Abstract
Summary
The purpose of this study was to determine whether priming-dose schedules of Cytoxan (Cyt) could result in increased antileukemic effectiveness in L1210 leukemic mice. In three experiments, each initial dose of Cyt was followed by various schedules of Cyt. When the interval between doses was short (2 days), the optimal treatment was found to consist of a high priming dose followed by markedly reduced regular doses. At longer intervals (5 and 7 days), the optimal modality was a constant-dose schedule. On constant-dose schedules, a longer interval between treatments was advantageous. When loading-dose schedules were included, the longest surviving group was observed when a shorter interval was employed.
The results of an experiment in which mice were inoculated with log dilutions of L1210 and treated with a course of Cyt suggest that the percentage of tumor cells killed by Cyt may diminish with larger tumor-cell populations. It is further suggested that the diminished percent kill may become evident only after the tumor is very large.
The current observations support the concept that Cyt is at least partially cell-specific.
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