The development of suitable methods for purging the malignant cells contaminating the bone marrow of patients with cancer may offer a better chance of success for autologous bone marrow transplantation. In this paper, we further describe our efforts at purging acute myelogenous leukemia cells. HL-60, a promyelocytic leukemia cell line, was used as a model. 4-Hydroperoxycyclophosphamide (4-HC), VP-16-213 (VP-16), and Adriamycin were used alone or in combination to develop the best method to purge HL-60 cells. The cytotoxicity of 29.2 μg/ml (100 μm) of 4-HC was 99.8 ± 0.12% (SD) on HL-60 cells and 82.5% on colony forming units-granulocyte, macrophage. Ninety-nine % of HL-60 cells and 72.7% of colony forming units-granulocyte, macrophage were inhibited by VP-16 at a concentration of 25 μg/ml (42.5 μm). The cytotoxicity of 1.5 μg/ml (2.76 μm) of Adriamycin on HL-60 cells was 98.6 ± 0.8% and inhibited colony forming units-granulocyte, macrophage by 50.8%. The cytotoxicity and interactions of any two drug combinations at different combination ratios and the different effect levels were quantitatively determined by median effect plot and the multiple drug effect equation (T-C. Chou and P. Talalay. Adv. Enzyme Regul. 22: 27–55, 1984). The combination of 4-HC and VP-16 at a 4-HC:VP-16 drug ratio of 1:0.342 was found to be the best for selective toxicity towards HL-60 cells and was superior to the 4-HC-Adriamycin or VP-16 Adriamycin combination for usefulness in purging bone marrow.

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This work was supported in part by the American Cancer Society and by NIH Grants CA-19117, and CA-27569, and CA-18856.

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