Abstract
Using equilibrium dialysis and sedimentation velocity analysis, we have characterized the binding of the anti-tumor drug daunomycin to chicken erythrocyte chromatin before and after depletion of linker histones and to its constitutive DNA under several ionic strengths (5, 25, and 75 mM NaCl). The equilibrium dialysis experiments reveal that the drug binds cooperatively to both the chromatin fractions and to the DNA counterpart within the range of ionic strength used in this study. A significant decrease in the binding affinity was observed at 75 mM NaCl. At any given salt concentration, daunomycin exhibits higher binding affinity for DNA than for linker histone-depleted chromatin or chromatin (in decreasing order). Binding of daunomycin to DNA does not significantly affect the sedimentation coefficient of the molecule. This is in contrast to binding to chromatin and to its linker histone-depleted counterpart. In these instances, preferential binding of the drug to the linker DNA regions induces an unfolding of the chromatin fiber that is followed by aggregation, presumably because of histone-DNA interfiber interactions.
Highlights
Daunomycin is an anthracycline antibiotic widely used as a potent chemotherapeutic agent in the treatment of various cancers (1, 2)
The structure of this pharmacologically active drug consists of two distinct domains (Fig. 1): a planar aglycon chromophore that intercalates between adjacent base pairs of DNA and an amino sugar ring that lies in the minor groove of the DNA double helix (3, 4)
The salt dependence of the sedimentation coefficient observed for the chromatin fraction before and after stripping of the linker histones is in agreement with earlier results (26, 28, 29)
Summary
Daunomycin is an anthracycline antibiotic widely used as a potent chemotherapeutic agent in the treatment of various cancers (1, 2). Studies on its mechanism of action indicate that nuclear DNA is an important target for daunomycin. The structure of this pharmacologically active drug consists of two distinct domains (Fig. 1): a planar aglycon chromophore that intercalates between adjacent base pairs of DNA and an amino sugar ring that lies in the minor groove of the DNA double helix (3, 4). How the presence of chromosomal proteins might modulate the binding of this drug to DNA and how in turn chromatin structure is affected by the binding of the drug are important questions that need to answered to understand the biological mechanism of action of daunomycin. The results are compared with those obtained with the same chromatin fraction upon depletion of linker histones and with the purified constitutive DNA counterpart
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