Luminescent biological probes derived from ruthenium(II) estradiol polypyridine complexes

Four luminescent ruthenium(II) polypyridine estradiol complexes Ru(NwedgeN)2(bpy-estradiol)](PF6)2 (NwedgeN = 2,2'-bipyridine (bpy), 4,7-diphenyl-1,10-phenanthroline (Ph2-phen); bpy-estradiol = 5-(4-(17alpha-ethynylestradiolyl)phenyl)-2,2'-bipyridine (bpy-ph-est), 4-(N-(6-(4-(17alpha-ethynylestradiolyl)benzoylamino)hexyl)aminomethyl)-4'-methyl-2,2'-bipyridine (mbpy-C6-est)) have been designed as new luminescent biological probes. The lipophilicity and photophysical and electrochemical properties of these complexes have been investigated. Upon photoexcitation, all the complexes exhibited intense and long-lived triplet metal-to-ligand charge-transfer (3MLCT) (dpi(Ru) --> pi*(diimine)) emission in fluid solutions at 298 K and in low-temperature glass. The binding of the complexes to estrogen receptor-alpha (ERalpha) has been studied by emission titrations. The Ph2-phen complexes showed emission enhancement and increased lifetimes upon binding to the protein. Additionally, the cytotoxicity of the complexes toward the HeLa cell line has been examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay and the IC50 values ranged from 83.1 to 166.6 microM (cisplatin showed an IC50 value of 34.3 microM under the same experimental conditions). Furthermore, the cellular uptake of the complexes has been investigated by flow cytometry and laser-scanning confocal microscopy.