title: Polyamine effects on purine-purine-pyrimidine triple helix formation by phosphodiester and phosphorothioate oligodeoxyribonucleotides.
abstract: Utilization of oligodeoxyribonucleotides to inhibit specific gene transcription in vivo (antigene strategy) requires the efficient formation of triple helices under physiological conditions. However, pyrimidine-motif triplexes are not favored at physiological pH, and physiological concentrations of potassium cations hamper purine-motif triplex formation. Here we investigated the effects of polyamines on promoting triplex formation by G/T-rich oligodeoxyribonucleotides containing either phosphodiester or a diastereomeric mixture of phosphorothioate linkages. Compared with Mg2+, equimolar concentrations of polyamines greatly facilitated purine-motif triplex formation with the following order of effectiveness: spermine > spermidine > putrescine. At low polyamine concentrations, phosphorothioate oligonucleotides were better at triplex formation than the corresponding phosphodiester oligonucleotides. Kinetic studies indicated that polyamines facilitated triplex formation by increasing the rate of oligonucleotide-duplex DNA association. However, triplex accumulation with either oligonucleotide was still low under physiological conditions (140 mM K+, 10 mM Mg2+, 1 mM spermine). The inhibitory effects of K+ could be partially overcome with high concentrations of Mg2+ or spermine, with phosphodiester oligonucleotides being better able to form triplexes than phosphorothioates under these conditions.
authors.affiliation: Department of Tumor Biology, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: M
authors.initials: M
authors.lastname: Musso
authors.forename: M W
authors.initials: MW
authors.lastname: Van Dyke
mesh_terms: D001483:Base Sequence; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D010755:Organophosphates / Q000737:chemistry; D011073:Polyamines / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011687:Purines / Q000737:chemistry*; D011700:Putrescine / Q000494:pharmacology; D011743:Pyrimidines / Q000737:chemistry*; D013095:Spermidine / Q000494:pharmacology; D013096:Spermine / Q000494:pharmacology; D013873:Thionucleotides / Q000737:chemistry
chemical_list: D009838:Oligodeoxyribonucleotides; D010755:Organophosphates; D011073:Polyamines; D011687:Purines; D011743:Pyrimidines; D013873:Thionucleotides; D013096:Spermine; D008274:Magnesium; D011188:Potassium; D013095:Spermidine; D011700:Putrescine