title: Photosensitization of DNA damage by a new cationic pyropheophorbide derivative: sequence-specific formation of a frank scission.
abstract: Pyropheophorbides are red-absorbing porphyrin-like photosensitizers that may interact with DNA either by intercalation or by external binding with self-stacking according to the value of the nucleotide to chromophore molar ratio (N/C). This article reports on the nature and sequence selectivity of the DNA damage photoinduced by a water-soluble chlorhydrate of aminopyropheophorbide. First, this pyropheophorbide is shown to induce on irradiation the cleavage of phiX174 DNA by both Type-I and -II mechanisms, suggested by scavengers and D2O effects. These conclusions are then improved by sequencing experiments performed on a 20-mer oligodeoxynucleotide (ODN) irradiated at wavelengths >345 nm in the presence of the dye, N/C varying from 2.5 to 0.5. Oxidation of all guanine residues to the same extent is observed after piperidine treatment on both single- and double-stranded ODN. Moreover, unexpectedly, a remarkable sequence-selective cleavage occurring at a 5'-CG-3' site is detected before alkali treatment. This frank break is clearly predominant for a low nucleotide to chromophore molar ratio, corresponding to a self-stacking of the dye along the DNA helix. The electrophoretic properties of the band suggest that this lesion results from a sugar oxidation, which leads via a base release to a ribonolactone residue. The proposal is supported by high-performance liquid chromatography-matrix-assisted laser desorption-ionization mass spectrometry experiments that also reveal other sequence-selective frank scissions of lower intensity at 5'-GC-3' or other 5'-CG-3' sites. This sequence selectivity is discussed with regard to the binding selectivity of cationic porphyrins.
authors.affiliation: Laboratoire des Interactions Moléculaires, Réactivité Chimique et Photochimique, UMR CNRS 5623, Université Paul Sabatier, Toulouse cedex, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Kanony
authors.forename: Anne-Sylvie
authors.initials: AS
authors.lastname: Fabiano-Tixier
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Ravanat
authors.forename: Patricia
authors.initials: P
authors.lastname: Vicendo
authors.forename: Nicole
authors.initials: N
authors.lastname: Paillous
mesh_terms: D002412:Cations / Q000737:chemistry / Q000494:pharmacology; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000494:pharmacology*; D004249:DNA Damage / Q000187:drug effects* / Q000528:radiation effects*; D018384:Oxidative Stress; D017319:Photosensitizing Agents / Q000737:chemistry / Q000494:pharmacology*; D010957:Plasmids / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D011166:Porphyrins / Q000737:chemistry* / Q000494:pharmacology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D002412:Cations; D017319:Photosensitizing Agents; D011166:Porphyrins; C414345:aminopyropheophorbide; D002734:Chlorophyll