Serum-protein interactions with anticancer Ru(III) complexes KP1019 and KP418 characterized by EPR

Abstract

The compounds imidazolium [trans-[RuCl(4)(1H-imidazole)(2)] (KP418) and indazolium [trans-RuCl(4)(1H-indazole)(2)] (KP1019) both show significant anticancer activity, with the latter recently having completed phase I clinical trials. An important component of this success has been associated with targeted delivery of the complexes to cancer cells by serum proteins. In this study, electron paramagnetic resonance (EPR) measurements, combined with incubation under physiological conditions, and separation of protein-bound fractions, have been used to characterize the interactions of these complexes with human serum albumin (hsA), human serum transferrin (hsTf) apoprotein, and whole human serum. The strong EPR signals observed in these experiments demonstrate that both complexes are primarily retained in the 3+ oxidation state in the presence of serum components. Rapid, noncovalent binding of KP1019 was observed in the presence of both hsA and serum, indicating that the predominant interactions occur within the hydrophobic binding sites of hsA. This sequestering process correlates with the low levels of side effects observed in clinical trials of the complex. At longer incubation times, the noncovalently bound complexes are converted slowly to a protein-coordinated form. Noncovalent interactions are not observed in the presence apo-hsTf, where only slow binding of KP1019 via ligand exchange with the protein occurs. By contrast, hydrophobic interactions of KP418 with hsA only occur with the aquated products of the complex, a process that also dominates in serum. In the presence of apo-hsTf, KP418 interacts directly with the protein through exchange of ligands, as observed with KP1019.

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

“…S1) [30][31][32]. Initial rapid binding of KP1019 takes place in a non-covalent manner at the hydrophobic binding sites of HSA, however after a longer incubation time the type of the interaction is converted slowly to a protein-coordinated form [33]. Similar behavior of NAMI-A and its pyridine analogues was found recently based on mainly electron paramagnetic resonance spectroscopic measurements [34,35].…”

“…In recent years, researchers have become interested in determining the binding sites of metallodrugs on biomolecules for improved design of next generation drug candidates. It is known that KP1019 binds to HSA initially in a non-covalent manner then the coordination of histidine nitrogen(s) to the Ru(III) centre takes place [33]. The spectrofluorimetric quenching studies and the ultrafiltration (vide supra) cannot give information about the feature of the binding mode whether it is non-covalent or coordinative.…”

Development of the application of speciation in chemistry

“…The rate of aquation (Cl -/H 2 O exchange) of these Ru(III) complexes is affected greatly by the pH, temperature, and the concentrations of chloride and HCO 3 -ions [230,231], while their redox potentials are in the range of physiological reductants [227]. Thus, aquation and reduction, e.g., by ascorbate, may be possible under the serum conditions, although the binding to serum proteins hinders the efficiency of these processes [231,232]. In addition, serum protein binding has significant effects on biodistribution, the half-life in the circulation, and clearance, which ultimately affect the pharmacokinetic profile of the drug.…”

Rákellenes gallium- és platinafém komplexek oldatkémiája, kölcsönhatásuk vérszérum-fehérjékkel és DNS-sel

“…A kölcsönhatást a KP1019 esetén már számos kutatócsoport vizsgálta, azonban ezek a kötőhelyek hollétéről viszonylag kevés információval szolgáltak [4,45,121]. Ismert, hogy a KP1019 a HSA-hoz először másodlagos kölcsönhatások révén kötődik, majd ez órák alatt koordinatív kötésbe megy át [45]. Elsődleges célunk a gyors, másodlagos kölcsönhatások révén kialakuló kötődés tanulmányozása volt.…”

“…Kapilláris elektroforézis -induktívan csatolt plazma -tömegspektrometriás (CE-ICP-MS) mérések szerint a fiziológiás arányokat közelítő 10:1 arányú HSA:Tf keverékben a KP1019 98%-a HSA-hoz kötődött [44]. A HSA-hoz először másodlagos kölcsönhatások révén kötődik, majd ez később a kloridionok részleges elvesztésével koordinatív kötésbe megy át [45].A KP1339 biológiai hatása és farmakokinetikai viselkedése a KP1019-cel gyakorlatilag megegyezik, így a vizsgálatokat ma már főként a KP1339-cel végzik [41,46,47]. 11…”