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Identification of the human liver cytochrome P450 isoenzyme responsible for the 6-methylhydroxylation of the novel anticancer drug 5,6-dimethylxanthenone-4-acetic acid.
Drug Metab Dispos. 2000 Dec; 28(12):1449-56.DM

Abstract

In vitro studies were conducted to identify the hepatic cytochrome P450 (CYP) isoenzyme involved in the 6-methylhydroxylation of 5, 6-dimethylxanthenone-4-acetic acid (DMXAA) by using a human liver library (n = 14). The metabolite 6-hydroxymethyl-5-methylxanthenone-4-acetic acid (6-OH-MXAA) was determined by HPLC with fluorescence detection. The metabolite formed in human liver microsomes and by cDNA-expressed CYP isoform was identified by liquid chromatography mass spectrometry as 6-OH-MXAA. In human liver microsomes (n = 14), 6-methylhydroxylation of DMXAA followed monophasic Michaelis-Menten kinetics, with a mean apparent K(m) of 21 +/- 5 microM and V(max) of 0.043 +/- 0.019 nmol/min/mg. An approximate 10-fold interindividual variation in the intrinsic clearance (V(max)/K(m)) of DMXAA 6-methylhydroxylation in human liver microsomes was observed. The involvement of CYP1A2 in DMXAA metabolism by human livers was demonstrated by the following: 1) the potent inhibition of DMXAA metabolism by furafylline (k(inact) = 0.23 +/- 0.04 min(-1), K'(app) = 15.6 +/- 6.7 microM) and alpha-naphthoflavone (K(i) = 0.036 microM), but not by cimetidine, ketoconazole, tolbutamide, quinidine, chlorzoxazone, diethyldithiocarbamate, troleandomycin, and sulfaphenazole; 2) when incubated with human lymphoblastoid cell microsomes containing cDNA-expressed CYP isoenzymes, DMXAA was metabolized only by CYP1A2, with an apparent K(m) of 6.2 +/- 1.5 microM and V(max) of 0.014 +/- 0.001 nmol/min/mg, but not by CYP2A6, CYP2B6, CYP2C9 (Arg(144)), CYP2C19, CYP2D6 (Val(374)), CYP2E1, and CYP3A4; 3) a significant correlation (r = 0.90; P <.001) between 6-methylhydroxylation of DMXAA and 7-ethoxyresorufin O-deethylation; and 4) a significant correlation (r = 0.75; P <.01) between the CYP1A protein level determined by Western blots and DMXAA 6-methylhydroxylation.

Authors+Show Affiliations

Zhou S
Department of Pharmacology and Clinical Pharmacology, The University of Auckland, Auckland, New Zealand.
Paxton JW
No affiliation info available
Tingle MD
No affiliation info available
Kestell P
No affiliation info available

MeSH

AdultAgedAntineoplastic AgentsBlotting, WesternChromatography, High Pressure LiquidCytochrome P-450 Enzyme InhibitorsCytochrome P-450 Enzyme SystemDNA, ComplementaryFemaleHumansHydroxylationIn Vitro TechniquesIsoenzymesLiverMaleMethylationMicrosomes, LiverMiddle AgedProteinsSubcellular FractionsXanthenesXanthones

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

11095582

Citation

Zhou, S, et al. "Identification of the Human Liver Cytochrome P450 Isoenzyme Responsible for the 6-methylhydroxylation of the Novel Anticancer Drug 5,6-dimethylxanthenone-4-acetic Acid." Drug Metabolism and Disposition: the Biological Fate of Chemicals, vol. 28, no. 12, 2000, pp. 1449-56.
Zhou S, Paxton JW, Tingle MD, et al. Identification of the human liver cytochrome P450 isoenzyme responsible for the 6-methylhydroxylation of the novel anticancer drug 5,6-dimethylxanthenone-4-acetic acid. Drug Metab Dispos. 2000;28(12):1449-56.
Zhou, S., Paxton, J. W., Tingle, M. D., & Kestell, P. (2000). Identification of the human liver cytochrome P450 isoenzyme responsible for the 6-methylhydroxylation of the novel anticancer drug 5,6-dimethylxanthenone-4-acetic acid. Drug Metabolism and Disposition: the Biological Fate of Chemicals, 28(12), 1449-56.
Zhou S, et al. Identification of the Human Liver Cytochrome P450 Isoenzyme Responsible for the 6-methylhydroxylation of the Novel Anticancer Drug 5,6-dimethylxanthenone-4-acetic Acid. Drug Metab Dispos. 2000;28(12):1449-56. PubMed PMID: 11095582.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Identification of the human liver cytochrome P450 isoenzyme responsible for the 6-methylhydroxylation of the novel anticancer drug 5,6-dimethylxanthenone-4-acetic acid. AU - Zhou,S, AU - Paxton,J W, AU - Tingle,M D, AU - Kestell,P, PY - 2000/11/30/pubmed PY - 2001/3/3/medline PY - 2000/11/30/entrez SP - 1449 EP - 56 JF - Drug metabolism and disposition: the biological fate of chemicals JO - Drug Metab Dispos VL - 28 IS - 12 N2 - In vitro studies were conducted to identify the hepatic cytochrome P450 (CYP) isoenzyme involved in the 6-methylhydroxylation of 5, 6-dimethylxanthenone-4-acetic acid (DMXAA) by using a human liver library (n = 14). The metabolite 6-hydroxymethyl-5-methylxanthenone-4-acetic acid (6-OH-MXAA) was determined by HPLC with fluorescence detection. The metabolite formed in human liver microsomes and by cDNA-expressed CYP isoform was identified by liquid chromatography mass spectrometry as 6-OH-MXAA. In human liver microsomes (n = 14), 6-methylhydroxylation of DMXAA followed monophasic Michaelis-Menten kinetics, with a mean apparent K(m) of 21 +/- 5 microM and V(max) of 0.043 +/- 0.019 nmol/min/mg. An approximate 10-fold interindividual variation in the intrinsic clearance (V(max)/K(m)) of DMXAA 6-methylhydroxylation in human liver microsomes was observed. The involvement of CYP1A2 in DMXAA metabolism by human livers was demonstrated by the following: 1) the potent inhibition of DMXAA metabolism by furafylline (k(inact) = 0.23 +/- 0.04 min(-1), K'(app) = 15.6 +/- 6.7 microM) and alpha-naphthoflavone (K(i) = 0.036 microM), but not by cimetidine, ketoconazole, tolbutamide, quinidine, chlorzoxazone, diethyldithiocarbamate, troleandomycin, and sulfaphenazole; 2) when incubated with human lymphoblastoid cell microsomes containing cDNA-expressed CYP isoenzymes, DMXAA was metabolized only by CYP1A2, with an apparent K(m) of 6.2 +/- 1.5 microM and V(max) of 0.014 +/- 0.001 nmol/min/mg, but not by CYP2A6, CYP2B6, CYP2C9 (Arg(144)), CYP2C19, CYP2D6 (Val(374)), CYP2E1, and CYP3A4; 3) a significant correlation (r = 0.90; P <.001) between 6-methylhydroxylation of DMXAA and 7-ethoxyresorufin O-deethylation; and 4) a significant correlation (r = 0.75; P <.01) between the CYP1A protein level determined by Western blots and DMXAA 6-methylhydroxylation. SN - 0090-9556 UR - https://www.unboundmedicine.com/medline/citation/11095582/Identification_of_the_human_liver_cytochrome_P450_isoenzyme_responsible_for_the_6_methylhydroxylation_of_the_novel_anticancer_drug_56_dimethylxanthenone_4_acetic_acid_ DB - PRIME DP - Unbound Medicine ER -