Methyl protodioscin induces G₂/M arrest and apoptosis in K562 cells with the hyperpolarization of mitochondria

Methyl protodioscin is a furostanol bisglycoside with antitumor properties. The present study investigated its effects on human chronic myelogenous leukemia K562 cells. Cell cycle analysis showed that methyl protodioscin caused distinct G₂/M arrest, with the appearance of polyploidy population. The levels of cyclin B1 decreased, whereas Cdc2 kept at a steady level. Subsequent apoptosis after G₂/M blockage was demonstrated through DNA fragmentation and the annexin V staining assay. Methyl protodioscin induced a biphasic alteration (i.e. an early hyperpolarization, followed by depolarization) in mitochondrial membrane potential of K562 cells. The transient decline of intracellular Ca²⁺ concentration was observed at early stage. The generation of reactive oxygen species was also detected. The anti-apoptotic Bcl-x_L transiently increased and then decreased. And the pro-apoptotic Bax was markedly up-regulated. Taken together, these data demonstrated that methyl protodioscin inhibits K562 cell proliferation via G₂/M arrest and apoptosis, with mitochondrial hyperpolarization and the disruption of Ca²⁺ homeostasis playing important roles.