Schedule-Dependent Antitumor Activity and Toxicity of Combinations of 5-Fluorouracil and Cisplatin/Carboplatin against L1210 Leukemia-Bearing Mice

The combination of cisplatin (CDDP) and 5-fluorouracil (5-FU) has been reported to show marked therapeutic effects on experimental tumors and human malignancies, such as head and neck cancer. In these clinical studies, CDDP was administered on day 1 and followed by a 5-d continuous infusion of 5-FU. However, it was repeatedly shown that the sequence of 5-FU followed by CDDP is more active and less toxic in tumor-bearing animals. Thus, the optimal administration schedule of CDDP and 5-FU against L1210 murine leukemia was examined and compared with that of the combination of 5-FU and carboplatin (JM-8). The combinations of 5-FU (days 1 to 5) and CDDP, given either on day 1 or on day 5, showed a similar level of antitumor activity and toxicity. On the other hand, the combinations of 5-FU (days 1 to 5) and JM-8 given on day 5 showed significantly higher antitumor activity and rather less toxicity, as compared with the combinations on the reverse sequence. Thus, the treatment sequence of platinum compounds followed by a 5-d continuous infusion of 5-FU in many clinical studies appears to be extremely favorable to CDDP than JM-8. In addition, pathological examinations of died mice showed that accumulation of ascites and pleural effusion was inhibited most effectively by JM-8, given alone or in combination with 5-FU. These results strongly suggest that the combination of 5-FU followed by JM-8 will be expected to show more excellent antitumor activity against human malignancies, and may be especially useful in patients who are unable to tolerate CDDP-related toxicity.