We are studying the biochemical basis for the chemotherapeutic effectiveness of L-asparaginase. This anti-tumor treatment has been employed for many years, but the precise lesion rendering certain cells sensitive to this treatment is not known. We have examined the asparagine synthetase from both tumor and normal cells. In addition, we have begun to examine the role of asparagine-dependent glycine synthesis in tumor cell metabolism. We have evidence that while asparagine synthesis may be limited in L-asparaginase sensitive tumor cells, the actual cause of cell death may be the loss of an asparagine-dependent metabolite. We propose to study the regulation of asparagine synthetase in both normal and tumor cells. Our evidence indicates that there may be a covalent modification of the enzyme that is responsible for control of activity. We will explore the possibilty that this covalent change may be related to alkaline phosphatase which is found in high levels in sensitive cells. We will also study the enzymes of both asparagine and asparagine-linked glycine metabolism. This will include the enzymes converting asparagine to alpha- ketosuccinamate and oxaloacetate, and the enzymes producing glyoxylate from hydroxyproline. We have identified the enzyme that catalyzes the NADPH- dependent hydroxylation of glutamic acid so we will explore the possibility that glutamic acid is a carbon source for pyruvate and glyoxylate. The relevance of these enzymes to the metabolism of, and differences between, L5178Y and L5178Y/ASN cells will be examined. It is hoped that results of these studies will provide an explanation for selective tumor cell sensitivity to L-asparaginase therapy. It may then be possible to design more effective chemotherapeutic protocols and to develop reliable diagnostic techniques.
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