Alterations in genes of the EGFR signaling pathway and their relationship to EGFR tyrosine kinase inhibitor sensitivity in lung cancer cell lines.
BACKGROUND
Deregulation of EGFR signaling is common in non-small cell lung cancers (NSCLC) and this finding led to the development of tyrosine kinase inhibitors (TKIs) that are highly effective in a subset of NSCLC. Mutations of EGFR (mEGFR) and copy number gains (CNGs) of EGFR (gEGFR) and HER2 (gHER2) have been reported to predict for TKI response. Mutations in KRAS (mKRAS) are associated with primary resistance to TKIs.


RESULTS
We investigated the relationship between mutations, CNGs and response to TKIs in a large panel of NSCLC cell lines. Genes studied were EGFR, HER2, HER3 HER4, KRAS, BRAF and PIK3CA. Mutations were detected by sequencing, while CNGs were determined by quantitative PCR (qPCR), fluorescence in situ hybridization (FISH) and array comparative genomic hybridization (aCGH). IC50 values for the TKIs gefitinib (Iressa) and erlotinib (Tarceva) were determined by MTS assay. For any of the seven genes tested, mutations (39/77, 50.6%), copy number gains (50/77, 64.9%) or either (65/77, 84.4%) were frequent in NSCLC lines. Mutations of EGFR (13%) and KRAS (24.7%) were frequent, while they were less frequent for the other genes. The three techniques for determining CNG were well correlated, and qPCR data were used for further analyses. CNGs were relatively frequent for EGFR and KRAS in adenocarcinomas. While mutations were largely mutually exclusive, CNGs were not. EGFR and KRAS mutant lines frequently demonstrated mutant allele specific imbalance i.e. the mutant form was usually in great excess compared to the wild type form. On a molar basis, sensitivity to gefitinib and erlotinib were highly correlated. Multivariate analyses led to the following results: 1. mEGFR and gEGFR and gHER2 were independent factors related to gefitinib sensitivity, in descending order of importance. 2. mKRAS was associated with increased in vitro resistance to gefitinib.


CONCLUSIONS
Our in vitro studies confirm and extend clinical observations and demonstrate the relative importance of both EGFR mutations and CNGs and HER2 CNGs in the sensitivity to TKIs.
Gandhi
Jeet
J
Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Zhang
Jianling
J
Xie
Yang
Y
Soh
Junichi
J
Shigematsu
Hisayuki
H
Zhang
Wei
W
Yamamoto
Hiromasa
H
Peyton
Michael
M
Girard
Luc
L
Lockwood
William W
WW
Lam
Wan L
WL
Varella-Garcia
Marileila
M
Minna
John D
JD
Gazdar
Adi F
AF
D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D004252:DNA Mutational Analysis; D066246:ErbB Receptors / Q000235:genetics* / Q000378:metabolism; D000077156:Gefitinib; D018628:Gene Dosage; D006801:Humans; D009154:Mutation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D011799:Quinazolines / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics*; D018631:ras Proteins / Q000235:genetics*
D066246:ErbB Receptors; D000077156:Gefitinib; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D018631:ras Proteins; C117307:KRAS protein, human; C508053:ERBB2 protein, human