Functional inactivation of the oestrogen receptor by the antioestrogen, ZM 182780, sensitises tumour cells to reactive oxygen species.

Reactive oxygen species (ROS) play a fundamental role in both apoptotic and necrotic cell death. Their importance is highlighted by studies showing that they mediate cell death in response to radiotherapy and to some forms of chemotherapy. Here we provide the first evidence for a role of ROS in response to an antiendocrine agent currently undergoing clinical trials. Using the oestrogen receptor (ER) containing rat pituitary GH3 cell line, we show that cell death is induced by the pure steroidal antioestrogen, ZM 182780, and that this is blocked by the antioxidant, N-acetyl cysteine (NAC). By flow cytometry, we show that, prior to the onset of DNA breakdown measured by ELISA, ZM 182780 exposure has no significant effect on intracellular oxidant concentrations. In contrast, ZM 182780 exposure greatly increases sensitivity to oxidants generated by blocking cellular antioxidant pathways and from exogenous administration of hydrogen peroxide (H2O2). As both necrosis and apoptosis are controlled by mitochondrial function, further experiments conducted to determine mitochondrial membrane potential (Delta|gWm) have indicated that the ZM 182780-induced loss of ER function increases the ease with which oxidants collapse mitochondrial activity and, as a consequence, cell death.