Abstract 2337: The adenosine A2A receptor antagonist CPI-444 blocks adenosine-mediated T-cell suppression and exhibits antitumor activity alone and in combination with anti-PD-1 and anti-PD-L1
Authors: Willingham Stephen , Ho Po , Leone Robert , Piccione Emily , Choy Carmen , Hotson Andrew , Buggy Joseph , Powell Jonathan , Miller Richard 
Published: July 2016

Abstract
Elevated levels of extracellular adenosine within the tumor microenvironment create an immunosuppressive niche that promotes tumor growth and metastasis. Adenosine signaling via the A2A receptor (A2AR) on immune cells suppresses anti-tumor immunity and limits the efficacy of immunotherapies such as anti-PD-L1 or anti-PD-1 monoclonal antibodies (mAbs).
CPI-444 is an oral A2AR antagonist that has been evaluated previously in phase 1 clinical trials for non-oncology indications. CPI-444 demonstrates binding to A2AR with a Ki of 3.5 nM and &gt; 50-fold selectivity over other adenosine receptor subtypes. We examined the immune activating and anti-tumor properties of CPI-444 alone and in combination with anti-PD-1/PDL-1 mAbs.
In vitro studies using activated primary human T cells demonstrated that CPI-444 fully inhibited the production of intracellular cAMP following incubation of the cells with 5’-N-ethylcarboxamidoadenosine (NECA), a stable analog of adenosine. A2AR agonists suppressed rapid TCR-mediated ERK phosphorylation and, subsequently, production of IL-2 and IFNγ by activated T cells; blockade of A2AR with CPI-444 restored T cell signaling and function.
The efficacy of CPI-444 was evaluated in MC38 and CT26 syngeneic mouse tumor models. In the MC38 model, daily treatment of mice with CPI-444 (1, 10, 100 mg/kg) led to a dose-dependent reduction in tumor growth, leading to full tumor elimination in 9/30 treated mice. New tumors failed to establish when the cured mice were re-challenged with MC38 cells, indicating that CPI-444 induced systemic anti-tumor immune memory. Combining CPI-444 with anti-PD-L1 mAb treatment in the MC38 model synergistically inhibited tumor growth and led to elimination of tumors in 9/10 treated mice. In the CT26 model, CPI-444 alone or anti-PD-1 alone led to non-significant reductions in tumor growth; however the combination of CPI-444 and anti-PD-1 led to a synergistic inhibition of tumor growth and prolonged survival compared to either agent alone. These results, and others, suggest that adenosine signaling may be an important resistance mechanism in tumors that incompletely respond to anti-PD-1/PD-L1 mAb therapy.
Based on these results and others, we plan to initiate a Phase 1b clinical trial to examine safety, tolerability, biomarkers, and preliminary efficacy of CPI-444 as a single agent and in combination with anti-PD-L1 (atezolizumab) in patients with solid tumors.
Citation Format: Stephen Willingham, Po Ho, Robert Leone, Emily Piccione, Carmen Choy, Andrew Hotson, Joseph Buggy, Jonathan Powell, Richard Miller. The adenosine A2A receptor antagonist CPI-444 blocks adenosine-mediated T-cell suppression and exhibits antitumor activity alone and in combination with anti-PD-1 and anti-PD-L1. [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 2337.