Abstract 4155: The RAF/MEK clamp avutometinib (VS-6766) induces an immunogenic tumor microenvironment and potentiates the efficacy of anti-PD-1
Authors: Coma Silvia , Arcas Miriam Molina , Downward Julian , Pachter Jonathan A. 
Published: April 2023

The RAS/RAF/MEK/ERK (MAPK) pathway is one of the most commonly mutated oncogenic pathways in human cancers. Although RAS, RAF and MEK have been validated as anticancer targets with approval of KRAS G12C, BRAF and MEK inhibitors, combination strategies with chemotherapy, targeted therapies and/or immune checkpoint inhibitors may be optimal for deep and durable response. Avutometinib (avuto, VS-6766) is a unique RAF/MEK clamp that potently inhibits MEK kinase activity and induces a dominant negative RAF/MEK complex preventing phosphorylation of MEK by ARAF, BRAF and CRAF. Preclinically, avuto has shown strong anti-proliferative potency across tumor cell lines carrying various MAPK pathway alterations. Clinically, avuto monotherapy has shown responses in gynecological cancers and KRAS mutant non-small cell lung cancer. Here, we tested the immune modulatory effects of avuto on tumor cells and tumor-infiltrating immune cells and assessed anti-tumor efficacy in mice treated with avuto in combination with an anti-PD1 antibody. In a panel of KRAS and BRAF mutant human tumor cell lines, avuto treatment increased the expression of MHC-I complex genes, including B2M, HLA-A and TAP1. In the CT26 KRAS G12D syngeneic colorectal cancer model, upregulation of B2M and TAP1 by avuto was confirmed in vivo, suggesting that avuto may increase antigen presentation. Furthermore, avuto upregulated the expression of markers of T cells (CD8, PDCD1), NK cell activation (NCR1) and interferon response (IFNG, IRF7, IL12) in the CT26 model. Interestingly, all these pro-immune changes observed with avuto were stronger than those observed with an equivalent dose level of the MEK-only inhibitor trametinib. Avuto also increased expression of B2M, CD8A, PDCD1, NCR1 and IRF7 in a KPARG12C orthotopic lung cancer model. Flow cytometry analysis showed that avuto also significantly increased MHC-II expression by tumor cells and the numbers of CD8 T cells and M1 macrophages, and significantly decreased monocytic and granulocytic MDSCs. These immune changes indicate that avuto induces an immunogenic tumor microenvironment that may potentiate the efficacy of immuno-oncology agents such as anti-PD-1. Accordingly, in the CT26 model, whereas avuto and anti-PD-1 each delayed tumor growth, combination of avuto with anti-PD-1 increased antitumor efficacy and prolonged survival. Furthermore, all complete responders in the avuto + anti-PD-1 group were able to reject a re-challenge with CT26 tumor cells and showed increased CD8 and CD4 effector memory T cells relative to untreated naïve control mice, indicating that avuto + anti-PD-1 treatment induces durable immune memory. These results support clinical evaluation of avutometinib in combination with an anti-PD-1 antibody for treatment of patients with solid tumors harboring MAPK pathway alterations such as KRAS or BRAF mutations.

Citation Format: Silvia Coma, Miriam Molina Arcas, Julian Downward, Jonathan A. Pachter. The RAF/MEK clamp avutometinib (VS-6766) induces an immunogenic tumor microenvironment and potentiates the efficacy of anti-PD-1. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4155.