title: Inhibition of MDR1 expression with altritol-modified siRNAs.
abstract: Altritol-modified nucleic acids (ANAs) support RNA-like A-form structures when included in oligonucleotide duplexes. Thus altritol residues seem suitable as candidates for the chemical modification of siRNAs. Here we report that ANA-modified siRNAs targeting the MDR1 gene can exhibit improved efficacy as compared to unmodified controls. This was particularly true of ANA modifications at or near the 3' end of the sense or antisense strands, while modification at the 5' end of the antisense strand resulted in complete loss of activity. Multiple ANA modifications within the sense strand were also well tolerated. Duplexes with ANA modifications at appropriate positions in both strands were generally more effective than duplexes with one modified and one unmodified strand. Initial evidence suggests that the loss of activity associated with ANA modification of the 5'-antisense strand may be due to reduced phosphorylation at this site by cellular kinases. Treatment of drug resistant cells with MDR1-targeted siRNAs resulted in reduction of P-glycoprotein (Pgp) expression, parallel reduction in MDR1 message levels, increased accumulation of the Pgp substrate rhodamine 123, and reduced resistance to anti-tumor drugs. Interestingly, the duration of action of some of the ANA-modified siRNAs was substantially greater than that of unmodified controls. These observations suggest that altritol modifications may be helpful in developing siRNAs with enhanced pharmacological effectiveness.
authors.affiliation: Department of Pharmacology, School of Medicine, University of North Carolina Chapel Hill NC 27599, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Fisher
authors.forename: Mikhail
authors.initials: M
authors.lastname: Abramov
authors.forename: Arthur
authors.initials: A
authors.lastname: Van Aerschot
authors.forename: Dong
authors.initials: D
authors.lastname: Xu
authors.forename: Rudolph L
authors.initials: RL
authors.lastname: Juliano
authors.forename: Piet
authors.initials: P
authors.lastname: Herdewijn
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D004305:Dose-Response Relationship, Drug; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000737:chemistry* / Q000494:pharmacology; D020112:Rhodamine 123 / Q000032:analysis; D013402:Sugar Alcohols / Q000737:chemistry*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013402:Sugar Alcohols; D020112:Rhodamine 123; C042890:altritol