title: Improving RNA interference in mammalian cells by 4'-thio-modified small interfering RNA (siRNA): effect on siRNA activity and nuclease stability when used in combination with 2'-O-alkyl modifications.
abstract: A systematic structure-activity relationship study of 4'-thioribose containing small interfering RNAs (siRNAs) has led to the identification of highly potent and stable antisense constructs. To enable this optimization effort for both in vitro and in vivo applications, we have significantly improved the yields of 4'-thioribonucleosides by using a chirally pure (R)-sulfoxide precursor. siRNA duplexes containing strategically placed regions of 4'-thio-RNA were synthesized and evaluated for RNA interference activity and plasma stability. Stretches of 4'-thio-RNA were well tolerated in both the antisense and sense strands. However, optimization of both the number and placement of 4'-thioribonucleosides was necessary for maximal potency. These optimized siRNAs were generally equipotent or superior to native siRNAs and exhibited increased thermal and plasma stability. Furthermore, significant improvements in siRNA activity and plasma stability were achieved by judicious combination of 4'-thioribose with 2'-O-methyl and 2'-O-methoxyethyl modifications. These optimized 4'-thio-siRNAs may be valuable for developing stable siRNAs for therapeutic applications.
authors.affiliation: Department of Medicinal Chemistry and Antisense Core Research, Isis Pharmaceuticals Inc., Carlsbad, California 92008, USA.
authors.forename: Prasad
authors.initials: P
authors.lastname: Dande
authors.forename: Thazha P
authors.initials: TP
authors.lastname: Prakash
authors.forename: Namir
authors.initials: N
authors.lastname: Sioufi
authors.forename: Hans
authors.initials: H
authors.lastname: Gaus
authors.forename: Russell
authors.initials: R
authors.lastname: Jarres
authors.forename: Andreas
authors.initials: A
authors.lastname: Berdeja
authors.forename: Eric E
authors.initials: EE
authors.lastname: Swayze
authors.forename: Richard H
authors.initials: RH
authors.lastname: Griffey
authors.forename: Balkrishen
authors.initials: B
authors.lastname: Bhat
mesh_terms: D000818:Animals; D004355:Drug Stability; D006367:HeLa Cells; D006361:Heating; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009943:Organophosphorus Compounds / Q000138:chemical synthesis / Q000737:chemistry; D051059:PTEN Phosphohydrolase / Q000096:biosynthesis / Q000235:genetics; D010949:Plasma; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D012260:Ribonucleases / Q000097:blood*; D012266:Ribose / Q000737:chemistry; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013454:Sulfoxides / Q000737:chemistry; D013872:Thionucleosides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D009943:Organophosphorus Compounds; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013454:Sulfoxides; D013872:Thionucleosides; C434331:phosphoramidite; D012266:Ribose; D012260:Ribonucleases; D051059:PTEN Phosphohydrolase