Sequential methotrexate (MTX) and 5-fluorouracil (FU) in human tumor xenografts.

Human and animal tumor-lines heterotransplanted in nude mice were treated with MTX and FU sequentially. In order to investigate the relationship between tumor response and drug toxicity sequence, time and dose of both MTX and FU were varied. Pretreatment with MTX followed by FU with intervals of 3 or 24 h produced superior therapeutic results when compared to single administration of MTX or FU, simultaneous treatment, or the reverse sequence. In the MTX followed by FU regimen, dose reduction of either MTX or FU tended to decrease the anti-tumor effect. To investigate the toxic effects of different regimens, tumor-free nude mice were treated with MTX and FU the same way as the tumor-bearing animals. In this case, toxicity (weight loss, leukopenia) was more pronounced in those schedules with the best therapeutic results. However, toxicity appears to be more clearly related to the applied FU-dose.