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Cancer Chemotherapy Research Program, Pharmaceuticals Division, Biomedical Products Department, E. I. Du Pont de Nemours and Co., Inc., Wilmington, Delaware 19898
Exposure of cultured clone A human colon tumor cells to 25 to 75 µM of NSC 368390 [6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarboxylic acid sodium salt, DuP 785] for 48 to 72 h resulted in a 99.9% cell kill as determined by clonogenic assay. Cells exposed to NSC 368390 became depleted in intracellular pools of uridine 5'-triphosphate and cytidine 5'-triphosphate. Both uridine 5'-triphosphate and cytidine 5'-triphosphate were decreased to 50% of levels in control cells at 3 h and were undetectable at 15 h after addition of 25 µM of NSC 368390 to the cultures. Similar effects were observed in L1210 leukemia cells. Addition of 0.1 mM of uridine or cytidine restored intracellular pools of uridine 5'-triphosphate and cytidine 5'-triphosphate to control levels and rescued clone A cells from NSC 368390 cytotoxicity. Addition of uridine circumvented NSC 368390 cytotoxicity in L1210 cells, but addition of cytidine did not. This result is consistent with the fact that L1210 cells lack cytidine deaminase and thus cannot form uridine or its anabolites from cytidine. These results indicated that NSC 368390 inhibits a step in the de novo biosynthetic pathway leading to uridine 5'-monophosphate. Therefore, the effects of NSC 368390 on the six enzymes that comprise the de novo pathway leading to the formation of uridine 5'-monophosphate were examined. The results showed that NSC 368390 was a potent inhibitor of dihydroorotate dehydrogenase, the fourth enzyme in the pathway; thus, this study demonstrates that NSC 368390 exerts its tumoricidal effect by inhibiting a step in de novo pyrimidine biosynthesis resulting in the depletion of critical precursors for RNA and DNA synthesis.
1 To whom requests for reprints should be addressed, at Du Pont Company, Glenolden Laboratory, 500 S. Ridgeway Avenue, Glenolden, PA 19036.
Received 2/11/86. Revised 5/ 6/86. Accepted 6/27/86.
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