Probing the binding site of a new synthesized anti-cancer compound to HSA via competitive ligand binding method

Abstract

In the present study, site marker competitive experiments using diazepam and indomethacin were carried out in order to identify the binding location of a new designed anti-cancer compound (1,10-phenanthroline butyl dithiocarbamato palladium(II) nitrate), named Pd(II) complex, on human serum albumin (HSA) by different spectroscopic techniques (UV–visible, fluorescence and circular dichroism (CD)) at two temperatures of 25 and 37°C. By the analysis of fluorescence spectra, it was observed that the Pd(II) complex has an ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The number of binding sites and the association binding constants as well as the thermodynamic parameters of Pd(II) complex were calculated at both temperatures. The quantitative analysis of CD spectra represented that Pd(II) complex induced significantly alterations in the secondary structure of the protein via decreasing in the content of α helical structure of protein. In order to identify the binding location of the Pd(II) complex on HSA, site marker competitive experiments were carried out using diazepam and indomethacin. By the competitive experiments it was observed that the Pd(II) complex and diazepam bind to the same position of HSA (drug site II) and during chemotherapy the arrangement of the use of these drugs is so important.Our results suggest that the new synthesized Pd(II) complex can bind to the blood carrier protein of HSA and change the tertiary and secondary structures of protein, which can be considered as side effects of these new synthesized drugs.