Biomarker and clinical activity of CPI-444, a novel small molecule inhibitor of A2A receptor (A2AR), in a Ph1b study in advanced cancers

Abstract

Background: Adenosine is immunosuppressive and is produced at high concentrations in tumors by both CD73 and direct release from tumor cells. Adenosine activates A2AR, an immune checkpoint that leads to direct suppression of effector T cells and stimulation of regulatory T cells. CPI-444 is an oral, selective A2AR inhibitor that has been well tolerated in Ph 1 and 2 studies in non-oncology indications. CPI-444 shows activity in multiple preclinical tumor models as a single agent and synergistic efficacy when given in combination with other checkpoint inhibitors, including anti-PD-L1. Methods: CPI-444, with or without the investigational agent atezolizumab (anti-PD-L1), is being studied in an ongoing Ph1b trial in solid tumor patients ( pts). Pts with either lung, melanoma, triple negative breast, bladder, colorectal, renal, or head and neck cancers are treated at various doses of either single agent CPI-444 or combined with atezolizumab. After a dose selection stage, pts are treated in 10 disease specific cohorts (5 single agent and 5 combination). Cohorts may be expanded based on response criteria: complete response, partial response or stable disease (SD). Biomarkers are evaluated including immune cells by flow cytometry in peripheral blood and pre/post treatment tumor biopsies as well as adenosine pathway modulation by immunohistochemistry and gene expression. Results: In 7 pts treated to date, CPI-444 has been well tolerated with no Grade 3 or 4 treatment related adverse events. 2 pts (1 combination and 1 single agent) have reached the first efficacy assessment by CT and both demonstrated SD (unconfirmed at 2 months); these 2 pts, and 4 others who have not yet reached efficacy evaluation, remain on treatment. In the two pts with SD, peripheral blood showed increases in PD-1 + CD8+ cells (1.7 and 2.4 fold compared to baseline). This is consistent with preclinical models and reflect effector T cell activation, similar to reports by others in patients treated with anti-PD-L1. Conclusions: CPI-444 is well tolerated and demonstrates biological activity indicating activation of T cell immunity. This is the first demonstration of treatment-associated immune modulation in cancer patients receiving an adenosine antagonist.