title: Gamma-glutamyltranspeptidase expression regulates the growth-inhibitory activity of the anti-tumor prodrug gamma-L-glutaminyl-4-hydroxy-3-iodobenzene.
abstract: gamma-L-glutaminyl-4-hydroxy-3-iodobenzene (I-GHB), a novel iodinated analog of gamma-L-glutaminyl-4-hydroxybenzene (GHB), demonstrates greater anti-tumor activity in human and in murine melanoma cell lines. These phenolic amides are substrates for gamma-glutamyltranspeptidase (GGTP; E.C. 2.3.2.2), a cell-membrane-associated ecto-enzyme which is elevated 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 GGTP-catalyzed reactions. The growth-inhibitory activity of I-GHB and GHB in pigmented B16-BL6 melanoma cells was blocked significantly by rabbit anti-rat GGTP polyclonal antibodies. The combination of L-serine and sodium borate, a specific transition-state inhibitor of GGTP, as well as acivicin, a glutamine antagonist and irreversible GGTP inhibitor, inhibited the killing of BL6 cells by GHB and I-GHB. To further define the role of GGTP expression in the regulation of phenolic amide cytotoxicity, GGTP-negative Chinese hamster ovary cells (CHO-K1) were transfected with a functional rat renal cDNA representing the full-length GGTP transcript. I-GHB and GHB were significantly more cytotoxic in GGTP 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 inhibited GGTP-catalyzed formation of polymerized products from these phenolic 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 that GGTP-catalyzed hydrolysis of the anti-tumor pro-drugs I-GHB and GHB to 4-aminophenols mediates the expression of antitumor activity.
authors.affiliation: Department of Radiation Oncology, University of Pittsburgh School of Medicine, PA 15213.
authors.forename: J A
authors.initials: JA
authors.lastname: Prezioso
authors.forename: R P
authors.initials: RP
authors.lastname: Hughey
authors.forename: N
authors.initials: N
authors.lastname: Wang
authors.forename: K M
authors.initials: KM
authors.lastname: Damodaran
authors.forename: W D
authors.initials: WD
authors.lastname: Bloomer
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D001881:Borates / Q000494:pharmacology; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002455:Cell Division; D006224:Cricetinae; D005973:Glutamine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006868:Hydrolysis; D007555:Isoxazoles / Q000494:pharmacology; D008543:Melanins / Q000096:biosynthesis; D008546:Melanoma, Experimental / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D010636:Phenols / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D011355:Prodrugs / Q000378:metabolism* / Q000494:pharmacology; D012694:Serine / Q000494:pharmacology; D014162:Transfection; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D001881:Borates; D007555:Isoxazoles; D008543:Melanins; D010636:Phenols; D011355:Prodrugs; D005973:Glutamine; C079662:gamma-glutaminyl-4-hydroxy-3-iodobenzene; D012694:Serine; C010634:sodium borate; D005723:gamma-Glutamyltransferase; D005978:Glutathione; C006303:acivicin