The objective is to participate in the design and testing of new antifolates for use in cancer chemotherapy based on knowledge of folate metabolism. The interaction of folate coenzymes and antimetabolites with folate enzymes of known or potential relevance to cancer chemotherapy will be studied. The program will center on three major areas: 1) Development of an in vitro enzyme system designed to test current hypotheses concerning the interaction of the three enzymes of the thymidylate cycle, dihydrofolate reductase, thymidylate synthase and serine hydroxymethyltransferase.-The central question addressed is: What is the effect of simultaneous inhibition of two of the three enzymes of the cycle on net dTMP formation? Current hypotheses predict antagonism. Our results with bacterial growth studies show that synergistic inhibition can be obtained. 2) Interaction of polyglutamyl 1 inhibitors and coenzymes with folate enzymes.-Polyglutamyl derivatives of folates and of folate antagonists can have a much higher affinity for folate enzymes than the monoglutamate forms. We will study polyglutamate forms of methotrexate, 10-deazaaminopterin, 10-ethyl-10-deazaaminopterin and 5,8-dideaza-10-propargylfolate. The last two compounds named are inhibitors of dihydrofolate reductase and thymidylate synthase respectively and both are in clinical trial. The enzymes to be studied are those mentioned in 1) plus the transformylating enzymes of purine biosynthesis. The enzymes will be derived from cultured human cells, L1210 cells and bacteria. 3) Evaluation of new antifolates synthesized in the laboratories by microbiological assay and enzyme inhibition. Additional studies include: 1) Studies on the metabolism of the natural diastereomer of 5-formyletrahydrofolate in human colon carcinoma xenografts with particular attention to the enhanced antitumor effect when combined with fluorouracil. 2) Studies on the inhibition of dihydrofolate reductase from methotrexate-resistant human squamous cells. 3) Studies on the anti-tumor activity of diastereomers of 5-methyltetrahydrohomofolate. and 4) Studies on the inhibition of thymidylate synthase by combinations of pyrimidine antagonists and folylpolyglutamate analogs.
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