Synergistic effect of amphotericin B and 1,3-bis(2-chloroethyl)-1-nitrosourea against a transplantable AKR leukemia.

Long-term survivors of mice bearing a transplanted leukemia have been obtained following treatment with a combination of amphotericin B and 1, 3-bis(2-chloroethyl)1-nitrosourea. The proportion of mice surviving at 28 days depended upon the order and timing of drug adminis tration. Optimal results were obtained when 0.5 mg am photericin B was given 24 hr before 0.2 mg l, 3-bis(2-chloroethyl)-l-nitrosourea. Spleen colony assays showed that the survivors harbored viable leukemic cells for a number of days following treatment. Nevertheless, with the most effective regimen, about 75% of the survivors appeared healthy and had no detectable leukemic cells at the end of the 28-day period of observation. The survivors were resistant to further rechallenge with IO6 leukemic cells, a dose that caused fatal