YC-1 potentiates the antitumor activity of gefitinib by inhibiting HIF-1α and promoting the endocytic trafficking and degradation of EGFR in gefitinib-resistant non-small-cell lung cancer cells

The tyrosine kinase inhibitor (TKI) gefitinib exerts good therapeutic effect on NSCLC patients with sensitive EGFR-activating mutations. However, most patients ultimately relapse due to the development of drug resistance after 6-12 months of treatment. Here, we showed that a HIF-1 a inhibitor, YC-1, potentiated the antitumor efficacy of gefitinib by promoting EGFR degradation in a panel of human NSCLC cells with wild-type or mutant EGFRs. YC-1 alone had little effect on NSCLC cell survival but significantly enhanced the antigrowth and proapoptotic effects of gefitinib. In insensitive NSCLC cell lines, gefitinib efficiently inhibited the phosphorylation of EGFR but not the downstream signaling of ERK, AKT and STAT3; however, when combined with YC-1 treatment, these signaling pathways were strongly impaired. Gefitinib treatment induced EGFR arrest in the early endosome, and YC-1 treatment promoted delayed EGFR transport into the late endosome as well as receptor degradation. Moreover, the YC-1-induced reduction of HIF-1 alpha protein was associated with the enhancement of EGFR degradation. HIF-1 alpha knockdown promoted EGFR degradation, showing synergistic antigrowth and proapoptotic effects similar to those of the gefitinib and YC-1 combination treatment in NSCLC cells. Our findings provide a novel combination treatment strategy with gefitinib and YC-1 to extend the usage of gefitinib and overcome gefitinib resistance in NSCLC patients.