Tamoxifen blocks both proliferation and voltage-dependent K+ channels of neuroblastoma cells.

The effects of tamoxifen (TAM) on cell proliferation and voltage-dependent K+ channels were studied on the mouse neuroblastoma cells NG 108-15. TAM inhibited cell proliferation with an effective dose inducing a half maximum effect (ED50) of 2 microM and was cytotoxic from and beyond 2.5 microM. TAM accelerated the apparent inactivation of the whole cell K+ current with an apparent dissociation constant of 0.46 microM, and shifted the peak K+ conductance-voltage curve towards negative voltages with an apparent dissociation constant of 1.07 microM. The K+ flux at the resting potential, calculated from the time integral of the K+ current recorded during depolarizations, was decreased by TAM. The effect of TAM on the cell proliferation was perfectly correlated with the effect of TAM on the resting K+ flux. The results suggest that cell mitosis is, in some way, controlled by the functioning of K+ channels and that the antitumour action of tamoxifen could be due to its interaction with K+ channels.