Marcellomycin, a newly developed
anthracycline antibiotic with
antineoplastic activity, was tested as an inducer of differentiation of the human promyelocytic
leukemia cell line HL-60 in vitro. The percentage of cells reducing nitro blue tetrazolium, an indication of a stimulus-induced respiratory burst typical of mature phagocytes, was used as a functional measure of the extent of differentiation.
Marcellomycin was a potent inducer of maturation, with 95% of the cells expressing a terminally differentiated state after 10 days of exposure to a concentration of 40 nM
anthracycline. Cells exposed to
marcellomycin exhibited a 35-fold increase in their total
superoxide anion-generating capacity, an 80% increase in
acid phosphatase activity, and a loss of
myeloperoxidase and
chloroacetate esterase activities. In addition,
marcellomycin-treated cells stained negatively for
alpha-naphthyl acetate esterase. These findings provided evidence for the granulocytic nature of the mature cells. In contrast,
marcellomycin was not an effective inducer of differentiation of Friend murine
erythroleukemia cells. Studies on the relationship between structure and the ability to induce differentiation of HL-60
leukemia cells demonstrated that removal from the
marcellomycin molecule of the terminal 2-deoxyfucose (
musettamycin) or its substitution by cinerulose (
aclacinomycin A) did not alter differentiation-inducing capacity. However, removal of the carbomethoxy group from the C-10 position of
marcellomycin substantially reduced its potency as an initiator of maturation, and removal of the two terminal 2-deoxyfucose moieties (
pyrromycin) decreased both potency and the maximal percentage of differentiated cells produced in the population. The
monosaccharide anthracyclines Adriamycin and
carminomycin were completely inactive as inducers of HL-60
leukemia cell maturation. The results suggest that certain
anthracyclines would be reasonable candidate drugs to use in a clinical trial aimed at reducing the leukemic stem cell burden through maturation rather than through cytodestruction.