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

In vitro exposure of a human lymphoblastoid cell line (WIL-2) to the antifolate metoprine (DDMP), when followed by the addition of exogenous deoxyuridine, led to intracellular accumulation of deoxyuridine triphosphate (dUTP) and incorporation of deoxyuridine monophosphate (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 stability of antifolate-induced misincorporation of dUMP into DNA was not elucidated, it was clear that antifolates can directly perturb the quality as well as the quantity of DNA synthesized by drug-treated cells.