Abstract: Mutactimycin, a new anthracycline antibiotic, consists of 5 components: mutac-timycin A, B, C, D and 7-deoxymutactimycinone A. Mutactimycin components differ from each other in suppressing proliferation and inducing differentiation of human erythroleukemia K-562 cells. Determined by benzidine staining, the percentage of K-562 cells with hemoglobin expression was86% by mutactimycin C. The peak percentage of benzidine positive cells appeared on day 5 or 6.The differentiated cells were partially reversed after drug removal.The induced cells lost the clonogenicity in soft-agar. The kinetics of differentiation induced by mutactimycin C, in comparison with other known anthracycline antibiotics, was similar to that by doxorubicin, epirubicin anddaunorubicin. Mutactimycin C was more active than aclarubicin A. The structure-activity relationship for mutactimycin components suggested that the substituting groups on C3, C11, and the saccharide on C7 might be important for their activities.

Key words: Mutactimycin, K-562 cells, Differentiation, Strtucture-activity relationship