A Beclin 1-targeting stapled peptide synergizes with erlotinib to potently inhibit proliferation of non-small-cell lung cancer cells

Epidermal Growth Factor Receptor (EGFR) is a major drug target for non-small-cell lung carcinoma (NSCLC). Tyrosine Kinase Inhibitors (TKIs) like erlotinib are potent inhibitors of EGFR and have achieved impressive clinical success against NSCLC. However, NSCLC cells readily develop resistance to TKIs by acquiring mutations in EGFR or other oncogenes. Novel strategies to inhibit EGFR are needed to overcome this urgent problem of TKI resistance. Beclin 1 is an essential autophagy protein and is intimately involved in tumorigenesis and EGFR signaling. Here we present data to show that a Beclin 1-targeting stapled peptide Tat-SP4 can inhibit the EGFR signaling pathway by enhancing the Beclin 1-mediated endolysosomal degradation of EGFR. This inhibition mechanism is orthogonal to that employed by TKIs and is effective against either wild-type or mutant EGFR. Tat-SP4 alone showed moderate anti-proliferative efficacy in NSCLC cells but synergized with erlotinib to potently inhibit NSCLC proliferation. These results suggest that Beclin 1-targeting stapled peptides may be used in combination with TKIs to enhance their efficacy, particularly for NSCLC subtypes refractory to current regiments.