Rhenium(I) Polypyridine Biotin Isothiocyanate Complexes as the First Luminescent Biotinylation Reagents: Synthesis, Photophysical Properties, Biological Labeling, Cytotoxicity, and Imaging Studies

Citations Over TimeTop 10% of 2007 papers

Abstract

We report here the design of the first class of luminescent biotinylation reagents derived from rhenium(I) polypyridine complexes. These complexes [Re(N−N)(CO)3(py-biotin-NCS)](PF6) (py-biotin-NCS = 3-isothiocyanato-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = 1,10-phenanthroline (phen) (1a), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4-phen) (2a), 4,7-diphenyl-1,10-phenanthroline (Ph2-phen) (3a)), containing a biotin unit and an isothiocyanate moiety, have been synthesized from the precursor amine complexes [Re(N−N)(CO)3(py-biotin-NH2)](PF6) (py-biotin-NH2 = 3-amino-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = phen (1c), Me4-phen (2c), Ph2-phen (3c)). To investigate the amine-specific reactivity of the isothiocyanate complexes 1a−3a, they have been reacted with a model substrate ethylamine, resulting in the formation of the thiourea complexes [Re(N−N)(CO)3(py-biotin-TU-Et)](PF6) (py-biotin-TU-Et = 3-ethylthioureidyl-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = phen (1b), Me4-phen (2b), Ph2-phen (3b)). All the rhenium(I) complexes have been characterized, and their photophysical properties have been studied. The avidin-binding properties of the thiourea complexes 1b−3b have been examined by the 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assay. Titration results indicated that the complexes exhibited emission enhancement by ca. 1.4−1.5-fold upon binding to avidin, and the lifetimes were elongated to ca. 0.8−2.0 μs. Additionally, we have biotinylated bovine serum albumin (BSA) with the isothiocyanate complexes. All the resultant rhenium−BSA bioconjugates displayed intense and long-lived orange-yellow to greenish-yellow emission upon irradiation in aqueous buffer under ambient conditions. The avidin-binding properties of the bioconjugates have been investigated using the HABA assay. Furthermore, the cytotoxicity of the thiourea complexes 1b−3b toward the HeLa cells has been examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC50 values were determined to be ca. 17.5−28.5 μM, which are comparable to that of cisplatin (26.7 μM) under the same conditions. The cellular uptake of complex 3b has been investigated by fluorescence microscopy, and the results showed that the complex was localized in the perinuclear region after interiorization.

Related Papers

• → The Avidin–Biotin Complex (ABC) Method and Other Avidin–Biotin Binding Methods(2009)101 cited
• → Switchavidin: Reversible Biotin–Avidin–Biotin Bridges with High Affinity and Specificity(2014)36 cited
• → [54] Avidin-biotin mediated immunoassays: Overview(1990)30 cited
• → Avidin-induced lysis of biotinylated erythrocytes by homologous complement via the alternative pathway depends on avidin's ability of multipoint binding with biotinylated membrane(1992)19 cited
• → Metabolism, in the Rat, of Biotin Injected Intraperitoneally as the Avidin-Biotin Complex(1973)17 cited