Tags

Type your tag names separated by a space and hit enter

CYP2D6-mediated catalysis of tamoxifen aromatic hydroxylation with an NIH shift: similar hydroxylation mechanism in chicken, rat and human liver microsomes.
Xenobiotica. 2003 Feb; 33(2):141-51.X

Abstract

1. 4-Tritiated-tamoxifen (4-[(3)H]-tamoxifen) and 4-deuterated-tamoxifen (4-[(2)H]-tamoxifen) were synthesized to examine tamoxifen metabolism by human P450 (CYP) forms and also for the possibility of determining tamoxifen-4-hydroxylation in humans in vivo. 2. Liver microsomes from several species and cDNA-expressed human P450s were incubated with 4-[(3)H]-tamoxifen and the reaction monitored by assaying 4-hydroxytamoxifen (4-OH-tam) and (3)H(2)O formed. However, tamoxifen-4-hydroxylation did not generate stoichiometric amounts of (3)H(2)O and the expected unlabelled 4-OH-tam but instead yielded radiolabelled 4-OH-tam, apparently from [(3)H]-migration to the ortho-position, referred to as the NIH shift. 3. CYP2D6 was the prime catalyst of tam-4-hydroxylation, whereas CYP2B6, 2C9 and 2C19 yielded only low levels of 4-OH-tam; nevertheless, in all cases the 4-OH-tam was radioactive, apparently resulting from reactions involving an NIH shift. 4. Chicken liver microsomal preparation, being catalytically the most active in tamoxifen-4-hydroxylation, was incubated with deuterated tamoxifen (4-[(2)H]-tamoxifen) in order to determine whether an NIH shift occurs. Ion-trap mass-spectrometry of the HPLC-purified 4-OH-tam, from that incubation, indicated about 60% of [(2)H]-retention in 4-OH-tam, signifying an NIH shift. These findings indicate that the aromatic hydroxylation of tamoxifen does not entail hydroxyl insertion with an Sn2-displacement of hydrogen or a hydrogen isotope ((2)H or (3)H), but apparently involves epoxidation followed by migration of the (3)H, (2)H or (1)H to the ortho-position, and dissociation of the (1)H in preference to (3)H or (2)H, i.e. retention of the hydrogen isotope appears to be related to the bond strengths: C-(3)H>C-(2)H>C-(1)H.

Authors+Show Affiliations

Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605-2324, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

12623757

Citation

Hu, Y, et al. "CYP2D6-mediated Catalysis of Tamoxifen Aromatic Hydroxylation With an NIH Shift: Similar Hydroxylation Mechanism in Chicken, Rat and Human Liver Microsomes." Xenobiotica; the Fate of Foreign Compounds in Biological Systems, vol. 33, no. 2, 2003, pp. 141-51.
Hu Y, Dehal SS, Hynd G, et al. CYP2D6-mediated catalysis of tamoxifen aromatic hydroxylation with an NIH shift: similar hydroxylation mechanism in chicken, rat and human liver microsomes. Xenobiotica. 2003;33(2):141-51.
Hu, Y., Dehal, S. S., Hynd, G., Jones, G. B., & Kupfer, D. (2003). CYP2D6-mediated catalysis of tamoxifen aromatic hydroxylation with an NIH shift: similar hydroxylation mechanism in chicken, rat and human liver microsomes. Xenobiotica; the Fate of Foreign Compounds in Biological Systems, 33(2), 141-51.
Hu Y, et al. CYP2D6-mediated Catalysis of Tamoxifen Aromatic Hydroxylation With an NIH Shift: Similar Hydroxylation Mechanism in Chicken, Rat and Human Liver Microsomes. Xenobiotica. 2003;33(2):141-51. PubMed PMID: 12623757.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - CYP2D6-mediated catalysis of tamoxifen aromatic hydroxylation with an NIH shift: similar hydroxylation mechanism in chicken, rat and human liver microsomes. AU - Hu,Y, AU - Dehal,S S, AU - Hynd,G, AU - Jones,G B, AU - Kupfer,D, PY - 2003/3/8/pubmed PY - 2003/9/23/medline PY - 2003/3/8/entrez SP - 141 EP - 51 JF - Xenobiotica; the fate of foreign compounds in biological systems JO - Xenobiotica VL - 33 IS - 2 N2 - 1. 4-Tritiated-tamoxifen (4-[(3)H]-tamoxifen) and 4-deuterated-tamoxifen (4-[(2)H]-tamoxifen) were synthesized to examine tamoxifen metabolism by human P450 (CYP) forms and also for the possibility of determining tamoxifen-4-hydroxylation in humans in vivo. 2. Liver microsomes from several species and cDNA-expressed human P450s were incubated with 4-[(3)H]-tamoxifen and the reaction monitored by assaying 4-hydroxytamoxifen (4-OH-tam) and (3)H(2)O formed. However, tamoxifen-4-hydroxylation did not generate stoichiometric amounts of (3)H(2)O and the expected unlabelled 4-OH-tam but instead yielded radiolabelled 4-OH-tam, apparently from [(3)H]-migration to the ortho-position, referred to as the NIH shift. 3. CYP2D6 was the prime catalyst of tam-4-hydroxylation, whereas CYP2B6, 2C9 and 2C19 yielded only low levels of 4-OH-tam; nevertheless, in all cases the 4-OH-tam was radioactive, apparently resulting from reactions involving an NIH shift. 4. Chicken liver microsomal preparation, being catalytically the most active in tamoxifen-4-hydroxylation, was incubated with deuterated tamoxifen (4-[(2)H]-tamoxifen) in order to determine whether an NIH shift occurs. Ion-trap mass-spectrometry of the HPLC-purified 4-OH-tam, from that incubation, indicated about 60% of [(2)H]-retention in 4-OH-tam, signifying an NIH shift. These findings indicate that the aromatic hydroxylation of tamoxifen does not entail hydroxyl insertion with an Sn2-displacement of hydrogen or a hydrogen isotope ((2)H or (3)H), but apparently involves epoxidation followed by migration of the (3)H, (2)H or (1)H to the ortho-position, and dissociation of the (1)H in preference to (3)H or (2)H, i.e. retention of the hydrogen isotope appears to be related to the bond strengths: C-(3)H>C-(2)H>C-(1)H. SN - 0049-8254 UR - https://www.unboundmedicine.com/medline/citation/12623757/CYP2D6_mediated_catalysis_of_tamoxifen_aromatic_hydroxylation_with_an_NIH_shift:_similar_hydroxylation_mechanism_in_chicken_rat_and_human_liver_microsomes_ L2 - https://www.tandfonline.com/doi/full/10.1080/0049825021000042733 DB - PRIME DP - Unbound Medicine ER -