Mitoxantrone is a potent antitumor drug, widely used in the treatment of various cancers. In the present study, we have investigated and compared the affinity of anticancer drug, mitoxantrone, to EDTA-soluble chromatin (SE-chromatin), DNA and histones employing UV/Vis, fluorescence, CD spectroscopy, gel electrophoresis and equilibrium dialysis techniques. The results showed that the interaction of mitoxantrone with SE-chromatin proceeds into compaction/aggregation as revealed by reduction in the absorbencies at 608 and 260 nm (hypochromicity) and disappearance of both histones and DNA on the gels. Mitoxantrone interacts strongly with histone proteins in solution making structural changes in the molecule as shown by CD and fluorescence analysis. The binding isotherms demonstrate a positive cooperative binding pattern for the chromatin-mitoxantrone interaction. It is suggested higher binding affinity of mitoxantrone to chromatin compared to DNA implying that the histone proteins may play an important role in the chromatin-mitoxantrone interaction process.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][2][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][10][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][14][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].

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Although lead is widely recognized as a toxic substance in the environment and directly damage DNA, no studies are available on lead interaction with chromatin and histone proteins. In this work, we have examined the effect of lead nitrate on EDTA-soluble chromatin (SE chromatin), DNA and histones in solution using absorption and fluorescence spectroscopy, thermal denaturation and gel electrophoresis techniques. The results demonstrate that lead nitrate binds with higher affinity to chromatin than to DNA and produces an insoluble complex as monitored at 400 nm. Binding of lead to DNA decreases its Tm, increases its fluorescence intensity and exhibits hypochromicity at 210 nm which reveal that both DNA bases and the backbone participate in the lead-DNA interaction. Lead also binds strongly to histone proteins in the absence of DNA. The results suggest that although lead destabilizes DNA structure, in the chromatin, the binding of lead introduces some sort of compaction and aggregation, and the histone proteins play a key role in this aspect. This chromatin condensation, upon lead exposure, in turn may decrease fidelity of DNA, and inhibits DNA and RNA synthesis, the process that introduces lead toxicity at the chromatin level.

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Chromatin has been successfully used as a tool for the study of genome function in cancers. Vincristine as a vinca alkaloid anticancer drug exerts its action by binding to tubulins. In this study the effect of vincristine on DNA and chromatin was investigated employing various spectroscopy techniques as well as thermal denaturation, equilibrium dialysis and DNA-cellulose affinity. The results showed that the binding of vincristine to DNA and chromatin reduced absorbance at both 260 and 210 nm with different extent. Chromopheres of chromatin quenched with the drug and fluorescence emission intensity decreased in a dose-dependent manner. Chromatin exhibited higher emission intensity changes compared to DNA. Upon addition of vincristine, Tm of DNA and chromatin exhibited hypochromicity without any shift in Tm. The binding of the drug induced structural changes in both positive and negative extremes of circular dichroism spectra and exhibited a cooperative binding pattern as illustrated by a positive slope observed in low r values of the binding isotherm. Vincristine showed higher binding affinity to double stranded DNA compared to single stranded one. The results suggest that vincristine binds with higher affinity to chromatin compared to DNA. The interaction is through intercalation along with binding to phosphate sugar backbone and histone proteins play fundamental role in this process. The binding of the drug to chromatin opens a new insight into vincristine action in the cell nucleus.