Exploration of the Pharmacophore for Cytoskeletal Targeting Ruthenium Polypyridyl Complexes

Ruthenium(II) trisdiimine complexes of the formula, [Ru(dip)_n (L-L)_3-n ]²⁺ , where n=0-3; dip=4,7-diphenyl-1,10-phenanthroline; L-L=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) were prepared and tested for cytotoxicity in two cell lines (H358, MCF7). Cellular uptake and subcellular localization were determined by harvesting treated cells and determining the ruthenium concentration in whole or fractionated cells (cytosolic, nuclear, mitochondrial/ ER/Golgi, and cytoskeletal proteins) by Ru ICP-MS. The logP values for the chloride salts of these complexes were measured and the data were analyzed to determine the role of lipophilicity versus structure in the various biological assays. Cellular uptake increased with lipophilicity but shows the biggest jump when the complex contains two or more dip ligands. Significantly, preferential cytoskeletal localization is also correlated with increased cytotoxicity. All of the RPCs promote tubulin polymerization in vitro, but [Ru(dip)₂ phen]²⁺ and [Ru(dip)₃ ]²⁺ show the strongest activity. Analysis of the pellet formed by centrifugation of MTs formed in the presence of [Ru(dip)₂ phen]²⁺ establish a binding stoichiometry of one RPC per tubulin heterodimer. Complexes of the general formula [Ru(dip)₂ (L-L)]²⁺ possess the necessary characteristics to target the cytoskeleton in live cells and increase cytotoxicity, however the nature of the L-L ligand does influence the extent of the effect.