Study of the binding affinity of anticancer drug, vincristine, to chromatin histone proteins by using spectroscopic methods

Vincristine is the most effective anticancer drug, widely used in the treatment of various cancers. Chromatin is composed of nucleosome units consisted of DNA and histone proteins. In the present study, for the first time the interaction of anticancer drug vincristine with histone H1 and core histone proteins in solution was investigated using fluorescence, UV and CD spectroscopy techniques. The results showed that in the presence of vincristine, fluorescence emission intensities were reduced in a dose dependent manner, representing quenching of the drug with aromatic residues located in the globular head domain of histone proteins. Stern-Volmer constant and binding affinity of the drug to histone H1 was higher than core histone proteins. The binding of vincristine to histones induced structural changes in circular dichroism spectra revealing increase of α-helix content of the histones. Moreover, vincristine increased UV absorbance of H1 and core histones at 210 nm (hyperchromicity). In conclusion it is suggested that vincristine, by its domains, can penetrate into globular head domain of histones. Also the binding affinity of vincristine to histone H1 is higher than to core histones, possibly because H1 is located in linker region which is more exposed and accessible to environment