhibition, and clinical relevance are explored through the lens of racial differences. This review will touch on the biological variations that have been explored thus far between AA and EA males with PCa to offer rationale for investigating PARPi response in the context of race at both the basic science and the clinical development levels.

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.

TALAPRO-3 clinical trial protocol: phase III study of talazoparib plus enzalutamide in metastatic castration-sensitive prostate cancer

Poly(ADP-ribose) polymerase inhibitors in combination with androgen-receptor signaling inhibitors are a promising therapeutic option for patients with metastatic castration-sensitive prostate cancer (mCSPC) and homologous recombination repair (HRR) gene alterations. Here, we describe the design and rationale of the multinational, phase III, TALAPRO-3 study comparing talazoparib plus enzalutamide versus placebo plus enzalutamide in patients with mCSPC and HRR gene alterations. The primary end point is investigator-assessed radiographic progression-free survival (rPFS) per RECIST 1.1 in soft tissue, or per PCWG3 criteria in bone. The TALAPRO-3 study will demonstrate whether the addition of talazoparib can improve the efficacy of enzalutamide as assessed by rPFS in patients with mCSPC and HRR gene alterations undergoing androgen deprivation therapy. Clinical Trial Registration:NCT04821622 (ClinicalTrials.gov) Registry Name: Study of Talazoparib With Enzalutamide in Men With DDR Gene Mutated mCSPC. Date of Registration: 29 March 2021.

Predictive and prognostic biomarkers in urological tumours

Advancements in cutting-edge molecular profiling techniques, such as next-generation sequencing and bioinformatic analytic tools, have allowed researchers to examine tumour biology in detail and stratify patients based on factors linked with clinical outcome and response to therapy. This manuscript highlights the most relevant prognostic and predictive biomarkers in kidney, bladder, prostate and testicular cancers with recognised impact in clinical practice. In bladder and prostate cancer, new genetic acquisitions concerning the biology of tumours have modified the therapeutic scenario and led to the approval of target directed therapies, increasing the quality of patient care. Thus, it has become of paramount importance to choose adequate molecular tests, i.e., FGFR screening for urothelial cancer and BRCA1-2 alterations for prostate cancer, to guide the treatment plan for patients. While no tissue or blood-based biomarkers are currently used in routine clinical practice for renal cell carcinoma and testicular cancers, the field is quickly expanding. In kidney tumours, gene expression signatures might be the key to identify patients who will respond better to immunotherapy or anti-angiogenic drugs. In testicular germ cell tumours, the use of microRNA has outperformed conventional serum biomarkers in the diagnosis of primary tumours, prediction of chemoresistance, follow-up monitoring, and relapse prediction.

PARP inhibitors for prostate cancer

Poly(ADP-ribose) polymerase (PARP) inhibitors have transformed the treatment landscape for patients with metastatic castration-resistant prostate cancer (mCRPC) and alterations in DNA damage response genes. This has also led to widespread use of genomic testing in all patients with mCRPC. The current review will give an overview of (1) the current understanding of the interplay between DNA damage response and PARP enzymes; (2) the clinical landscape of PARP inhibitors, including the combination of PARP inhibitors with other agents such as androgen-receptor signaling agents; (3) biomarkers related to PARP inhibitor response and resistance; and (4) considerations for interpreting genomic testing results and treating patients with PARP inhibitors.

PARP Inhibitors in Metastatic Castration-Resistant Prostate Cancer: Unraveling the Therapeutic Landscape

The treatment landscape of metastatic prostate cancer (mPCa) is rapidly evolving with the recent approvals of poly-ADP ribose polymerase inhibitors (PARPis) as monotherapy or as part of combination therapy with androgen receptor pathway inhibitors in patients with metastatic castration-resistant prostate cancer (mCRPC). Already part of the therapeutic armamentarium in different types of advanced cancers, these molecules have shaped a new era in mPCa by targeting genomic pathways altered in these patients, leading to promising responses. These agents act by inhibiting poly-ADP ribose polymerase (PARP) enzymes involved in repairing single-strand breaks in the DNA. Based on the PROfound and TRITON3 trials, olaparib and rucaparib were respectively approved as monotherapy in pretreated patients with mCRPC and alterations in prespecified genes. The combinations of olaparib with abiraterone (PROpel) and niraparib with abiraterone (MAGNITUDE) were approved as first-line options in patients with mCRPC and alterations in BRCA1/2, whereas the combination of talazoparib with enzalutamide (TALAPRO-2) was approved in the same setting in patients with alterations in any of the HRR genes, which are found in around a quarter of patients with advanced prostate cancer. Additional trials are already underway to assess these agents in an earlier hormone-sensitive setting. Future directions will include refining the treatment sequencing in patients with mCRPC in the clinic while taking into account the financial toxicity as well as the potential side effects encountered with these therapies and elucidating their mechanism of action in patients with non-altered HRR genes. Herein, we review the biological rationale behind using PARPis in mCRPC and the key aforementioned clinical trials that paved the way for these approvals.

Development of PARP inhibitors in advanced prostate cancer

The relatively high prevalence of alterations in the homologous recombination repair (HRR) pathway described in advanced prostate cancer provides a unique opportunity to develop therapeutic strategies that take advantage of the decreased tumor ability to repair DNA damage. Poly ADP-ribose polymerase (PARP) inhibitors have been demonstrated to improve the outcomes of metastatic castration-resistant prostate cancer (mCRPC) patients with HRR defects, particularly in those with BRCA1/2 alterations. To expand the benefit of PARPi to patients without detectable HRR alterations, multiple studies are addressing potential synergies between PARP inhibition (PARPi) and androgen receptor pathway inhibitors (ARSi), radiation, radioligand therapy, chemotherapy, or immunotherapy, and these strategies are also being evaluated in the hormone-sensitive setting. In this review, we summarize the development of PARPi in prostate cancer, the potential synergies, and combinations being investigated as well as the future directions of PARPi for the management of the disease.

First-line talazoparib with enzalutamide in HRR-deficient metastatic castration-resistant prostate cancer: the phase 3 TALAPRO-2 trial

Preclinical evidence has suggested an interplay between the androgen receptor, which largely drives the growth of prostate cancer cells, and poly(ADP-ribose) polymerase. This association provides a rationale for their co-inhibition for the treatment of metastatic castration-resistant prostate cancer (mCRPC), an area of unmet medical need. The phase 3 TALAPRO-2 study investigated combining the poly(ADP-ribose) polymerase inhibitor talazoparib with enzalutamide versus enzalutamide alone as first-line treatment of mCRPC. Patients were prospectively assessed for tumor alterations in DNA damage response genes involved in homologous recombination repair (HRR). Two cohorts were enrolled sequentially: an all-comers cohort that was enrolled first (cohort 1; N = 805 (169 were HRR-deficient)), followed by an HRR-deficient-only cohort (cohort 2; N = 230). We present results from the alpha-controlled primary analysis for the combined HRR-deficient population (N = 399). Patients were randomized in a 1:1 ratio to talazoparib or placebo, plus enzalutamide. The primary endpoint, radiographic progression-free survival, was met (median not reached at the time of the analysis for the talazoparib group versus 13.8 months for the placebo group; hazard ratio, 0.45; 95% confidence interval, 0.33 to 0.61; P < 0.0001). Data for overall survival, a key secondary endpoint, are immature but favor talazoparib (hazard ratio, 0.69; 95% confidence interval, 0.46 to 1.03; P = 0.07). Common adverse events in the talazoparib group were anemia, fatigue and neutropenia. Combining talazoparib with enzalutamide significantly improved radiographic progression-free survival in patients with mCRPC harboring HRR gene alterations, supporting talazoparib plus enzalutamide as a potential first-line treatment for these patients. ClinicalTrials.gov Identifier: NCT03395197 .

PARP inhibitors alone or in combination for prostate cancer

DNA repair genomic aberrations in the Homologous Recombination pathway are identifiable in up to 25% of patients with advanced prostate cancer, making them more likely to benefit from treatment with poly (ADP-ribose) polymerase inhibitors (PARPi) alone or in combination with other therapies, particularly when BRCA driver genomic aberrations are documented. Although several clinical trials have demonstrated the efficacy of this approach, the validation of reliable biomarkers predictive of response still needs further improvement to refine patient selection. In this setting, the characterization of resistance mechanisms and the validation of novel biomarkers are critical to maximize clinical benefit and to develop novel treatment combinations to improve outcomes. In this review, we summarize the development of PARPi in prostate cancer as single agent as well as the efficacy of their combination with other drugs, and the future directions for their implementation in the management of advanced prostate cancer.

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.

Combining Novel Hormonal Therapies with a Poly (ADP-Ribose) Polymerase Inhibitor for Metastatic Castration-Resistant Prostate Cancer: Emerging Evidence

Preclinical and clinical studies have suggested potential synergies of combining poly (ADP-ribose) polymerase (PARP) inhibitors and novel hormonal therapies (NHT) for patients with metastatic castration-resistant prostate cancer (mCRPC). We systematically searched PubMed, ClinicalTrials.gov and ASCO-GU annual meeting abstracts up to March 2023 to identify potential phase III trials reporting the use of combining PARP inhibitors with NHT in the first-line setting for mCRPC. A total of four phase III trials met the criteria for subsequent review. Emerging data suggested that the radiographic progression-free survival (rPFS) was significantly longer in the PARP inhibitor combined with NHT group versus the placebo plus NHT group for the first-line setting of biomarker-unselected mCRPC patients, especially for patients with homologous recombination repair (HRR) mutation (HRR m), and with the greatest benefit for BRCA1/2 mutation (BRCA1/2 m) populations. Final overall survival (OS) data of the PROpel trial indicated a significant improvement in median OS for mCRPC patients with HRR m and BRCA1/2 m receiving olaparib + abiraterone. Prior taxane-based chemotherapy might not influence the efficacy of the combination. Compared with the current standard-of-care therapies, combining NHT with PARP inhibitors could achieve a significant survival benefit in the first-line setting for mCRPC patients with HRR and BRCA1/2 mutations.

Determining magnitude of benefit from poly(ADP-ribose) polymerase inhibitors in prostate cancer

The treatment landscape for castration-resistant prostate cancer (mCRPC) is undergoing significant advancements, particularly with the emergence of poly(ADP-ribose) polymerase inhibitors and their recent US FDA authorizations. The combination of olaparib with abiraterone and prednisone/prednisolone has gained approval for mCRPC patients harboring confirmed BRCA mutations. Subsequently, talazoparib in combination with enzalutamide was approved for patients with mutations in homologous recombination repair genes. Nevertheless, emerging evidence suggests that these treatments may confer benefits irrespective of specific biomarkers. While the understanding of biomarkers in therapy selection for mCRPC is expanding, further data are warranted to provide comprehensive elucidation for guiding clinical practice.

The Androgen Receptor Does Not Directly Regulate the Transcription of DNA Damage Response Genes

The clinical success of combined androgen deprivation therapy (ADT) and radiotherapy (RT) in prostate cancer created interest in understanding the mechanistic links between androgen receptor (AR) signaling and the DNA damage response (DDR). Convergent data have led to a model where AR both regulates, and is regulated by, the DDR. Integral to this model is that the AR regulates the transcription of DDR genes both at a steady state and in response to ionizing radiation (IR). In this study, we sought to determine which immediate transcriptional changes are induced by IR in an AR-dependent manner. Using PRO-seq to quantify changes in nascent RNA transcription in response to IR, the AR antagonist enzalutamide, or the combination of the two, we find that enzalutamide treatment significantly decreased expression of canonical AR target genes but had no effect on DDR gene sets in prostate cancer cells. Surprisingly, we also found that the AR is not a primary regulator of DDR genes either in response to IR or at a steady state in asynchronously growing prostate cancer cells.

IMPLICATIONS

Our data indicate that the clinical benefit of combining ADT with RT is not due to direct AR regulation of DDR gene transcription, and that the field needs to consider alternative mechanisms for this clinical benefit.

Poly(adenosine diphosphate-ribose) polymerase inhibitor combinations in first-line metastatic castrate-resistant prostate cancer setting: a systematic review and meta-analysis

OBJECTIVES

To compare radiographic progression-free survival (rPFS), overall survival (OS), and treatment-emergent adverse events (TEAEs) among patients with metastatic castrate-resistant prostate cancer (mCRPC) receiving a combination of first-line poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) plus androgen receptor axis-targeted agents (ARAT) vs placebo/ARAT.

MATERIALS AND METHODS

We conducted a systematic review/meta-analysis of all published Phase III randomised controlled trials using EMBASE, MEDLINE, and Cochrane (inception until 6 June 2023). Published full-text manuscripts and conference abstracts were inclusion eligible. Study selection/data extraction were independently performed by two authors. The Cochrane Risk-of-Bias 2 Tool was used, and certainty of evidence assessed using the Grading of Recommendations, Assessment, Development, and Evaluations framework. Pooled hazard ratios (HRs) and relative risks, with corresponding confidence intervals (CIs), were generated using random-effects models.

RESULTS

Three trials were identified: PROpel, MAGNITUDE, and TALAPRO-2. Compared to placebo/ARAT, the PARPi/ARAT combination was associated with a 35% rPFS improvement in the overall cohort (HR 0.65, 95% CI 0.56-0.76), with 68%, 45%, and 26% improvements in the BReast CAncer gene 1/gene 2 (BRCA1/2)-mutated (BRCA1/2m; P < 0.001), homologous recombination repair-mutated (HRRm; P < 0.001), and non-HRRm cohorts (P = 0.003), respectively. OS data maturity ranged from 31% to 48%, with overall cohort OS data unavailable from MAGNITUDE. The PROpel/TALAPRO-2 pooled analysis demonstrated a 16% OS improvement in the overall cohort (HR 0.84, 95 CI 0.72-0.98; P = 0.02). OS in the HRRm (HR 0.76, 95% CI 0.61-0.95) and the BRCA1/2m cohorts (HR 0.53, 95% CI 0.18-1.56) were improved, with a higher effect magnitude compared to the overall cohort. This combination was associated with a 45% relative risk increase in Grade ≥3 TEAEs, including 6.22-fold for Grade ≥3 anaemia (31.9% vs 4.9%).

CONCLUSIONS

The addition of PARPi to ARAT in the first-line mCRPC setting is associated with rPFS benefits across subgroups, with the greatest magnitude of benefit in BRCA1/2m patients. OS benefits remain inconsistent irrespective of HRRm status, with significant increases in Grade ≥3 TEAEs, particularly anaemia. Currently, we suggest this combined approach be selectively offered to HRRm patients, preferentially BRCA1/2m.

A review of biological targets and therapeutic approaches in the management of triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is a heterogeneous, aggressive phenotype of breast cancer with associated chemoresistance. The development of chemo- or radioresistance could be attributed to diverse tumor microenvironments, overexpression of membrane proteins (transporters), epigenetic changes, and alteration of the cell signaling pathways/genes associated with the development of cancer stem cells (CSCs).

AIM OF REVIEW

Due to the diverse and heterogeneous nature of TNBC, therapeutic response to the existing modalities offers limited scope and thus results in reccurance after therapy. To establish landmark therapeutic efficacy, a number of novel therapeutic modalities have been proposed. In addition, reversal of the resistance that developed during treatment may be altered by employing appropriate therapeutic modalities. This review aims to discuss the plethora of investigations carried out, which will help readers understand and make an appropriate choice of therapy directed toward complete elimination of TNBC.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This manuscript addresses the major contributory factors from the tumor microenvironment that are responsible for the development of chemoresistance and poor prognosis. The associated cellular events and molecular mechanism-based therapeutic interventions have been explained in detail. Inhibition of ABC transporters, cell signaling pathways associated with CSCs, and epigenetic modification offers promising results in this regard. TNBC progression, invasion, metastasis and recurrence can also be inhibited by blocking multiple cell signaling pathways, targeting specific receptors/epigenetic targets, disrupting bioenergetics and generating reactive oxygen species (ROS).

Enzalutamide combination with Arsenic trioxide suppresses the progression of castration-resistant prostate cancer

The study aimed to investigate the anti-tumor effects and underlying mechanisms of Enzalutamide (ENZ) and Arsenic trioxide (ATO) co-treatment on castration-resistant prostate cancer (CRPC). The effects on C4-2B cells were initially evaluated by colony formation assay, FACS analysis, and DNA fragmentation detection. Bioinformatics methods including mRNA-sequencing and gene enrichment analysis were used to screen the underlying target genes and pathways related to their actions. Western blot was employed to assess the expression levels of protein-related angiogenesis, apoptosis, DNA repair, and the screened genes. Finally, the effects were further verified in subcutaneous tumor models and tissue sections from the xenografts. It was found that not only could ENZ combination with ATO significantly inhibit cell proliferation and angiogenesis, but also induce cell arrest and apoptosis in C4-2B cells. In addition, interruption of the DNA damage repair-related pathways also occurred as a result of their combined effects. Western blot analysis further suggested that proteins involved in these pathways, especially P-ATR and P-CHEK1 were significantly reduced. In addition, their combination also inhibited the tumor growth of xenografts. Altogether, ENZ combination with ATO synergistically improved the therapeutic effects and suppressed CRPC progression through regulation of the ATR-CHEK1-CDC25C pathway.

Small molecule tractable PARP inhibitors: Scaffold construction approaches, mechanistic insights and structure activity relationship

Diverse drug design strategies viz. molecular hybridization, substituent installation, scaffold hopping, isosteric replacement, high-throughput screening, induction and separation of chirality, structure modifications of phytoconstituents and use of structural templates have been exhaustively leveraged in the last decade to load the chemical toolbox of PARP inhibitors. Resultantly, numerous promising scaffolds have been pinpointed that in turn have led to the resuscitation of the credence to PARP inhibitors as cancer therapeutics. This review briefly presents the physiological functions of PARPs, the pharmacokinetics, and pharmacodynamics, and the interaction profiles of FDA-approved PARP inhibitors. Comprehensively covered is the section on the drug design strategies employed by drug discovery enthusiasts for furnishing PARP inhibitors. The impact of structural variations in the template of designed scaffolds on enzymatic and cellular activity (structure-activity relationship studies) has been discussed. The insights gained through the biological evaluation such as profiling of physicochemical properties andin vitroADME properties, PK assessments, and high-dose pharmacology are covered.

Mechanistic Insights on Localized to Metastatic Prostate Cancer Transition and Therapeutic Opportunities

Prostate cancer is the most common non-cutaneous cancer among American men. Multiple mechanisms are involved in tumorigenesis and progression to metastases. While androgen deprivation therapy remains the cornerstone of treatment, progression to castration-resistant disease becomes inevitable. Aberrant pathway activations of PI3K/AKT due to PTEN loss, epithelial-mesenchymal transition pathways, homologous recombination repair, and DNA repair pathway mechanisms of resistance and cross-talk lead to opportunities for therapeutic targeting in metastatic castration-resistant prostate cancer. This review focuses on mechanisms of progression and key trials that evaluate the drugs and combinations that exploit these pathways.

PARPing up the right tree; an overview of PARP inhibitors for metastatic castration-resistant prostate cancer

PARP inhibitors (PARPi) are transforming the current treatment landscape of metastatic castration-resistant prostate cancer. By reanalysing published data on olaparib, talazoparib, rucaparib and niraparib, we provide a concise overview of responses by molecular subgroup. As monotherapy, all PARPi showed comparable efficacy and the same hierarchy in responsiveness: patients with tumours harbouring aberrations in BRCA1 or BRCA2 (BRCAm) evidently demonstrate superior responses when compared to aberrations in other homologous recombination repair (HRR) related genes. Niraparib seems to cause more grade ≥3 adverse events in comparison to other PARPi. PARPi have also been combined with androgen-receptor signalling inhibitors (ARSI) for both patients with tumours harbouring aberrations in HRR genes (HRRm), and molecularly unselected patients. Compared to wildtype, BRCAm patients responded best, followed by HRRm. Olaparib-abiraterone, niraparib-abiraterone, and talazoparib-enzalutamide all prolonged progression-free survival compared to an ARSI alone in HRRm patients. In the non-HRRm subgroup, only olaparib-abiraterone and talazoparib-enzalutamide were effective. Results for the combination of rucaparib with enzalutamide are yet to be reported. The rate of grade ≥3 adverse events for the combination regimens is 10-30% higher when compared to an ARSI alone. Given the limited efficacy in unselected patients, these PARPi-ARSI combinations may be best reserved for selected patients.

Poly (ADP-Ribose) polymerase 1 and parthanatos in neurological diseases: From pathogenesis to therapeutic opportunities

Poly (ADP-ribose) polymerase-1 (PARP-1) is the most extensively studied member of the PARP superfamily, with its primary function being the facilitation of DNA damage repair processes. Parthanatos is a type of regulated cell death cascade initiated by PARP-1 hyperactivation, which involves multiple subroutines, including the accumulation of ADP-ribose polymers (PAR), binding of PAR and apoptosis-inducing factor (AIF), release of AIF from the mitochondria, the translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and massive MIF-mediated DNA fragmentation. Over the past few decades, the role of PARP-1 in central nervous system health and disease has received increasing attention. In this review, we discuss the biological functions of PARP-1 in neural cell proliferation and differentiation, memory formation, brain ageing, and epigenetic regulation. We then elaborate on the involvement of PARP-1 and PARP-1-dependant parthanatos in various neuropathological processes, such as oxidative stress, neuroinflammation, mitochondrial dysfunction, excitotoxicity, autophagy damage, and endoplasmic reticulum (ER) stress. Additional highlight contains PARP-1's implications in the initiation, progression, and therapeutic opportunities for different neurological illnesses, including neurodegenerative diseases, stroke, autism spectrum disorder (ASD), multiple sclerosis (MS), epilepsy, and neuropathic pain (NP). Finally, emerging insights into the repurposing of PARP inhibitors for the management of neurological diseases are provided. This review aims to summarize the exciting advancements in the critical role of PARP-1 in neurological disorders, which may open new avenues for therapeutic options targeting PARP-1 or parthanatos.

Advances in the treatment of metastatic prostate cancer

The field of metastatic prostate cancer (mPCa) has seen unprecedented therapeutic advances in the past decade. In the past 2 years, recent approvals include the triplet therapy regimens of androgen deprivation therapy (ADT), docetaxel, and an androgen receptor (AR) pathway inhibitor (ARPI) in the castration-sensitive setting and lutetium-177 vipivotide tetraxetan (177Lu-PSMA-617) and the combination of poly(ADP) ribose polymerase (PARP) inhibitors (PARPis) and ARPIs in the castration-resistant setting. With many agents currently undergoing investigation in registration trials, the therapeutic armamentarium will expand rapidly, making treatment selection and sequencing challenging. Herein, we review the landmark clinical trials ongoing or reported in the past 2 years, discuss the optimal approach to treatment selection, and provide insight into future directions.

The biology behind combining poly [ADP ribose] polymerase and androgen receptor inhibition for metastatic castration-resistant prostate cancer

For about a decade, poly [ADP ribose] polymerases (PARP) inhibitors have been used almost exclusively to treat tumours that are deficient in one of the BRCA genes. In advanced prostate cancer, which is largely driven by the activity of the androgen receptor (AR), accumulating preclinical evidence has suggested an interplay between the AR and PARP, which could be therapeutically exploited independently of defects in the tumour's DNA homologous recombination repair (HRR) machinery. This includes the regulation of HRR genes by the AR, a mutual influence between the activities of PARP and the AR, and the co-localisation of BRCA2 to the retinoblastoma gene in the human genome. Based on these findings, randomised clinical trials have been initiated to study the addition of a PARP inhibitor to AR pathway inhibitor therapy. Three of four randomised studies demonstrated a significantly increased anti-tumour activity in men with metastatic prostate cancer, irrespective of HRR gene alterations. In this review, we summarise the available preclinical evidence that provides the rationale for the combination of inhibitors for PARP and the AR and discuss how it might contribute to the efficacy observed in the clinic.

Systemic Therapies for Metastatic Castration-Resistant Prostate Cancer: An Updated Review

The introduction of novel therapeutic agents for advanced prostate cancer has led to a wide range of treatment options for patients with metastatic castration-resistant prostate cancer (mCRPC). In the past decade, new treatment options for mCRPC, including abiraterone, enzalutamide, docetaxel, cabazitaxel, sipuleucel-T, radium-223, 177Lu-PSMA-617, and Olaparib, have demonstrated a survival benefit in phase 3 trials. Bone-modifying agents have become part of the overall treatment strategy for mCRPC, in which denosumab and zoledronic acid reduce skeletal-related events. Recently, androgen receptor-signaling inhibitors (ARSIs) and docetaxel have been used upfront against metastatic castration-sensitive prostate cancer. Further, triplet therapy with ARSI, docetaxel, and androgen deprivation therapy is emerging. However, cross-resistance may occur between these treatments, and the optimal treatment sequence must be considered. The sequential administration of ARSIs, such as abiraterone and enzalutamide, is associated with limited efficacy; however, cabazitaxel is effective for patients with mCRPC who were previously treated with docetaxel and had disease progression during treatment with ARSI. Radioligand therapy with 177Lu-PSMA-617 is a new effective class of therapy for patients with advanced PSMA-positive mCRPC. Tumors with gene alterations that affect homologous recombination repair, such as BRCA1 and BRCA2 alterations, are sensitive to poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors in mCRPC. This review sought to highlight recent advances in systemic therapy for mCRPC and strategies to support patient selection and treatment sequencing.

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.

Targeted Therapy for Cancers: From Ongoing Clinical Trials to FDA-Approved Drugs

The development of targeted therapies has revolutionized cancer treatment, offering improved efficacy with reduced side effects compared with traditional chemotherapy. This review highlights the current landscape of targeted therapy in lung cancer, colorectal cancer, and prostate cancer, focusing on key molecular targets. Moreover, it aligns with US Food and Drug Administration (FDA)-approved drugs and drug candidates. In lung cancer, mutations in the epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) gene rearrangements have emerged as significant targets. FDA-approved drugs like osimertinib and crizotinib specifically inhibit these aberrant pathways, providing remarkable benefits in patients with EGFR-mutated or ALK-positive lung cancer. Colorectal cancer treatment has been shaped by targeting the vascular endothelial growth factor (VEGF) and EGFR. Bevacizumab and cetuximab are prominent FDA-approved agents that hinder VEGF and EGFR signaling, significantly enhancing outcomes in metastatic colorectal cancer patients. In prostate cancer, androgen receptor (AR) targeting is pivotal. Drugs like enzalutamide, apalutamide, and darolutamide effectively inhibit AR signaling, demonstrating efficacy in castration-resistant prostate cancer. This review further highlights promising targets like mesenchymal-epithelial transition (MET), ROS1, BRAF, and poly(ADP-ribose) polymeras (PARP) in specific cancer subsets, along with ongoing clinical trials that continue to shape the future of targeted therapy.

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.

An overview of hormonal directed pharmacotherapy for the treatment of prostate cancer

INTRODUCTION

Prostate cancer is the most common malignancy in the male. Androgen-deprivation therapy (ADT) has been the mainstay in the treatment of metastatic prostate cancer however, due to the outgrowth of castration-resistant cell population the disease inevitably progresses to an aggressive, difficult to handle stage.

AREAS COVERED

We have reviewed the literature regarding hormonal-directed therapy prostate cancer. New agents, namely abiraterone acetate, combined with prednisone, and next generation antiandrogens (enzalutamide, apalutamide and darolutamide) have shown considerable efficacy, not only in patients with metastatic but also in those with non-metastatic disease, either castration resistant (CRPC) or hormone sensitive (HSPC).

EXPERT OPINION

The addition of abiraterone and of the second-generation antiandrogens to our therapeutic armamentarium has improved prognosis ofprostate cancer in the last decade. Abiraterone is a viable option in patients with metastatic disease (hormone-sensitive and castration-resistant), whereas all next-generation antiandrogens have demonstrated efficacy in terms of metastasis-free and overall survival in non-metastatic CRPC. In addition, enzalutamide has also been found efficacious in mCRPC and mHSPC, while apalutamide in mHSPC. Currently there are no reliable data to indicate a potential superiority of one of these agents over the others in CRPC or HSPC as there are no relevant head to head studies . Sequencing hormone treatment modalities, chemotherapies and immunotherapies have not reached a consensus as yet. Randomized controlled trials are warranted to clearly define the role of novel antiandrogens in the treatment of prostate cancer. The choice of treatment should be individualized following discussion with the patient .

PARP Inhibitors for Prostate Cancer: Tangled up in PROfound and PROpel (and TALAPRO-2) Blues

The combination of PARP and androgen receptor signalling inhibitors is best reserved for cases for which we expect an overall survival benefit on the basis of disease biology. The data to date should encourage us to perform more, not less, testing for DNA repair defects.

Increased SIRT3 combined with PARP inhibition rescues motor function of SBMA mice

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease with substantial mitochondrial and metabolic dysfunctions. SBMA is caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Activating or increasing the NAD+-dependent deacetylase, SIRT3, reduced oxidative stress and death of cells modeling SBMA. However, increasing diminished SIRT3 in AR100Q mice failed to reduce acetylation of the SIRT3 target/antioxidant, SOD2, and had no effect on increased total acetylated peptides in quadriceps. Yet, overexpressing SIRT3 resulted in a trend of motor recovery, and corrected TCA cycle activity by decreasing acetylation of SIRT3 target proteins. We sought to boost blunted SIRT3 activity by replenishing diminished NAD+ with PARP inhibition. Although NAD+ was not affected, overexpressing SIRT3 with PARP inhibition fully restored hexokinase activity, correcting the glycolytic pathway in AR100Q quadriceps, and rescued motor endurance of SBMA mice. These data demonstrate that targeting metabolic anomalies can restore motor function downstream of polyQ-expanded AR.