Cytotoxic activity of 5'-deoxy-5-fluorouridine in cultured human tumors

The cytotoxic activity of 5'-deoxy-5-fluorouridine (5'-ddFUrd) was established in six cultured human tumor lines: 47-DN and MCF-7 breast carcinomas, MG-63 osteosarcoma, HCT-8 colon carcinoma, Colo-357 pancreatic carcinoma, and HL-60 promyelocytic leukemia. Cells were exposed to a wide range of 5'-dFUrd concentrations (from 0.1 microM to 1.0 mM) for 3, 6, or 24 hrs, and then cloned using standard in vitro clonogenic assays. 5'-dFUrd exhibited its best activity in the 47-DN and MCF-7 breast cell lines and in the MG-63 osteosarcoma line (3-hr LD50 values of 32, 34, and 38 microM, respectively). Less activity was observed in the HCT-8 colon (LD50 = 195 microM) and Colo-357 pancreatic (LD50 = 155 microM) tumor lines, and ver poor activity was noted in the HL-60 leukemia cell line (LD50 = 465 microM). The metabolism of 5'-dFUrd to 5-FU (FUra) and FUra-nucleotides was determined and found to directly correlate with the potency of 5'-FUrd in these cell lines. These results suggest that: (a) there is a marked variation in sensitivity of human cancer cells of different tissue origin to 5'-dFUrd, (b) there is a direct relationship between the sensitivity of human cells to 5'-dFUrd and the ability of the cell to metabolize 5'-dFUrd to FUra, and (c) increasing exposure period of cells to 5'-dFUrd did not markedly alter 5'-dFUrd potency in all human cancer cells examined, with the exception of the 47-DN breast cancer cells.