d‐ Versus l‐Glucose Conjugation: Mitochondrial Targeting of a Light‐Activated Dual‐Mode‐of‐Action Ruthenium‐Based Anticancer Prodrug

Abstract

Light‐activated ruthenium polypyridyl anticancer prodrugs often suffer from poor water solubility, poor selectivity, and/or ill‐defined intracellular targets. Coordination of the d‐ or l‐glucose thioether ligand 3 (2‐(2‐(2‐(methylthio)ethoxy)ethoxy)ethyl‐β‐glucopyranoside) to the highly lipophilic ruthenium complex [Ru(tpy)(dppn)(H2O)]2+ ([1]2+; dppn=benzo[i]dipyrido‐[3,2‐a:2′,3′‐c]phenazine, tpy=2,2′:6′,2′′‐terpyridine) solved all these problems at once. The two enantiomers of [Ru(tpy)(dppn)(3)][PF6]2, [d‐2][PF6]2 and [l‐2][PF6]2, were soluble in water, which allowed the influence of the chirality of the glucose moiety on uptake, toxicity, and intracellular localization of the prodrug to be probed without changing any other physicochemical properties. Both compounds showed mild, but different, cytotoxicity in A549 (human lung carcinoma) and MCF‐7 (human breast adenocarcinoma) cancer cells in the dark, whereas following low doses of visible light irradiation (3.1 J cm−2 at λ = 454 nm), a similar, but high cytotoxicity (EC50 < 1 μm), was observed. Irrespective of the chirality, both slightly emissive Ru complexes were found in the mitochondria, and two modes of action may contribute to light‐induced cell death: 1) the glucose thioether ligand is photosubstituted by water, thus [1]2+, which interacts with DNA at an exceptionally high 400:1 base pair/Ru ratio, is released; 2) both [1]2+ and [2]2+ produce massive amounts of singlet oxygen, which leads to very efficient photodynamic DNA cleavage.

The development of anticancer ruthenium(ii) complexes: from single molecule compounds to nanomaterials

“…The complexes contained either a D- or L-glucose. 256 The D-glucose, 14r , was present in the mitochondria and had significant photocytotoxicity in A549 cells, with an IC 50 value of 0.72 μM due to both 1 O 2 production and ligand exchange upon irradiation at 454 nm.…”

Effects of the Bidentate Ligand on the Photophysical Properties, Cellular Uptake, and (Photo)cytotoxicity of Glycoconjugates Based on the [Ru(tpy)(NN)(L)]2+ Scaffold

“…Chloride complexes [ 1 a ]Cl, [ 2 a ]Cl, [ 4 a ]Cl, [ 5 a ]Cl, [ 7 a ]Cl, [ 8 a ]Cl, and the ligand 2‐(2‐(2‐(methylthio)ethoxy)ethoxy)ethyl‐β‐d‐glucopyranoside ( R ) were synthesized as reported previously. Complexes [ 3 a ]Cl and [ 6 a ]Cl were synthesized by reacting [Ru(tpy)Cl 3 ] with the bidentate ligand dpq or pmip in the presence of triethylamine as a reducing agent.…”

“…Silica column purification of the crude complexes, followed by size exclusion chromatography, afforded the thioether‐glucose ruthenium conjugates [ 1 b ](PF 6 ) 2 , [ 2 b ](PF 6 ) 2 and [ 4 b ](PF 6 ) 2 as orange to red solids and [ 8 b ](PF 6 ) 2 as a purple solid. To ease purification of the pmip complex [ 6 b ](PF 6 ) 2 , the synthesis was carried out similarly to the previously reported synthesis of [ 5 b ](PF 6 ) 2 by first converting the chloride precursor [ 5 a ]Cl to the aqua species [Ru(tpy)(pmip)(H 2 O)](PF 6 ) 2 using AgNO 3 and NH 4 PF 6 followed by reaction of the thioether ligand with the aqua complex. Similarly, the syntheses of [ 3 b ](PF 6 ) 2 and [ 7 b ](PF 6 ) 2 were carried out in the presence of AgPF 6 to ensure in situ conversion of the chlorido precursor into the aqua species before coordination of the thioether ligand.…”

“…Many other examples of ruthenium complexes used as photosensitive agents releasing anticancer molecules have been developed by the group of Turro, Gasser, Glazer, Kodanko, and Bonnet . Following up on our initial work using thioether monodentate ligands to cage cytotoxic aqua ruthenium complexes, we report here a series of related chloride complexes [ 1 a ]Cl–[ 8 a ]Cl having the general formula [Ru(tpy)(N−N)(Cl)]Cl with N−N=bpy (2,2′‐bipyridine), phen (1,10‐phenanthroline), dpq (pyrazino[2,3‐ f ][1,10]phenanthroline), dppz (dipyrido[3,2‐ a :2′,3′‐ c ]phenazine, dppn (benzo[ i ]dipyrido[3,2‐ a :2′,3′‐ c ]phenazine), pmip (2‐(4‐methylphenyl)‐1 H ‐imidazo[4,5‐ f ][1,10]phenanthroline), pymi (( E )‐ N ‐phenyl‐1‐(pyridin‐2‐yl)methanimine), or azpy (2‐(phenylazo)pyridine), and of their water‐soluble derivatives [Ru(tpy)(N−N)( R )](PF 6 ) 2 ([ 1 b ](PF 6 ) 2 –[ 8 b ](PF 6 ) 2 ), in which R =(2‐(2‐(2‐(methylthio)ethoxy)ethoxy)ethyl‐β‐d‐glucopyranoside is a thioether‐glucose conjugate (Figure ).…”

Photoactivation of Anticancer Ru Complexes in Deep Tissue: How Deep Can We Go?

“…Ru complexes, analogues of platinum anticancer drugs, are importantly proposed to also be promising anticancer agents . One advantage of photoactivated Ru complexes is that they are usually less toxic to non‐irradiated tissues, only becoming more toxic in tumor cells through photoactivation . Photoactivated Ru‐containing materials have already shown anticancer effects in a tumor‐bearing mouse model .…”