toremifene and Neuroblastoma

1. The regulation of Maxi Cl(-) channels by 17beta-oestradiol and non-steroidal triphenylethylene antioestrogens represents a rapid, non-classical effect of these compounds. In the present study we have investigated the signalling pathways used for the regulation of Maxi Cl(-) channel activity by oestrogens and antioestrogens in C1300 neuroblastoma cells. 2. Whole-cell Maxi Cl(-) currents were readily and reversibly activated by tamoxifen, toremifene and the membrane-impermeant ethyl-bromide tamoxifen, only when applied to the extracellular medium. 3. Pre-treatment of C1300 cells with oestrogen or cAMP prevented the antioestrogen-induced activation of Maxi Cl(-) channels. The inhibitory effect of 17beta-oestradiol and cAMP was abolished by the kinase inhibitor staurosporine. 4. Current activation was unaffected by the removal of intracellular Ca(2+) and Mg(2+), but was completely abolished in the presence of okadaic acid. These results are consistent with the participation of an okadaic acid-sensitive serine/threonine protein phosphatase in the activation of Maxi Cl(-) channels. However, neither oestrogen or antioestrogen treatment modified the total activity of the two major serine/threonine phosphatases, PP1 and PP2A, in C1300 cells. 5. Although the role of these Maxi Cl(-) channels remains unknown, our findings suggest strongly that their modulation by oestrogens and antioestrogens is linked to intracellular signalling pathways.

Topics: Animals; Carcinogens; Chloride Channels; Chlorides; Cyclic AMP; Enzyme Inhibitors; Estradiol; Estrogen Antagonists; Ion Channel Gating; Mice; Neuroblastoma; Okadaic Acid; Patch-Clamp Techniques; Phosphoprotein Phosphatases; Phosphorylation; Selective Estrogen Receptor Modulators; Signal Transduction; Staurosporine; Stilbenes; Tamoxifen; Toremifene; Tumor Cells, Cultured

The presence of volume-activated chloride channels has been examined in neuroblastoma C1300 cells using the whole-cell configuration of the patch-clamp technique. Chloride channels could not be detected under isotonic conditions. However, hypotonic challenge induced slowly developed inward and outward anionic currents that exhibited outward rectification and inactivation at the most depolarizing potentials, features that were similar to the currents described in other cell preparations where volume-activated Cl- channels have been associated with the expression of P-glycoprotein. This hypotonicity-activated Cl- currents could be reversibly blocked by extracellular exposure to toremifene, a novel synthetic antioestrogen. The fact that toremifene and its analog tamoxifen, have been shown to block P-glycoprotein-associated chloride channels and to reverse P-glycoprotein associated multidrug resistance in a number of cell lines suggest that P-glycoprotein could be involved in the generation of hypotonic-induced chloride conductance in neuroblastoma cells.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Cell Size; Chloride Channels; Chlorides; Estrogen Antagonists; Membrane Potentials; Mice; Nerve Tissue Proteins; Neuroblastoma; Patch-Clamp Techniques; Tamoxifen; Toremifene; Tumor Cells, Cultured