title: Reductive amination-assisted quantitation of tamoxifen and its metabolites by liquid phase chromatography tandem mass spectrometry.
abstract: Tamoxifen, a hormonal therapy drug against estrogen receptor-positive breast cancer, can be metabolized by cytochrome P450 enzymes such as CYP3A4 and CYP3A5, and converted to N-desmethyltamoxifen, which is subsequently, metabolized by CYP2D6 and inverted to form 4-hydroxy-N-desmethyltamoxifen (endoxifen). Conventional mass spectrometry (MS) analyses of tamoxifen and its metabolites require isotopic internal standards (ISs). In this study, endoxifen and N-desmethyltamoxifen amine groups were modified by reductive amination with formaldehyde-D2 to produce new metabolite molecules. Both endoxifen and N-desmethyltamoxifen generated their corresponding D2-methyl modified analogs. This method is expected to simplify MS detection and overcome the difficulty in selecting adequate ISs when tamoxifen metabolites are analyzed by absolute quantification. It identified tamoxifen, D2-methyl modified endoxifen, and D2-methyl modified N-desmethyltamoxifen with a linearity ranging from 2 to 5000 ng/mL with correlation coefficient (R(2)) values of 0.9868, 0.9849, and 0.9880, respectively. Furthermore, this reductive amination-based method may enhance the signal intensities of D2-methyl modified N-desmethyltamoxifen and endoxifen, thus facilitating the MS detection.
authors.affiliation: Department of Biotechnology, College of Life Science, Kaohsiung Medical University, Kaohsiung 80708, Taiwan; Institute of Biomedical Science, College of Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan. Electronic address: liang0615@kmu.edu.tw.
authors.forename: Shih-Shin
authors.initials: SS
authors.lastname: Liang
authors.affiliation: Department of Public Health, College of Health Science, Kaohsiung Medical University, Kaohsiung 80708, Taiwan; Center of Excellence for Environmental Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
authors.forename: Tsu-Nai
authors.initials: TN
authors.lastname: Wang
authors.affiliation: Department of Biotechnology, College of Life Science, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
authors.forename: Chien-Chih
authors.initials: CC
authors.lastname: Chiu
authors.affiliation: Institute of Clinical Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
authors.forename: Po-Lin
authors.initials: PL
authors.lastname: Kuo
authors.affiliation: Department of Biotechnology, College of Life Science, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
authors.forename: Mei-Fang
authors.initials: MF
authors.lastname: Huang
authors.affiliation: Department of Biotechnology, College of Life Science, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
authors.forename: Meng-Chieh
authors.initials: MC
authors.lastname: Liu
authors.affiliation: Headquarters of Research Centers, Kaohsiung Medical University, Kaohsiung 80708, Taiwan; Department of Obstetrics and Gynecology, Kaohsiung Medical University Hospital, Kaohsiung 80708, Taiwan. Electronic address: tsaieing@kmu.edu.tw.
authors.forename: Eing-Mei
authors.initials: EM
authors.lastname: Tsai
mesh_terms: D000586:Amination; D018931:Antineoplastic Agents, Hormonal / Q000097:blood* / Q000737:chemistry; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000097:blood* / Q000737:chemistry; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen; C055492:4-hydroxy-N-desmethyltamoxifen; C028787:N-desmethyltamoxifen
keywords: Absolute quantification; Endoxifen; N-Desmethyltamoxifen; Reductive amination; Tamoxifen