Antifolate-induced misincorporation of deoxyuridine monophosphate into DNA: inhibition of high molecular weight DNA synthesis in human lymphoblastoid cells.

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Abstract
In vitro exposure of a human lymphoblastoid cell line (WIL-2) to the antifolate metoprine [2,4-diamino-5-(3'',4''-dichlorophenyl)-6-methylpyrimidine, DDMP], when followed by the addition of exogenous deoxyuridine, led to intracellular accumulation of dUTP and incorporation of dUMP into DNA. When newly synthesized DNA was extracted from DDMP-treated cells that had been labeled with deoxyuridine for up to 3 min, most of the DNA synthesized was no larger than 4 S on alkaline sucrose gradients. In contrast, the predominant form of newly synthesized alkali-stable DNA in cells not treated with drug was larger than 4 S. Abnormal progression of DNA synthesis, degradation of newly synthesized DNA, or both occurred as a delayed consequence of DDMP treatment in the absence of exogenous deoxyuridine when thymidine was used to label DNA of DDMP-treated WIL-2 cells. Although the toxic impact on cell viability and genetic stability of antifolate-induced misincorporation of dUMP into DNA was not elucidated, it was clear the antifolates can directly perturb the quality as well as the quantity of DNA synthesized by drug-treated cells.