Abstract
The anti-breast cancer drug tamoxifen has recently been shown to cause an increase in intracellular free-Ca2+ concentrations ([Ca2+]i) in renal tubular cells, breast cells and bladder cells. Because tamoxifen is known to alter ovary function in human patients and in rats, the present study was aimed at exploring whether tamoxifen could alter Ca2+ movement in Chinese hamster ovary (CHO-K1) cells. Cytosolic free-Ca2+ levels in populations of cells have been explored by using fura-2 as a fluorescent Ca2+ indicator. Tamoxifen at concentrations above 1 µM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 8 µM. The Ca2+ signal was reduced by removing extracellular Ca2+, but was not affected by nifedipine, verapamil, diltiazem or ICI 182,780 (an estrogen receptor antagonist). Pretreatment with 1 µM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) to deplete the endoplasmic reticulum Ca2+ abolished 10 µM tamoxifen-induced Ca2+ release. Neither inhibition of phospholipase C with 2 µM U73122 nor depletion of ryanodine-sensitive Ca2+ stores with 50 µM ryanodine affected tamoxifen-induced Ca2+ release. Cell proliferation assays using ELISA revealed that overnight incubation with 5–10 µM tamoxifen inhibited cell proliferation by 20%, and 20 µM tamoxifen killed all cells. Together, the results suggest that, in CHO-K1 cells, tamoxifen induced a [Ca2+]i increase by causing store-Ca2+ release from the endoplasmic reticulum in an phospholipase C-independent manner, and by inducing Ca2+ influx. The action of tamoxifen appears to be dissociated from estrogen receptor activation. Longer incubation with tamoxifen (>5 µM) was cytotoxic.
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Acknowledgements
This work was supported by grants from National Science Council, Taiwan (NSC90-2320-B-075B-006), and Veterans General Hospital-Kaohsiung to C.R.J. (VGHKS91-17), to A.J.C. (VGHKS91-58), to H.T.C (VGHKS91-21), and to J.K.H. (VGHKS91-97).
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Jan, CR., An-Jen, C., Chang, HT. et al. The anti-breast cancer drug tamoxifen alters Ca2+ movement in Chinese hamster ovary (CHO-K1) cells. Arch Toxicol 77, 160–166 (2003). https://doi.org/10.1007/s00204-002-0420-0
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DOI: https://doi.org/10.1007/s00204-002-0420-0