Eukaryotic Cell Toxicity and HSA Binding of [Ru(Me 4 phen)(bb 7 )] 2+ and the Effect of Encapsulation in Cucurbit[10]uril.

The toxicity (IC50) of a series of mononuclear ruthenium complexes containing bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane (bb(n)) as a tetradentate ligand against three eukaryotic cell lines-BHK (baby hamster kidney), Caco-2 (heterogeneous human epithelial colorectal adenocarcinoma) and Hep-G2 (liver carcinoma)-have been determined. The results demonstrate that cis-alpha-[Ru(Me(4)phen)(bb(7))](2+) (designated as alpha-Me(4)phen-bb(7), where Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) showed little toxicity toward the three cell lines, and was considerably less toxic than cis-alpha-[{Ru(phen)(bb(12)}](2)+ (alpha-phen-bb(12)) and the dinuclear complex [{Ru(phen)2}2{mu-bb(12)}](4+) Fluorescence spectroscopy was used to study the binding of the ruthenium complexes with human serum albumin (HSA). The binding of alpha-Me(4)phen-bb(7) to the macrocyclic host molecule cucurbit[10]uril (Q[10]) was examined by NMR spectroscopy. Large upfield H-1 NMR chemical shift changes observed for the methylene protons in the bb(7) ligand upon addition of Q[10], coupled with the observation of several intermolecular ROEs in ROESY spectra, indicated that alpha-Me(4)phen-bb(7) methylene carbons within the cavity and the metal center positioned outside one of the portals. Simple molecular modeling confirmed the feasibility of the binding model. An alpha-Me(4)phen-bb(7) -Q[10] binding constant of 9.9 +/- 0.2 x 10 6 M-1 was determined by luminescence spectroscopy. Q[10]-encapsulation decreased the toxicity of alpha-Me(4)phen-bb(7) against the three eukaryotic cell lines and increased the binding affinity of the ruthenium complex for HSA. Confocal microscopy experiments indicated that the level of accumulation of alpha-Me(4)phen-7in BHK cells is not significantly affected by 0[10]-encapsulation. Taken together, the combined results suggest that alpha-Me(4)phen-7 could be a good candidate as a new antimicrobial agent, and Q[10]-encapsulation could be a method to improve the pharmacokinetics of the ruthenium complex.