METABOLIC-ACTIVATION AND BINDING OF MITOTANE IN ADRENAL-CORTEX HOMOGENATES

Mitotane lorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane, o,p'-DDD] is an adrenocorticolytic agent of value in the treatment of adrenocort ical carcinoma and Gushing's syndrome. In support of a program to deve lop agents superior to mitotane, it is the purpose of this study to ex plore the relationship of the metabolism of mitotane to its binding to adrenal cortex tissue from several sources. The objective was to dete ct the mitotane moiety responsible for its covalent binding in various test systems. Studies were conducted with an I-125-labeled analog of mitotane, chlorophenyl)-1-(4-iodophenyl)-2,2-dichloroethane, prior to a comparison to results with lower specific activity [C-14]mitotane. W ith dog adrenal cortical whole homogenates, the majority of covalent b inding was to proteins with an additional one-sixth of the total bound radioactivity associated with a phospholipid fraction. No radioactivi ty was associated with DNA. The rank order of species in regard to met abolism and protein binding was bovine > dog > rat adrenal homogenates > human normal adrenal or tumor homogenates. The percentage of radioa ctivity recovered from the hydrolysates of those fractions was uniform ly high. In addition, the only metabolite present in the hydrolysates corresponded to 1-(2-chlorophenyl)-1-(4-iodophenyl)acetic acid from th e iodo analog of o,p'DDD and the corresponding o,p'-dichlorodiphenylac etic acid (o,p'-DDA) from o,p'-DDD. Our results are consistent with an acyl chloride being the reactive intermediate formed from the dichlor omethyl moiety of mitotane, which leads to both DDA metabolite formati on and binding to adrenal cortical bionucleophiles.