DESIGN, SYNTHESIS, AND EVALUATION OF LATENT ALKYLATING-AGENTS ACTIVATED BY GLUTATHIONE-S-TRANSFERASE

In search of compounds with improved specificity for targeting the imp ortant cancer-associated P1-1 glutathione S-transferase (GST) isozyme, new analogs 4 and 5 of the previously reported glutathione S-transfer ase (GST)-activated latent alkylating agent lpha-amino-beta-[[[2-[[bis [bis(2-chloroethyl)amino xy]ethyl]sulfonyl]propionyl]-(R)-(-)-phenylgl ycine (3) have been designed, synthesized, and evaluated. One of the d iastereomers of 4 exhibited good selectivity for GST P1-1. The tetrabr omo analog 5 of the tetrachloro compound 3 maintained its specificity and was found to be more readily activated by GSTs than 3. The GST act ivation concept was further broadened through design, synthesis, and e valuation of a novel latent urethane mustard 8 and its diethyl ester 9 . Interestingly, 8 showed very good specificity for P1-1 GST. Cell cul ture studies were carried out on 4, 5, 8, and 9 using cell lines engin eered to have varying levels of GST P1-1 isozyme. New analogs 4 and 5 exhibited increased toxicity to cell lines with overexpressed GST P1-1 isozyme. The urethane mustard 8 and its diethyl ester 9 were found to be not as toxic. However, they too exhibited more toxicity to a cell line engineered to have elevated P1-1 levels, which was in agreement w ith the observed in vitro specificity of 8 for P1-1 GST isozyme. Mecha nistic studies on alkaline as well as enzyme-catalyzed decomposition o f latent mustard 3 provided experimental proof for the hypothesis that 3 breaks down into an active phosphoramidate mustard and a reactive v inyl sulfone. The alkylating nature of the decomposition products was further demonstrated by trapping those transient species as relatively stable diethyldithiocarbamic acid adducts. These results substantiall y extend previous efforts to develop drugs targeting GST and provide a paradigm for development of other latent drugs.