Dipyridamole augments the antitumor effects of fluorinated pyrimidines.

: The antitumor effects of 5-fluorouracil (5-FU) and its analogues when combined with dipyridamole (DP) were investigated using B16 melanoma cells, in vitro and in vivo. First, the enhancement of 5-FU cytotoxicity by DP was examined in vitro. Cell growth was suppressed significantly by combining 5-FU and a nontoxic dose of DP (2.5 micrograms/ml) as compared to 5-FU alone. Next, the effect of DP was examined in vivo in combination with 5-FU, tegafur (FT) and UFT. UFT had the most remarkable antitumor effect when given in a single equimolar dose. Although DP alone did not affect tumor growth, the growth inhibition by antitumor drugs was augmented by DP. DP enhanced the antitumor effect of UFT significantly (P less than 0.05), and combination treatment with UFT and DP proved to be the most effective regimen for inhibiting growth of B16 melanoma. Combination treatment with UFT and DP shows promise for clinical cancer.