A monoclonal antibody to rat liver cytochrome P450 IIC11 strongly and regiospecifically inhibits constitutive benzo[a]pyrene metabolism and DNA binding.
The monoclonal antibody MAb 1-68-11, prepared to constitutive cytochrome P450 IIC11 (2c/RLM5) from male Sprague-Dawley rat liver, was used to study the contribution of the class of cytochrome P450s epitopically related to P450 IIC11 to the regiospecific metabolism of benzo[a]pyrene (BP) and its binding to DNA. The effect of MAb 1-68-11 was determined on the conversion of BP to BP-9,10-dihydrodiol, BP-7,8-dihydrodiol, BP-4,5-dihydrodiol, BP phenols, and BP quinones, and on the P450-dependent DNA binding catalyzed by P450 in microsomes from uninduced male and female Wistar and Sprague-Dawley rat livers, as well as 3-methylcholanthrene- and phenobarbital (PB)-induced male Wistar rat livers. In liver microsomes from untreated male rats, MAb 1-68-11 inhibited BP-9,10-dihydrodiol formation by 80%; in liver microsomes from untreated female rats, the inhibition was 100%. BP-7,8-dihydrodiol formation was inhibited from 38 to 77% in microsomes from males and 50% in those from females. In microsomes from PB-induced rats, inhibition of the 9,10-dihydrodiol and the 7,8-dihydrodiol was 90% and 73%, respectively, whereas BP-4,5-dihydrodiol formation was enhanced 80%. In microsomes from 3-methylcholanthrene-treated rats, no inhibition of MAb 1-68-11 was observed on either the metabolism of BP or its binding to DNA. In contrast, the binding of BP to DNA was completely inhibited by MAb 1-68-11 in microsomes from uninduced male Wistar rats and 70% in PB-induced microsomes. 32P-postlabeling analysis showed that formation of the major stable adduct, BP diol epoxide bound at C-10 to the 2-amino of deoxyguanosine, was strongly inhibited in uninduced and PB-induced microsomes. Formation of the major labile BP-DNA adduct 7-(benzo[a]pyren-6-yl) guanine (BP-N7Gua) was inhibited about 60% in microsomes from untreated male Wistar rats. These results show that MAb 1-68-11 regiospecifically inhibits cytochrome P450 IIC11 and epitopically related P450s that metabolize BP at the 7,8 and 9,10 positions. MAb 1-68-11 also inhibits enzyme-catalyzed binding of BP to DNA in the specific formation of BP-N7Gua and adducts detected by the 32P-postlabeling technique.
Todorovic
R
R
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198-6805.
Devanesan
P D
PD
Cavalieri
E L
EL
Rogan
E G
EG
Park
S S
SS
Gelboin
H V
HV
D000818:Animals; D000911:Antibodies, Monoclonal; D001189:Aryl Hydrocarbon Hydroxylases; D001564:Benzo(a)pyrene / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology; D004247:DNA / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D018736:DNA Adducts; D005260:Female; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors* / Q000276:immunology
D000911:Antibodies, Monoclonal; D065607:Cytochrome P-450 Enzyme Inhibitors; D018736:DNA Adducts; C056612:benzo(a)pyrene-DNA adduct; D001564:Benzo(a)pyrene; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase