Abstract 530: Preclinical evaluation of avutometinib (VS-6766; RAF/MEK clamp) in combination with EGFR inhibition in colorectal cancer patient-derived xenograft (PDX) models harboring KRAS mutations
Authors: Wang Chongkai , Coma Silvia , Pachter Jonathan , Fakih Marwan 
Published: June 2023

Abstract
Background KRAS mutation (mt) occurs in ~43% of patients with colorectal cancer (CRC) with KRAS G12D, G12V and G13D being most prevalent. Avutometinib (avuto, VS-6766) is a unique RAF/MEK clamp that inhibits MEK kinase activity and induces dominant negative RAF/MEK complexes preventing the re-activation of MEK by RAF. Preclinically, avuto inhibited proliferation of KRAS mt CRC cell lines. Clinically, avuto monotherapy produced clinical responses in gynecological cancers and KRAS mt non-small cell lung cancer.
Methods 3D proliferation assays were used to quantify synergy between avuto and agents targeting other nodes in the MAPK pathway or parallel signaling pathways. We evaluated the antitumor effects of avuto alone or in combination with panitumumab in CRC PDX models with KRASG12V, concurrent KRASG12V and PIK3CA, or KRASG12D mutations. Mice bearing PDX tumors were randomized into groups of 6 mice treated with avuto alone or in combination with panitumumab for 21 days with tumor volume measured twice weekly.
Results In 3D proliferation assays with a panel of KRAS mt CRC cell lines (including G12D, G12V and G13D mutations), the EGFR/ErbB family inhibitor afatinib showed the strongest synergy score with avuto relative to inhibitors of SHP2, ERK1/2, mTOR or CDK4/6. Based on the synergy of avuto with afatinib, the combination of avuto with the anti-EGFR antibody panitumumab was tested in KRAS mt CRC PDX models. In a KRASG12V PDX model, tumor regression (11%) was seen in 1/6 mice treated with avuto alone. No tumor regression was seen in mice treated with panitumumab monotherapy. The combination of avuto and panitumumab led to significant tumor regression (&gt;40%) in 5/6 mice following 21 days of treatment. In a KRASG12V PDX model with concurrent PIK3CA mutations, no tumor regression was seen in mice treated with either avuto or panitumumab alone. The combination of avuto and panitumumab led to initial tumor stabilization followed by tumor growth in 3/6 mice. In a KRASG12D PDX model, tumor regression (17%) was seen in 1/6 mice treated with avuto and 0/6 with panitumumab. Tumor regression (13% and 18%) was noted in 2/6 mice treated with the combination of avuto and panitumumab.
Conclusion In KRAS mt CRC cell lines, strong synergy was observed between avuto and afatinib. In KRAS mt CRC PDX models in vivo, avuto monotherapy showed tumor growth inhibition but limited tumor regression, and panitmumab monotherapy failed to show tumor regressions. The combination of avuto and panitumumab showed significant anti-tumor activity in a CRC PDX model harboring KRASG12V with less tumor regression observed in a KRASG12D PDX model or in a KRASG12V PDX model with concurrent PIK3CA mutation. These results support the ongoing clinical evaluation of avutometinib in combination with the anti-EGFR antibody cetuximab for treatment of KRAS mt CRC (NCT05200442).
Citation Format: Chongkai Wang, Silvia Coma, Jonathan Pachter, Marwan Fakih. Preclinical evaluation of avutometinib (VS-6766; RAF/MEK clamp) in combination with EGFR inhibition in colorectal cancer patient-derived xenograft (PDX) models harboring KRAS mutations [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 530.