Colon cancer-derived oncogenic EGFR G724S mutant identified by whole genome sequence analysis is dependent on asymmetric dimerization and sensitive to cetuximab

Abstract

BackgroundInhibition of the activated epidermal growth factor receptor (EGFR) with either enzymatic kinase inhibitors or anti-EGFR antibodies such as cetuximab, is an effective modality of treatment for multiple human cancers. Enzymatic EGFR inhibitors are effective for lung adenocarcinomas with somatic kinase domain EGFR mutations while, paradoxically, anti-EGFR antibodies are more effective in colon and head and neck cancers where EGFR mutations occur less frequently. In colorectal cancer, anti-EGFR antibodies are routinely used as second-line therapy of KRAS wild-type tumors. However, detailed mechanisms and genomic predictors for pharmacological response to these antibodies in colon cancer remain unclear.FindingsWe describe a case of colorectal adenocarcinoma, which was found to harbor a kinase domain mutation, G724S, in EGFR through whole genome sequencing. We show that G724S mutant EGFR is oncogenic and that it differs from classic lung cancer derived EGFR mutants in that it is cetuximab responsive in vitro, yet relatively insensitive to small molecule kinase inhibitors. Through biochemical and cellular pharmacologic studies, we have determined that cells harboring the colon cancer-derived G719S and G724S mutants are responsive to cetuximab therapy in vitro and found that the requirement for asymmetric dimerization of these mutant EGFR to promote cellular transformation may explain their greater inhibition by cetuximab than small-molecule kinase inhibitors.ConclusionThe colon-cancer derived G719S and G724S mutants are oncogenic and sensitive in vitro to cetuximab. These data suggest that patients with these mutations may benefit from the use of anti-EGFR antibodies as part of the first-line therapy.

Colorectal adenocarcinoma‐derived EGFR mutants are oncogenic and sensitive to EGFR‐targeted monoclonal antibodies, cetuximab and panitumumab

“…S4 and S4). Consistent with such inhibitory effects, the levels of p‐EGFR, p‐STAT5, p‐AKT and p‐ERK1/2 were significantly abolished in both cell lines after drug treatment (Figs. S4 and S4).…”

“…S5). These results demonstrate that in addition to the previously known G719S and G724S mutants, R165Q, R222C, P596L and K708R mutants are tumorigenic and exhibit a significant response to cetuximab and/or panitumumab, suggesting that these EGFR activating mutations may function as genomic determinants of response to the drugs.…”

“…Our previous studies demonstrated that there is a close correlation between dimerization dependency and the pharmacological effects of cetuximab, so we then tested this relationship in the colon‐cancer derived EGFR oncogenic mutants . While overexpression of dimerization‐competent EGFR mutations including G63R, E114K, R165Q, R222C, S492R, P596L, K708R, E709K and G724S render Ba/F3 cells to grow in the absence of IL‐3 (Fig.…”

“…EGFR mutations in CRC are relatively rare but mutations such as S492R located in EGFR subdomain III of the extracellular domain were identified to induce acquired resistance to cetuximab through prevention of binding . Additionally, the G724S mutant EGFR identified in colorectal adenocarcinoma is oncogenic and sensitive to cetuximab, suggesting that EGFR mutations can not only act as oncogenic drivers of CRC, but also as genomic predictors of cetuximab response among CRC patients harboring such mutations …”

Identification of an “Exceptional Responder” Cell Line to MEK1 Inhibition: Clinical Implications for MEK-Targeted Therapy

“…SW48 is a colorectal cancer cell line with three detected mutations in MAP2K1 (Q56P, H119Y, and D351G), as well as an activating mutation in EGFR (G719S). Our laboratory previously characterized the dependency of this cell line on EGFR signaling using the EGFR inhibitor cetuximab both in vitro and in xenografts (27). SW48 cells were also included in Project Achilles, resulting in a moderate dependence score to MAP2K1 knockdown (−0.3).…”