title: Stabilization of triple helical DNA by a benzopyridoquinoxaline intercalator.
abstract: Biophysical, footprinting, and chemical probing experiments are described which characterize the triple helix-stabilizing effects of a benzo[f]pyridoquinoxaline derivative BfPQ-4,3 structurally related to the previously reported benzo[f]pyridoindole compound BePI [Mergny et al. (1992) Science 256, 1681-1684]. Two parallel triple helix model systems have been investigated; one in which the third strand matched perfectly a 27 base pair purine-pyrimidine motif in target DNA and another in which the third strand was one nucleotide longer, i.e., a 28-mer. In the latter system, the pairing of the (Y)28 third strand to the (Y.R)27 target induces the formation of a bulge containing at least one unpaired base, which can be evidenced by chemical probing experiments with osmium tetroxide. BPQ, which uinwinds a duplex DNA by 17 degrees as judged by viscometric experiments and otherwise behaves as a typical nonspecific intercalculating drug, promotes the formation of Y.R.Y parallel triple helix containing both T.A.T and C.G.C+ triplets. Both DNase I and MPE.FeII footprinting experiments concur that triplex formation with the target (Y.R)27 sequence can be detected in the presence of BPQ at about 10-fold lower oligonucleotide concentrations than are required to produce an equivalent footprint in the absence of the drug. In addition, BPQ will promote binding to the polypurine-polypyrimidine target sequence by the longer mismatched oligonucleotide, providing significant stabilization of the parallel bulge-containing(Y.R)27,(Y)28 triplex with nearly the same efficiency as the bulge-free (Y.R)27.(Y)28 triplex. Thus in vivo BPQ might enhance the formation of both undesired and desired DNA triplexes. By performing an MPE*FeII probing reaction with a 5'-32 P-labeled oligonucleotide third strand, we have obtained evidence that BPQ is actually bound to the triplex region and may distort in a sequence-specific fashion.
authors.affiliation: Department of Pharmacology, University of Cambridge, England.
authors.forename: C
authors.initials: C
authors.lastname: Marchand
authors.forename: C
authors.initials: C
authors.lastname: Bailly
authors.forename: C H
authors.initials: CH
authors.lastname: Nguyen
authors.forename: E
authors.initials: E
authors.lastname: Bisagni
authors.forename: T
authors.initials: T
authors.lastname: Garestier
authors.forename: C
authors.initials: C
authors.lastname: Hélène
authors.forename: M J
authors.initials: MJ
authors.lastname: Waring
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry* / Q000187:drug effects; D018983:DNA Footprinting; D003850:Deoxyribonuclease I; D007211:Indoles / Q000494:pharmacology; D007364:Intercalating Agents / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D011725:Pyridines / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology*
chemical_list: C099093:11-(((dimethylamino)propyl)amino)-3-methoxy-8-methylbenzo(f)pyrido(4,3-b)quinoxaline; D007211:Indoles; D007364:Intercalating Agents; D011725:Pyridines; D011810:Quinoxalines; C082732:3-methoxy-7H-8-methyl-11-((3'-amino)propylamino)benzo(e)pyrido(4,3-b)indole; D004247:DNA; D003850:Deoxyribonuclease I