Effect of siRNAs targeting the EGFR T790M mutation in a non-small cell lung cancer cell line resistant to EGFR tyrosine kinase inhibitors and combination with various agents.

The epidermal growth factor receptor (EGFR) is a validated therapeutic target in non-small cell lung cancer (NSCLC). However, some mutations confer resistance to current available agents, especially the frequently occurring T790M mutation. In the current study, we have examined, in a NSCLC cell line H1975 containing both L858R and T790M mutations, the effect of T790M-specific-siRNAs versus other EGFR-specific-siRNAs. T790M-specific-siRNAs were able to inhibit T790M and EGFR mRNA, to reduce EGFR protein expression, as well as to reduce the cell growth and induce cell caspase activity in H1975 cells. However, this effect showed less potency compared to the other EGFR-specific-siRNAs. EGFR-specific-siRNAs strongly inhibited cell growth and induced apoptosis in H358, H1650, H292, HCC827 and also in H1975 cells, which showed weak response to tyrosine kinase inhibitors (TKIs) or cetuximab. The addition of T790M-specific-siRNAs could rescue the sensitivity of T790M mutant H1975 cells to TKIs. The combination of T790M-specific-siRNAs and cetuximab also additively enhanced cell growth inhibition and induction of apoptosis in H1975 cells. Among the anti-EGFR agents tested, the strongest biological effect was observed when afatinib was combined with T790M-specific-siRNAs. Afatinib also offered extra effect when combined with cetuximab in H1975 cells. In conclusion, knock-down of T790M transcript by siRNAs further decreases the cell growth of T790M mutant lung cancer cells that are treated with TKIs or cetuximab. The combination of a potent, irreversible kinase inhibitor such as afatinib, with T790M-specific-siRNAs should be further investigated as a new strategy in the treatment of lung cancer containing the resistant T790M mutation.