Cetuximab co-treatment with KRAS G12C inhibitors fulzerasib and sotorasib in human KRAS G12C non-small cell lung cancer cells.

Resistance to KRAS G12C inhibitors is a major cause of poor prognosis in non-small cell lung cancer (NSCLC). Sotorasib and fulzerasib target the KRAS protein in the guanosine diphosphate (GDP)-bound inactive state. Used in monotherapy in non-small cell lung cancer (NSCLC) patients, these drugs yielded response rates of 41% and 49% and median progression-free survival of 6.3 and 9.7 months, respectively. Mounting evidence points out that feedback activation of epidermal growth factor receptor (EGFR) inhibits the hydrolysis of KRAS guanosine triphosphate (GTP)-bound active state and reactivates RAS-mitogen-activated protein kinase (MAPK) signaling, leading to drug resistance. Here, we demonstrated that cetuximab enhanced the antitumor growth effect of fulzerasib in vitro in H358 cells and prolonged the survival of mice bearing subcutaneous H358 xenografts. Moreover, we demonstrated that cotreatment suppressed the expression of ERK, AKT, as well as MRAS and YAP1. Additionally, the combination of fulzerasib with cetuximab also abolished the viability of H358 cells, being less effective for H23 and H2030 cells. This effect was accompanied by YAP1 and MRAS overexpression, especially in H2030 cells. Ultimately, we demonstrated that MIG6, a feedback negative regulator of EGFR, is suppressed in the three cell lines starting at the 24-h time point with fulzerasib or sotorasib. Concurrently, ASS1, initially low in all three cell lines, was upregulated following therapy with fulzerasib or sotorasib, with or without cetuximab. These alterations were associated with increased fumarate levels in all three cell lines examined. Notably, the cotreatment response of H358 cells mirrors clinical trials with KRAS G12C colorectal cancer and NSCLC patients, where the combination of cetuximab with KRAS G12C inhibitors resulted in increased response and progression-free survival. Our findings provide insight into further tailoring EGFR inhibitor cotreatment in KRAS G12C NSCLC patients.