title: Increased potency of an aptameric G-rich oligonucleotide is associated with novel functional properties of phosphorothioate linkages.
abstract: We previously showed that inhibition of the expression of CD28 (an essential immune receptor on T cells) mediated by a phosphorothioate (PS)-modified aptameric oligodeoxynucleotide (ODN) sequence, GR1, resulted in reduced T cell responses in vitro and in vivo. Using GR1 sequences differing only in the amount of terminal PS linkages (chimeric SO-ODN), the present study demonstrated that even after a substantial reduction in PS linkages, this 18-mer ODN sequence could still confer functionality in the ODN-mediated inhibition of CD28 expression. We showed that secondary structure and full retention of the ability to form a specific protein-ODN complex and to increase cellular uptake in activated Jurkat T cells were critical parameters in the determination of the magnitude of bioactivity of chimeric SO-ODN. We report that a chimeric SO-ODN with terminal PS linkages that total 9 (ICN 17221) or 12 (ICN 17263) was sufficient to inhibit CD28 expression and suppress in vivo inflammatory ear responses to contact allergen in mice with similar potency to the 17-thioate S-ODN (ICN 16064). Interestingly, all chimeric SO-ODN showed similar in vitro nuclease resistance. These data suggest alternate functional properties for PS linkages, unrelated to nuclease resistance, in enhancing the bioactivity of a G-rich aptamer.
authors.affiliation: Immunology Laboratory, ICN Research Center, Costa Mesa, CA 92626, USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Tam
authors.forename: S
authors.initials: S
authors.lastname: Wu-Pong
authors.forename: B
authors.initials: B
authors.lastname: Pai
authors.forename: C
authors.initials: C
authors.lastname: Lim
authors.forename: A
authors.initials: A
authors.lastname: Chan
authors.forename: D F
authors.initials: DF
authors.lastname: Thomas
authors.forename: T
authors.initials: T
authors.lastname: Milovanovic
authors.forename: J
authors.initials: J
authors.lastname: Bard
authors.forename: P J
authors.initials: PJ
authors.lastname: Middleton
mesh_terms: D000818:Animals; D018106:CD28 Antigens / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D006147:Guanine / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D013816:Thermodynamics; D013873:Thionucleotides / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018106:CD28 Antigens; D009841:Oligonucleotides; D013873:Thionucleotides; D006147:Guanine