Abstract 5579: Strategic inhibition of adenosine A2A receptor (A2AR) by CPI-444 improves CD8+:Treg ratios and enhances T-cell killing of a HER-2/neu expressing murine tumor

Abstract

Abstract It has been demonstrated that a higher CD8+ to CD4+FoxP3+ T regulatory cells (Tregs) ratio coincides with improved therapeutic outcomes for patients receiving immunotherapies in the clinic. The last several years of research have drawn attention to many such therapeutics and strategies. Adenosine is an abundant extracellular signaling molecule in the tumor microenvironment (TME) of many cancers. Signal transduction through the GPCR A2AR enhances the immunosuppressive activity of Tregs while simultaneously attenuating tumor-specific CD4+/CD8+ T cells. We have evaluated the appropriate coordination and dosing for a small-molecule inhibitor of A2AR in a Her-2/neu expressing murine model of breast cancer. We have demonstrated its capacity to augment existing therapeutic strategies in this tolerant model. To test our hypotheses on the ability of the small molecule to work in concert with existing therapeutics, we tested the role of CPI-444 when given with a T cell-inducing vaccine. Neu-expressing mammary tumor bearing HER-2/neu transgenic (Neu-N) mice were administered combinations of low-dose cyclophosphamide (Cy) to deplete Tregs, followed one day later with a granulocyte-macrophage colony-stimulating factor (GM-CSF) and neu-expressing whole cell vaccine (GVAX). The day following administration of GVAX, mice received adoptively transferred high-avidity naïve neu-specific CD8+ T cells intravenously one day after vaccination. Administration of specific components in this strategy (i.e. Cy, GVAX, adoptive transfer) were altered to gain insight into the mechanistic effects of CPI-444 in vivo through analysis of tumor progression, tumor clearance, and flow cytometric analysis of the TIL. Mice treated with the A2AR inhibitor or the vehicle control were administered each by oral gavage daily for 14 days (survival) or until 4 days post-adoptive transfer (TIL) at the peak infiltrate time. Of the strategies tested, Cy, followed by concomitant administration of GVAX with 100mg/kg of CPI-444 for 14 days, and a single adoptive therapy treatment provided a 55% overall survival (OS) compared with 0%-20% OS in vehicle controls (P<0.005). Further, we have observed both broad and specific changes in the T cell compartment of the tumor-infiltrating leukocyte (TIL) population. Broadly we have observed a refinement in the T cell portion of the TIL with decreased numbers of T cells overall, but an increase in specific prognostic ratios, namely a relative increase in favorability of the CD8+:Treg ratio when compared to controls (P<0.05). We hypothesize that strategic combination therapy of CPI-444 with existing therapeutics can refine the local immune profile to enhance favorable outcomes in vivo. CPI-444 is currently involved in numerous clinical trials; this work may provide rationale for the expansion of these trials into new cancer types. Citation Format: Blake A. Scott, Todd Armstrong, Stephen Willingham, Ian McCaffery, Elizabeth M. Jaffee. Strategic inhibition of adenosine A2A receptor (A2AR) by CPI-444 improves CD8+:Treg ratios and enhances T-cell killing of a HER-2/neu expressing murine tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5579. doi:10.1158/1538-7445.AM2017-5579