The goal of this research project is to develop more effective therapeutic strategies for treating cancer based on antagonism of the amino acid glutamine. The glutamine antimetabolites DON (6-diazo-5-oxo-L-norleucine) and Acivicin ([Alpha-S,5,S]-Alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid) have been shown to possess promising antitumor activity against a wide variety of animal and human neoplasms, including colon, mammary and lung carcinomas, and sarcomas. These drugs, however, have limited potential when used as single agents in treatment of cancer in humans because of severe toxicity which prevents increasing drug doses into the required therapeutic range. Administration of the enzyme glutaminase greatly reduces the concentration of glutamine in the tumor-bearing host and initial experiments have indicated that co-administration of low (nontoxic) doses of glutaminase enhances the therapeutic index of DON and Acivicin.
The aim of the proposed research is to further develop the potential of glutamine antagonism in treatment of cancer and identify the human neoplasms with greatest sensitivity to this treatment. Specifically, we propose to: 1) Determine the degree of sensitivity of a wide variety of human tumor cell lines growing in culture to the glutamine antimetabolites DON and Acivicin, employing the soft agar clonogenic assay. We will also study the effects of the antimetabolites on macromolecular synthesis by culturing tumor cells for brief periods in media containing the usual glutamine concentration and in glutamine-deficient media. 2) Inoculate a wide variety of human tumor cell lines into athymic nude mice and determine the effects of treatment with glutaminase and glutamine antagonists on tumor growth and animal survival time. We will determine the correlation between in vitro drug sensitivity and in vivo therapeutic response. 3) Investigate the mechanism(s) whereby tumor cells develop resistance to DON and Acivicin and determine to what extent co-administration of glutaminase can prevent or delay the onset of drug resistance. Cross-resistance between DON and Acivicin will also be studied. 4) Evaluate the therapeutic effectiveness of glutaminase which has been conjugated to tumor-specific monoclonal antibodies. We expect that the localization of glutaminase on the surface of tumor cells will cause selective depletion of glutamine in the vicinity of the tumor. This should result in increased toxicity of glutamine antimetabolites to tumor cells and reduced toxicity to normal host tissues where glutamine levels remain relatively high.
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