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

The exposure of HL-60 human promyelocytic leukemia cells to 0.5 µm 5-fluoro-2′-[³H]deoxyuridine (FdUrd) for 16 hr resulted in the incorporation of 5.14 ± 0.31 (S.D.) × 10^-7 mol FdUrd into DNA per mol of DNA nucleotide, which corresponds to 0.146 ± 0.082 pmol FdUrd per 10⁷ cells. Pretreatment with 50 µm deoxythymidine 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 µm [³H]FdUrd. Pretreatment with 0.5 µm methotrexate for 3 hr also increased the [³H]FdUrd incorporation into newly synthesized DNA approximately 5-fold. The coexistence of deoxythymidine or methotrexate with [³H]FdUrd, however, led to decreased incorporation of FdUrd into DNA.

More than 50% of the radioactivity in DNA separated by Cs₂SO₄ equilibrium density gradient centrifugation was proven to be fluorodeoxyuridylate by means of its binding to Lactobacillus casei deoxythymidine monophosphate synthetase.