Disulfide Cleavage in a Dimeric Epipolythiodioxopiperazine Natural Product Diminishes Its Apoptosis-Inducing Effect but Enhances Autophagy in Tumor Cells

Gliocladicillin C (3) is a cytotoxic epipolythiodioxopiperazine (ETP) isolated from the Ophiocordyceps-associated fungus Clonostachys rogersoniana. Although the disulfides/polysulfides in ETPs are believed to account for their cytotoxicity, and 11′-deoxyverticillin A was demonstrated to induce apoptosis and autophagy, how they mediate apoptosis and autophagy remained unknown. Here, we revealed that 3 activated caspase-dependent apoptosis and autophagy in human tumor cells, while the prepared disulfide-cleavage product failed to induce reactive oxygen species production and PARP cleavage, but further enhanced the autophagic flux compared to 3. Gliocladicillin C and its derivative also increased the phosphorylation of AMP-activated protein kinase and stimulated autophagy by affecting the glycolytic pathway. These results demonstrated that the disulfides played an essential role in inducing apoptosis, but not autophagy.