Combined Effect of X Radiation and 5-Fluorouracil on Survival of Transplanted Leukemic Cells2

The effect of 5-fluorouracil (5-FU) and X radiation on the survival of transplanted leukemic cells was studied in syngeneic AKR mice. A single intravenous injection of 0.6 mg 5-FU reduced the surviving fraction of leukemic cells to 10-2 of the untreated control. A similar reduction in the surviving fraction was found after 400 R total-body radiation. However, a marked synergistic cytocidal response was observed when 5-FU was given within 8 hours after radiation. The degree of synergism was less if the drug was given before radiation. In this case, the synergistic effect was greatest when 5-FU was given 14–24 hours preceding radiation. Hopefully, this study will serve to initiate closely supervised clinical trials with these two agents in combination, on which a more rational clinical treatment regimen can be formulated.