LAUSR

Selective KRAS G12C inhibitors, including AMG510 (sotorasib) and MRTX849 (adagrasib), have exhibited clinical activity in patients with non-small cell lung cancer (NSCLC); however, drug resistance and relapse inevitably occur through various mechanisms, which limits the ability of these therapeutic agents to achieve durable responses. Resistance mechanisms include feedback reactivation of compensatory, oncogenic signaling pathways and the attainment of a drug-tolerant state, each of which allows cancer cells to survive the anti-tumor effects of these highly active drugs. Compensatory mechanisms ameliorating KRAS blockade include HRAS/NRAS and the PI3K-AKT-mTOR pathway. Tipifarnib is a clinical stage farnesyltransferase inhibitor known to inhibit multiple farnesylation-dependent proteins in tumor cells. We have recently shown that tipifarnib can prevent feedback-mediated adaptive resistance to the PI3Kα inhibitor, alpelisib, through inhibition of both HRAS and RHEB, allowing simultaneous blockade of two key nodes of the oncogenic MAPK- and PI3K-signaling pathways. In another example, tipifarnib has been demonstrated by others to inhibit the ability of tumor cells to enter a drug-tolerant state induced by the EGFR inhibitor, osimertinib, in EGFR-mutant NSCLC models. In these models, inhibition of farnesylation of certain RHO proteins appear to contribute to the death of drug-tolerant cells prior to the emergence of acquired resistance mutations. Building on these two mechanisms of how tipifarnib may prevent adaptive resistance, we propose that tipifarnib can be used as an effective partner drug to delay or prevent the onset of adaptive resistance to KRAS G12C inhibitors. We have conducted in vitro 2D and 3D viability and regrowth experiments using combinations of tipifarnib with KRAS G12C inhibitors and have observed synergistic, anti-proliferative effects in KRAS G12C NSCLC cell lines as well as enhanced activity of combination in a KRAS G12C NSCLC PDX model. We are currently expanding the scope of in vitro and in vivo combination studies to further evaluate the molecular mechanism(s) of resistance that tipifarnib targets when combined with KRAS G12C inhibitors. Citation Format: Hetika Vora Patel, Alison Smith, Stacia Chan, Linda Kessler, Francis Burrows, Shivani Malik. Combination of tipifarnib with KRAS G12C inhibitors to prevent adaptive resistance [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 1079.