Effects of thermochemotherapy [1-hexylcarbamoyl-5-fluorouracil (HCFU) combined with hyperthermia]: a basic study on the most effective timing and sequence in vivo.

1-Hexylcarbamoyl-5-fluorouracil (HCFU) is known to be hydrolyzed to 5-fluorouracil (5-FU) by heating. We have previously reported the enhancement of the antitumor effects of HCFU when combined with hyperthermia (1). This study aimed at determining the most effective timing schedule for HCFU combined with hyperthermia for clinical application. On the third, 6th, 9th, 12th and 15th day after transplantation, HCFU (80 mg/kg) was administered and hyperthermia induced. The antitumor effect was evaluated by the measurement of tumor volume. 5-FU concentration in the tumor tissue was analyzed on the 12th day after transplantation after administering 150 mg/kg HCFU, with or without hyperthermia (43.5 degrees C, 45 min). 5-FU concentration in serum and other tissues (kidney, liver and submandibular gland) were also analyzed. The concentration was measured by a high performance liquid chromatograph (HPLC) following Mori et al 's method (2). An enhanced antitumor effect and a significant increase in 5-FU concentration in tumor tissue were observed in post-heated groups of mice as compared with pre-heated groups and groups given HCFU alone. The results showed that HCFU given 1 to 2 hours prior to hyperthermia was the most effective treatment.