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Introduction: High levels of immunosuppressive adenosine are found in the tumor microenvironment, reaching 50-100 μM in experimental models. Adenosine exerts its effects on immune cells primarily through the adenosine receptors A2aR/A2bR, which increase intracellular levels of cyclic AMP, leading to CREB phosphorylation (pCREB). We have previously shown that the dual A2aR/A2bR antagonist AB928 is capable of inhibiting adenosine-induced pCREB in healthy human volunteer (HV) blood lymphocytes. AB928 has also been shown to relieve adenosine-mediated T-cell suppression in vitro and exhibit combinatorial effects with standard-of-care chemotherapeutics in mouse syngeneic tumor models. Herein, we show that AB928 is capable of inhibiting NECA-induced gene expression changes and CREB phosphorylation in non-small cell lung carcinoma (NSCLC) patient whole blood (WB). Additionally, observations from our in vitro human studies showing the combinatorial effect of AB928 and α-PD-1 were reproduced in B16F10 syngeneic tumors. Methods: Human WB was stimulated with 5 μM of NECA and flow cytometry was used to quantify AB928-mediated inhibition of pCREB and CD3ζ phosphorylation. B16F10 tumors were treated with α-PD-1 +/- AB928 and gene expression was determined from excised mouse tumors using the nCounter PanCancer panel. Results: To ensure AB928 can successfully inhibit the high levels of intratumoral adenosine, we found that 5 μM NECA provides maximal stimulation and is significantly more potent (>20 fold) than adenosine in the pCREB assay. Additional experiments demonstrated that AB928 has comparable potency in NECA-stimulated WB from both HV and NSCLC patients. In addition to blocking downstream signaling, NanoString analysis showed that AB928 could prevent NECA-stimulated gene expression changes in NSCLC WB. We also found that NECA stimulation, alone or in combination with PD-1 inhibition, significantly reduced proximal TCR signaling, leading to reduced levels of CD3ζ phosphorylation at TYR142 (pTYR142). These reduced pTYR142 levels, with and without α-PD-1, could be significantly rescued by AB928, suggesting that blocking adenosine immunosuppression may provide additional benefit to PD-1 inhibition in tumors. Consistent with these results, AB928 was capable of suppressing growth (volume in mm3) of B16-F10 tumors both as a single agent (vehicle: 462 +/- 58; AB928: 292 +/- 55; p Conclusions: Collectively, these results support a role for AB928 in relieving adenosine-mediated immunosuppression by blocking A2aR/A2bR-induced signaling events, gene expression changes, and suppressing tumor growth in vivo. Citation Format: Daniel M. DiRenzo, Nell Narasappa, Dana Piovesan, Devika Ashok, Park Adam, Jenna L. Jeffrey, Manmohan R. Leleti, Joanne B.L. Tan, Lisa Seitz, Steve W. Young, Jay P. Powers, Matthew J. Walters. The dual A2aR/A2bR antagonist AB928 reverses adenosine-mediated immune suppression and inhibits tumor growth in vivo [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A10.

Introduction: Extracellular adenosine (ADO), present at high concentrations in the tumor microenvironment (TME), suppresses immune function via inhibition of T-cell, natural killer (NK) cell, and dendritic cell (DC) activation. Intratumoral generation of ADO depends on the sequential catabolism of ATP by two ecto-nucleotidases CD39 (ATP→AMP) and CD73 (AMP→ADO). Inhibition of CD73 eliminates a major pathway of ADO production in the TME and can reverse ADO-mediated immune suppression. Here we present the preclinical characterization of AB680, a novel, highly potent, reversible and selective small-molecule inhibitor of CD73, currently in preclinical development as a potential antitumor agent. The link between CD73 levels present in different tissues, efficacy in mouse tumor models, plasma and tumor exposure, and projected human pharmacokinetic (PK) profile can be combined to provide an expected AB680 dosing strategy for the upcoming first-in-human clinical trial. Methods: The potency of AB680 against human CD73 was determined using CHO-CD73 cells, blood CD8+ T-cells, recombinant human CD73, and serum/plasma using either malachite green assay, AMP-Glo assay, or LCMS/MS. The selectivity of AB680 against related ecto-nucleotidases was also assessed using similar methods. Quantitation of soluble CD73 in mouse and human serum, and mouse tumor homogenates, was performed via in-house developed and validated ELISA or Western blot methods. Syngeneic mouse tumor models were established to assess the efficacy of AB680 at multiple doses. AB680 levels in plasma and tumor associated with each dosing regimen were determined via LCMS/MS. The potency of AB680 in an intratumoral setting was determined using various biochemical methods. The effects of AB680 on syngeneic tumor volumes were assessed in prophylactic and therapeutic settings. The PK properties of AB680 were evaluated in multiple preclinical species and a projected human dosing schedule for AB680 was determined via allometric scaling. Results: AB680 is a highly potent, reversible and selective inhibitor of CD73 activity (IC50 < 0.01 nM on human CD8+ T-cells), which retains its high potency in the presence of human serum. Inhibition of AMP hydrolysis by AB680 completely reversed ADO-mediated suppression of CD4+ and CD8+ T-cell effector function, as measured by cytokine secretion and proliferation. The in vivo efficacy of AB680, as measured by its ability to restrict tumor growth at doses as low as 10 mg/kg once daily, is reflective of the following parameters: 1) plasma half-life, 2) partitioning from blood to tumor compartment, 3) potency against soluble CD73 in plasma or serum, and 4) potency against membrane-bound CD73. The PK properties of AB680 in rodent and non-rodent species are characterized by very low clearance and long half-lives. The combination of in vitro potency against mouse and human soluble and membrane-bound CD73, in vivo tumor growth regulation observed in mouse models, quantification of mouse and human CD73 levels, and the projected human PK profile for AB680 have resulted in predicted human PK properties (projected half life: 4-14 days) suitable for intravenous dosing on a schedule consistent with typical monoclonal antibody dosing cycles. Conclusions: AB680 is a highly potent and selective small-molecule inhibitor of CD73 which can mitigate AMP and ADO-mediated tumor immunosuppression by potently blocking the production of ADO. AB680 exhibits a unique projected human PK profile suitable for parental administration and is expected to enter clinical development in 2018. Citation Format: Joanne B.L. Tan, Jie Chen, Elaine Ginn, Devika Ashok, Amy E Anderson, Jesus Banuelos, Kristen Zhang, Amber Pham, Timothy Park, Ada Chen, Xiaoning Zhao, Kenneth K.V. Lawson, Jenna Jeffreys, Jarek Kalisiak, Manmohan R. Leleti, Matthew J. Walters, Jay P. Powers. Preclinical pharmacokinetic and pharmacodynamic characterization of AB680, a small-molecule CD73 inhibitor for cancer immunotherapy [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 A157.