Seoane Ruzo, SamuelÁlvarez Bermúdez, María JoséSendón Lago, Juan JoséMartínez Ordóñez, AnxoAbdul-Hadi, SorayaMaestro Saavedra, Miguel AnxoMouriño Mosquera, AntonioPérez Fernández, Román2020-06-162020-06-162013Seoane, S.; Bermudez, M.A.; Sendon-Lago, J.; Martinez-Ordoñez, A.; Abdul-Hadi, S.; Maestro, M.; Mouriño, A.; Perez-Fernandez, R. 26,26,26,27,27,27-Hexadeuterated-1,25-Dihydroxyvitamin D3 (1,25D-d6) As Adjuvant of Chemotherapy in Breast Cancer Cell Lines. Cancers 2014, 6, 67-78http://hdl.handle.net/10347/23007It 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 modelseng© 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/)http://creativecommons.org/licenses/by/3.0/1a,25-dihydroxyvitamin D326,26,26,27,27,27-hexadeuterated 1a25-dihydroxyvitamin D3Vitamin DDeuterated vitamin DChemotheraphyBreast cancerjournal article10.3390/cancers60100672072-6694open access