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Anaerobic DNA cleavage activity in red light and photocytotoxicity of (pyridine-2-thiol)cobalt(III) complexes of phenanthroline bases

Lahiri, Debojyoti and Roy, Sovan and Saha, Sounik and Majumdar, Ritankar and Dighe, Rajan R and Chakravarty, Akhil R (2010) Anaerobic DNA cleavage activity in red light and photocytotoxicity of (pyridine-2-thiol)cobalt(III) complexes of phenanthroline bases. In: Dalton Transactions (2003), 39 (7). pp. 1807-1816.

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Abstract

Cobalt(III) complexes [Co(pnt)(B)(2)](NO3)(2) (1-3) of pyridine-2-thiol (pnt) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d: 2',3'-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2',3'-c] phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The crystal structure of 1a as mixed ClO4- and PF6- salt of 1 shows a (CoN5S)-N-III coordination geometry in which the pnt and phen showed N,S- and N,N-donor binding modes, respectively. The complexes exhibit Co(III)/Co(II) redox couple near -0.3 V (vs. SCE) in 20% DMF-Tris-HCl buffer having 0.1 M TBAP. The complexes show binding propensity to calf thymus DNA giving K-b values within 2.2 x 10(4)-7.3 x 10(5) M-1. Thermal melting and viscosity data suggest DNA surface and/or groove binding of the complexes. The complexes show significant anaerobic DNA cleavage activity in red light under argon atmosphere possibly involving sulfide anion radical or thiyl radical species. The DNA cleavage reaction under aerobic medium in red light is found to involve both singlet oxygen and hydroxyl radical pathways. The dppz complex 3 shows non-specific BSA and lysozyme protein cleavage activity in UV-A light of 365 nm via both hydroxyl and singlet oxygen pathways. The dppz complex 3 exhibits photocytotoxicity in HeLa cervical cancer cells giving IC50 values of 767 nM and 19.38 mu M in UV-A light of 365 nm and in the dark, respectively. A significant reduction of the dark toxicity of the dppz base (IC50 = 8.34 mu M in dark) is observed on binding to the cobalt(III) center.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Royal Society of Chemistry.
Department/Centre: Division of Biological Sciences > Molecular Reproduction, Development & Genetics (formed by the merger of DBGL and CRBME)
Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 09 Mar 2010 07:37
Last Modified: 19 Sep 2010 05:56
URI: http://eprints.iisc.ernet.in/id/eprint/25919

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