Studies on the binding affinity of anticancer drug mitoxantrone to chromatin, DNA and histone proteins

Mitoxantrone is a synthetic antineoplastic drug, structurally similar to the anthracyclines, widely used as a potent chemotherapeutic agent in the treatment of various cancers such as advanced breast cancer, lymphoma and leukemia [1-3]. Widespread interest in mitoxantrone has arisen because of its apparent lower risk of cardiotoxic effects compared with the naturally occurring anthracyclines [4,5].Numerous studies on the mechanism of mitoxantrone action indicate that nuclear DNA is the major target for this drug [6,7]. The structure of mitoxantrone lacks the amino sugar moiety and tetracyclic ring (A) of anthracyclines but has a planar anthraquinone ring which intercalates between DNA base pairs and the nitrogen-containing side chains bind the negatively charged phosphate groups of DNA [7,8]. Binding of mitoxantrone to DNA causes DNA condensation and inhibits DNA replication and RNA transcription [9-11]. Also it is a potent inhibitor of topoisomeraseII, an enzyme known to be important for the repair of damaged DNA and this leads to single and double strand breaks [12].The binding of mitoxantrone to DNA has been studied in detail [13-15]. However, in the cell nucleus; DNA is compacted into a complex structure built from the interaction of histones with DNA named nucleosomes. These consist of 145 base pairs DNA wrapped around an octamer of core histones. There are 5 main histones: the linker histones of the H1 family and 4 core histones (H2A, H2B, H3 and H4) which are arranged in an octamer form [16]. How the presence of chromosomal proteins affect and modulate the binding of intercalating drugs to DNA, is an important question when trying to understand the mechanism of drug action at the chromatin level. To explore this question, we employed several experiments designed to clarify this question in more detail.In the present study, we attempted to examine and compare the effect of mitoxantrone on rat liver chromatin, DNA and histone proteins in solution to further und