Variant-selective and pan-RAS inhibitors enhance targeted agent activity in patient-derived multi-cell type tumor spheroids

Abstract RAS genes are among the most frequently altered oncogenes in cancer. Recently developed agents selectively target specific RAS variants or broadly inhibit multiple RAS alterations, including oncogenic variants and amplifications. Four RAS-targeted inhibitors were evaluated in combination with pathway-directed agents across twenty-nine solid tumor models, including twenty-six patient-derived lines from the NCI Patient-Derived Models Repository and three established cell lines. Multi-cell type tumor spheroids were generated using malignant (60%), endothelial (25%), and mesenchymal stem cells (15%). Drug response was assessed by seven-day viability and longitudinal volumetric imaging. As single agents, the KRAS G12C inhibitors elironrasib (RMC-6291) and divarasib, and the KRAS G12D inhibitor MRTX1133, demonstrated variant-selective activity. The pan-RAS(ON) inhibitor daraxonrasib (RMC-6236) suppressed growth across models harboring diverse RAS alterations and wild-type RAS, consistent with broader RAS pathway dependence. All four RAS inhibitors produced positive Bliss scores with SHP2 inhibition and reductions in viability and spheroid volume, consistent with vertical blockade of RAS-MAPK signaling. Daraxonrasib with the MEK inhibitor cobimetinib produced predominantly additive responses with localized Bliss-defined synergy. In addition, daraxonrasib and MRTX1133 combinations with PI3K-AKT-mTOR inhibitors reduced viability and localized positive Bliss scores, with many matrices remaining predominantly additive. MRTX1133 combinations reduced viability and produced the highest positive Bliss scores in KRAS G12D models, whereas daraxonrasib exhibited broader activity across RAS genotypes. These findings provide mechanistic support for rational combination strategies targeting convergent RAS effector pathways and inform the design of genotype-directed clinical trials.