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Selective Inhibition of Pyrimidine Biosynthesis and Effect on Proliferative Growth of Colonic Cancer Cells¹

Department of Pediatrics, Section of Developmental Medicine, Stanford University, Stanford, California 94305

A highly selective inhibition of de novo pyrimidine synthesis in the intact cell has been demonstrated by the action of N-(phosphonacetyl)-L-aspartate (PALA), a transition-state analog inhibitor of the reaction catalyzed by asparate transcarbamylase. The effect of pyrimidine deprivation induced by this agent on the viability and survival of human normal (WI-38) and colonic cancer cells (HT-29) was examined. The PALA-treated, pyrimidine-deprived cells failed to grow but demonstrated a normal rate of glucose utilization with impaired glycogen synthesis. Pyrimidine deprivation and lack of cell growth were maintained long after PALA removal. Growth inhibition of HT-29 cells by PALA was found to reflect an apparent steady state between newly formed and dying cells induced by limited pyrimidine availability. The highly selective nature of PALA action was confirmed by the ability of an exogenous source of pyrimidine to restore the normal growth pattern of the cell. Significant antitumor activity by PALA was found against a transplantable colonic tumor (line 26) carried in mice.

¹ This work was supported by USPHS Grants CA 14917, administered through the National Large Bowel Cancer Project, HD 000391, and HD 02147. Part of this work has been presented at the annual meeting of the Federation of American Societies for Experimental Biology, April 1 to 8, 1977, Chicago, Illinois.

² USPHS Postdoctoral Fellow, HD 00049.

Received 4/ 7/77. Accepted 6/ 2/77.

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