Effects of hyperthermia on the metabolism of 5-fluorouracil in vitro.

The effects of hyperthermia (38-42 degrees C) on the metabolism of 5-fluorouracil (5-FU) were examined using Ehrlich tumour cells (E-cells) and Sarcoma-180 cells (S-180 cells) in vitro. A temperature-dependent elevation of the intracellular concentration of 5-FU was observed in both types of tumour cell after incubation with 5-FU. The levels of 5-fluorouridine (FUR) and 5-fluoro-2'-deoxyuridine (FdUR), which are active metabolites of 5-FU, increased significantly after treatment of cells with 5-FU and hyperthermia. The highest concentrations of these active metabolites were found when the cells were incubated at 39 degrees C. The levels of alpha-fluoro-beta-ureido-propionic acid (FUPA) and F-beta-alanine, which are inactive catabolic metabolites of 5-FU, also increased when the cells were incubated at 39 degrees C. The percentage inhibition of thymidilate synthetase (TS) activity remained high (about 60-70%) at 39 degrees C for 240 min. These results suggest that the optimal temperature for potentiating the intracellular metabolism of 5-FU, in terms of both activation and inactivation, is 39 degrees C in vitro.