Metformin combined with nelfinavir induces SIRT3/mROS-dependent autophagy in human cervical cancer cells and xenograft in nude mice.

The molecular mechanisms underlying the antineoplastic properties of metformin combined with nelfinavir remain elusive. To explore this question, transmission electron microscopy (TEM) was used to observe the combinatorial effect of inducing autophagosome formation in human cervical cancer cells. Western blotting respectively assayed protein expression of LC3I, LC3II, Beclin-1, Autophagy-related protein 7 (Atg7), Autophagy-related protein 3 (Atg3), NAD-dependent deacetylase sirtuin-3 (SIRT3) and major histocompatibility complex class I chain-related gene A (MICA). Lactate dehydrogenase (LDH) cytotoxicity assay evaluated natural killer (NK) cell cytotoxicity in the presence of metformin and nelfinavir in combination or each drug alone. Using tumor xenografts in a nude mouse model, antitumor efficacy of the drug combination was assessed. We found that the drug combination could induce autophagosome formation in human cervical cancer cells. The biomarker proteins of autophagy, including Beclin-1, Atg7 and Atg3, decreased, but the ratios of LC3I/II increased. We also found that this drug combination sensitizes human cervical cancer cells to NK cell-mediated lysis by increasing the protein of SIRT3 and MICA. Moreover, this drug combination markedly induced autophagy of SiHa xenografts in nude mice. Therefore, it can be concluded that metformin, in combination with nelfinavir, can induce SIRT3/mROS-dependent autophagy and sensitize NK cell-mediated lysis in human cervical cancer cells and cervical cancer cell xenografts in nude mice. Thus, our findings have revealed the detailed molecular mechanisms underlying the antitumor effects of metformin in combination with nelfinavir in cervical cancer.