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Glutamyl hydrolase and the multitargeted antifolate LY231514
M S Rhee1, T J Ryan, J Galivan
1Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York 12201-0509, USA.
Cancer Chemotherapy and Pharmacology
|September 29, 1999
Summary
Glutamyl hydrolase (GH) effectively processes multitargeted antifolate (MTA) poly-gamma-glutamates. Higher GH activity reduces MTA
Area of Science:
- Biochemistry
- Enzymology
- Pharmacology
Background:
- Multitargeted antifolate (MTA) compounds are crucial in cancer therapy.
- The poly-glutamylation of antifolates influences their cellular activity and retention.
- Glutamyl hydrolase (GH) is a key enzyme in folate metabolism.
Purpose of the Study:
- To investigate the enzymatic activity of glutamyl hydrolase (GH) on multitargeted antifolate (MTA) poly-gamma-glutamates.
- To determine the impact of elevated GH levels on the pharmacological efficacy of MTA.
Main Methods:
- Purified human and rat GH were used to assess the cleavage of MTA poly-gamma-glutamates.
- H35 hepatoma cell lines with varying GH activity were employed to evaluate MTA-induced growth inhibition.
Main Results:
- MTA tri- and penta-gamma-glutamates served as efficient substrates for human GH, exceeding rates observed with MTX.
- Human GH preferentially hydrolyzed gamma-glutamyl bonds at the carboxyl end, while rat GH favored the innermost linkage.
- Intracellular accumulation of MTA poly-glutamates was significantly reduced in GH-overexpressing (H35D) cells, conferring resistance.
Conclusions:
- MTA poly-gamma-glutamates are readily hydrolyzed by GH, indicating an inverse relationship between cellular GH activity and MTA's pharmacological effectiveness.
- The findings highlight the importance of MTA's poly-glutamate forms in inhibiting thymidylate synthase (TS).
- This study provides further evidence for the inverse correlation between GH activity and antifolate drug efficacy.