An attempt at synchronization of marrow cells in acute leukemia: relationship to therapeutic response

The relationship between changes in the bone marrow labeling index and the patient's subsequent response to cycle-specific agents was studied by the South-eastern Cancer Study Group in adults with acute leukemia. Ninety-eight patients were randomized to one of two treatment regimens. Schedule 1 consisted of a single intravenous (i.v.) push of cytosine arabinoside followed in 48 hours by a large dose of oral methotrexate distributed over 24 hours and i.v. vincristine. Leucovorin rescue was employed to control the toxic effects of the high dose methotrexate and the cycle was repeated every 7 days. Schedule 2 differed only in that there were three daily injections of cytosine arabinoside preceding vincristine and methotrexate injections and each cycle was given every 10 days. Cell kinetic studies were performed in 30 patients and revealed that the majority of patients who had a response to therapy had some increase in the marrow labeling index 48 hours after cytosine arabinoside injection. In general, those patients who had no response to therapy had little change. There was no significant difference between schedules in the ability to induce an increase in labeling index 48 hours after cytosine arabinoside or in the increment achieved by the responders. However, there was a significant difference in the response rate seen with these schedules. Schedule 1 achieved only a 24% remission rate in acute nonlymphocytic leukemia (ANLL) while schedule 2 was associated with a 52% remission rate. In acute lymphoblastic leukemia (ALL) both schedules induced a 60% remission rate while none of the four patients with blast crisis of chronic granulocytic leukemia (CGL) responded. Analysis of the characteristics associated with remission revealed that more females achieved a remission than males and that the presence of pretreatment infection was the greatest contributing cause of early death and thus severely limited the ability to achieve a remission. As opposed to the current regimens used in ANLL, schedule 2 did not require significant bone marrow hypoplasia (as judged by the degree of hematological toxicity) to achieve a remission and there was no decrease in response seen with increasing age. The data suggest that increased efficiency of cycle-specific, antitumor agents may occur by increasing the proportion of human leukemic cells in DNA synthesis.