HER2 kinase domain mutation results in constitutive phosphorylation and activation of HER2 and EGFR and resistance to EGFR tyrosine kinase inhibitors

Summary eu gene mutations have been identified in lung cancer. Expression of a HER2 mutant containing a G776YVMA insertion in exon 20 was more potent than wild-type HER2 in associating with and activating signal transducers, phosphorylating EGFR, and inducing survival, invasiveness, and tumorigenicity. HER2YVMA transphosphorylated kinase-dead EGFRK721R and EGFRWT in the presence of EGFR tyrosine kinase inhibitors (TKIs). Knockdown of mutant HER2 in H1781 lung cancer cells increased apoptosis and restored sensitivity to EGFR TKIs. The HER2 inhibitors lapatinib, trastuzumab, and CI-1033 inhibited growth of H1781 cells and cells expressing exogenous HER2YVMA. These data suggest that (1) HER2YVMA activates cellular substrates more potently than HER2WT; and (2) cancer cells expressing this mutation remain sensitive to HER2-targeted therapies but insensitive to EGFR TKIs.