Serum Albumin Binding Inhibits Nuclear Uptake of Luminescent Metal‐Complex‐Based DNA Imaging Probes

Abstract

The DNA binding and cellular localization properties of a new luminescent heterobimetallic Ir(III) Ru(II) tetrapyridophenazine complex are reported. Surprisingly, in standard cell media, in which its tetracationic, isostructural Ru(II) Ru(II) analogue is localized in the nucleus, the new tricationic complex is poorly taken up by live cells and demonstrates no nuclear staining. Consequent cell-free studies reveal that the Ir(III) Ru(II) complex binds bovine serum albumin, BSA, in Sudlow's Site I with a similar increase in emission and binding affinity to that observed with DNA. Contrastingly, in serum-free conditions the complex is rapidly internalized by live cells, where it localizes in cell nuclei and functions as a DNA imaging agent. The absence of serum proteins also greatly alters the cytotoxicity of the complex, where high levels of oncosis/necrosis are observed due to this enhanced uptake. This suggests that simply increasing the lipophilicity of a DNA imaging probe to enhance cellular uptake can be counterproductive as, due to increased binding to serum albumin protein, this strategy can actually disrupt nuclear targeting.

The development of ruthenium(ii) polypyridyl complexes and conjugates forin vitrocellular andin vivoapplications

“…86,89 Interestingly, a subsequent study by the authors revealed that incorporation of two benzo[h]quinolone cyclometalating ligands around the Ir centre resulted in the complex 17 displaying an even higher rate of nuclear accumulation, relative to complex 16. 90 However, when cells were incubated with complex 17 in serum-containing medium, both the uptake and localisation of the complex dramatically changed, as shown in Fig. 5c.…”

“…With regards to cellular uptake and localisation, the lipophilicity of complexes has been further shown to play a profound role in both processes. 47,63,86,89,90,104 For example, the formation of lipophilic ion-pairs has recently been demonstrated to promote the cellular uptake and nuclear localisation of complexes which had previously been unable to enter live cells; 107 a strategy which could prove beneficial for other systems in the future. However, while increasing the lipophilicities of complexes can improve their uptake, it can also have a considerable impact on the nature of their interactions with biomolecules, such as proteins and membranes, which may in fact hinder their uptake, alter their subcellular localisation and/or influence the nature of their interactions with (or even the identity of) their molecular targets within cells.…”

“…However, while increasing the lipophilicities of complexes can improve their uptake, it can also have a considerable impact on the nature of their interactions with biomolecules, such as proteins and membranes, which may in fact hinder their uptake, alter their subcellular localisation and/or influence the nature of their interactions with (or even the identity of) their molecular targets within cells. 87,90 Researchers have developed complexes capable of selectively targeting and visualising specific organelles within cells, including the nucleus, mitochondria, lysosomes and endoplasmic reticulum, and have shown Ru(II) polypyridyl complexes to be excellent candidates for use as luminescent probes for ultra-resolution STED microscopy and two-photon imaging. 87,131,143,211,357,358 Furthermore, by conjugating functional molecules, such as targeting peptides, drug molecules and nanomaterials to Ru(II) complexes, the resulting conjugates can be targeted for specific cell types or subcellular organelles and imparted with additional properties such as enhanced solubility, multimodal drug action, altered biodistribution and enhanced circulation times in vivo, etc.…”

Ruthenium based antimicrobial theranostics – using nanoscopy to identify therapeutic targets and resistance mechanisms inStaphylococcus aureus

“…As part of a program to identify oligonuclear complexes that recognize biologically relevant ions and biomolecules, the Thomas group has been investigating the biological properties of Ru II , Os II , and Ir III complexes containing the rigidly planar poly-aromatic ligand tetrapyridophenazine, tpphz. [45][46][47][48][49][50] Most of this work has centred on their bio-imaging and therapeutic potential with eukaryotic cells. Butas our original report on cell imaging showed that the prototype system, [{Ru(phen) 2 } 2 (tpphz)] 4+ , 1 4+ , was readily taken up by S. aureus cells 46we set out to develop new dual imaging/antimicrobial theranostics based on this architecture.…”

The use of organolithium reagents for the synthesis of 4-aryl-2-phenylpyridines and their corresponding iridium(iii) complexes

“…Significantly, this allows for the harvesting of both singlet and triplet excitons within an OLED, theoretically allowing 100% internal quantum, and since their first deployment in these devices by Forrest et al, they have been the subject of numerous patents and papers. [12][13][14][15][16][17][18][19][20][21] Their emission spectra can be readily tuned by altering either the ancillary or 2-phenylpyridine ( ppy) ligand. [12][13][14][15][16][17][18][19][20][21] Their emission spectra can be readily tuned by altering either the ancillary or 2-phenylpyridine ( ppy) ligand.…”