Doxorubicin (Dox), a widely used anticancer
DNA-binding
drug, affects
chromatin in multiple ways, and these effects contribute to both its efficacy and its dose-limiting side effects, especially
cardiotoxicity. Here, we studied the effects of Dox on the
chromatin binding of the architectural
proteins high mobility group B1 (
HMGB1) and the linker
histone H1, and the
transcription factor retinoic acid receptor (RARĪ±) by fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS) in live cells. At lower doses, Dox increased the binding of
HMGB1 to
DNA while decreasing the binding of the linker
histone H1. At higher doses that correspond to the peak plasma concentrations achieved during
chemotherapy, Dox reduced the binding of
HMGB1 as well. This biphasic effect is interpreted in terms of a hierarchy of competition between the
ligands involved and Dox-induced local conformational changes of
nucleosome-free
DNA. Combined, FRAP and FCS mobility data suggest that Dox decreases the overall binding of RARĪ± to
DNA, an effect that was only partially overcome by agonist binding. The intertwined interactions described are likely to contribute to both the effects and side effects of Dox.