gamma-glutamyl transpeptidase-dependent mutagenicity and cytotoxicity of gamma-glutamyl derivatives: A model for biochemical targeting of chemotherapeutic agents

Many carcinomas in humans are rich in gamma-glutamyl transpeptidase (GGT). a plasma membrane enzyme that reacts with extracellular substrates. Thus, b iochemical targeting of chemotherapeutic agents may be achieved by converti ng anticancer drugs into their gamma-glutamyl derivatives. Chemical convers ion of phenylhydrazine (PH) and biochemical modification of daunomycin (DM) into their gamma-glutamyl derivatives gamma-glutamyl phenylhydrazine (GGPH ) and gamma-glutamyl DM (GGDM) resulted in the abolishment of their mutagen icity and cytotoxicity, as judged by decreased viability and increased muta nt yields in cultures of several Salmonella Ames strains. Commercial gamma- glutamyl-p-nitroanilide (GGPNA) was not toxic or mutagenic. Mutagenicity an d/or cytotoxicity of these gamma-glutamyl derivatives were restored upon re action with GGT, with concomitant release of PH, and p-nitroaniline (PNA). The GGT-dependent release of DM from GGDM was demonstrated by thin layer ch romatography (TLC), spectral analysis, and specific mutagenicity. Mutagenic ity and/or cytotoxicity of gamma-glutamyl derivatives increased in the pres ence of glycylglycine, a GGT activator, and decreased in the presence of se rine-borate, a GGT inhibitor. GGDM retained considerable DNA binding capaci ty. Its inability to kill and mutagenize was due to altered transport prope rties. The results are compatible with the notion that gamma-glutamylation is a feasible method for biochemical targeting of drugs containing a primar y amino group to GGT-rich tumors. Environ. Mol. Mutagen. 32:377-386 1998 (C ) 1998 Wiley-Liss, Inc.