Project description:Two PARP inhibitors (PARPi) olaparib and talazoparib have been approved in combination with novel-hormonal-therapies (NHTs) for the treatment of metastatic castration resistant prostate cancer (mCRPC) – in Europe independent of the HRR status. However, the underlying mechanism of action in HRR negative patients is still not fully understood. In the current study, we revealed that combining PARPi (olaparib or talazoparib) with NHTs (abiraterone, enzalutamide, or apalutamide) significantly reduced cell survival in HS LNCaP and CR DU145 and 22RV1 PCa cell lines. While PDOs did not respond to olaparib alone, talazoparib mono-treatment reduced survival >2-fold in one LN-metastatic PDO and marginally (1.1-fold) in the other two. NHTs using abiraterone, enzalutamide or apalutamide all significantly reduced survival in the two LN-metastatic PDOs but were ineffective in the bone-metastatic PDOs. Importantly, the combination of any of the PARPi with any of the NHTs demonstrated significantly greater cytotoxic effects across all PDOs. None of these PDOs displayed a profile typically linked to BRCAness, as identified by the HRDetect score. Sequential (NHT followed by PARPi) and simultaneous treatment strategies yielded comparable results. Transcriptomic and immunoblotting analyses revealed that NHTs downregulate the homologous recombination repair gene RAD51, inducing a "BRCAness-like" phenotype characterized by reduced RAD51 foci formation at DNA double-strand break (DSB) sites, and sensitizing tumor cells to PARPi. Consistently, among the LN-metastatic TSCs, 67% exhibited a substantial reduction in DSB repair capacity when treated with the combined regime compared to monotherapies. Further, proteomic analyses indicate that olaparib may suppress metastasis by inhibiting key pro-metastatic pathways, including epithelial-mesenchymal transition and angiogenesis. Collectively, we provide a mechanistic rationale for integrating NHTs with PARPi, regardless of treatment sequence, in treating mPCa patients. NHT induces a BRCAness-like phenotype, rendering cells sensitive to PARPi. Additionally, we establish the potential of PARPi to suppress metastasis in mPCa during the treatment course.

Project description:Purpose: PTEN loss-of-function occurs in ~50% of metastatic, castrate-resistant prostate cancer (mCRPC) patients, and associated with poor prognosis and responsiveness to standard-of-care therapies and immune checkpoint inhibitors. While PTEN loss-of-function hyperactivates PI3K signaling, combinatorial PI3K/AKT pathway and androgen deprivation therapy (ADT) has demonstrated limited anti-cancer efficacy in clinical trials. Here, we aimed to elucidate mechanism(s) of resistance to ADT/PI3K-AKT axis blockade, and to develop rational combinatorial strategies to effectively treat this molecular subset of mCRPC. Experimental design: Prostate-specific PTEN/p53-deficient genetically engineered mice (GEM) with established 150-200 mm3 tumors, as assessed by ultrasound, were treated with either ADT (degarelix), PI3K inhibitor (copanlisib), or anti-PD-1 antibody (aPD-1), as single agents or their combinations, and tumors were monitored by MRI and harvested for immune, transcriptomic and proteomic profiling, or ex vivo co-culture studies. Single-cell RNAseq on human mCRPC samples was performed using 10X Genomics platform. Results: Co-clinical trials in PTEN/p53-deficient GEM revealed that recruitment of PD-1-expressing tumor-associated macrophages (TAM) thwarts ADT/PI3Ki combination-induced tumor control. The addition of aPD-1 to ADT/PI3Ki combination led to TAM-dependent ~3-fold increase in anti-cancer responses. Mechanistically, decreased lactate production from PI3Ki-treated tumor cells suppressed histone lactylation within TAM, resulting in their anti-cancer phagocytic activation, which was augmented by ADT/aPD-1 treatment and abrogated by feedback activation of Wnt/β-catenin pathway. Single-cell RNA-sequencing analysis in mCRPC patient biopsy samples revealed a direct correlation between high glycolytic activity and TAM phagocytosis suppression. Conclusions: Immunometabolic strategies that reverse lactate and PD-1-mediated TAM immunosuppression, in combination with ADT, warrant further investigation in PTEN-deficient mCRPC patients.

Project description:Prostate cancer (PCa) is the second most lethal cancer in men in the United States. African American (AA) men have twice the incidence and death rate from the disease than European American (EA) men. Early-stage PCa is treated with hormone deprivation therapy, although patients frequently experience relapse. Advanced stage PCa is associated with increased expression and activity of the DNA damage/repair pathway enzyme, poly (ADP-ribose) polymerase 1 (PARP1). Furthermore, PARP1 inhibitors are FDA-approved for the treatment of advanced PCa tumors that carry mutations in components of a specific DNA damage/repair pathway termed homologous recombination repair (HRR). However, PARPi also provide benefit in model systems without HRR incompetencies. A number of different PARPi have now been developed, tested and approved for use in PCa. These inhibitors utilize multiple biochemical mechanisms of action and exhibit distinct potencies and toxicity profiles. While there is emerging evidence of differences in DNA damage/repair pathway enzyme expression between EA and AA men, PARP1 itself has not been fully explored in the context of race. This study hypothesized that 1) AA and EA PCa may respond differently to PARPi and 2) different PARPi may differentially impact the transcriptome, irrespective of HRR status. To test these hypotheses, PCa patient samples from a racially diverse cohort were examined to define race-based differences in PARP activity/expression. Additionally, biologically relevant doses of five clinically relevant PARPi were established across multiple PCa lines carrying different genetic backgrounds, HRR status, and hormone therapy sensitivities. Collectively, these findings demonstrate a link between racial background and PARP1 expression/activity and define a core transcriptional response that lies downstream of all five PARPi, while simultaneously defining transcriptional programs unique to each inhibitor. These findings broaden our understanding of the effector pathways downstream of individual PARPi and provide a compelling rationale for a broader exploration of the impact of race on the response to PARPi. They may also help refine personalized recommendations for use of specific PARPi.

Project description:The overall 5-year survival rate of patients with pancreatic ductal adenocarcinoma (PDAC) is only 13% and there is an unmet need for better therapies. For the minority (5-10%) of patients with homologous recombination repair (HRR) deficient PDAC tumors (BRCA1/2, PALB2 mutations), poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi) and platinum-based therapies offer the best-personalized treatment approach. However, the efficacy of these treatments is often limited due to inherent (HRR proficient tumors) or acquired drug resistance. We have previously shown that expression of BARD1 or BRCA1- Associated- Ring- Domain- 1, a DNA repair protein and an obligate binding partner of BRCA1, is post-transcriptionally upregulated by the pro-survival RNA binding protein HuR (ELAVL-1), in PDAC. Here, we evaluated BARD1’s functional role in PDAC cell biology and evaluated its potential as a therapeutic target in HRR-proficient PDAC. BARD1 expression was silenced in HRR- proficient PDAC cells using both small interfering RNAs and CRISPR/Cas9 deletion. Silencing BARD1 decreased cell proliferation and 3D matrigel invasion in vitro. Tumor growth of BARD1KO mouse xenografts was markedly impaired. Mechanistically, using RNA sequencing of BARD1 silenced cells, we found a de-enrichment of the epithelial-mesenchymal-transition (EMT) pathway and global downregulation of c-Myc-target genes, which control diverse cell signaling events in PDAC. BARD1 stabilized the c-Myc protein through inhibition of the ubiquitin–proteasome system. Further, to evaluate if BARD1 loss is synergistic with DNA damage agents, we employed a focused DNA damage drug library in BARD1 silenced cells and found that cells were uniquely sensitized to the PARP inhibitors class of drugs. Our proof-of-concept study implicates BARD1 as an attractive, exploitable therapeutic target for HRR proficient PDAC patients and presents a unique opportunity to expand the PDAC patient population that could benefit from PARP inhibitors in the clinical setting.

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CD73 inhibition overcomes adaptive immune resistance to PARP inhibition in models of prostate cancer

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