LAUSR

The development of covalent inhibitors targeting KRASG12C mutations offers a precision medicine approach to a large cohort of lung cancer patients previously lacking opportunities for targeted therapy. Despite promising initial responses ranging from disease control to partial response in most patients undergoing treatment, the efficacy of these inhibitors has been limited by a short duration of response. Several strategies have been advanced to delay or prevent acquired drug resistance in lung cancer patients treated with KRASG12C inhibitors. Many of these involve co-administration of other targeted therapies to prevent activation of Ras-dependent mitogen activated protein kinase (MAPK) signaling, which is a hallmark response to KRASG12C inhibitors. While this approach has proven effective in some patients, combination clinical trials and postmortem analysis of tumors that progressed on KRASG12C inhibitors demonstrate that non-MAPK-dependent mechanisms of resistance remain a major challenge. We have developed a panel of lung cancer cell lines with acquired resistance to the KRASG12C inhibitor sotorasib. While Erk phosphorylation is observed in all resistant models, treatment with a panel of Ras and MAPK pathway inhibitors demonstrates differential dependence on MAPK pathway activity, including complete MAPK independence in a resistant model derived from the H358 cell line. Mutation, transcription and phosphoproteomic analysis revealed that these resistant models exhibit metabolic reprogramming and activation of a variety of DNA damage response pathways. Based on differential phosphorylation of the transcriptional elongation kinases CDK12 and CDK13 in KRASG12C-treated cells, we hypothesized that inhibiting these kinases might prevent or revert acquired drug resistance. Our prior studies demonstrate that CDK12/13 inhibition reduces expression of a broad spectrum of DNA damage response and metabolic genes, and RNA sequencing confirms that these pathways are sensitive to the CDK12/13 inhibitor SR-4835 in both sotorasib-sensitive and -resistant cells. Resistant cells show differential responses to specific DNA damage-directed therapies and cell-line specific metabolic reprogramming, but up-front combinatorial treatment with SR-4835 prevents the development of acquired resistance to sotorasib across these models. Combined treatment with sotorasib and SR-4835 does not prevent Erk phosphorylation rebound; thus, the mechanism of SR-4835 in suppressing acquired resistance is independent of MAPK pathway reactivation. In vivo combination of sotorasib and SR-4835 potentiates drug response and prevents drug resistance in the H358 cell line, which can develop both MAPK-dependent and -independent drug resistance. These results demonstrate that targeting transcriptional elongation kinases in combination with sotorasib may benefit a broader spectrum of patients than MAPK-directed combination therapies and provide rationale for suppressing the DNA damage response and metabolic reprogramming as an approach to extend the efficacy of KRASG12C inhibitors. Citation Format: Yaakov E. Stern, Pompom Ghosh, Hitendra S. Solanki, Denis Imbody, Liznair Bridenstine, Hannah L. Walker-Mimms, John W. Mosior, Andrii Monastyrskyi, Derek R. Duckett, Eric B. Haura. Targeting transcriptional elongation kinases prevents adaptation to KRASG12C inhibitors in both MAPK-dependent and -independent models of acquired resistance [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr B035.