Design, Synthesis, and Evaluation of Latent Alkylating Agents Activated by Glutathione S-Transferase

Abstract

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.

Enzyme-Catalyzed Activation of Anticancer Prodrugs

“…This prodrug is activated by tyrosine-7 from the GST enzyme that abstracts a proton from TER286, resulting in a ␤-elimination reaction, subsequently generating a phosphorodiamidate (Fig. 17) (Lyttle et al, 1994;Satyam et al, 1996). The phosphorodiamidate spontaneously rearranges to an aziridinium agent that alkylates DNA.…”

Anticancer Drug Metabolism: Chemotherapy Resistance and New Therapeutic Approaches

“…The second strategy consists in designing prodrug activated by this enzyme in order to target specifically the tumor cells overexpressing GSTP1. Thus, novel alkylating agents have been synthetized (Lyttle et al, 1994;Satyam et al, 1996). Cleavage of these molecules by GSTP1 lead to the release of two metabolites: an inactive GSH conjugate and a phosphorodiamide compound.…”

Phase 1 Study of TLK286 (Telcyta) Administered Weekly in Advanced Malignancies

“…TLK286 is designed to target the enzyme glutathione S-transferase (GST) P1-1 for activation (1,2). The rationale for TLK286 is based on the observation that many common cancers have GST P1-1 levels two to four times those of matched normal tissues (3)(4)(5)(6)(7)(8)(9)(10)(11).…”

“…1; Ref. 1,2). Data suggest that the two electrophilic species cause a series of molecular events, including activation of the stress-response pathway that results in apoptosis (19).…”