PI3K inhibition sensitizes EGFR wild-type NSCLC cell lines to erlotinib chemotherapy

Tyrosine kinase inhibitors (TKIs) bring significant benefits for patients with cancers harboring epidermal growth factor receptor (EGFR) mutations. However, after treatment for a certain period, most patients ultimately acquire resistance. Numerous studies indicated that PI3K has an important role in tumor cell growth and drug sensitivity. Furthermore, inhibition of PI3K may lead to sensitization of non-small cell lung cancer (NSCLC) cells to EGFR-TKIs. The aim of the present study was to explore whether LY294002, an inhibitor of PI3K, is able to improve the sensitivity of NSCLC cell lines with wild-type EGFR to the EGFR-TKI erlotinib. An MTT assay was used to examine the effect of combined treatment with LY294002 and erlotinib on cell survival of two EGFR wild-type NSCLC cell lines, NCI-H661 and NCI-H460. Furthermore, flow cytometry was used to assess apoptosis in NCI-H661 and NCI-H460 cells after treatment with erlotinib and LY294002. In addition, the expression of downstream proteins was detected by western blot analysis. The results indicated that the number of viable NCI-H661 and NCI-H460 cells was dose-dependently reduced by erlotinib or LY294002. Compared to treatment with erlotinib alone, the cell apoptosis was enhanced if combined treatment of erlotinib and LY294002 was performed in NCI-H661 cells. Furthermore, combination treatment of erlotinib and LY294002 resulted in a significant reduction of phosphorylated p70S6K levels in NCI-H661 [PI3K catalytic subunit alpha (PI3KCA) wild-type] cells. However, this phenomenon was not observed in the NCI-H460 cell line (PIK3CA mutant-type). In conclusion, the present study indicated that inhibition of PI3K may have the potential to improve the sensitivity of NSCLC cells to an EGFR-TKI. However, the therapeutic effect may depend on the mutation status of PIK3CA.