title: Fluorescent copper(II) bis(thiosemicarbazonates): synthesis, structures, electron paramagnetic resonance, radiolabeling, in vitro cytotoxicity and confocal fluorescence microscopy studies.
abstract: Copper bis(4-ethyl-3-thiosemicarbazonato) acenaphthenequinone (1) and copper bis(4-methyl-3-thiosemicarbazonato) acenaphthenequinone (2) are synthesized and characterized in solution, in the solid state, and radiolabeled. Serum-protein binding radioassays show good stability in solution and about 25 % binding to protein over 1 h, which is comparable with the hypoxia selective tracer [(64)Cu(ATSM)]. Cyclic voltammetry shows fast and reversible reduction at redox potentials similar to the values known for hypoxia-selective copper compounds. However, despite this, complex 1 does not show any hypoxic-selective uptake in HeLa cells over 1-h standard assays. Possible reasons for this are studied by using the intrinsic fluorescence of the Cu(II) complexes to determine the cellular distributions and uptake mechanism by confocal microscopy. The complexes are found to bind to the external cell membrane and disperse evenly in the cytoplasm only after a very slow cell internalization (>1 h). No significant changes in distribution are observed by fluorescence imaging under hypoxic conditions. The rate of localization in the cytoplasm contrasts with their Zn(II) analogues, which are known to have fast cell uptake (up to 20 min) and a clear localization in lysosomes and mitochondria. The cytotoxicity mechanism of 1 over 24 h against a number of adherent cell lines is seen to be by membrane disruption and is of a comparable magnitude to that of [Cu(ATSM)], as demonstrated by methyl tetrazolium (MTT) and lactate dehydrogenase (LDH) assays.
authors.affiliation: Department of Chemistry, University of Bath, BA2 7AY Bath, UK. s.pascu@bath.ac.uk
authors.forename: Sofia I
authors.initials: SI
authors.lastname: Pascu
authors.forename: Philip A
authors.initials: PA
authors.lastname: Waghorn
authors.forename: Brett W C
authors.initials: BW
authors.lastname: Kennedy
authors.forename: Rory L
authors.initials: RL
authors.lastname: Arrowsmith
authors.forename: Simon R
authors.initials: SR
authors.lastname: Bayly
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Dilworth
authors.forename: Martin
authors.initials: M
authors.lastname: Christlieb
authors.forename: Rex M
authors.initials: RM
authors.lastname: Tyrrell
authors.forename: Julia
authors.initials: J
authors.lastname: Zhong
authors.forename: Radoslaw M
authors.initials: RM
authors.lastname: Kowalczyk
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Parvinder K
authors.initials: PK
authors.lastname: Aley
authors.forename: Grant C
authors.initials: GC
authors.lastname: Churchill
authors.forename: Franklin I
authors.initials: FI
authors.lastname: Aigbirhio
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D006801:Humans; D007553:Isotope Labeling; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000494:pharmacology; D013882:Thiosemicarbazones / Q000737:chemistry*
chemical_list: D000970:Antineoplastic Agents; D005456:Fluorescent Dyes; D019275:Radiopharmaceuticals; D013882:Thiosemicarbazones; D003300:Copper