Abstract 410P
Background
EGFR is involved in a dominant resistance mechanism to KRASG12C inhibitors in colorectal cancer. The antiproliferative effects of MRTX1133 in KRASG12D-mutant colorectal cancer (LS1741) showed strong synergism with cetuximab. In KRASG12C-mutant lung cancer patients, fulzerasib plus cetuximab attained an 80% response rate (KROCUS). The synergism of fulzerasib or sotorasib (KRASG12C inhibitors) with cetuximab in KRAS lung cancer cell lines was evaluated, as well as RAS signaling rebound, alterations in urea cycle, arginosuccinate synthase (ASS1) and fumarate levels.
Methods
KRAS G12C mutated cell lines, H358, H23, H2122, H1792, H2030 and Mia-PACA-2 were used. Reagents, antibodies, cetuximab and sotorasib were purchased. Fulzerasib was provided by Genfleet. Cell viability was assessed by MTT. The following primary antibodies were used for western blot analysis: EGFR Y1068, HER3 Y1289, FASN, EphA2 S897, YAP Y357, MIG6, ASS1, ERK1/2 T202/Y204, MRAS and Hsp90. Fumarate levels were measured.
Results
The IC50 values for both fulzerasib and sotorasib were very low in H358, H2122, and Mia PaCa-2 cells, but high in H2030 cells, and moderately elevated in the H23 cell line. The combination of these inhibitors with cetuximab (50 μg/ml) enhances cytotoxicity. Antiproliferative effects were more evident in H358 cells with a combination index of 0.53 when combined with fulzerasib. Other cell lines revealed slightly synergistic effects, less than 1, while additive effects were observed in H23 cells. Western blot showed elimination of ERK rebound (ERK1/2) caused by fulzerasib or sotorasib alone in H358 cells, attenuating YAP Y357 phosphorylation. Expression of ASS1 was very low in H23 compared to H358. In the latter, fumarate levels were not significantly altered with fulzerasib treatment.
Conclusions
Cetuximab combined with fulzerasib or sotorasib inhibits cell viability in H358 cell line, preventing ERK rebound and YAP1 activation. Levels of ASS1were stable before treatment. In contrast, ASS1 levels were low and upregulated after sotorasib treatment in H23 cells. Low ASS1 expression is shown to harbor an ominous prognosis. Further research could clarify the relevance of ASS1 as a biomarker and therapeutic target.
Funding
GenFleet Therapeutics Inc.
Disclosure
All authors have declared no conflicts of interest.