Abstract A062: RAS-GTP inhibition enhances antitumor efficacy of the RAF/MEK clamp avutometinib in NF1-associated Malignant Peripheral Nerve Sheath Tumors

Abstract Neurofibromatosis type 1- associated malignant peripheral nerve sheath tumor (NF1-MPNST) is the leading cause of death in patients with NF1 syndrome. A hallmark manifestation of NF1 tumors, including MPNST, is acquisition of somatic inactivation of the second NF1 allele and loss of NF1 protein function. The loss of NF1 function leads to hyperactive RAS oncoproteins and hyperactivation of downstream RAS-effector pathways, of which the RAF-MEK1/2-ERK1/2 (MAPK) signaling cascade plays a critical role. In this study, we evaluated the antitumor activity of the RAF/MEK clamp avutometinib in NF1-MPNST cells and tumor xenografts. Since avutometinib inhibits MEK activity and induces inactive complexes of MEK with the RAF kinases, potentially blocking RAF-mediated feedback, we hypothesized that avutometinib would have improved activity in NF1-MPNST compared to MEK-only inhibitors. As compared to MEK-only inhibitors trametinib or selumetinib, avutometinib inhibited RAF-mediated MEK phosphorylation in NF1-MPNST cells. In cell- and patient-derived xenograft models, avutometinib showed significantly better activity than trametinib or selumetinib in inhibiting tumor growth. In vivo pharmacodynamic assays indicated that avutometinib inhibited ERK1/2 signaling more potently than trametinib or selumetinib. However, in RAS-GTP pull down assays, treatment of NF1-MPNST cells with either avutometinib, trametinib or selumetinib led to increased RAS-GTP levels indicating RAS reactivation. Reconstitution of the GTPase-activating protein-related domain (GRD) of NF1 reversed RAS-GTP increase leading to more potent inhibition of ERK1/2 signaling. Further, a genome-wide CRISPR-Cas9 screen identified SHOC2, a positive regulator of ERK1/2 signaling that integrates RAS and RAF into multiprotein complex, as a key resistance factor to avutometinib in NF1-MPNST cells. Loss of SHOC2 sensitized NF1-MPNST cells to avutometinib treatment but didn’t suppress RAS-GTP accumulation. The role of RAS-GTP was further evaluated by combining avutometinib with SHP2, SOS1 or pan-RAS inhibitors in NF1-MPNST cells. The combination of avutometinib with a pan-RAS inhibitor was superior to the combination of avutometinib with a SHP2 inhibitor or with a SOS1 inhibitor in synergistic inhibition of cell proliferation. Furthermore, the combination of avutometinib with a pan-RAS inhibitor induced strong ERK1/2 signaling inhibition in NF1-MPNST cells and induced significant anti-tumor responses relative to the single agents in 3 xenograft models. We conclude that avutometinib in combination with a pan-RAS inhibitor could have clinical implications for patients with NF1-MPNST. Citation Format: Arnab Sarkar, Julie Fischer, Priyanka Chakravarty, Katia Campos, Teresa Marple, Silvia Coma, Jonathan A. Pachter, Angelina Vaseva. RAS-GTP inhibition enhances antitumor efficacy of the RAF/MEK clamp avutometinib in NF1-associated Malignant Peripheral Nerve Sheath Tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr A062.