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1 March 2000 DNA Damage Induced by 4,6,8,9-Tetramethyl-2H-furo[2,3-h]quinolin-2-one, a New Furocoumarin Analog: Photochemical Mechanisms
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Some photochemical and photobiological properties of 4,6,8,9-tetramethyl-2H-furo[2,3-h]quinolin-2-one (HFQ) were studied in comparison with its isomer 1,4,6,8-tetramethyl-2H-furo[2,3-h]quinolin-2-one (FQ) and 8-methoxypsoralen (8-MOP). The HFQ photobinds to DNA forming furan-side monoadducts (MAHFQ) that have molecular structure very similar to those of FQ (MAFQ). Unlike MA8-MOP and MAFQ, MAHFQ no longer photoreact. The HFQ, like FQ, produces moderate amounts of singlet oxygen but no superoxide anions. The HFQ and FQ induce numbers of DNA–protein cross-links (DPC), much more plentiful than those of 8-MOP (about two and seven times, respectively) but no interstrand cross-links. The mechanism of DPC formation was studied in vivo in mammalian cells by alkaline elution and in vitro using a new test mixing histones and DNA from calf thymus. The latter is a very useful technique for the double irradiation protocol. The DNA (or histones) are separately exposed to a first UVA dose in the presence of the sensitizer; then, after its unbound molecules have been removed, histones (or DNA) are added to assemble the chromatin-like complex that is irradiated again. According to in vitro and in vivo methods, DPC appear to be formed by FQ and 8-MOP by a biphotonic process that starts with monoadduct induction in DNA, followed by their conversion into DPC. In the resulting lesions, the sensitizer molecule forms a covalent bridge between the two macromolecules (DPC at length greater than zero). Instead, HFQ induces DPC by a monophotonic process; thus, HFQ is probably not a physical part of the bridge between DNA and proteins, which may be linked together directly, like DPC at zero length induced by UVC.

F. Bordin, F. Baccichetti, C. Marzano, F. Carlassare, G. Miolo, A. Chilin, and A. Guiotto "DNA Damage Induced by 4,6,8,9-Tetramethyl-2H-furo[2,3-h]quinolin-2-one, a New Furocoumarin Analog: Photochemical Mechanisms," Photochemistry and Photobiology 71(3), 254-262, (1 March 2000).<0254:DDIBTF>2.0.CO;2
Received: 28 July 1999; Accepted: 1 December 1999; Published: 1 March 2000

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