A novel treatment strategy for EGFR mutant NSCLC with T790M-mediated acquired resistance

The purpose of our study was to identify novel kinase inhibitors for the treatment of genetic subsets of non-small cell lung cancer (NSCLC). NSCLC cell lines (n = 8) with known oncogenic backgrounds (K-Ras, EGFR and EML4-ALK) were exposed to several kinase inhibitors and analyzed for cell growth/cytotoxicity and signaling. Gö6976, a classical protein kinase C inhibitor, showed high potency against mutated EGFR and was further validated in vitro using additional NSCLC lines (n = 4) and Ba/F3 models and in vivo using a xenograft model. Gö6976 was identified to be a potent inhibitor of mutated EGFR with IC50 values from 0.033 nM to 3.3 μM and down regulating phosphorylation of EGFR, AKT and ERK1/2 at concentrations in the range of the IC(50) values. Gö6976 has only a minor effect on wild-type EGFR and cell lines independent of signaling from the mutant EGFR. Most importantly, the activity of Gö6976 remains unchanged despite the presence of the T790M-mediated resistance, and it prevents the occurrence of this resistance in vitro. Gö6976 was also shown to significantly reduce tumor growth in an in vivo xenograft model with a EGFR-mutated NSCLC cell line containing T790M. These findings demonstrate that Gö6976 acts as a potent inhibitor of mutant EGFR despite the presence of T790M, the most important mechanism of acquired resistance for EGFR tyrosine kinase inhibitors, in both in vitro and in vivo models.