In search of compounds with improved specificity for targeting the important
cancer-associated P1-1
glutathione S-transferase (GST)
isozyme, new analogs 4 and 5 of the previously reported
glutathione S-transferase (GST)-activated latent
alkylating agent gamma-glutamyl-alpha-amino-beta-[[[2-[[bis[bis(2-chloroethyl)amino]ph osp horyl]oxy]ethyl]sulfonyl]propionyl]-(R)-(-)-phenylglycine (3) have been designed, synthesized, and evaluated. One of the diastereomers of 4 exhibited good selectivity for GST P1-1. The tetrabromo analog 5 of the tetrachloro compound 3 maintained its specificity and was found to be more readily activated by
GSTs than 3. The GST activation concept was further broadened through design, synthesis, and evaluation of a novel latent
urethane mustard 8 and its diethyl
ester 9. Interestingly, 8 showed very good specificity for P1-1 GST. Cell culture studies were carried out on 4, 5, 8, and 9 using cell lines engineered 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 with the observed in vitro specificity of 8 for P1-1 GST
isozyme. Mechanistic studies on alkaline as well as
enzyme-catalyzed decomposition of latent mustard 3 provided experimental proof for the hypothesis that 3 breaks down into an active
phosphoramidate mustard and a reactive
vinyl sulfone. The alkylating nature of the decomposition products was further demonstrated by trapping those transient species as relatively stable
diethyldithiocarbamic acid adducts. These results substantially extend previous efforts to develop drugs targeting GST and provide a paradigm for development of other latent drugs.