Novel Nucleoside Transport Inhibitors Potentiate The Activity Of Antitumor Drugs

The present study has found that antibiotics C3 3 68-A (CA) and C3368-B (CB), and a plant-derived compound, salvianolic acid A (SA), are active in the inhibition of nucleoside transport. These agents markedly inhibited nucleoside transport in Ehrlich carcinoma cells. For [³H]-thymidine transport, the IC₅₀ values of CA, CB, and SA were 4.6uM, 7.5uM and 18.1uM; and those for [³H]-uridine transport were 7.7uM, 9.6uM and 17.1uM, respectively.The 3 newly-found nucleoside transport inhibitors, CA, CB and SA, and 2 other recently reported nucleoside transport inhibitors, green tea extract (GTE) and catechin (CAT), all had fairly low cytotoxicity to tumor cells. In clonogenic assay, the IC₅₀ values of CA, CB, GTE, SA and CAT for human oral epidermoid cancer KB cells were 3.2uM, 64.9uM, 35.2uM, 44.7uM and 125uM; those for human hepatoma BEL-7402 cells were 44.6uM, 215uM, 157uM, 92.2uM and 699uM in NAG enzyme assay, respectively.CA, CB, GTE, SA, CAT and dipyridamole (DP) , the well-known nucleoside transport inhibitor, potentiated the cytotoxicity of 2 antimetabolites, methotrexate (MTX) and 5-fluorouracil (5FU). In clonogenic assay, CA, CB, GTE, SA, CAT and DP had synergistic effect with MTX in killing of KB carcinoma cells. CB, SA and DP also potentiated the effect of MTX on colony formation in hepatoma BEL-7402 cells. SA and DP blocked the reversal...