Studies using structural analogs and inbred strain differences to support a role for quinone methide metabolites of butylated hydroxytoluene (BHT) inmouse lung tumor promotion

Chronic treatment of BALE and GRS mice with BHT (2,6-di-tert-butyl-4-methyl phenol) following a single urethane injection increases lung tumor multipli city, but this does not occur in CXB4 mice. Previous data suggest that prom otion requires the conversion of BHT to a tert-butyl-hydroxylated metabolit e (BHTOH) in lung and the subsequent oxidation of this species to an electr ophilic quinone methide. To obtain additional evidence for the importance o f quinone methide formation, structural analogs that form less reactive qui none methides were tested and found to lack promoting activity in BHT-respo nsive mice. The possibility that promotion-unresponsive strains are unable to form BHTOH was tested by substituting this compound for BHT in the promo tion protocol using CXB4 mice. No promotion occurred, and in-vitro work dem onstrated that CXP4 mice are, in fact, capable of producing BHTOH and its q uinone methide, albeit in smaller quantities. Incubations with BALB lung mi crosomes and radiolabeled substrates confirmed that more covalent binding t o protein occurs with BHTOH than with BHT and, in addition, BHTOH quinone m ethide is considerably more toxic to mouse lung epithelial cells than BHT q uinone methide. These data are consistent with the hypothesis that a two-st ep oxidation process, i.e. hydroxylation and quinone methide formation, is required for the promotion of mouse lung tumors by BHT. (C) 2001 Elsevier S cience Ireland Ltd. All rights reserved.