Since the discovery of DNA as the genetic material carrier, the work towards the elucidation of DNA structure within the cell nucleus has become of great importance. Fluorescent microscopy using luminescent and cell membrane permeable organic DNA-binding molecule as probes is a well-established technique towards achieving this goal. Barton's group discovered that the cationic ruthenium complex[Ru(bpy)₂(dppz)]²⁺ (bpy=2,2'-bipyridine, dppz=dipyrido[3,2-a:2',3'-c] phenazine) functions as a molecular ‘light switch’ for DNA. Since then, there has been great attention drawn to the DNA binding properties of polypyridyl complexes of d⁶ octahedral metal ions, specifically towards the development of highly sensitive and structure-specific DNA probes.Until recently the research has been largely focused on the development of in vitro probes. However, few studies involving direct imaging of DNA in live cells with such systems have had very limited success, with poor membrane permeability still being ascribed as the major limiting factor. We found that not only the cellular, but more interestingly and importantly, the nuclear uptake of[Ru(bpy)₂(dppz)]²⁺ is remarkably enhanced by pentachlorophenol and two other structurally unrelated biochemical agents. Furthermore, enantioselective imaging of live-cell nuclear DNA is observed between the two chiral forms of Ru(Ⅱ) complexes. The underlying molecular mechanism is found to be the formation of novel lipophilic and relatively stable ion-pair complexes. This represents the first report for an unprecedented new method for delivering the DNA ‘light-switching’ Ru(Ⅱ) complexes into the nucleus of living cells via ion-pairing, which could serve as a promising general live-cell delivering method for other potentially bio-medically but cell-impermeable metal complexes.
Contents
1 Introduction
2 Predominant interactions between metal chelates and DNA
2.1 Irreversible binding with DNA
2.2 Reversible binding with DNA
3 Binding with intracellular DNA
3.1 Cellular uptake mechanism
3.2 Potential luminescent probe for intracellular DNA
3.3 Hydrophobicity and cellular uptake regulation
3.4 Appending targeting group for cellular uptake promotion
3.5 Active transport of chelates
3.6 Enhanced cellular uptake of “DNA light switch” Ru(Ⅱ) complex via forming lipophilic ion-pairing complexes
4 Methods for assessing cellular uptake
4.1 Transmission electron microscope
4.2 Raman spectra
4.3 Molecular labeling methods with fluorophore
4.4 Methods for quantitative uptake measurements
5 Cytotoxicity
6 The medical value for Ru(Ⅱ) polypyridyl complexes