Mechanism of metabolic activation of the potent carcinogen 7,12-dimethylbenz[a]anthracene.
The DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) previously identified in vitro and in vivo are stable adducts formed by reaction of the bay-region diol epoxides of DMBA with dG and dA. In this paper we report identification of several new DMBA-DNA adducts formed by one-electron oxidation, including two adducts lost from DNA by depurination, DMBA bound at the 12-methyl to the N-7 of adenine (Ade) or guanine (Gua) [7-methylbenz[a]anthracene (MBA-12-CH2-N7Ade or 7-MBA-12-CH2-N7Gua, respectively]. The in vitro systems used to study DNA adduct formation were DMBA activated by horseradish peroxidase or 3-methyl-cholanthrene-induced rat liver microsomes. The biologically-formed depurination adducts were identified by high-pressure liquid chromatography and by fluorescence line narrowing spectroscopy. Stable DMBA-DNA adducts were analyzed by the 32P-postlabeling method. Quantitation of DMBA-DNA adducts formed by microsomes showed about 99% as depurination adducts: 7-MBA-12-CH2-N7Ade (82%) and 7-MBA-12-CH2-N7Gua (17%). Stable adducts (1.4% of total) included one adduct spot that may contain adduct(s) formed from the diol epoxide (0.2%) and unidentified adducts (1.2%). Activation of DMBA by horseradish peroxidase afforded 56% of stable unidentified adducts and 44% of depurination adducts, with 36% of 7-MBA-12-CH2-N7Ade and 8% of 7-MBA-12-CH2-N7Gua. Adducts containing the bond to the DNA base at the 7-CH3 group of DMBA were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)
RamaKrishna
N V
NV
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198-6805.
Devanesan
P D
PD
Rogan
E G
EG
Cavalieri
E L
EL
Jeong
H
H
Jankowiak
R
R
Small
G J
GJ
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics* / Q000633:toxicity; D000225:Adenine / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D006147:Guanine / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000494:pharmacology; D066298:In Vitro Techniques; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats
D008748:Methylcholanthrene; D015127:9,10-Dimethyl-1,2-benzanthracene; D006147:Guanine; D004247:DNA; D006735:Horseradish Peroxidase; D000225:Adenine