The mechanism of aphidicolin bioinactivation by rat liver in vitro systems.
1. Aphidicolin is shown to undergo rapid metabolism by rat-liver microsomes resulting in its inactivation and loss of its DNA polymerase alpha/delta inhibition. Metabolism of aphidicolin was not observed with cytosolic enzymes of rat liver and was inconsistent with the involvement of microsomal 3 alpha-hydroxysteroid oxidoreductases. 2. Rates of aphidicolin inactivation as a function of microsomal enzyme induction (per nmol cytochrome P-450) followed the order: untreated microsomes greater than dexamethasone-induced greater than phenobarbital-induced greater than beta-naphthoflavone-induced greater than clofibrate-induced. 3. The principal metabolic process, constituting greater than 90% of the metabolic profile, produces 3-ketoaphidicolin 2, which exhibits approximately 10% of the activity of aphidicolin in inhibition of DNA polymerase alpha. This metabolic transformation, the oxidation of an alcohol to a ketone, is an unusual, but not unique conversion, for cytochrome P-450. 4. 3-Ketoaphidicolin 2 is an intermediate and ultimately undergoes 18-dehydroxymethylation to produce 18-noraphidicolinones 3, which are inactive in the inhibition of DNA polymerase alpha. 5. A specific constitutive cytochrome P-450 isozyme, involved in endogenous steroid regulation, was implicated as the species responsible for aphidicolin metabolism in vitro.
Edelson
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RE
Department of Chemistry, University of Virginia, Charlottesville 22901.
Gorycki
P D
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MacDonald
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TL
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000493:pharmacokinetics; D000998:Antiviral Agents / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000493:pharmacokinetics; D016590:Aphidicolin; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004257:DNA Polymerase II / Q000037:antagonists & inhibitors; D004224:Diterpenes / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000493:pharmacokinetics; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D000903:Antibiotics, Antineoplastic; D000998:Antiviral Agents; D004224:Diterpenes; D016590:Aphidicolin; D003577:Cytochrome P-450 Enzyme System; D004257:DNA Polymerase II