Oncogenic Transformation by Inhibitor-Sensitive and -Resistant EGFR Mutants

Abstract

BackgroundSomatic mutations in the kinase domain of the epidermal growth factor receptor tyrosine kinase gene EGFR are common in lung adenocarcinoma. The presence of mutations correlates with tumor sensitivity to the EGFR inhibitors erlotinib and gefitinib, but the transforming potential of specific mutations and their relationship to drug sensitivity have not been described.Methods and FindingsHere, we demonstrate that EGFR active site mutants are oncogenic. Mutant EGFR can transform both fibroblasts and lung epithelial cells in the absence of exogenous epidermal growth factor, as evidenced by anchorage-independent growth, focus formation, and tumor formation in immunocompromised mice. Transformation is associated with constitutive autophosphorylation of EGFR, Shc phosphorylation, and STAT pathway activation. Whereas transformation by most EGFR mutants confers on cells sensitivity to erlotinib and gefitinib, transformation by an exon 20 insertion makes cells resistant to these inhibitors but more sensitive to the irreversible inhibitor CL-387,785.ConclusionOncogenic transformation of cells by different EGFR mutants causes differential sensitivity to gefitinib and erlotinib. Treatment of lung cancers harboring EGFR exon 20 insertions may therefore require the development of alternative kinase inhibition strategies.

EGF-independent activation of cell-surface EGF receptors harboring mutations found in gefitinib-sensitive lung cancer

“…Jiang et al (2005) recently reported a similar observation for just the G695S and L834R EGFR mutants in Ba/F3 cells. Moreover, Greulich et al (2005) found that several of the EGFR mutants studied here can transform NIH 3T3 cells. Thus, from our own studies and those published recently by other groups Jiang et al, 2005;Chen et al, 2006;Sakai et al, 2006), it appears that the EGFR mutations identified in gefitinibresponsive lung cancer patients are oncogenic.…”

Molecular pathology of lung cancer: key to personalized medicine

“…[67][68][69][70][71] However, insertion mutations of exon 20, D770_N771 (insNPG), D770_N771 (insSVQ), D770_N771 (insG), and point mutations in exon 20 (V769L, N771T) were associated with EGFR TKI resistance. 12,195 This observation has been confirmed in an in vitro model in which insertion mutations in exon 20 rendered transformed cells less responsive to EGFR TKIs Figure 7 Suggested algorithm for molecular testing for patients with lung adenocarcinoma. The algorithm defines the rationale in selecting patients who could benefit from EGFR and EML4-ALKA targeted therapy.…”

“…Exons 18-21 in the tyrosine kinase region of the EGFR gene are scaled up; a detailed list of EGFR mutations in these exons associated with sensitivity (green) or resistance (orange) to EGFR TKI. 6,12,[67][68][69][70][71][80][81][82][83][84]195 The frequency of the mutations is labeled to the side of the color-coded bars. The most prevalent EGFR mutations are in-frame deletions of exon 19 (45%), followed by L858R substitution in exon 21 (41%).…”

“…195 Insertion mutation in exon 20 at 770 renders the EGFR 100-fold less sensitive to TKIs when compared with the sensitizing mutations. 195 The mutation T790M, which is associated with B50% of acquired resistance, has also been linked to primary resistance, although infrequently (o5% of such cases) (Figure 2). 179 Approximately 10-25% of EGFR-mutant lung adenocarcinomas do not respond to an EGFR TKI.…”

Autophosphorylation of the carboxyl‐terminal domain is not required for oncogenic transformation by lung‐cancer derived EGFR mutants

“…Soft agar assays were carried out in triplicate as previously described 15, 16. Photographed images of soft agar colonies taken after 2–3 weeks were quantified using Image J software (NIH).…”