Correlation Between Cellular Localization and Binding Preference to RNA, DNA, and Phospholipid Membrane for Luminescent Ruthenium(II) Complexes

Abstract

Because of their unique photophysical properties, sensitively depending on environment, ruthenium dipyridophenazine (dppz) complexes are interesting as probes for cellular imaging with fluorescence microscopy. Here three complexes derivatized with alkyl ether chains of varied length, which exhibit distinctly different cellular staining patterns by confocal laser scanning microscopy, are studied regarding their binding preference for rRNA compared with calf thymus DNA (ct-DNA) and phospholipid membranes. Co-staining with commercial RNA and membrane-specific dyes shows that whereas the least lipophilic complex exclusively stains DNA inside the nucleus, the most lipophilic complex preferentially stains membrane-rich parts of the cell. Interestingly, only the intermediate lipophilic complex shows intense staining of the RNA-rich nucleoli. The intracellular localizations of the probes correlate with their binding preferences concluded from spectroscopy measurements.

Tuning the Cellular Uptake Properties of Luminescent Heterobimetallic Iridium(III)–Ruthenium(II) DNA Imaging Probes

“…This is demonstrated in our work on the hydrophobic dinuclear Ru II tpphz complex [(Ru(DIP) 2 ) 2 (tpphz)] 4 + (DIP = 4,7-diphenyl-1,10-phenanthroline), which, despite possessing an appreciable affinity for DNA in cell-free conditions, targets the membrane-dense endoplasmic reticulum in cells. [58] Similar effects are seen in other studies, including those on prototypical Ru II (dppz) DNA-binding systems [59,60] and cyclometallated Ir III complexes. [61] Both 3 and 4 possess far superior cellular uptake properties than their dinuclear Ru II -Ru II analogue, the effectively isostructural ruthenium analogue 1, [37] indicating that the lower charge of the heterometallic species has facilitated increased cellular uptake rates.…”

The path for metal complexes to a DNA target

“…For example, Matson and coworkers synthesized a variety of dppz complexes of Ru derivatized with alkyl ether chains of various lengths and used confocal laser scanning microscopy to study their subcellular localization in CHO-K1 cells. 84 Using various RNA and membrane-specific dyes, they found, perhaps not surprisingly, that the least lipophilic compound localized in the nucleus, while the most lipophilic localized in membranes.…”

Covalent and non-covalent binding of metal complexes to RNA

“…Interestingly, the length of the alkyl ether chain influences the nucleic acid binding properties of the three metal complexes. The complex of intermediate lipophilicity accumulates in RNA-rich nucleoli, and in vitro studies confirmed that it has higher binding affinity for rRNA vs CT-DNA [152]. The authors suggest that the increased lipophylicity of the complex may account for this binding preference.…”

“…15b) [152]. It is known that ligand modifications influence cellular uptake and accumulation, and also nucleic acid binding properties of this class of compounds [6,9,152,154,155]. Interestingly, the length of the alkyl ether chain influences the nucleic acid binding properties of the three metal complexes.…”

“…There are a few studies in which RNA binding abilities of metal complexes are investigated spectroscopically, and compared with DNA [150,151]; (b) Ru-dppz complexes in which the dppz unit has been functionalized with long alkyl chains [152]. binding properties.…”