LLC cell lines’ response and resistance to KRAS G12C inhibitors.

e20710 Background: KRAS G12C mutations define a therapeutically targetable subset of non–small cell lung cancer (NSCLC); however, acquired resistance to covalent KRAS G12C inhibitors limits the durability of responses. The molecular determinants underlying differential sensitivity and resistance to these agents remain incompletely defined. Methods: KRAS G12C–mutant murine Lewis lung carcinoma (LLC) cell lines were evaluated in vitro, including parental cells and lines derived following prolonged exposure to KRAS G12C inhibition. Cells were treated with increasing concentrations of covalent KRAS G12C inhibitors, and proliferation was monitored over time. MAPK pathway activity was evaluated by immunoblotting for phosphorylated and total ERK1/2 and MEK1/2 following acute drug exposure, with signal intensities quantified and normalized to loading controls. Experiments were performed with biological replicates. Results: In parental KRAS G12C–mutant LLC cells, adagrasib treatment produced a clear, concentration-dependent reduction in proliferation across multiple concentrations, whereas sotorasib produced comparatively limited growth inhibition. LLC lines derived following continuous sotorasib exposure exhibited markedly reduced sensitivity to sotorasib but retained partial sensitivity to adagrasib. Analysis of downstream signaling revealed differential suppression of ERK and MEK phosphorylation between the two inhibitors, with resistant lines maintaining persistent MAPK pathway activity during sotorasib treatment. These signaling and proliferation patterns were consistent across multiple drug concentrations and time points. Conclusions: KRAS G12C–mutant lung cancer models with acquired resistance exhibit sustained MAPK pathway activity despite continued KRAS G12C inhibition, accompanied by distinct differences in growth suppression and downstream signaling between inhibitors. These findings suggest that resistance to KRAS G12C–targeted therapy is not uniform across the drug class and highlight the need to investigate drug-specific resistance mechanisms and strategies to modulate downstream pathway signaling.