Enhancement of the Incorporation of 5-Fluorodeoxyuridylate into DMA of HL-60 Cells by Metabolic Modulations1

The exposure of HL-60 human promyelocytic leukemia cells to 0.5 MM5-fluoro-2'-[3H]deoxyuridine (FdUrd) for 16 hr resulted in the incorporation of 5.14 ±0.31 (S.D.) x 10~7 mol FdUrd into DMA per mol of DMA nucleotide, which corresponds to 0.146 ± 0.082 pmol FdUrd per 107 cells. Pretreatment with 50 MMdeoxythymidine for 24 hr led to a 2.7-fold increase in the incorporation of this analogue into newly synthesized DNA during the ensuing 16-hr exposure to 0.5 MM [3H]FdUrd. Pretreatment with 0.5 MM methotrexate for 3 hr also increased the [3H]FdUrd incorporation into newly synthesized DNA approximately 5-fold. The coexist ence of deoxythymidine or methotrexate with [3H]FdUrd, how ever, led to decreased incorporation of FdUrd into DNA. More than 50% of the radioactivity in DNA separated by Cs2S04 equilibrium density gradient centrifugation was proven to be fluorodeoxyuridylate by means of its binding to Lactobacillus case/' deoxythymidine monophosphate synthetase.