OBJECTIVETo explore the correlation of ras gene to the drug resistance of nasopharyngeal carcinoma to cetuximab.

METHODSCultured 5-8F/Erbitux cells were induced by stepwise exposure to increasing doses of cetuximab. MTT assay was used to determine the IC50 (half inhibitory concentration) of cetuximab and the drug resistance index (RI). Western blotting was employed to detect the protein levels of H-ras and K-ras. Real-time PCR was used to detect the expression of H-ras and K-ras. Gene sequencing was performed to identify potential mutations in H-ras and K-ras genes.

RESULTSWe successfully induced cetuximab-resistant 5-8F/Erbitux hNPC cells by stepwise exposure to increasing doses of cetuximab. After treatment with cetuximab for 3 and 5 days, the RI of 5-8F/Erbitux cells was 1.2 and 1.1, respectively. The 5-8F/Erbitux cells had increased levels of H-ras and K-ras protein expressions (P<0.001) and enhanced gene expressions of H-ras (P=0.016) and ras-p21 (P=0.113) with decreased K-ras gene expression (P=0.000). Sequence analysis identified no mutations in the H-ras and K-ras genes in codons 12, 13, 59, and 61.

CONCLUSIONGene amplification and overexpression of H-ras is the major mechanism that causes the drug resistance of 5-8F/Erbitux cells to cetuximab.