Selectivity of 7-alkoxycoumarins as probe substrates for rat hepatic cytochrome P450 forms is influenced by the substitution pattern on the coumarin nucleus.
1. The O-dealkylation of 7-alkoxycoumarins is widely used as an assay to characterize cytochrome P450 (CYP) activity. These substrates can also undergo oxidative attack at additional sites on the coumarin nucleus, which may influence their apparent selectivity for particular CYP forms. 2. Accordingly, the effect of blockade of these additional sites was investigated on the selectivity towards rat hepatic CYP forms, with emphasis on the CYP1A and 2B forms. 3. Blockade of the 3-/4- and 6-positions resulted in substrates for which the CYP1A1/2 selectivity of the unsubstituted 7-alkoxycoumarins was altered to a CYP2B selectivity; this was achieved with little overall change in the molecular dimensions of the substrate. Limited analysis of other inducible CYP forms indicated at most only small effects of structure modification on activity. 4. The findings suggest that the sensitivity of probe substrates for CYP forms may be limited by the occurrence of competing side reactions of the substrate, and that better probes may be derived by blocking the sites of these side reactions.
Fry
J R
JR
School of Biomedical Sciences, Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK. jeff.fry@nottingham.ac.uk
Hammond
A H
AH
Jassi
K L
KL
Bass
A E
AE
Bruce
G
G
Laughton
C
C
Shaw
P N
PN
Bylov
I E
IE
Kovalenko
S M
SM
D015660:7-Alkoxycoumarin O-Dealkylase / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D003374:Coumarins / Q000737:chemistry / Q000378:metabolism*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D019362:Cytochrome P-450 CYP2B1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D008875:Middle Aged; D015335:Molecular Probes; D015394:Molecular Structure; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012642:Selegiline / Q000494:pharmacology; D013379:Substrate Specificity; D019324:beta-Naphthoflavone / Q000494:pharmacology
D003374:Coumarins; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D015335:Molecular Probes; D012642:Selegiline; D019324:beta-Naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D015660:7-Alkoxycoumarin O-Dealkylase; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D019362:Cytochrome P-450 CYP2B1; D010634:Phenobarbital