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Issue 11, 2010
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Enhanced photodynamic effect of cobalt(III) dipyridophenazine complex on thyrotropin receptor expressing HEK293 cells

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Ternary cobalt(III) complexes [CoL(B)] (1–3) of a trianionic tetradentate phenolate-based ligand (L) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyridoquinoxaline (dpq in 2) and dipyridophenazine (dppz in 3) are synthesized, characterized from X-ray crystallographic, analytical and spectral techniques, and their utility in photodynamic therapy (PDT) of thyroid diseases caused by TSH receptor dysfunction is probed. The complexes display a visible spectral band within the PDT spectral window at ∼690 nm. Photodynamic potential was estimated through DNA cleavage activity of the dpq and dppz complexes in UV-A light of 365 nm and red light of 676 nm. The reactions proceed via the hydroxyl radical pathway. The complexes retain their DNA photocleavage activity in red light under anaerobic conditions, a situation normally prevails in hypoxic tumor core. Investigation into the photocytotoxic potential of these complexes showed that the dppz complex 3 is approximately 4-fold more active in the HEK293 cells expressing human thyrotropin receptor (HEK293-hTSHR) than in the parental cell line and has an insignificant effect on an unrelated human cervical carcinoma cell line (HeLa). Photoexcitation of complex 3 in HEK293-hTSHR cells leads to damage hTSHR as evidenced from the decrease in cAMP formation both in absence and presence of hTSH and decrease in the TSHR immunofluorescence with a concomitant cytoplasmic translocation of the membrane protein, cadherin. The involvement of hTSHR is evidenced from the ability of complex 3 to bind to the extracellular domain of hTSHR (hTSHR-ECD) with a Kd value of 81 nM and from the photocleavage of hTSHR-ECD.

Graphical abstract: Enhanced photodynamic effect of cobalt(iii) dipyridophenazine complex on thyrotropin receptor expressing HEK293 cells

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The article was received on 10 Jul 2010, accepted on 14 Sep 2010 and first published on 21 Oct 2010

Article type: Paper
DOI: 10.1039/C0MT00028K
Metallomics, 2010,2, 754-765

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    Enhanced photodynamic effect of cobalt(III) dipyridophenazine complex on thyrotropin receptor expressing HEK293 cells

    S. Saha, R. Majumdar, R. R. Dighe and A. R. Chakravarty, Metallomics, 2010, 2, 754
    DOI: 10.1039/C0MT00028K

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