An octahedral rhenium cluster compound K₄[Re₆S₈(CN)₆]: synthesis, structural characterization and biodistribution

Polynuclear metal compounds may have considerable potential as metallic drugs. Some types of polyoxometalates, derived from Mo, W, Re and others, are able to be transported into cells and mitochondria. Certain representatives show antiviral and anti-tumour properties.[1-3] Deposited in target cells, metal clusters have promising properties to be used in photon activation therapy (PAT) or photodynamic therapy. In this nexus, octahedral cluster rhenium compounds possess bright red luminescence to make them interesting for medical treatment of cancer.[4] Furthermore, the combination of anti-tumour activity and photodynamic therapy can provide synergetic medical efficacy.
We want to present the synthesis, structural characterization and preliminary pharmacological properties of an octahedral rhenium cluster compound. In the latter concern, it is important to know its biodistribution, metabolism and toxicity. So, the goal of the work presented was the determination of biodistribution of K₄[Re₆S₈(CN)₆] and lethal dose LD₁₀₀ in rats. Experiments were carried out on male rats. As formulation the cluster compound K₄[Re₆S₈(CN)₆], dissolved in water (different concentrations in the range from 0.01 to 0.5%), was intra-peritoneally administered. The animals were distributed into 5 groups, each group had 5 rats; one rat was control. The formulation has been injected (one mL of solution every one hour during the day). It was determined that 0.5 mg of K₄[Re₆S₈₍CN)₆] per one gram of live weight of the rats provokes 100% fatal outcome of experimental animals during first day. This value was accepted as the lethal dose LD₁₀₀ at intraperitoneal administration of the compound.
Biodistribution experiments were carried out in the format of acute toxicity with single injecting preparation of 1/5LD₅₀ dose. The data of biodistribution are shown that the cluster compound is mainly accumulated in the liver the kidney and spleen. No correlation between the concentrations of rhenium and iron in the internal was found. This can be evidenced of the fact that cyanide groups of compound K₄[Re₆S₈(CN)₆] are indifferent to molecular forms of iron in which it is presented in organism. Accumulation in spleen may be interpreted as a location of cluster compound in immune structures. This allows to consider cluster rhenium complexes as promising compounds for treatment of lymphoma proliferation sicknesses and first of all the lymphomas.

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