Abstract 4364: Adenosine A2a receptor blockade as a means of enhancing immune checkpoint inhibition and adoptive T-cell therapy

Proceedings: AACR 107th Annual Meeting 2016; April 16-20, 2016; New Orleans, LA Adenosine signaling through the A2a receptor (A2aR) has pleiotropic immunosuppressive effects on a broad range of immune cells. Extracellular adenosine levels, which are typically very low in normal tissues, are elevated in the tumor microenvironment, allowing increased signaling through the A2aR. Previously, our lab and others have shown increased rejection of tumors in A2aR-null mice, demonstrating that adenosine signaling through A2aR limits immunologic response to tumors. Present work in our lab demonstrates the ability of a potent and specific, orally administered A2aR antagonist, CPI-444, to enhance immunologic response in mice. First, A2aR blockade with CPI-444 (1 mg/kg) in the peri-vaccination period led to significant expansion of antigen-specific T cells over untreated controls. Interestingly, antigen-specific CTLs from CPI-444 treated mice showed significantly lower expression of inhibitory checkpoint receptors, including PD-1 and TIM-3. Second, in an MC38 tumor model, daily treatment with CPI-444 (100 mg/kg) led to tumor growth suppression and survival benefit compared with vehicle-treated controls. Notably, tumor infiltrating regulatory T cells had significantly lower CTLA-4 and FoxP3 expression in CPI-444 treated mice. These initial immunologic findings of enhanced early CTL expansion and suppression of inhibitory co-signaling have important implications for applying A2aR blockade to immunotherapy in cancer. First, given the ability of CPI-444 to augment CTL expansion, we investigated its application to a therapeutic adoptive T cell transfer system using OVA-expressing B16 melanoma cell line. In mice with established tumors, daily CPI-444 (100 mg/kg) treatment initiated on the day of adoptive transfer of activated OVA-specific OT-I T cells led to suppressed tumor growth and increased survival versus vehicle treated controls. Second, in light of our data demonstrating its ability to suppress PD-1 in CTLs, we theorized that CPI-444 may lower the threshold for effective anti-PD-1 therapy and achieve synergistic effects as combination therapy. Indeed, daily CPI-444 (100 mg/kg) treatment combined with anti-PD-1 treatment showed robust antitumor effect in the CT26 tumor model, with complete tumor rejection in 7/9 mice (vs. 2/10 mice in the anti-PD-1 alone group). Survival was markedly improved in mice receiving combination treatment versus either CPI-444 or anti-PD-1 alone. In as much as increased adenosine in the tumor microenvironment is partly a consequence of dysregulated cancer cell metabolism, we hypothesized that targeting tumor metabolism would enhance the efficacy of A2aR antagonism. To this end, inhibition of tumor glutamine metabolism potently augmented the efficacy of CPI-444 in a CT26 model. Overall, our data suggest that A2aR antagonism can enhance the efficacy of immunotherapy in the form of checkpoint blockade and adoptive cellular therapy. Citation Format: Robert D. Leone, Judson M. Englert, Chih-Hsien Cheng, Jiayu Wen, Min-Hee Oh, Im-Hong Sun, Chirag Patel, Ian A. Bettencourt, Jonathan D. Powell. Adenosine A2a receptor blockade as a means of enhancing immune checkpoint inhibition and adoptive T-cell therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4364.