Abstract
Confocal microscopy was used to study the intracellular localisation of a series of inert polypyridylruthenium(II) complexes with three eukaryotic cells lines - baby hamster kidney (BHK), human embryonic kidney (HEK-293) and liver carcinoma (Hep-G2). Co-staining experiments with the DNA-selective dye DAPI demonstrated that the di-, tri- and tetra-nuclear polypyridylruthenium(II) complexes that are linked by the bis[4(4'-methyl-2,2'-bipyridyl)]-1,12-dodecane bridging ligand ("bb12") showed a high degree of selectivity for the nucleus of the eukaryotic cells. Additional co-localisation experiments with the general nucleic acid stain SYTO 9 indicated that the ruthenium complexes showed a considerable preference for the RNA-rich nucleolus, rather than chromosomal DNA. No significant differences were observed in the intracellular localisation between the ΔΔ and ΛΛ enantiomers of the dinuclear complex. Cytotoxicity assays carried out over 72 hours indicated that the ruthenium complexes, particularly the tri- and tetra-nuclear species, were significantly toxic to the eukaryotic cells. However, when the activity of the least cytotoxic compound (the ΔΔ enantiomer of the dinuclear species) was determined over a 24 hour period, the results indicated that the ruthenium complex was approximately a 100-fold less toxic to liver and kidney cells than to Gram positive bacteria. Circular dichroism (CD) spectroscopy was used to examine the effect of the ΔΔ and ΛΛ enantiomers of the dinuclear complex on the solution conformations of RNA and DNA. The CD experiments indicated that the RNA maintained the A-type conformation, and the DNA the B-type structure, upon binding by the ruthenium complexes.
Highlights
We have subsequently shown that dinuclear analogues have even greater antimicrobial potential: [{Ru( phen)2}2{μ-bbn}]4+ {“Rubbn”; where phen = 1,10-phenanthroline; bbn = bis[4(4′-methyl-2,2′-bipyridyl)]-1,n-alkane for n = 5, 7, 10, 12 and 16 – see Fig. 1} showed excellent activity, and they maintained the activity against drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA).[20]
Based upon our previous studies on the antimicrobial activities and the corresponding toxicities to eukaryotic cell lines,[20] Rubb[12] appears to have the best therapeutic window of the dinuclear complexes
In order to determine the biologically relevant concentrations of the ruthenium complexes, and to ascertain the toxicity of the tri- and tetra-nuclear species against eukaryotic cells for the first time, the IC50 values of Rubb[12], Rubb12-tri and Rubb12-tetra were determined against three cell lines (BHK, HEK-293 and Hep-G2)
Summary
There has been significant interest over the last forty years in the non-covalent interactions of inert transition metal complexes with DNA and RNA.[1,2,3] In particular, the nucleic acid binding properties of ruthenium(II) complexes containing polypyridyl ligands have been extensively studied.[4,5,6,7,8] These metal complexes have a rigid octahedral framework and can interact with nucleic acids through a variety of different modes, withMore recently, due to the nucleic binding properties of inert polypyridylruthenium(II) complexes, there has been increasing interest in their biological properties.[9,10,11,12,13,14,15,16] A variety of mononuclear and dinuclear complexes have shown good in vitro anticancer activity, which is generally considered to be due to DNA binding. Richard Keene et al RNA and DNA binding of inert oligonuclear ruthenium(II) complexes in live eukaryotic cells
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