Abstract: AimTo investigate the inhibitory activity of salvianolic acid A (SAA) on nucleoside transport in cancer cells and its antitumor effect. Methods［3H］thymidine and ［3H］uridine transport assays were used to determine the inhibitory activity on nucleoside transport in Ehrlich carcinoma cells. The cytotoxicity to cultured cancer cells was examined with clonogenic assay. The antitumor effect in vivo was evaluated with transplantable tumor model in mice. ResultsSAA was shown to inhibit thymidine and uridine transport in Ehrlich carcinoma cells with IC₅₀ values of 18.1 and 17.1 μmol·L^-1, respectively. By clonogenic assay, the IC₅₀ of SAA for KB cells was 44.7 μmol·L^-1. SAA markedly potentiated the cytotoxicity of 5-FU and mitomycin C in KB cells as well as the cytotoxicity of MTX in human hepatoma BEL-7402 cells. For in vivo experiment, sarcoma 180 cells were transplanted sc in mice and tested drugs were administered ip. When administered separately, SAA at 200 mg·kg^-1 and 5-FU at 10 mg·kg^-1 inhibited tumor growth by 41% and 27%, respectively. Combination of the two drugs inhibited tumor growth by 63% (CDI=0.86). ConclusionSAA is active in blocking nucleoside transport in cancer cells and potentiates the cytotoxicity of chemotherapeutic drugs. As an agent showing moderate antitumor effect in vivo, SAA might be useful in combination cancer therapy.