Seoane, SamuelBermúdez, María JoséSendón Lago, Juan JoséMartínez Ordóñez, AnxoAbdul-Hadi, SorayaMaestro, MiguelMouriño, AntonioPérez-Fernández, Román2017-09-262017-09-26Cancers 2014, Vol. 6, Pages 67-782072-6694http://hdl.handle.net/2183/19529It has been demonstrated that 1,25-dihydroxyvitamin D3 (1,25D) and some of its analogues have antitumor activity. 1,25D labeled with deuterium (26,26,26,27,27,27-hexadeuterated 1a,25-dihydroxyvitamin D3, or 1,25D-d6) is commonly used as internal standard for 1,25D liquid chromatography-mass spectrometry (LC-MS) quantification. In the present study using human breast cancer cell lines, the biological activity of 1,25D-d6 administered alone and in combination with two commonly used antineoplastic agents, 5-fluorouracil and etoposide, was evaluated. Using an MTT assay, flow cytometry, and western blots, our data demonstrated that 1,25D-d6 has effects similar to the natural hormone on cell proliferation, cell cycle, and apoptosis. Furthermore, the combination of 1,25D-d6 and etoposide enhances the antitumoral effects of both compounds. Interestingly, the antitumoral effect is higher in the more aggressive MDA-MB-231 breast cancer cell line. Our data indicate that 1,25D-d6 administered alone or in combination with chemotherapy could be a good experimental method for accurately quantifying active 1,25D levels in cultures or in biological fluids, on both in vitro breast cancer cell lines and in vivo animal experimental models.engReconocimiento 3.0http://creativecommons.org/licenses/by/3.0/1a,25-dihydroxyvitamin d₃26,26,26,27,27,27-hexadeuterated 1a,25-dihydroxyvitamin d₃Vitamin dDeuterated vitamin dChemotheraphyBreast cancerjournal articleopen access