Synthesis and structure determination of 6-methylbenzo[a]pyrene-deoxyribonucleoside adducts and their identification and quantitation in vitro and inmouse skin

Activation of the moderate L carcinogen 6-methylbenzo[a]pyrene (6-CH3BP) by one-electron oxidation to form DNA adducts was studied. Iodine oxidation o f 6-CH3BP in the presence of dGuo produces BP-6-CH2-N(2)dGuo, BP-6-CH2-N7Gu a and a mixture of 6-CH3BP-(1&3)-N7Gua, whereas in the presence of Ade the adducts BP-6-CH2-N1Ade, BP-6-CH2-N3Ade, DP-6-CH2-N7Ade and 6-CH3BP-(1&3)-N1 Ade are obtained. Furthermore, for the first time an aromatic hydrocarbon r adical cation afforded an adduct with dThd, the stable adduct BP-6-CH2-N3dT hd. Formation of these adducts indicates that the 6-CH3BP radical cation ha s charge localized at the 6, 1 and 3 position. When 6-CH3BP was activated b y horseradish peroxidase in the presence of DNA, two depurinating adducts w ere identified, BP-6-CH(2)N7Gua (48%) and 6-CH3BP-(1&3)-N7Gua (23%), with 2 9% unidentified stable adducts. In the binding of 6-CH3BP catalyzed by rat liver microsomes, the same two depurinating adducts, BP-6-CH2-N7Gua (22%) a nd 6-CH3BP-(1&3)-N7Gua (10%), were identified, with 68% unidentified stable adducts. In 6-CH3BP-treated mouse skin, the two depurinating adducts, BP-6 -CH2-N7Gua and 6-CH3BP-(1&3)-N7Gua, were identified. Although quantitation of these two adducts was not possible due to coelution of metabolites on HP LC, they appeared to be the major adducts found in mouse skin. These result s show that 6-CH3BP forms depurinating adducts only with the guanine base o f DNA, both in vitro and in mouse skin. The weaker reactivity of 6-CH3BP ra dical cation vs. BP radical cation could account for the weaker tumor-initi ating activity of 6-CH3BP in comparison to that of BP. (C) 2000 Published b y Elsevier Science Ireland Ltd. All rights reserved.