Abstract B032: Combined A2AR and PARP inhibition in homologous recombination deficient (HRD) castrate-resistant prostate cancer (CRPC)
Authors: McCann Patrick J. , Mao Wendy , Chaimowitz Matthew , Houthys Erika , Marillier Reece , Bansal Shruti , An Julia , Piersaint Jason A. , Sen Namita , Drake Charles G. , Spina Catherine S. 
Published: June 2023

Abstract
Background: In response to cellular death and hypoxia, ATP is passively released into the extracellular space. ATP undergoes rapid stepwise conversion to the potent, immune-suppressive adenosine by ectoenzymes CD39 and CD73. Engagement of adenosine with the A2A and A2B receptors (A2AR, A2BR) promote the suppressive effects of adenosine. Early-phase clinical trials in men with metastatic castration-resistant prostate cancer (CRPC) suggest that A2AR antagonism may mitigate adenosine-driven immunosuppression in the tumor microenvironment (TME). The effect of A2AR antagonism on tumor cells themselves is unknown. Investigating combination treatments to promote both immune and tumor-intrinsic anti-tumor activity, we hypothesize that inhibition of adenosine signaling through the A2AR combined with PARP inhibition is an effective combination therapy for men with homologous repair deficient (HRD) CRPC. Methods: Here, we interrogate publicly available prostate cancer genomic datasets in the cBioPortal to evaluate the incidence of mutational and copy number alterations in the ENTPD1 (CD39), NT5E (CD73), and ADORA2A (A2AR) genes. Using an A2AR antagonist, we examine the effects of blocking A2AR signaling on tumor cell viability and expression of CD39, CD73, A2AR, and PARP expression in two androgen-insensitive human prostate cancer cell lines, DU145 and PC3. In DU145 and PC3 xenograft models, we tested A2AR antagonist, PARP inhibitor, or a combination of A2AR antagonist and PARP inhibitor, compared to vehicle alone on tumor growth. Results: Assessment of mutational and copy number alterations of ENTPD1 (CD39), NT5E (CD73), and ADORA2A (A2AR) in localized and metastatic prostate cancer reveals that the ADORA2A gene is amplified 10 times more frequently (2.4% vs. 0.2%, p&lt;0.01) in the metastatic setting. Stratifying the metastatic cohort by anti-androgen treatments, we found that in patients with prior abiraterone and/or enzalutamide exposure, ADORA2A was more commonly amplified (4.4% vs. 0.7%, p&lt;0.005), whereas ENTPD1 or NT5E were not. In both DU145 and PC3 cell lines, A2AR antagonism drives a dose dependent increase in cell death and expressions of A2AR, CD39, and CD73, especially in the DU145 cell line characterized by multiple missense mutations in key genes in the homologous recombination pathway. In both the DU145 and PC3 xenograft models, treatment with an A2AR antagonist or PARP inhibitor monotherapy did not significantly influence tumor volumes. However, when combined, A2AR antagonism plus PARP inhibition resulted in a 59% reduction in tumor volume (196.3 mm3 vs. 479.6 mm3, p&lt;0.001) in the DU145 model, compared to vehicle-treated control. In the PC3 model, with fewer alterations to the HR pathway, monotherapy also had no influence on tumor volume. When combined, A2AR antagonism plus PARP inhibition caused a 43% reduction in volume (304.1 mm3 vs. 538.2.0 mm3, p&lt;0.05). Conclusion: These data suggest that combined A2AR and PARP inhibition may be an effective therapeutic combination for HRD metastatic castration-resistant prostate cancer.
Citation Format: Patrick J. McCann, Wendy Mao, Matthew Chaimowitz, Erika Houthys, Reece Marillier, Shruti Bansal, Julia An, Jason A. Piersaint, Namita Sen, Charles G. Drake, Catherine S. Spina. Combined A2AR and PARP inhibition in homologous recombination deficient (HRD) castrate-resistant prostate cancer (CRPC) [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B032.