Cucurbitacin E Exerts Anti-Proliferative Activity via Promoting p62-Dependent Apoptosis in Human Non-Small-Cell Lung Cancer A549 Cells

EGFR tyrosine kinase inhibitors (TKIs) are the first-line treatment for advanced EGFR-mutated non-small-cell lung cancer (NSCLC). However, NSCLC patients with wild-type EGFR and KRAS mutation are ineligible for EGFR-TKIs. Therefore, the discovery of new therapeutic agents is urgently needed for NSCLC patients who cannot receive targeted therapies. Natural products possess tremendous chemical diversity and have been extensively investigated for their anticancer activity. In this study, we found that Cucurbitacin E (Cu E), a triterpene of cucurbitacins widely presented in the edible plants of the Cucurbitaceae family, significantly inhibits the viability and proliferation of A549 cells that harbor wild-type EGFR and KRAS mutation. Our results revealed that Cu E increases cell-cycle arrest at G2/M and subG1 phase. Mechanistically, Cu E significantly inhibits the phosphorylation and protein levels of regulatory proteins and hinders G2/M cell-cycle progression. Meanwhile, the treatment of Cu E resulted in DNA damage response and apoptosis. For the first time, we observed that Cu E induces incomplete autophagy as evidenced by increased LC3B-II expression and p62-accumulation. Knockdown of p62 rescued the cells from Cu E-mediated anti-proliferative effect, apoptosis, DNA damage, and ROS production. These findings suggest that Cu E is a promising drug candidate for NSCLC.