Characterization of the binding sites of the anticancer ruthenium(III) complexes KP1019 and KP1339 on human serum albumin via competition studies

Abstract

Indazolium trans-[tetrachloridobis(1H-indazole)ruthenate(III)] (KP1019) and its Na + analogue (KP1339) are two of the most prominent non-platinum antitumor metal complexes currently undergoing clinical trials. After intravenous administration, they are known to bind to human serum albumin (HSA) in a non-covalent manner. In order to elucidate their HSA binding sites, displacement reactions with the established site markers warfarin and dansylglycine as well as bilirubin were monitored by spectrofluorimetry, ultrafiltration−UV-vis spectrophotometry and/or capillary zone electrophoresis. Conditional stability constants for the binding of KP1019 and KP1339 to sites I and II of HSA were determined, indicating that both Ru(III) compounds bind into both sites with moderately to strong affinity (logK 1 ' = 5.3-5.8). No preference for either binding site was found and similar results were obtained for both metal complexes, demonstrating low influence of the counter ion on the binding event.

Comparative solution equilibrium studies on pentamethylcyclopentadienyl rhodium complexes of 2,2ʹ-bipyridine and ethylenediamine and their interaction with human serum albumin

“…The excitation wavelengths were 295, 310 or 335 nm depending on the type of the experiment and the emission was read in the range of 310-650 nm. The quenching (K Q ') or displacement constants (K WF ' and K DG ') were calculated with the computer program PSEQUAD [35] based on the equilibrium processes and mass-balance equations for the components detailed in the Supplementary data using the same approach applied in our previous works [36,37]. 1 H NMR studies were carried out on a Bruker Ultrashield 500 Plus instrument.…”

“…Additionally, displacement reactions with WF and DG, which are known site marker fluorescence probes for the binding sites I and II of HSA [37,60], were carried out. Displacement of the site marker from its binding pocket is accompanied by a considerable decrease in the intensity.…”

Investigation of the binding of cis/trans-[MCl4(1H-indazole)(NO)]− (M = Ru, Os) complexes to human serum albumin

“…Detailed studies on the interaction of the ruthenium(III) complexes KP1019 and its sodium analogue (KP1339) with HSA were reported previously [15]. Both metallodrugs were found to bind into sites I and II with moderately strong affinity and this binding event is rather fast, taking place within several minutes.…”

“…Additionally EPR spin labeling method was used in the case of complex 5. Since the studied compounds show hydrolytic decomposition at neither 25 nor 37 °C (see section 3.2), and the conditional binding constants of the applied site marker probes towards HSA were found to be fairy similar at both temperature values in our former work [15]; here the measurements with the protein were conducted at 25 °C.…”

“…Solutions of WF and DG were prepared prior to the analyses with one equivalent of NaOH and their concentrations were calculated on the basis of their UVvisible (UV-vis) spectra:  308 nm (WF) = 14475 M −1 cm −1 ,  327 nm (DG) = 5068 M −1 cm −1 [15]. All samples were prepared at 25 °C in 20 mM phosphate buffer (pH 7.40) containing 0.10 M NaCl.…”