Survival of L1210 leukemia cells and normal hematopoietic stem cells following in vivo administration of cyclocytidine.

The survival of L1210 cells following increasing doses of cyclocytidine (cyclo-C) was determined by spleen colony assay. For single dose, cyclo-C was effective reaching a fractional survival of less than 10(-3) at 10 mg/mouse. This is significantly more effective than a similar dose of arabinosyl cytosine (ara-C) given by rapid infusion. The time-survival curve demonstrated extended cytotoxicity following a single 10 mg/mouse dose of cyclo-C as expected for a long-acting agent. When a 24-hour infusion was examined, however, ara-C was more effective than cyclo-C by a factor of about 10. The clinical implication of this is discussed.