Multidrug resistance (MDR) occurs frequently after long-term chemotherapy, resulting in refractory cancer and tumor recurrence. Therefore, combatting MDR is an important issue. Autophagy, a self-degradative system, universally arises during the treatment of sensitive and MDR cancer. Autophagy can be a double-edged sword for MDR tumors: it participates in the development of MDR and protects cancer cells from chemotherapeutics but can also kill MDR cancer cells in which apoptosis pathways are inactive. Autophagy induced by anticancer drugs could also activate apoptosis signaling pathways in MDR cells, facilitating MDR reversal. Therefore, research on the regulation of autophagy to combat MDR is expanding and is becoming increasingly important. We summarize advanced studies of autophagy in MDR tumors, including the variable role of autophagy in MDR cancer cells.

While searching for natural anti-hepatocellular carcinoma (HCC) components in Ailanthus altissima, we discovered that ailanthone had potent antineoplastic activity against HCC. However, the molecular mechanisms underlying the antitumor effect of ailanthone on HCC have not been examined. In this study, the antitumor activity and the underlying mechanisms of ailanthone were evaluated in vitro and in vivo. Mechanistic studies showed that ailanthone induced G0/G1-phase cell cycle arrest, as indicated by decreased expression of cyclins and CDKs and increased expression of p21 and p27. Our results demonstrated that ailanthone triggered DNA damage characterized by activation of the ATM/ATR pathway. Moreover, ailanthone-induced cell death was associated with apoptosis, as evidenced by an increased ratio of cells in the subG1 phase and by PARP cleavage and caspase activation. Ailanthone-induced apoptosis was mitochondrion-mediated and involved the PI3K/AKT signaling pathway in Huh7 cells. In vivo studies demonstrated that ailanthone inhibited the growth and angiogenesis of tumor xenografts without significant secondary adverse effects, indicating its safety for treating HCC. In conclusion, our study is the first to report the efficacy of ailanthone against Huh7 cells and to elucidate its underlying molecular mechanisms. These findings suggest that ailanthone is a potential agent for the treatment of liver cancer.

Betulinic acid (BA) and its derivatives are a class of high-profile drug candidates, but their anticancer effects on resistant cancer have rarely been reported. Although a few studies indicated mitophagy is related with drug resistance, its role in different cancer types and anticancer agents treatment remains largely unclear. Here, we find that B5G1, a new derivative of BA, induces cell death in multidrug resistant cancer cells HepG2/ADM and MCF-7/ADR through mitochondrial-apoptosis pathway. B5G1 also triggers mitophagy independent on Atg5/Beclin 1. Further mechanistic study indicates that B5G1 upregulates PTEN-induced putative kinase 1 (PINK1) to recruit Parkin to mitochondria followed by ubiquitination of Mfn2 to initiate mitophagy. Inhibition of mitophagy by PINK1 siRNA, mdivi-1, or bafilomycin A1 (Baf A1) promotes B5G1-induced cell death. In addition, ROS production and mitochondrial damage in B5G1-treated HepG2/ADM cells cause mitochondrial apoptosis and mitophagy. In vivo study shown that B5G1 dramatically inhibits HepG2/ADM xenograft growth accompanied by apoptosis and mitophagy induction. Together, our results provide the first demonstration that B5G1, as a novel mitophagy inducer, has the potential to be developed into a drug candidate for treating multidrug resistant cancer.

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