Abstract B53: Differential response of distinct KRAS mutants to SHP2 inhibition
Authors: Mainardi Sara , Bosma Astrid , Mulero-Sánchez Antonio , Bernards René 
Published: June 2021

Abstract
Introduction: RAS is mutated in 30% of tumors and is still considered “undruggable.” Among RAS genes KRAS is the most frequently mutated, mostly at residues G12, G13 and Q61, impairing its intrinsic and GAP-mediated GTP hydrolysis capacity (Prior et al., Cancer Res 2012). Nevertheless, specific mutations are differently distributed in human cancers (G12 89%, G13 9%, Q61 1%). In particular, G12D (36%) is prevalent over G12C (14%) and G12V (23%). Distinct oncogenic mutations differently affect RAS GTP hydrolysis capacity (Lu et al., Sci Rep 2016; Hunter et al., Mol Cancer Research 2015), with G12C preserving the highest GTPase activity and Q61 mutants being the most compromised. This implies that some KRAS mutants could be sensitive to upstream regulation, as suggested by the in vivo sensitivity of KRAS mutant tumors to SHP2 inhibitors (Mainardi et al. and Ruess et al., Nat Med 2018; Fedele et al., Cancer Discov 2018). In order to finely predict the response to the SHP2 inhibitor SHP099 (Chen et al., Nature 2016) in KRAS mutant patients, we used a panel of isogenic Rasless murine embryonic fibroblasts (MEFs) (Esposito et al., Semin Cancer Biol 2018) expressing human wild-type or mutant (G13D, G12C, G12D, G12V or Q61R) KRAS genes, and studied their response to SHP099, either alone or in combination with the MEK inhibitor AZD6244.
Materials and Method: The panel of isogenic RAS-dependent MEFs was provided by the NCI RAS Initiative. In vitro, RAS-GTP loading was evaluated and dose-response curves generated based on cell viability assays. For xenograft experiments, 5x106 cells were subcutaneously injected in NSG mice. After tumor establishment (200mm3) mice were treated either with vehicle, SHP099 75mg/kg, AZD6244 25 mg/Kg or a combination of the last two.
Results and Discussion: In vitro, we found that when cultured in 3% FCS, the most GTPase-proficient KRAS mutants (G13D and G12C) are more sensitive to SHP099 as compared to the most impaired (G12D and Q61R). Response to SHP099 was accompanied by a reduction in RAS-GTP loading. Surprisingly, in vivo results using xenograft models showed no correlation between residual GTPase activity of the mutants and sensitivity to SHP099. Nevertheless, synergy between SHP2 and MEK inhibitors treatment was more pronounced in the GTPase-proficent mutants, suggesting a possible correlation between residual intrinsic GTP hydrolysis capacity of the mutants and their resistance to MEK inhibitors through feedback activation of receptor tyrosine kinases (Sun et al., Cell Rep 2014).
Conclusion: Our data confirm single-agent activity of SHP099 against proliferation driven by a subset of KRAS mutants, and suggest that mutants with higher residual GTPase capacity could better benefit from combined SHP2 and MEK inhibition.
Citation Format: Sara Mainardi, Astrid Bosma, Antonio Mulero-Sánchez, René Bernards. Differential response of distinct KRAS mutants to SHP2 inhibition [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr B53.