Abstract A87: The A2AR antagonist AZD4635 prevents adenosine-mediated immunosuppression in tumor microenvironment and enhances antitumor immunity partly by enhancing CD103+ dendritic cells

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Abstract Adenosine signaling via the adenosine 2A receptor (A2AR) is emerging as an important regulatory mechanism of immune responses. Adenosine levels are increased in the tumor microenvironment by the CD39/CD73 axis and adenosine signaling through the adenosine 2A receptor (A2AR) on immune cells elicits a range of immunosuppressive effects that promote tumor growth and limit the efficacy of immune checkpoint inhibitors. We provide evidence that AZD4635, an oral A2AR antagonist, inhibits downstream signaling causing enhanced antigen presentation by CD103+ DCs and increased T-cell activation. In our in vitro assays, NECA (a stable analog of adenosine) caused potent suppression of CD3/CD28 stimulated IFNγ secretion in T cells with 1 μM NECA leading to 80% suppression of IFNγ secretion. Incubation of CD8+ T cells with AZD4635 restored IFNγ secretion back to baseline levels with an observed EC50 of 0.053μM and 0.598 μM at 0.1 and 1 μM NECA, respectively. Treatment of mice bearing CT26 colorectal carcinoma and MC38 colorectal carcinoma with AZD4635 monotherapy led to tumor growth inhibition with (TGI) of 44% and 73%, respectively, and in combination with anti-PD-1 with a TGI of 73% and 91%, respectively. Ex vivo analysis of MC38 OVA tumor-bearing mice showed increase in intratumoral CD8 T cells and CD103+DCs in treated groups compared to control. In particular, combination treatment increased the frequency of OVA antigen specific CD8+ T cells as measured by % of cells expressing the activation marker CD25 (2-fold increase) or the proliferation marker Ki67 (2-fold increase). Aligned with increased tumor antigen-specific T-cell response was a 2-fold increase of intratumoral CD103+ DCs. CD103+DCs play a critical role in tumor antigen trafficking and cross-priming to T cells, which are crucial for successful tumor rejection. In vitro, treatment of CD103+ DCs with NECA suppressed about 50% of pinocytosis (uptake of fluorescent beads) and antigen presentation (OVA peptides), which was almost completely rescued by AZD4635 treatment. We extend these studies into human DCs, and show adenosine promotes a tolerogenic phenotype that can be reversed with AZD4635 restoring antigen presentation and T-cell costimulation by DCs, leading to 50% increase in priming and expansion of antigen-specific T cells compared to adenosine-treated group. Our results support the role of adenosine signaling as an intrinsic negative regulator of CD103+ DC maturation and priming. We show that potent inhibition of A2AR with AZD4635 reduces tumor burden and enhances antitumor immunity. Our preclinical data support the evaluation of AZD4635 as a single agent and in combination with durvalumab (αPD-L1 antibody) in patients with solid malignancies (www.clinicaltrials.gov- NCT02740985, NCT03980821). Citation Format: Dinesh Chandra, Christine M. Barbon, Alexandra Borodovsky, Yanjun Wang, Minwei Ye, Laura Prickett, Kris Sachsenmeier, Wenlin Shao, Carl Barrett, Stephen Fawell, Deanna A. Mele, Alwin Schuller. The A2AR antagonist AZD4635 prevents adenosine-mediated immunosuppression in tumor microenvironment and enhances antitumor immunity partly by enhancing CD103+ dendritic cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A87.