Parthenolide induces superoxide anion production by stimulating EGF receptor in MDA-MB-231 breast cancer cells

The sesquiterpene lactone parthenolide (PN) has recently attracted considerable attention because of its anti-microbial, anti-inflammatory and anticancer effects. However, the mechanism of its cytotoxic action on tumor cells remains scarcely defined. We recently provided evidence that the effect exerted by PN in MDA-MB-231 breast cancer cells was mediated by the production of reactive oxygen species (ROS). The present study shows that PN promoted the phosphorylation of EGF receptor (phospho-EGFR) at Tyr1173, an event which was observed already at 1 h of incubation with 25 µM PN and reached a peak at 8-16 h. This effect seemed to be a consequence of ROS production, because N-acetylcysteine (NAC), a powerful ROS scavenger, prevented the increment of phospho-EGFR levels. In addition fluorescence analyses performed using dihydroethidium demonstrated that PN stimulated the production of superoxide anion already at 2-3 h of incubation and the effect further increased prolonging the time of treatment, reaching a peak at 8-16 h. Superoxide anion production was markedly hampered by apocynin, a well known NADPH oxidase (NOX) inhibitor, suggesting that the effect was dependent on NOX activity. The finding that AG1478, an EGFR kinase inhibitor, substantially blocked both EGFR phosphorylation and superoxide anion production strongly suggested that phosphorylation of EGFR can be responsible for the activation of NOX with the consequent production of superoxide anion. Therefore, EGFR phosphorylation can exert a key role in the production of superoxide anion and ROS induced by PN in MDA-MB-231 cells.