Glutathione-S-transferase Activates Novel Alkylating Agents

Abstract

Alkylating agents which are activated by glutathion-S-transferases (GSTs) have been designed and synthesized. The model compound gamma-glutamyl-alpha-amino-beta-[(2-ethyl N,N,N',N'-tetraethylphosphorodiamidate) sulfonyl]propionylglycine (1) and the nitrogen mustards gamma-glutamyl-alpha- amino-beta-[[2-ethyl N,N,N',N'-tetrakis (2-chloroethyl)phosphorodiamidate] sulfonyl]propionylglycine (2) and gamma-glutamyl-alpha-amino-beta-[[2-ethyl-N,N,N',N'-tetrakis(2- chloroethyl)phosphorodiamidate]sulfonyl]-propionyl-(R)-(-)-phenylg lycine (3) were prepared via multistep chemical synthesis. The compounds were tested with recombinant human A1-1, M1a-1a and P1-1 GSTs. HPLC studies showed that the compounds were differentially and catalytically cleaved by biologically relevant concentrations of the GSTs. Mass spectral studies of the cleavage mixture of 2 showed that M1a-1a GST liberated the cytotoxic phosphate moiety needed for efficacy as an alkylating agent. Cell culture studies with MCF-7 breast cancer cells showed that 1 was not toxic at 200 microM, while 2 and 3 showed IC50S of 40.6 and 37.5 microM, respectively, for the same cell line. MCF-7 cells transfected to overexpress P1-1 GST showed enhanced sensitivity with 2 and 3, with IC50S of 20.9 and 9.5 microM, respectively. This result correlates well with the rates of cleavage of 2 and 3 by P1-1 GST observed in vitro and demonstrates that higher levels of cellular P1-1 GST will give increased sensitivity to these drugs.

The role of glutathione-S-transferase in anti-cancer drug resistance

“…This is the lead compound from a novel class of latent drugs activated in cancer cells by GSTP1-1 (Lyttle et al, 1994b). GSTP1-1 promotes a b-elimination reaction that cleaves TLK286 into a GSH analogue and nitrogen mustard that can alkylate cellular nucleophiles (Figure 3) .…”

Glutathione S-transferase polymorphisms: cancer incidence and therapy

“…Prodrugs Lyttle et al, 1994). TLK286 is cleaved by a GSTP1*A-promoted b-elimination reaction into a nitrogen mustard and GSH analog that can then alkylate cellular nucleophiles (Morgan et al, 1998).…”

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.…”