Imaging of the nuclei of living tumor cells by novel ruthenium(ii) complexes coordinated with 6-chloro-5-hydroxylpyrido[3,2-a]phenazine

Abstract

Two novel ruthenium(II) complexes coordinated with 6-chloro-5-hydroxylpyrido [3,2-a]phenazine (CQM), [Ru(L) 2 (CQM)]ClO 4 [L = 1,10-phenanthroline, (1) and 2,2'bipyridine, (2)], were investigated as potent fluorescence probes to track the dynamic changes in the nuclei of living cells. Confocal laser technology was used to observe their colocation inside the cells. Results showed that both complexes were uptaken by HepG2 cells, especially for 1, which was localized in the cell nuclei, whereas 2 was distributed in the cell nuclei and mitochondria. Further studies by real-time fluorescence observation revealed that 1 rapidly entered the living cells, namely, HepG2, HeLa and MCF-7 cells, imagined the dynamic in the nuclei of living tumor cells, and exhibited low toxicity to cells. Results demonstrated that 1 may be developed as a novel fluorescence probe for living cell nucleus.This study facilitates the development of fluorescence chemosensors with metal complexes. IntroductionNumerous studies have been performed to develop simple, sensitive, specific, and robust fluorescence probes/sensors for biochemistry, molecular biology, and clinical diagnostics. 1 Although many organic dyes have been designed and investigated, the utilization of these organic dyes is still limited because of their poor water solubility, low photo-stability, and high toxicity. [2][3][4][5] To overcome the drawbacks of organic dyes, transition metal complexes, especially the versatile ruthenium(II) complexes, have increasingly attracted attention as potential fluorescence probes because of their wide spectral range, long-term luminescence and large Stokes shifts. 6-10 Several recent notable reviews have shown that luminescent ruthenium(II) complexes have emerged as promising candidates for wide application in chemosensors, biolabeling, in vivo tumor imaging, and live cell compartmentalization staining, such as in the nucleus, in the cytoplasm, in endosome, in mitochondria, in lysosomes and endoplasmic reticulum. [11][12][13][14][15][16] Ruthenium complexes with dipyridophenazine (dppz) ligands have been frequently investigated because of their strong DNA binding and their extraordinary photophysical properties. 17,18 In particular, these compounds have been paid much attention because of their "light switch effect". These compounds are highly luminescent when intercalated into DNA and virtually nonemissive in aqueous solution, which is advantageous for fluorescence microscopy. For example, Barton et al. explored the cellular uptake of ruthenium(II) complexes and found that the complex cation [Ru(DIP) 2 (DPPZ)] 2+ (dip=4,7-diphenyl-1,10-

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

“…While the complex [Ru(bpy)2(CQM)] 1+ (19) was emissive, it did not show the "luminescence light-switching" activity seen for [Ru(bpy)2(dppz)] 2+ . 104,105 As with the cyclometalated dppz analogues, this monocationic complex was significantly more lipophilic (log P = +0.10 as its perchlorate salt) than [Ru(bpy)2(dppz)] 2+ . Complex 19 was found to be taken up by human liver carcinoma HepG2 cells and localise in both the nucleus and mitochondria of cells, as shown in Fig.…”

“…In 2015, by incorporating the 6-chloro-5-hydroxylpyrido[3,2a]-phenazine (CQM) into their complexes, which was designed to mimic the extended dppz ligand, 104 Ding et al were able to decrease the positive charge of their Ru complexes, while avoiding such loss of luminescence. While the complex [Ru(bpy)2(CQM)] 1+ (19) was emissive, it did not show the "luminescence light-switching" activity seen for [Ru(bpy)2(dppz)] 2+ .…”

“…6b. 104 In addition to decreasing the charge of Ru complexes, the CQM ligand-type is now being used to move the absorbance of Ru complexes into the 600 -700 nm region to achieve long wavelength activation. 106 The modulation in the lipophilicities of these complexes is summarised in Table 1 to highlight the influence of the ligand and charge on the lipophilicities of these Ru complexes.…”

“…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.…”

Redox Center Modification of Lapachones towards the Synthesis of Nitrogen Heterocycles as Selective Fluorescent Mitochondrial Imaging Probes

“…Fluorescent phenazines and their complexes and also fluorescent imidazolesmay be used to stain different cell organelles. Among the innumerable possibilities for specific staining in live cells, mitochondria are organelles of paramount importance .…”