Malformin A1 promotes cell death through induction of apoptosis, necrosis and autophagy in prostate cancer cells

Malformin A(1) (MA(1)), a cyclopentapeptide isolated from fungal origin, has been identified to induce varieties of intriguing biological activities. Here, we reported the mode of mechanism underlying MA(1)-mediated cytotoxicity through induction of apoptosis, necrosis and autophagy in prostate cancer (PCa) cells. Human PCa cells PC3 and LNCaP were treated with MA(1), and cell viability, apoptosis, necrosis, mitochondrial damage, oxidative stress and autophagy were analyzed, respectively. Pharmacological inhibitors, transient transfection of plasmids and siRNAs were then used to identify the roles of oxidative stress and autophagy in MA(1)-triggered cell death. In both PC3 and LNCaP cells, MA(1) inhibited cell proliferation and triggered oxidative stress via the rapid accumulation of reactive oxygen species and a decrease in mitochondrial transmembrane potential. Mitochondrial damage by MA(1) triggered caspase activation and intracellular ATP deletion, leading to apoptosis and necrosis, respectively. Meanwhile, MA(1) activated autophagy as indicated by conversion of LC3BI to LC3BII and increased GFP-tagged LC3B punctate dots. Pharmacological inhibition of autophagy or knocking down LC3B attenuated MA(1)-mediated cell death. Excessive oxidative stress and decreased ATP stimulated AMPK/mTOR pathway, which led to induction of MA(1)-mediated autophagy. Coaction of apoptotic, necrotic and autophagic cell death induced by mitochondrial damage defines a novel mechanism contributing to the growth suppression of MA(1) in prostate cancer cells, and activation of autophagy might be a potential strategy for improving its chemotherapeutic effects.