title: Emissive behavior, cytotoxic activity, cellular uptake, and PEGylation properties of new luminescent rhenium(I) polypyridine poly(ethylene glycol) complexes.
abstract: We report here a new class of biological reagents derived from luminescent rhenium(I) polypyridine complexes modified with a poly(ethylene glycol) (PEG) pendant. The PEG-amine complexes [Re(N(^)N)(CO)(3)(py-PEG-NH(2))](PF(6)) (py-PEG-NH(2) = 3-amino-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine, MW(PEG) = 5000 Da, PDI(PEG) < 1.08; N(^)N = 1,10-phenanthroline (phen) (1-PEG-NH(2)), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me(4)-phen) (2-PEG-NH(2)), 4,7-diphenyl-1,10-phenanthroline (Ph(2)-phen) (3-PEG-NH(2))) and [Re(bpy-PEG)(CO)(3)(py-NH(2))](PF(6)) (bpy-PEG = 4-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine; py-NH(2) = 3-aminopyridine) (4-PEG-NH(2)) have been synthesized and characterized. The photophysical properties, lipophilicity, water solubility, cytotoxic activity, and cellular uptake properties of these complexes have been compared to those of their PEG-free counterparts [Re(N(^)N)(CO)(3)(py-Et-NH(2))](PF(6)) (py-Et-NH(2) = 3-amino-5-(N-(ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-Et-NH(2)), Me(4)-phen (2-Et-NH(2)), Ph(2)-phen (3-Et-NH(2))) and [Re(bpy-Et)(CO)(3)(py-NH(2))](PF(6)) (bpy-Et = 4-(N-(ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine) (4-Et-NH(2)). The PEG complexes exhibited significantly higher water solubility and lower cytotoxicity (IC(50) = 6.6 to 1152 μM) than their PEG-free counterparts (IC(50) = 3.6 to 159 μM), indicating that the covalent attachment of a PEG pendant to rhenium(I) polypyridine complexes is an effective way to increase their biocompatibility. The amine complexes 1-PEG-NH(2)-4-PEG-NH(2) have been activated with thiophosgene to yield the isothiocyanate complexes [Re(N(^)N)(CO)(3)(py-PEG-NCS)](PF(6)) (py-PEG-NCS = 3-isothiocyanato-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-PEG-NCS), Me(4)-phen (2-PEG-NCS), Ph(2)-phen (3-PEG-NCS)), and [Re(bpy-PEG)(CO)(3)(py-NCS)](PF(6)) (py-NCS = 3-isothiocyanatopyridine) (4-PEG-NCS) as a new class of luminescent PEGylation reagents. To examine their PEGylation properties, these isothiocyanate complexes have been reacted with a model substrate n-butylamine, resulting in the formation of the thiourea complexes [Re(N(^)N)(CO)(3)(py-PEG-Bu)](PF(6)) (py-PEG-Bu = 3-n-butylthioureidyl-5-(N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)aminocarbonyl)pyridine; N(^)N = phen (1-PEG-Bu), Me(4)-phen (2-PEG-Bu), Ph(2)-phen (3-PEG-Bu)), and [Re(bpy-PEG)(CO)(3)(py-Bu)](PF(6)) (py-Bu = 3-n-butylthioureidylpyridine) (4-PEG-Bu). Additionally, bovine serum albumin (BSA) and poly(ethyleneimine) (PEI) have been PEGylated with the isothiocyanate complexes to yield bioconjugates 1-PEG-BSA-4-PEG-BSA and 1-PEG-PEI-4-PEG-PEI, respectively. Upon irradiation, all the PEGylated BSA and PEI conjugates exhibited intense and long-lived emission in aqueous buffer under ambient conditions. The DNA-binding and polyplex-formation properties of conjugate 3-PEG-PEI have been studied and compared with those of unmodified PEI. Furthermore, the in vivo toxicity of complex 3-PEG-NH(2) and its PEG-free counterpart 3-Et-NH(2) has been investigated using zebrafish embryos as an animal model. Embryos treated with the PEG complex at high concentrations revealed delayed hatching, which has been ascribed to hypoxia as a result of adhering of the complex to the external surface of the chorion.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, PR China.
authors.forename: Alex Wing-Tat
authors.initials: AW
authors.lastname: Choi
authors.forename: Man-Wai
authors.initials: MW
authors.lastname: Louie
authors.forename: Steve Po-Yam
authors.initials: SP
authors.lastname: Li
authors.forename: Hua-Wei
authors.initials: HW
authors.lastname: Liu
authors.forename: Bruce Ting-Ngok
authors.initials: BT
authors.lastname: Chan
authors.forename: Tonlex Chun-Ying
authors.initials: TC
authors.lastname: Lam
authors.forename: Alex Chun-Chi
authors.initials: AC
authors.lastname: Lin
authors.forename: Shuk-Han
authors.initials: SH
authors.lastname: Cheng
authors.forename: Kenneth Kam-Wing
authors.initials: KK
authors.lastname: Lo
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D002945:Cisplatin / Q000494:pharmacology; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D004625:Embryo, Nonmammalian / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D049449:Luminescence; D018613:Microscopy, Confocal; D023421:Models, Animal; D015394:Molecular Structure; D010777:Photochemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D012995:Solubility; D014867:Water / Q000737:chemistry*; D015027:Zebrafish
chemical_list: D000970:Antineoplastic Agents; D056831:Coordination Complexes; D014867:Water; D011092:Polyethylene Glycols; D012211:Rhenium; D002945:Cisplatin