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Glutamyl hydrolase: properties and pharmacologic impact
1Division of Molecular Medicine, Wadsworth Center, New York Department of Health, Albany 12201-0509, USA.
Seminars in Oncology
|December 22, 1999
Summary
Glutamyl hydrolase cleaves poly-gamma-glutamate chains in folates and antifolates. This enzyme may enhance antifolate therapy by reducing polyglutamate forms, suggesting a new therapeutic strategy.
Area of Science:
- Biochemistry
- Enzymology
- Pharmacology
Background:
- Glutamyl hydrolase (GH) cleaves poly-gamma-glutamate chains in folates and antifolates.
- GH is primarily lysosomal but also secreted, with high mRNA levels in human liver and kidney.
- Cellular GH activity is linked to antifolate metabolism and resistance.
Purpose of the Study:
- To investigate the hydrolysis products of methotrexate-gamma-glu4 and MTA-gamma-glu4 by baculovirus-expressed human GH.
- To examine the role of GH activity in cell lines resistant to 5,10-dideazatetrahydrofolate (lometrexol).
- To explore the potential of GH modulation in antifolate therapy.
Main Methods:
- Baculovirus expression of human GH.
- Enzymatic hydrolysis assays using methotrexate-gamma-glu4 and MTA-gamma-glu4.
- Measurement of GH activity and polyglutamate levels in resistant cell lines.
Main Results:
- Hydrolysis of methotrexate-gamma-glu4 and MTA-gamma-glu4 yielded glu and gamma-glu2.
- 5,10-dideazatetrahydrofolate-resistant cell lines exhibited sevenfold higher GH activity.
- These resistant cells showed reduced levels of antifolate polyglutamates (60-90%) and folyl poly-gamma-glutamates (30%).
Conclusions:
- Glutamyl hydrolase specifically cleaves the terminal gamma-glutamate residues from antifolate polyglutamates.
- Elevated GH activity is associated with reduced intracellular polyglutamated antifolates.
- Modulating GH activity could be a viable strategy to enhance antifolate efficacy in cancer therapy.