GAMMA-GLUTAMYL-TRANSPEPTIDASE EXPRESSION REGULATES THE GROWTH-INHIBITORY ACTIVITY OF THE ANTITUMOR PRODRUG GAMMA-1-GLUTAMINYL-4-HYDROXY-3-IODOBENZENE

gamma-L-glutaminyl-4-hydroxy-3-iodobenzene (I-GHB), a novel iodinated analog of gamma-L-glutaminyl-4-hydroxybenzene (GHB), demonstrates grea ter anti-tumor activity in human and in murine melanoma cell lines. Th ese phenolic amides are substrates for gamma-glutamyltranspeptidase (G GTP; E.C. 2.3.2.2), a cell-membrane-associated ecto-enzyme which is el evated in a number of tumor systems. We now present data to show that the growth-inhibitory activity of I-GHB and GHB may be mediated via GG TP-catalyzed reactions. The growth-inhibitory activity of I-GHB and GH B in pigmented B16-BL6 melanoma cells was blocked significantly by rab bit anti-rat GGTP polyclonal antibodies. The combination of L-serine a nd sodium borate, a specific transition-state inhibitor of GGTP, as we ll as acivicin, a glutamine antagonist and irreversible GGTP inhibitor , inhibited the killing of BL6 cells by GHB and I-GHB. To further defi ne the role of GGTP expression in the regulation of phenolic amide cyt otoxicity, GGTP-negative Chinese hamster ovary cells (CHO-K1) were tra nsfected with a functional rat renal cDNA representing the full-length GGTP transcript. I-GHB and GHB were significantly more cytotoxic in G GTP cDNA transfected Chinese hamster ovary (CHO-K1-GGTP) cells than in non-transfected CHO-K1 cells. The combination of L-serine and sodium borate blocked the cytotoxic activity of these pro-drugs and also inhi bited GGTP-catalyzed formation of polymerized products from these phen olic amides in intact BL6 melanoma and CHO-K1-GGTP cells. Furthermore, melanin formation from GHB was not observed in non-transfected CHO-K1 cells lacking GGTP expression. The combined data strongly suggest tha t GGTP-catalyzed hydrolysis of the anti-tumor pro-drugs I-GHB and GHB to 4-aminophenols mediates the expression of anti-tumor activity. (C) 1994 Wiley-Liss, Inc.