Pharmacologic and genetic studies on the modulatory effects of butylated hydroxytoluene on mouse lung adenoma formation.

Food additive butylated hydroxytoluene (BHT) (CAS: 128-37-0; 2,6-di-tert-butyl-p-cresol) can modulate the formation of lung adenomas in mice treated with the carcinogen urethan (CAS: 51-79-6; ethyl ester carbamic acid). An ip injection of BHT administered 6 hours before a single urethan injection decreased the number of tumors formed, whereas six weekly BHT injections following a single urethan dose increased tumor multiplicity. Biotransformation of BHT was apparently required for both prophylaxis and enhancement. Pretreatment of mice with cedrene, which perturbs drug metabolism, prevented both of these BHT activities. Analogues of BHT with different substitutions at position 6 of the phenol ring also affected tumor formation. 2-tert-Butyl-4-methylphenol inhibited, not enhanced, adenoma formation. 2-tert-Butyl-4,6-dimethylphenol (BDMP) (CAS: 1879-09-0; 6-tert-butyl-2,4-xylenol); increased tumor number in A/J but not in the BALB/cByJ mouse strain; its prophylactic activity could not be measured since urethan injection following BDMP treatment was lethal. Thus the presence of an alkyl group at this site on the phenol ring was not required for prophylaxis but was necessary for tumor enhancement. These results were consistent with the possibility that different BHT metabolites were responsible for each effect. Adenoma formation was enhanced by BHT in four strains of mice with a U+ phenotype (susceptible to urethan-induced lung adenomas); these strains were A, BALB/cBy, SWR/J, and RIIIS/J. BHT had no such effect, however, in the U+ strain 129/J. A U+ B- phenotype (urethan inducible but unresponsive to BHT enhancement) also was found among the recombinant inbred lines originally derived from a cross between U+B+ BALB/-cByJ and U-/B- C57BL/6ByJ progenitor strains. This finding showed that the genes determining sensitivity to urethan and to BHT had recombined independently of each other. An inability to metabolize BHT was probably not involved in the B- phenotype, since BHT caused reversible lung damage in the 2 U+B- recombinant inbred lines and strain 129, and biotransformation was required for this effect. These U+B- mice thus can be used to characterize the lung toxic effects of BHT in the absence of its tumor-enhancing activity and will serve as valuable controls in studies on mechanisms of tumor enhancement.