Fluorescent copper(II) bis(thiosemicarbazonates): synthesis, structures, electron paramagnetic resonance, radiolabeling, in vitro cytotoxicity and confocal fluorescence microscopy studies

Sofia I Pascu, Philip A Waghorn, Brett W C Kennedy, Rory L Arrowsmith, Simon R Bayly, Jonathan R Dilworth, Martin Christlieb, Rex M Tyrrell, Julia Zhong, Radoslaw M Kowalczyk, David Collison, Parvinder K Aley, Grant C Churchill, Franklin I Aigbirhio

Research output: Contribution to journalArticle

46 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)506-519
Number of pages14
JournalChemistry - An Asian Journal
Volume5
Issue number3
Early online date18 Feb 2010
DOIs
Publication statusPublished - 1 Mar 2010

Keywords

  • antineoplastic agents
  • cell death
  • cell line, tumor
  • copper
  • electron spin resonance Spectroscopy
  • fluorescent dyes
  • humans
  • isotope labeling
  • microscopy, fluorescence
  • molecular structure
  • radiopharmaceuticals
  • thiosemicarbazones
  • cytotoxicity
  • electrochemistry
  • fluorescence spectroscopy
  • positron emission tomography
  • x-ray diffraction

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