Abstract 4147: EOS100850, an A2Areceptor antagonist with prolonged pharmacodynamic activity, mediates the generation ofspecific durable immune responses in a murine breast cancer model
Authors: Pirson Romain , Michaux Anne-Catherine , Jamart Diane , Preillon Julie , Frederix Kim , Basilico Paola , Martinoli Chiara , Leroy Xavier , Driessens Gregory , Houthuys Erica , Chappel Scott , Crosignani Stefano , Marillier Reece 
Published: August 2019

Abstract
We and others have shown that extracellular adenosine (Ado), acting predominantly through the A2A receptor (A2AR), mediates immunosuppression through different modes of action. These include suppression of Th1 responses and cytotoxicity as well as increasing the activity of Tregs and MDSC. We therefore developed EOS100850, a novel, non-brain penetrant and highly selective inhibitor of A2AR with sub-nanomolar Ki. As compared to other A2AR antagonist in development, EOS100850 maintain its potency in high Ado environment (&gt;10uM).
To better characterize the Ado levels found in the tumor microenvironment, we first assessed extra-cellular Ado concentrations by microdialysis. Concentrations measured in mouse and human tumors were elevated compared to normal skin and confirmed that immune cells infiltrating the tumor microenviroment are confronted with elevated suppressive Ado levels.
To demonstrate and compare the ability of EOS100850 to inhibit A2AR signaling in vivo with other molecules in development, we measured the in vivo pharmacodynamic (PD) modulation of A2AR activity by investigating its ability to inhibit CREB phosphorylation (pCREB) following activation of the Ado receptor by NECA, an A2AR agonist. While EOS100850 demonstrated complete inhibition of pCREB 30 minutes after oral gavage at a dose as low as 0.1 mg/kg, other A2AR inhibitors required much higher concentrations to achieve a similar effect. Remarkably, 24 hours after dosing, more than 60% of inhibition of pCREB was still observed, at a dose of 10 mg/kg when the EOS100850 antagonist was no longer detectable in the plasma. These results demonstrate that EOS100850 has a PD activity that extends well beyond its PK, which can be explained by a long residence time.
To demonstrate the in vivo antitumor efficacy of EOS100850, we used the murine syngeneic breast cancer model, EMT-6. EOS100850 administered in combination with anti-CTLA-4 mAb increased the number of complete responders (CR) and significantly reduced tumor growth compared with anti-CTLA-4 single agent treatment. Furthermore, the CR were protected against re-inoculation with EMT6 but not irrelevant CT26 tumor. Lastly, flow cytometry and RNAseq analysis, performed on tumors taken during the course of treatment, confirmed the potential of EOS100850 as single agent or in combination with anti-CTLA4 to induce a pro-inflammatory response that correlate with tumor regression.
This best-in-class profile of EOS100850 A2A receptor antagonist supports its progression into clinical development.
Citation Format: Romain Pirson, Anne-Catherine Michaux, Diane Jamart, Julie Preillon, Kim Frederix, Paola Basilico, Chiara Martinoli, Xavier Leroy, Gregory Driessens, Erica Houthuys, Scott Chappel, Stefano Crosignani, Reece Marillier. EOS100850, an A2Areceptor antagonist with prolonged pharmacodynamic activity, mediates the generation ofspecific durable immune responses in a murine breast cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4147.