One of the most common biochemical correlates of alkylating agent resistance is an elevation of intracellular levels of the ubiquitous nonprotein thiol, glutathione(GSH). The overall objective of the proposed studies is to evaluate possible mechanism(s) by which GSH levels are increased in drug resistant tumor cells. It is our hypothesis that increased GSH in resistant tumor cells is attributable to drug-induced alterations in the activity of key enzymes or substrates involved in biosynthesis of this important tripeptide. Consequently we plan to focus our initial investigations on changes in what we consider to be three prime candidates: GCS, the rate limiting enzyme in GSH synthesis; gamma-glutamyl transpeptidase (GGT), the initial step in a GSH salvage pathway; and intracellular cysteine, a key amino acid precursor. We have spent the past 12 months developing the requisite assays and cloning and sequencing the cDNA for gamma-glutamylcysteine synthetase (GCS) from human kidney and believe we are now in an unique position to initiate this type of investigation. Specifically, we will compare the activity of these enzymes in select pairs of sensitive and alkylating agent resistant cell lines; correlate differences in enzyme activity with the expression of GCS and GGT genes; determine whether transfection of GCS or GGT cDNAs can alter GSH levels and response to alkylating agents; and examine the effect of buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis being evaluated clinically as a potential modifier of tumor GSH levels, on the regulation and activity of these important regulators of GSH biosynthesis. These evaluations will include assessment of these parameters in lymphocytes from patients participating in our Phase I clinical trial of BSO. This comprehensive investigation of molecular and biochemical mechanisms responsible for the elevation of GSH and their response to GSH modulating agents could contribute significantly to understanding the molecular and cellular pharmacology of this important thiol in the response of cells to anti-neoplastic agents.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA057549-03
Application #
2098276
Study Section
Experimental Therapeutics Subcommittee 1 (ET)
Project Start
1992-07-07
Project End
1995-06-30
Budget Start
1994-07-01
Budget End
1995-06-30
Support Year
3
Fiscal Year
1994
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Dahl, E L; Mulcahy, R T (2001) Cell-type specific differences in glutamate cysteine ligase transcriptional regulation demonstrate independent subunit control. Toxicol Sci 61:265-72
Wild, A C; Mulcahy, R T (2000) Regulation of gamma-glutamylcysteine synthetase subunit gene expression: insights into transcriptional control of antioxidant defenses. Free Radic Res 32:281-301
Gipp, J J; Mulcahy, R T (2000) Structure of the human glutamate-L-cysteine ligase catalytic (GLCLC) subunit gene. Cytogenet Cell Genet 88:130-2
Zipper, L M; Mulcahy, R T (2000) Inhibition of ERK and p38 MAP kinases inhibits binding of Nrf2 and induction of GCS genes. Biochem Biophys Res Commun 278:484-92
Wild, A C; Moinova, H R; Mulcahy, R T (1999) Regulation of gamma-glutamylcysteine synthetase subunit gene expression by the transcription factor Nrf2. J Biol Chem 274:33627-36
Moinova, H R; Mulcahy, R T (1999) Up-regulation of the human gamma-glutamylcysteine synthetase regulatory subunit gene involves binding of Nrf-2 to an electrophile responsive element. Biochem Biophys Res Commun 261:661-8
Griffith, O W; Mulcahy, R T (1999) The enzymes of glutathione synthesis: gamma-glutamylcysteine synthetase. Adv Enzymol Relat Areas Mol Biol 73:209-67, xii
Moellering, D; Mc Andrew, J; Patel, R P et al. (1999) The induction of GSH synthesis by nanomolar concentrations of NO in endothelial cells: a role for gamma-glutamylcysteine synthetase and gamma-glutamyl transpeptidase. FEBS Lett 448:292-6
Wild, A C; Mulcahy, R T (1999) Pyrrolidine dithiocarbamate up-regulates the expression of the genes encoding the catalytic and regulatory subunits of gamma-glutamylcysteine synthetase and increases intracellular glutathione levels. Biochem J 338 ( Pt 3):659-65
Wild, A C; Gipp, J J; Mulcahy, T (1998) Overlapping antioxidant response element and PMA response element sequences mediate basal and beta-naphthoflavone-induced expression of the human gamma-glutamylcysteine synthetase catalytic subunit gene. Biochem J 332 ( Pt 2):373-81

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