Abstract 1071: Targeting A2aR in mouse Pten -deficient prostate cancer

Inactivation of PTEN occurs frequently in advanced human prostate cancer and can promote an immunosuppressive tumor microenvironment (TME). Extracellular adenosine can be produced by tumors which can in turn modulate anti-inflammatory and immunosuppressive effects via interactions with the A2a receptor (A2aR). Here, we used a transgenic mouse model of Pten-deficient prostate cancer to characterize adenosine-mediated immunosuppression in the TME and evaluate the effects of A2aR blockade. Transcriptomic analysis of normal wildtype prostate and Pten-deficient prostate tumors revealed enriched signatures for genes downregulated after a A2aR knockdown or upregulated after A2aR stimulation. Moreover, androgen withdrawal led to increased expression of the A2aR-stimulated responsive genes Cxcl2/3/5, Il1b, S100a8, Ptgs2 and Thbs1. Immunohistochemical staining of CD73, the ecto-enzyme responsible for producing extracellular adenosine, showed heterogeneous staining ranging from negative to focally strong in epithelial cancer cells and was strongly expressed in immune cells. A2aR was also strongly expressed on immune infiltrates. We used the oral A2aR antagonist AZD4635 to determine the immunosuppressive activity of extracellular adenosine and evaluate its antitumor activity in the context of castration-naïve (CNPC), castration-sensitive (CSPC) and castration-resistant (CRPC) prostate cancer. Four weeks of treatment with AZD4635 led to a 12.1% (P=0.140) reduction of tumor burden compared to control mice. Notably a subset of these mice (4/8) had tumor reductions greater than 20%. For the CSPC/CRPC models, mice were orchidectomized and treated with apalutamide with or without AZD4635 for four or eight weeks to represent CSPC or CRPC phenotypes, respectively. In these settings, treatment with AZD4635 improved the reduction of tumor burden by 16.4% (P=0.165) and 16.8% (P=0.123) in CSPC and CRPC, respectively. Despite similar reduction rates between the cohorts, a greater proportion of AZD4635 treated mice were below the median distribution in the CRPC setting compared to the CSPC setting, 50% (4/8) vs 70% (7/10), respectively. Immunophenotyping showed an increase in the abundance of dendritic cells in tumors and tumor draining lymph nodes of AZD4635-treated mice in the CPNC setting. Whereas a shift in M2 to M1 macrophage, decrease of PD1hi CD8 T cells and an increase in genes related to cytotoxic lymphocyte activity (Gzma, Gzmb, Prf1, Klrg1, and B3gat1) were observed in A