Abstract 6368: Correlative preclinical studies to elucidate mechanisms of synergy of the combination of the RAF/MEK clamp avutometinib and the FAK inhibitor defactinib in low grade serous ovarian cancer

Abstract Background: Low-grade serous ovarian cancer (LGSOC) is a rare and distinct cancer in which ∼70% of patients have aberrations in MAPK pathway-associated genes. Following a phase 1 study (FRAME; NCT03875820) of the combination of the RAF/MEK clamp avutometinib with the FAK inhibitor defactinib in LGSOC, a phase 2 study (RAMP-201; NCT04625270) showed a higher response rate for this combination (31% ORR in overall LGSOC population; 44% ORR in patients with mutant KRAS) relative to avutometinib monotherapy (17% ORR in overall LGSOC population; 23% ORR in patients with mutant KRAS). Methods: 3D proliferation studies were conducted to assess synergy between avutometinib and defactinib in a patient-derived LGSOC organoid model. This organoid model was used in in-vivo experiments with vehicle, avutometinib, VS-4718 (FAK inhibitor) and the combination for 2 weeks. Tumor samples were collected 2 hours after the last dose and analyzed for p-ERK and p-FAK by IHC, RNA seq and mass spectrometry to understand the contribution of individual drugs and their combinatorial effects. Results: The combination of avutometinib with defactinib in organoids was synergistic (combination index = 0.53). In-vivo, the combination induced tumor regressions in 5/6 animals, whereas avutometinib or VS-4718 alone induced tumor growth inhibition but with no tumor regression. The combination significantly reduced pERK (p=0.0003) and pFAK (p=0.0172) relative to control. Analyzing the gene expression data using multiple MAPK signatures, the combination of avutometinib and VS-4718 caused significantly greater inhibition of the MAPK pathway relative to avutometinib alone. At the individual gene level, avutometinib + VS-4718 induced significant inhibition of the MAPK pathway genes SPRY4, EPHA2, ETV4, ETV5 and CCND1 relative to avutometinib alone, and this inhibition of SPRY4 and EPHA2 was confirmed at the protein level. Further, using multiple MYC signatures, avutometinib alone significantly induced MYC signaling, whereas the combination inhibited MYC signaling. Finally, significant inhibition of PI3K pathway signatures was also observed with the combination of avutometinib + VS-4718, whereas neither avutometinib nor VS-4718 alone showed a significant effect on the PI3K signatures. Conclusions: The combination of avutometinib with defactinib has shown preclinical and clinical activity in LGSOC greater than avutometinib alone, and is being evaluated in a randomized phase 3 trial in patients with LGSOC (RAMP-301; NCT06072781). These preclinical studies show that avutometinib + FAK inhibitor inhibits MAPK pathway signaling more strongly than avutometinib alone. Further, putative mechanisms of resistance to avutometinib, including MYC and PI3K signaling, were overcome by the combination of avutometinib with a FAK inhibitor in LGSOC models. Citation Format: Lisa Pickard, Konstantinos Mitsopolous, Theo Roumeliotis, Silvia Coma, Laura Hover, Alexis De Haven Brandon, Bora Gurel, Jiin Song, Priya S. Hibshman, A Cole Edwards, Jeffrey A. Klomp, Clint A. Stalnecker, Adrienne D. Cox, Jyoti Choudhary, Channing Der, Jonathan A. Pachter, Udai Banerji. Correlative preclinical studies to elucidate mechanisms of synergy of the combination of the RAF/MEK clamp avutometinib and the FAK inhibitor defactinib in low grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6368.