Introduction: Adenosine, generated through the hydrolysis of extracellular adenosine monophosphate (AMP) by the ecto-nucleotidase CD73, is an important mechanism for immunosuppression in cancer development. Adenosine’s suppressive effects on immune cells are driven primarily through 2 of the 4 adenosine receptors, A2aR and A2bR. We have previously shown that adenosine-mediated suppression of T-cells can be blocked by the dual A2aR/A2bR antagonist, AB928. Herein, we show that AB928 is capable of relieving adenosine-mediated immune suppression using human in vitro cell cultures, advanced gene expression studies, and mouse syngeneic tumor models. Methods: The ability of AB928 to inhibit adenosine-mediated suppression of dendritic cell function in vitro was assessed using human monocyte-derived dendritic cells (moDC). Briefly, moDC were generated from freshly isolated CD14+ monocytes and differentiated with IL-4/GM-CSF for 7 days +/- adenosine/EHNA +/- AB928. Cells were then taken for NanoString analysis or placed in a mixed lymphocyte reaction (MLR) with CD4+ T-cells. Mouse syngeneic tumor studies were conducted using C57BL/6 mice inoculated with mouse mammary tumor AT3-OVA or melanoma B16-F10 cells. Tumors were subsequently treated with doxorubicin, oxaliplatin, or α-PD-1 +/- AB928. Results: Quantitative immunohistochemistry and analysis of public gene expression databases identified individual human tumor types that express high levels of adenosine processing enzymes. Most notably, non-small cell lung, renal, triple-negative breast, ovarian, colorectal, and gastroesophageal cancers were found to have the most favorable expression profiles for interventions targeting the adenosine pathway. Additionally, a high degree of correlation was found between transcript and protein measurements for CD73 (r2 = 0.87), illustrating the robust and reproducible nature of these techniques. In human in vitro cell cultures, moDC differentiated in the presence of adenosine showed a decreased ability to stimulate IFN-γ secretion from allogenic CD4+ T-cells in a MLR. This suppression was significantly reversed by addition of AB928. Next, multiplexed gene expression profiling using NanoString identified a cassette of 39 genes (>2.0 fold change, p <0.05) that were regulated by adenosine during moDC differentiation. Similarly to the MLR results, AB928 showed rescue of these gene expression changes, further supporting the role for A2aR/A2bR in adenosine-mediated suppression of dendritic cell maturation. The antitumor effects of AB928 were demonstrated in vivo using AT3-OVA tumors treated with anthracycline chemotherapy. Concurrent treatment with AB928 and chemotherapy resulted in significantly reduced tumor volume when compared to chemotherapy alone (doxorubicin: 86 +/- 12 mg; AB928 + doxorubicin: 28 +/- 2 mg; p<0.001); similar results were observed for the combination of AB928 and oxaliplatin. Further, gene expression analysis and histologic analyses showed increased immune cell infiltrate and stromal response in tumors treated with chemotherapy and AB928 in combination. AB928 was also capable of suppressing growth of B16-F10 tumors both as a single agent or in combination with α-PD-1 therapy (α-PD-1: 324 +/- 54 mm3; AB928 + α-PD-1: 180 +/- 35 mm3; p<0.05). Conclusions: Collectively, these results support the importance of targeting both A2aR and A2bR to relieve adenosine-mediated immunosuppression in the context of cancer biology. Furthermore, AB928 increases the antitumor immune response leading to suppressed tumor growth and increased immune cell infiltration in mouse syngeneic tumors. AB928 has successfully completed a phase 1 study in healthy volunteers and has begun clinical trials in subjects with cancer.

Citation Format: Daniel DiRenzo, Dana Piovesan, Joanne Tan, Dillon H. Miles, Manmohan R. Leleti, Timothy Park, Ferdie Soriano, Bryan Handlos, Jenna L. Jeffrey, Ehesan U. Sharif, Brandon R. Rosen, Ulrike Schindler, Jay P. Powers, Matthew J. Walters. AB928, a dual antagonist of the A2aR and A2bR adenosine receptors, relieves adenosine-mediated immune suppression [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A162.