Alkyne Functionalization of a Photoactivated Ruthenium Polypyridyl Complex for Click-Enabled Serum Albumin Interaction Studies

Abstract

Studying metal-protein interactions is key for understanding the fate of metallodrugs in biological systems. When a metal complex is not emissive and too weakly bound for mass spectrometry analysis, however, it may become challenging to study such interactions. In this work a synthetic procedure was developed for the alkyne functionalization of a photolabile ruthenium polypyridyl complex, [Ru­(tpy)­(bpy)­(Hmte)]­(PF6)2, where tpy = 2,2′:6′,2′′-terpyridine, bpy = 2,2′-bipyridine, and Hmte = 2-(methylthio)­ethanol. In the functionalized complex [Ru­(HCC-tpy)­(bpy)­(Hmte)]­(PF6)2, where HCC-tpy = 4′-ethynyl-2,2′:6′,2′′-terpyridine, the alkyne group can be used for bioorthogonal ligation to an azide-labeled fluorophore using copper-catalyzed “click” chemistry. We developed a gel-based click chemistry method to study the interaction between this ruthenium complex and bovine serum albumin (BSA). Our results demonstrate that visualization of the interaction between the metal complex and the protein is possible, even when this interaction is too weak to be studied by conventional means such as UV–vis spectroscopy or ESI mass spectrometry. In addition, the weak metal complex-protein interaction is controlled by visible light irradiation, i.e., the complex and the protein do not interact in the dark, but they do interact via weak van der Waals interactions after light activation of the complex, which triggers photosubstitution of the Hmte ligand.

Ruthenium-based PACT agents based on bisquinoline chelates: synthesis, photochemistry, and cytotoxicity

“… a In water b In methanol- d 4 ;[ 39 ] c Data taken from Bahreman et al [ 18 ] d Data Busemann et al [ 40 ] …”

Water-Soluble Dioxidovanadium(V) Complexes of Aroylhydrazones: DNA/BSA Interactions, Hydrophobicity, and Cell-Selective Anticancer Potential

“…It is advantageous to study serum albumin, as the limited number of binding sites with high specificity plays a pivotal role in the transportation and delivery of different endogenous and exogenous species . Bovine serum albumin (BSA), having a 76% sequence homology for human serum albumins (HSA), has been broadly studied, as it is the most abundant model protein of blood plasma. , From literature reports, it has been observed that vanadium complexes showing higher DNA and protein binding ability exhibited better cytotoxicity, and so the assessment of this ability is an important aspect prior to anticancer studies, ,,,− but the involvement of several other mechanisms of cellular activity may also be possible. − In some reports, the cellular cytotoxicity activity of transition-metal complexes (V and Cu) follows a mechanism of action different from DNA and protein interactions. − Possibly, the increased electron density in the aromatic ring systems, aqueous solubility, membrane permeability, or specific hydrophobic interactions in target binding pockets lead to an increase in cytotoxicity. ,− In this context, due to hydrophobicity, enhancement in the bioavailability of a drug by its internalization to the target cells and ability to reach the site of action is another point of interest. , Thus, in this work, we have sought to correlate the behavior of complexes in aqueous stability, hydrophobicity, DNA/protein interactions related to their cytotoxicity.…”

“…53 Bovine serum albumin (BSA), having a 76% sequence homology for human serum albumins (HSA), has been broadly studied, as it is the most abundant model protein of blood plasma. 53,54 From literature reports, it has been observed that vanadium complexes showing higher DNA and protein binding ability exhibited better cytotoxicity, and so the assessment of this ability is an important aspect prior to anticancer studies, 17,33,36,55−57 but the involvement of several other mechanisms of cellular activity may also be possible. 58−60 In some reports, the cellular cytotoxicity activity of transitionmetal complexes (V and Cu) follows a mechanism of action different from DNA and protein interactions.…”

4′-(N-(Propan-1,2-dienyl)pyrrol-2-yl)-2,2′:6′,2″-terpyridine

“…Thus, the preparation of terpyridine derivatives that contain a functionalized pyrrole is of interest in the fields of both organic synthesis and material science. This article describes how pyrrole-containing terpyridine 1 was obtained as an unexpected product during attempts to prepare compound 2 (Figure 1), which features an alkyne chain for possible future functionalization [15].…”