Abstract 1675: Evaluation of combination strategies with RAS-targeted inhibitors in multi-cell type spheroids

Abstract RAS genes are among the most frequently mutated oncogenes in cancer. Though previously considered undruggable, agents have recently been developed that specifically target RAS. The agents can be categorized as (1) those that selectively target specific RAS oncoproteins and (2) pan-RAS inhibitors that target a wide range of RAS alterations, including oncogenic variants and amplifications. This study evaluated the activity of four novel RAS-targeted inhibitors in combination with other targeted agents in thirty solid tumor cell lines of diverse cancer types. These included twenty-six patient-derived cancer cell lines from the NCI Patient-Derived Models Repository (https://pdmr.cancer.gov/) and four established cell lines. The cells were grown as multi-cell type (mct) tumor spheroids from 60% malignant cells, 25% endothelial cells, and 15% mesenchymal stem cells. All agents were tested at concentrations up to the clinical Cmax value, if known or 10 µM. As single agents, the KRAS-G12C inhibitors RMC-6291 and divarasib, along with the KRAS-G12D inhibitor MRTX-1133, demonstrated selective activity against the mct tumor spheroids harboring the targeted variants. In contrast, the pan-RAS(ON) inhibitor RMC-6236 demonstrated activity against the mct tumor spheroids harboring a range of KRAS variants or wild-type KRAS. When used in combination, each of the four RAS-targeted inhibitors exhibited strong synergistic effects with SHP2 inhibitors as determined by the Bliss independence model and reductions in cell viability and spheroid volume. In tumor models harboring different KRAS variants, the pan-RAS(ON) inhibitor showed increased cytotoxicity with the MEK inhibitor cobimetinib, as well as PI3K-AKT-mTOR pathway inhibitors, such as inavolisib (PI3Kα), ipatasertib (AKT), and sapanisertib (mTORC1/2). When the same agents were combined with variant-specific KRAS inhibitors similar effects were observed in mct tumor spheroids carrying the corresponding RAS variant. These preclinical findings might provide guidance for the selection of combination regimens with KRAS inhibitors to improve clinical efficacy. Funded by NCI Contract No. 75N91019D00024. Citation Format: Thomas S. Dexheimer, Nathan P. Coussens, Thomas E. Silvers, Eric M. Jones, Naoko Takebe, James H. Doroshow, Beverly A. Teicher. Evaluation of combination strategies with RAS-targeted inhibitors in multi-cell type spheroids [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 1675.