This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dehal, S. S. Articles by Kupfer, D. Search for Related Content PubMed PubMed Citation Articles by Dehal, S. S. Articles by Kupfer, D.

CYP2D6 Catalyzes Tamoxifen 4-Hydroxylation in Human Liver¹

Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545

The major metabolites of tamoxifen (tam) formed by animal and human liver microsomes are mono-N-demethylated tam, 4-hydroxy-tam (4-OH-tam), and tam-N-oxide. The N-desmethylated-tam and 4-OH-tam are formed by P450s, whereas the N-oxide is primarily formed by flavin-containing monooxygenase. Because 4-OH-tam is a highly potent antiestrogen (and possibly is the active anticancer tam metabolite) and is on the path of formation of the reactive intermediate that binds covalently to proteins and DNA, it was of importance to identify the P450(s) catalyzing its formation. In the current study, three different preparations of expressed human P450s in Escherichia coli, lymphoblastoma cells, and insect cell line and livers from several human donors were used to identify the P450 isoform catalyzing the 4-hydroxylation (preliminary results were reported by Dehal et al., Eleventh International Symposium on Microsomes and Drug Oxidations, p. 71. Los Angeles, 1996). Tam metabolism was examined with human CYP2C8, 2C9, 2C18, 2C19, and 2D6 expressed in E. coli. These P450s were reconstituted with P450 reductase and lipid and were incubated with 50 µM [³H]tam and NADPH at 37°C for 60 min. Essentially all of the recombinant P450s catalyzed the N-demethylation to various degrees; however, only 2D6 yielded detectable levels of 4-OH-tam. The inclusion of cytochrome b₅ in the reconstituted system of 2D6 and 2C9 did not significantly affect the rate of 4-hydroxylation, indicating that b₅ is not essential for this activity. Tam metabolism by CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2D6, 2E1, and 3A4, expressed in lymphoblastoma cells, revealed that only 2D6 significantly catalyzed the 4-hydroxylation. Tam metabolism by CYP2D6 coexpressed with P450 reductase in a baculovirus infected insect cell line ("supersomes") exhibited marked tam 4-hydroxy-lation. In an experiment with human liver microsomes, the inclusion of quinidine, a specific 2D6 inhibitor, resulted in approximately 50% inhibition of tam 4-hydroxylation without affecting N-demethylation. Polyclonal antibodies raised against 2D6 moderately inhibited (approximately 30%) the 4-hydroxylation in human liver microsomes. These results demonstrate a significant contribution by CYP2D6 to the catalysis of tam-4-hydroxylation by human liver.

¹ This studdy was made possible by USPHS Grant ES 00834 from the National Institute of Environmental Health Sciences, NIH. A preliminary account of this study was presented at the 11th International Symposium on Microsomes and Drug Oxidations, Los Angeles, CA, July 21–24, 1996.

² To whom requests for reprints should be addressed, at Worcester Foundation for Biomedical Research, 222 Maple Avenue, Shrewsbury, MA 01545. Phone: (508) 842-8921; Fax: (508) 842-9632; E-mail: kupfer@sci.wfbr.edu.

Received 2/ 3/97. Accepted 6/13/97.

This article has been cited by other articles:

				Y. Zheng, D. Sun, A. K. Sharma, G. Chen, S. Amin, and P. Lazarus Elimination of Antiestrogenic Effects of Active Tamoxifen Metabolites by Glucuronidation Drug Metab. Dispos., October 1, 2007; 35(10): 1942 - 1948. [Abstract] [Full Text] [PDF]

				W. Chu, A. Fyles, E. M. Sellers, D. R. McCready, J. Murphy, T. Pal, and S. A. Narod Association between CYP3A4 genotype and risk of endometrial cancer following tamoxifen use Carcinogenesis, October 1, 2007; 28(10): 2139 - 2142. [Abstract] [Full Text] [PDF]

				J. Yu, M. J. I. Paine, J.-D. Marechal, C. A. Kemp, C. J. Ward, S. Brown, M. J. Sutcliffe, G. C. K. Roberts, E. M. Rankin, and C. R. Wolf IN SILICO PREDICTION OF DRUG BINDING TO CYP2D6: IDENTIFICATION OF A NEW METABOLITE OF METOCLOPRAMIDE Drug Metab. Dispos., August 1, 2006; 34(8): 1386 - 1392. [Abstract] [Full Text] [PDF]

				Z. Desta, B. A. Ward, N. V. Soukhova, and D. A. Flockhart Comprehensive Evaluation of Tamoxifen Sequential Biotransformation by the Human Cytochrome P450 System in Vitro: Prominent Roles for CYP3A and CYP2D6 J. Pharmacol. Exp. Ther., September 1, 2004; 310(3): 1062 - 1075. [Abstract] [Full Text] [PDF]

				M.E. Heres-Pulido, I. Duenas-Garcia, L. Castaneda-Partida, A. Sanchez-Garcia, M. Contreras-Sousa, A. Duran-Diaz, and U. Graf Genotoxicity of tamoxifen citrate and 4-nitroquinoline-1-oxide in the wing spot test of Drosophila melanogaster Mutagenesis, May 1, 2004; 19(3): 187 - 193. [Abstract] [Full Text] [PDF]

				E. R. Kisanga, J. Gjerde, A. Guerrieri-Gonzaga, F. Pigatto, A. Pesci-Feltri, C. Robertson, D. Serrano, G. Pelosi, A. Decensi, and E. A. Lien Tamoxifen and Metabolite Concentrations in Serum and Breast Cancer Tissue during Three Dose Regimens in a Randomized Preoperative Trial Clin. Cancer Res., April 1, 2004; 10(7): 2336 - 2343. [Abstract] [Full Text] [PDF]

				M. P. Goetz and C. L. Loprinzi A Hot Flash on Tamoxifen Metabolism J Natl Cancer Inst, December 3, 2003; 95(23): 1734 - 1735. [Full Text] [PDF]

				V. Stearns, M. D. Johnson, J. M. Rae, A. Morocho, A. Novielli, P. Bhargava, D. F. Hayes, Z. Desta, and D. A. Flockhart Active Tamoxifen Metabolite Plasma Concentrations After Coadministration of Tamoxifen and the Selective Serotonin Reuptake Inhibitor Paroxetine J Natl Cancer Inst, December 3, 2003; 95(23): 1758 - 1764. [Abstract] [Full Text] [PDF]

				S. Maiti and G. Chen Tamoxifen Induction of Aryl Sulfotransferase and Hydroxysteroid Sulfotransferase in Male and Female Rat Liver and Intestine Drug Metab. Dispos., May 1, 2003; 31(5): 637 - 644. [Abstract] [Full Text] [PDF]

				B. Rochat, E. M. J. Gillam, and M. S. Lennard Evaluation of Recombinant Cytochromes P450 Activity in Metabolic Pathways Drug Metab. Dispos., January 1, 2003; 31(1): 145 - 146. [Full Text] [PDF]

				D. J. Boocock, K. Brown, A. H. Gibbs, E. Sanchez, K. W. Turteltaub, and I. N.H. White Identification of human CYP forms involved in the activation of tamoxifen and irreversible binding to DNA Carcinogenesis, November 1, 2002; 23(11): 1897 - 1902. [Abstract] [Full Text] [PDF]

				H. K. Crewe, L. M. Notley, R. M. Wunsch, M. S. Lennard, and E. M. J. Gillam Metabolism of Tamoxifen by Recombinant Human Cytochrome P450 Enzymes: Formation of the 4-Hydroxy, 4'-Hydroxy and N-Desmethyl Metabolites and Isomerization of trans-4-Hydroxytamoxifen Drug Metab. Dispos., August 1, 2002; 30(8): 869 - 874. [Abstract] [Full Text] [PDF]

				C. Sridar, U. M. Kent, L. M. Notley, E. M. J. Gillam, and P. F. Hollenberg Effect of Tamoxifen on the Enzymatic Activity of Human Cytochrome CYP2B6 J. Pharmacol. Exp. Ther., June 1, 2002; 301(3): 945 - 952. [Abstract] [Full Text] [PDF]

				T. Kasahara, M. Hashiba, T. Harada, and M. Degawa Change in the gene expression of hepatic tamoxifen-metabolizing enzymes during the process of tamoxifen-induced hepatocarcinogenesis in female rats Carcinogenesis, March 1, 2002; 23(3): 491 - 498. [Abstract] [Full Text] [PDF]

				S. Mandlekar, V. Hebbar, K. Christov, and A-N. T. Kong Pharmacodynamics of Tamoxifen and Its 4-Hydroxy and N-Desmethyl Metabolites: Activation of Caspases and Induction of Apoptosis in Rat Mammary Tumors and in Human Breast Cancer Cell Lines Cancer Res., December 1, 2000; 60(23): 6601 - 6606. [Abstract] [Full Text]

				S. Katchamart, D. M. Stresser, S. S. Dehal, D. Kupfer, and D. E. Williams Concurrent Flavin-Containing Monooxygenase Down-Regulation and Cytochrome P-450 Induction by Dietary Indoles in Rat: Implications for Drug-Drug Interaction Drug Metab. Dispos., August 1, 2000; 28(8): 930 - 936. [Abstract] [Full Text]

				I. N.H. White The tamoxifen dilemma Carcinogenesis, July 1, 1999; 20(7): 1153 - 1160. [Abstract] [Full Text] [PDF]

				S. S. Dehal and D. Kupfer Cytochrome P-450 3A and 2D6 Catalyze Ortho Hydroxylation of 4-Hydroxytamoxifen and 3-Hydroxytamoxifen (Droloxifene) Yielding Tamoxifen Catechol: Involvement of Catechols in Covalent Binding to Hepatic Proteins Drug Metab. Dispos., June 1, 1999; 27(6): 681 - 688. [Abstract] [Full Text]

				S. S. Dehal, A. M. H. Brodie, and D. Kupfer The Aromatase Inactivator 4-Hydroxyandrostenedione (4-OH-A) Inhibits Tamoxifen Metabolism by Rat Hepatic Cytochrome P-450 3A: Potential for Drug-Drug Interaction of Tamoxifen and 4-OH-A in Combined Anti-Breast Cancer Therapy Drug Metab. Dispos., March 1, 1999; 27(3): 389 - 394. [Abstract] [Full Text]

				F. A. Beland, L. P. McDaniel, and M. M. Marques Comparison of the DNA adducts formed by tamoxifen and 4-hydroxytamoxifen in vivo Carcinogenesis, March 1, 1999; 20(3): 471 - 477. [Abstract] [Full Text] [PDF]