Inhibition of
heat shock protein 90 (Hsp90) can lead to degradation of multiple client
proteins, which are involved in
tumor progression.
Epidermal growth factor receptor (EGFR) is one of the most potent oncogenic client
proteins of Hsp90. Targeted inhibition of EGFR has shown clinical efficacy in the treatment of patients with
non-small-cell lung cancer (NSCLC). However, primary and acquired resistance to the existing EGFR inhibitors is a major clinical problem. In the present study, we investigated the effect of the novel Hsp90 inhibitor
CH5164840 on the antitumor activity of
erlotinib. The NSCLC cell lines and xenograft models were treated with
CH5164840 and
erlotinib to examine their mechanisms of action and cell growth inhibition. We found that
CH5164840 showed remarkable antitumor activity against NSCLC cell lines and xenograft models. The addition of
CH5164840 enhanced the antitumor activity of
erlotinib against NCI-H292 EGFR-overexpressing xenograft models. Phosphorylation of Stat3 increased with
erlotinib treatment in NCI-H292 cells, which was abrogated by Hsp90 inhibition. Furthermore, in a NCI-H1975 T790M mutation
erlotinib-resistant model,
CH5164840 enhanced the antitumor activity of
erlotinib despite the low efficacy of
erlotinib treatment alone. In addition, ERK signaling was effectively suppressed by combination treatment with
erlotinib and
CH5164840 in a NCI-H1975
erlotinib-resistant model. Taken together, these data indicate that
CH5164840 has potent antitumor activity and is highly effective in combination with
erlotinib against NSCLC
tumors with EGFR overexpression and mutations. Our results support the therapeutic potential of
CH5164840 as a Hsp90 inhibitor for combination
therapy with EGFR-targeting agents against EGFR-addicted NSCLC.