Abstract LB-C09: The KRASG12C inhibitor MRTX849 reconditions the tumor immune microenvironment and leads to durable complete responses in combination with anti-PD-1 therapy in a syngeneic mouse model
Authors: Briere David M , Calinisan Andrew , Aranda Ruth , Sudhakar Niranjan , Hargis Lauren , Gatto Sole , Fernandez-Banet Julio , Pavlicek Adam , Engstrom Lars D , Hallin Jill , Christensen James G , Olson Peter 
Published: March 2020

Abstract
After decades of research, covalent inhibitors targeting KRASG12C are entering clinical trials. KRASG12C mutations are found in 14% of non-small cell lung cancer (NSCLC) adenocarcinoma as well as several other cancer types at lower frequencies. KRASG12C mutations are smoking-associated transversion mutations that are associated with a relatively high total mutation burden (TMB) and PD-L1 positivity. Although pembrolizumab is clinically active in KRAS-mutant NSCLC, response rates remain modest and strategies to augment the clinical activity of checkpoint inhibitor (CPI) therapy is an area of major clinical investigation. MRTX849 was identified as a potent, selective, and covalent KRASG12C inhibitor presently in clinical development. To evaluate the potential of MRTX849 to augment CPI therapy, the impact of MRTX849 on immune signaling molecules and response to anti-PD-1 therapy was evaluated. In a panel of human xenograft models, MRTX849 increased MHC Class I protein expression and decreased RNA and circulating protein expression of signaling molecules including VEGFA, CXCL1 and CXCL8, demonstrating MRTX849 modulates factors that are implicated in antigen presentation or an immunosuppressive tumor microenvironment through a tumor cell-mediated mechanism. In a CT26 syngeneic mouse model engineered to express KRASG12C, MRTX849 decreased intratumoral immunosuppressive myeloid-derived suppressor cell (MDSC) populations and increased immune-enhancing M1-polarized macrophages, dendritic cells, CD4+ and CD8+ T cell populations when administered as a single agent. These effects were also observed in tumors from MRTX849 plus anti-PD-1 treated mice. In efficacy studies, MRTX849 plus anti-PD-1 antibody treatment resulted in durable, complete responses in six out of ten animals whereas all but one of the tumors eventually progressed in the anti-PD-1 or MRTX849 single agent treatment groups. To further interrogate the mechanism of response to the combination, the six mice with complete responses were re-implanted with CT26KRASG12C cell inoculum and tumors failed to form, demonstrating combination-treated mice developed durable anti-tumor immunity. In summary, these data demonstrate MRTX849 in combination with anti-PD-1 therapy leads to durable complete regressions through an immune-mediated anti-tumor response.
Citation Format: David M Briere, Andrew Calinisan, Ruth Aranda, Niranjan Sudhakar, Lauren Hargis, Sole Gatto, Julio Fernandez-Banet, Adam Pavlicek, Lars D Engstrom, Jill Hallin, James G Christensen, Peter Olson. The KRASG12C inhibitor MRTX849 reconditions the tumor immune microenvironment and leads to durable complete responses in combination with anti-PD-1 therapy in a syngeneic mouse model [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-C09. doi:10.1158/1535-7163.TARG-19-LB-C09