title: Biotransformation of melatonin in human breast cancer cell lines: role of sulfotransferase 1A1.
abstract: The biologically active melatonin metabolite, 6-hydroxymelatonin (6-OHMel), is conjugated to form 6-hydroxymelatonin sulfate (6-OHMelS). To elucidate the role of the sulfotransferase (SULT) enzyme 1A1, considerably expressed in normal and malignant human breast cells, we measured the formation of 6-OHMelS by ELISA in hormone-dependent MCF-7 and hormone-independent MDA-MB231 (MDA) breast cancer cell lines after stable transfection with SULT1A1. In parent MDA cells, low SULT1A1 mRNA expression was associated with moderate 6-OHMelS formation as determined after application (24 hr) of 0.1 microM 6-OHMel. As expected, overexpression of SULT1A1 in MDA cells resulted in a 2.9- and 110-fold increase in 6-OHMelS in the cytosol and cellular supernatant respectively. Furthermore, 6.3- and 115-fold increases were observed after 0.5 microM, and 12.6- and 101-fold increases after 1 microM 6-OHMel respectively. In MCF-7 cells, because of high basal SULT1A1 expression, only two- to threefold increases in 6-OHMelS were observed after transfection with the enzyme. In total, 866 and 539 pmol/mg protein 6-OHMelS were formed from 1 microM 6-OHMel in SULT1A1 overexpressing MDA and MCF-7 cells, respectively, whereas application of 1 microM melatonin produced only <1% of 6-OHMelS. Possible interactions with the SULT1A1 substrate tamoxifen (tam), an anti-estrogen applied in the therapy of breast cancer, were also studied. A concentration of 1 microM tam increased 6-OHMelS formation by approximately threefold in the presence of 1 microM melatonin or 1 microM 6-OHMel respectively. However, no alterations were detected after application of 1 microM 4-hydroxy-tamoxifen. In summary, we demonstrate the importance of SULT1A1 for the biotransformation of 6-OHMel in human breast cancer cells. Our data further suggest that tam can modulate melatonin biotransformation.
authors.affiliation: Center for Physiology and Pathophysiology, Medical University of Vienna, Vienna, Austria.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Aust
authors.forename: Walter
authors.initials: W
authors.lastname: Jaeger
authors.forename: Martin
authors.initials: M
authors.lastname: Klimpfinger
authors.forename: Klaus
authors.initials: K
authors.lastname: Mayer
authors.forename: Günther
authors.initials: G
authors.lastname: Baravalle
authors.forename: Cem
authors.initials: C
authors.lastname: Ekmekcioglu
authors.forename: Theresia
authors.initials: T
authors.lastname: Thalhammer
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D015239:Arylsulfotransferase / Q000235:genetics / Q000502:physiology*; D001711:Biotransformation; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology*; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006801:Humans; D008550:Melatonin / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000493:pharmacokinetics*; D012333:RNA, Messenger / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology; D014162:Transfection
chemical_list: D018931:Antineoplastic Agents, Hormonal; D012333:RNA, Messenger; D013629:Tamoxifen; C054513:6-sulfatoxymelatonin; D015239:Arylsulfotransferase; C117544:SULT1A1 protein, human; D008550:Melatonin