Kinetically-inert polypyridylruthenium(II) complexes as therapeutic agents

Due to the clinical success and limitations of platinum-based anticancer drugs, there has been considerable interest in the development of new therapeutic agents based upon other transition metals, in particular ruthenium. There have now been many studies demonstrating the anticancer and antimicrobial properties of kinetically-inert polypyridylruthenium(II) complexes. This review showcases the diverse range of polypyridylruthenium complexes that exhibit significant biological activity, and discusses the relationship between their chemical structure and biological processing (cellular uptake and localisation) in eukaryotic cells. Perhaps more importantly, this review also highlights several recent studies that have shown kinetically-inert polypyridylruthenium(II) complexes can exhibit anticancer activity in in vivo trials – studies that provide the "proof of concept" that this class of metal-based agent has real clinical potential

Synthesis and biological properties of tetranuclear ruthenium complexes containing the bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane ligand

Linear and non-linear tetranuclear ruthenium(II) complexes containing the bridging ligand bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane have been synthesised and their biological properties examined. The minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) of the ruthenium(II) complexes were determined against six strains of bacteria: Gram-positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA); and the Gram-negative Escherichia coli (E. coli) strains MG1655, APEC, UPEC and Pseudomonas aeruginosa (P. aeruginosa). The results showed that both tetranuclear complexes had significant antimicrobial activity, with the non-linear (branched) species (Rubb7-TNL) having slightly higher activity than the corresponding linear analogue (Rubb7-TL). The corresponding toxicity against three eukaryotic cell lines − BHK (baby hamster kidney), Caco-2 (heterogeneous human epithelial colorectal adenocarcinoma) and Hep-G2 (liver carcinoma) − have also been determined. Interestingly, both Rubb7-TNL and Rubb7-TL were as toxic to the eukaryotic cells as they were to the bacteria, a rarity for kinetically-inert cationic polypyridylruthenium(II) complexes, and exhibited lower IC50 values than cisplatin over 24-, 48- or 72-hour incubation times. Fluorescence spectroscopy was used to study the binding of the ruthenium complexes with human serum albumin (HSA). Rubb7-TNL and Rubb7-TL exhibited strong HSA binding, with equilibrium binding constants in the order of 107 M-1. Confocal microscopy was used to examine the cellular localisation of Rubb7-TNL in BHK cells. The results indicated that the ruthenium complex localised in the nucleolus. Significant accumulation was also observed in the cytoplasm, but not in the mitochondria. Taken together, the results of this study suggest that Rubb7-TNL is an unlikely candidate as an antimicrobial agent, but may have potential as an anticancer drug

Differential anticancer activities of the geometric isomers of dinuclear iridium(III) complexes

The anticancer activities of dinuclear iridium(III) complexes [{Ir(tpy)Cl}2{μ-bbn}]4+ {Cl-Irbbn; tpy = 2,2':6',2"-terpyridine, bbn = bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane (n = 7, 12 and 16)} against MCF-7 and MDA-MB-231 breast cancer cell lines have been determined. The activities of the Cl-Irbbn complexes increased with increasing chain length, the Cl-Irbb16 complex showing the best anticancer properties. However, while Cl-Irbb16 was active against the metastatic MDA-MB-231 cells (3 μM), it was relatively inactive against the nonmetastatic MCF-7 line (29 μM). The three geometric isomers of Cl-Irbb16 were isolated and characterised by NMR spectroscopy and mass spectrometry, and their anticancer activities, lipophilicities (log P) and DNA-binding abilities were examined. The trans,trans (t,t) isomer (IC50 = 2 μM against MDA-MB-231) showed considerably greater anticancer activity than the cis,trans (c,t) and cis,cis (c,c) isomers (8 and 31 μM, respectively). From log P measurements, the t,t isomer of Cl-Irbb16 (log P = –0.62) was found to be slightly more lipophilic than the other geometric isomers (–0.95 and –0.98 for the c,c and c,t isomers, respectively). Calf-thymus (CT) DNA-binding experiments demonstrated that the t,t isomer did induce a different alteration to the helix conformation compared to the other isomers. The results of this study also highlight the significance of the differences in three-dimensional shape that can be obtained through geometric isomerism for octahedral coordination complexes

Polypyridylruthenium(II) complexes exert anti-schistosome activity and inhibit parasite acetylcholinesterases.

Schistosomiasis affects over 200 million people and there are concerns whether the current chemotherapeutic control strategy (periodic mass drug administration with praziquantel (PZQ)-the only licenced anti-schistosome compound) is sustainable, necessitating the development of new drugs.We investigated the anti-schistosome efficacy of polypyridylruthenium(II) complexes and showed they were active against all intra-mammalian stages of S. mansoni. Two compounds, Rubb12-tri and Rubb7-tnl, which were among the most potent in their ability to kill schistosomula and adult worms and inhibit egg hatching in vitro, were assessed for their efficacy in a mouse model of schistosomiasis using 5 consecutive daily i.v. doses of 2 mg/kg (Rubb12-tri) and 10 mg/kg (Rubb7-tnl). Mice treated with Rubb12-tri showed an average 42% reduction (P = 0.009), over two independent trials, in adult worm burden. Liver egg burdens were not significantly decreased in either drug-treated group but ova from both of these groups showed significant decreases in hatching ability (Rubb12-tri-68%, Rubb7-tnl-56%) and were significantly morphologically altered (Rubb12-tri-62% abnormal, Rubb7-tnl-35% abnormal). We hypothesize that the drugs exerted their activity, at least partially, through inhibition of both neuronal and tegumental acetylcholinesterases (AChEs), as worms treated in vitro showed significant decreases in activity of these enzymes. Further, treated parasites exhibited a significantly decreased ability to uptake glucose, significantly depleted glycogen stores and withered tubercules (a site of glycogen storage), implying drug-mediated interference in this nutrient acquisition pathway.Our data provide compelling evidence that ruthenium complexes are effective against all intra-mammalian stages of schistosomes, including schistosomula (refractory to PZQ) and eggs (agents of disease transmissibility). Further, the results of this study suggest that schistosome AChE is a target of ruthenium drugs, a finding that can inform modification of current compounds to identify analogues which are even more effective and selective against schistosomes

Effect of Rubb₁₂-tri and Rubb₁₆-tnl on adult <i>S</i>. <i>mansoni</i> glucose uptake and storage ability.

<p>Worms were cultured in Basch media for 24 h in the presence of a sub-lethal dose (5 μM) of Rubb₁₂-tri or Rubb₁₆-tnl. Worms were then incubated for 24 h in DMEM containing 1 mg/ml glucose. PBS extracts were then made from equal amounts of control and treated worms and 30 ug of each extract was used to determine the glycogen content of the worms using a modified glucose oxidase assay. (A) Amount of glucose in media collected from control and treated <i>S</i>. <i>mansoni</i> worms. (B) Levels of glycogen in extracts made from control and treated <i>S</i>. <i>mansoni</i> worms. For all assays, data are the average of triplicate biological and technical experiments ± SE. Differences were measured by ANOVA. *<i>P</i> ≤ 0.05, **<i>P</i> ≤ 0.01, ***<i>P</i> ≤ 0.001, **** <i>P</i> ≤ 0.0001. (C) Scanning electron micrographs of adult male <i>S</i>. <i>mansoni</i> worm tegument after incubation with 5 μM Rubb₁₂–tri; (I) intact tubercles of control worms; (II) withered tubercules of treated worms.</p

Effect of ruthenium complexes on AChE activity in adult <i>S</i>. <i>mansoni</i> extracts.

<p>Concentration-dependent inhibition of AChE activity in <i>S</i>. <i>mansoni</i> adult extracts when treated with Rubb₁₂-tri, a representative member of the ruthenium complexes tested, as determined by Ellman assay. (A) Dose-response curve of Rubb₁₂-tri. (B) Lineweaver-Burk inhibition plot of AChE activity in <i>S</i>. <i>mansoni</i> adult extracts in the presence of Rubb₁₂-tri. Data represent the average of triplicate experiments ± SE.</p

The kinetically inert tri-nuclear (Rubb_n-tri), linear tetra-nuclear Rubb_n-tl and non-linear tetra-nuclear Rubb_n-tnl) ruthenium(II) complexes.

<p>The kinetically inert tri-nuclear (Rubb_n-tri), linear tetra-nuclear Rubb_n-tl and non-linear tetra-nuclear Rubb_n-tnl) ruthenium(II) complexes.</p

Potency of selected ruthenium complexes against <i>S</i>. <i>mansoni</i> schistosomula after 48 h treatment.

<p>Potency of selected ruthenium complexes against <i>S</i>. <i>mansoni</i> schistosomula after 48 h treatment.</p

<i>In vivo</i> effect of Rubb₁₂-tri and Rubb₇-tnl on <i>S</i>. <i>mansoni</i>-infected mice.

<p>(A) Effect of Rubb₁₂-tri and Rubb₇-tnl on adult worm burden. Symbols represent data from individual mice and are the combination of two independent trials (trial 1 PBS control—n = 8 mice, trial 1 Rubb₁₂-tri-treated—n = 8 mice, trial 1 Rubb₇-tnl-treated—n = 6 mice, trial 2 PBS control—n = 7 mice, trial 2 Rubb₁₂-tri-treated—n = 7 mice, trial 2 Rubb₇-tnl-treated—n = 8 mice). (B) Surface AChE activity of worms recovered from control and treated mice. Data are the average of triplicate technical assays ± SE on extracts made from worms (five pairs) pooled from each group of each of the two trials. (C) Hatching viability of eggs obtained from the pooled livers of control and treated mice from trial 1 (PBS control—n = 8, Rubb₁₂-tri-treated—n = 8, Rubb₇-tnl-treated—n = 6). Data are the average of ten replicate counts ± SE of hatched miracidia. (D) Eggs were harvested from triplicate sets of worms (five pairs) from a pool of each group of trial 2 (PBS control—n = 7 mice, Rubb₁₂-tri-treated—n = 7 mice, Rubb₇-tnl-treated—n = 8 mice) after culturing the parasites for 24 h in Basch media and the percentage of mature, morphologically “normal” eggs released from worms recovered from control and treated mice was assessed. Data are the average counts ± SE of eggs released from triplicate sets (five pairs) of worms from trial 2. Differences were measured by ANOVA. *<i>P</i> ≤ 0.05, **<i>P</i> ≤ 0.01, ***<i>P</i> ≤ 0.001, **** <i>P</i> ≤ 0.0001. (E) Auto-fluorescence images (20×) of eggs released from worms recovered from (I and II) control and (III and IV) treated mice.</p