Mechanisms underlying effect of the mycotoxin cytochalasin B on induction of cytotoxicity, modulation of cell cycle, Ca homeostasis and ROS production in human breast cells.

Cytochalasin B, a cell-permeable mycotoxin isolated from the fungus Phoma spp., shows a wide range of biological effects, among which its potent antitumor activity has raised great interests in different models. However, the cytotoxic activity of cytochalasin B and its underlying mechanisms have not been elucidated in breast cells. This study examined the effect of cytochalasin B on MCF 10A human breast epithelial cells and ZR-75-1 human breast cancer cells. Cytochalasin B (10-20μM) concentration-dependently induced cytotoxicity, cell cycle arrest, and [Ca] rises in ZR-75-1 cells but not in MCF 10A cells. In ZR-75-1 cells, cytochalasin B triggered G2/M phase arrest through the modulation of CDK1, cyclin B1, p53, p27 and p21 expressions. The Ca signal response induced by cytochalasin B was reduced by removing extracellular Ca and was inhibited by the store-operated Ca channel blocker 2-APB and SKF96365. In Ca-free medium, cytochalasin B induced Ca release through thapsigargin-sensitive endoplasmic reticulum stores. Moreover, cytochalasin B increased HO levels but reduced GSH levels. The apoptotic effects evoked by cytochalasin B were partially inhibited by prechelating cytosolic Ca with BAPTA-AM and the antioxidant NAC. Together, in ZR-75-1 cells but not in MCF 10A cells, cytochalasin B activated Ca-associated mitochondrial apoptotic pathways that involved G2/M phase arrest and ROS signaling. Furthermore, cytochalasin B induced [Ca] rises by releasing Ca from the endoplasmic reticulum and causing Ca influx through 2-APB or SKF96365-sensitive store-operated Ca entry. Our findings provide new insights into the possible application of cytochalasin B in human breast cancer therapy.