Probing the binding of docetaxel to a calf thymus dna-histone h1 complex by circular dichroism (cd) spectroscopy and viscometric studies

Sara Kharazmi-khorassani,1 Reza asaran darban,2 Jamshidkhan chamani,3,*

1. Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
2. Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
3. Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract

Introduction

Cancer is a major health challenge around the world. docetaxel is a chemotherapy drug which are effective for some cancers including breast, lung, head and neck, and ovarian cancer. dna is a macro molecule that has an important role in the biochemical process because of its uses in various types of therapy (1). small molecules such as docetaxel have the ability to bind to dna to indicate the structural features of dna, the sources of some diseases and the mechanism of action of some drugs. histones are alkaline proteins that are found in nuclei of eukaryotic cell which package and order the dna nucleosomes. in this study we evaluated the interaction between docetaxel and calf thymus dna (ct -dna) in the absence and presence of h1 using circular dichroism (cd), viscosity measurement to found a different affinity of docetaxel to ct-dna with various sides in ct-dna.

Methods

The circular dichroism (cd) spectra was done through a jasco j-815 spectropolarimeter using a quartz cell (japan) at the room temperature. the absorption range of all cd spectra were between 240 to 300 at the nitrogen atmosphere with a distance of 1 nm at a scan rate of 50 nm m-1. the spectrum of buffer solution (tris-hcl, ph = 6.8) was registered and subtracted from the spectrum of ct-dna-docetaxel and (ctdna-h1) docetaxel and h1 with docetaxel. the viscosity measurements were performed through an oswald viscometer at constant temperature of 298 k. in the absence and presence of docetaxel, the concentration of ct-dna and the ct-dna-h1 complex in tris–hcl buffer solution (ph = 6.8) were fixed at 0.5 mm and for measure the flow time a digital stop watch was used.

Results

The circular dichroism methodology demonstrated the conformational changes in ctdna and h1-ct dna complex on the interaction with docetaxel. this results suggested an intercalative binding mode of docetaxel to the ctdna structure. viscosity was used as a method to explain the binding mode of docetaxel to ctdna and the complex of h1-ct-dna. docetaxel bound to ctdna by intercalative binding but in the presence of h1 docetaxel bound to ctdna by groove binding.

Conclusion

In summary, the research of the interaction between docetaxel with ctdna and the complex of h1-ct dna as binary and ternary systems would showed useful information in further understanding the mechanism of action and pharmacokinetics to design anti-cancer drugs.

Keywords

Docetaxel; ctdna; viscometry; cd