The siRNA sequence and guide strand overhangs are determinants of in vivo duration of silencing.
The use of short interfering RNAs (siRNA) in animals for target validation or as potential therapeutics is hindered by the short physical half-life when delivered as unencapsulated material and in turn the short active half-life of siRNAs in vivo. Here we demonstrate that the character of the two 3'-overhang nucleotides of the guide strand of siRNAs is a determinant of the duration of silencing by siRNAs both in vivo and in tissue culture cells. We demonstrate that deoxyribonucleotides in the guide strand overhang of siRNAs have a negative impact on maintenance of both the in vitro and in vivo activity of siRNAs over time. Overhangs that contain ribonucleotides or 2'-O-methyl modified nucleotides do not demonstrate this same impairment. We also demonstrate that the sequence of an siRNA is a determinant of the duration of silencing of siRNAs directed against the same target even when those siRNAs have equivalent activities in vitro. Our experiments have determined that a measurable duration parameter exists, distinct from both maximum silencing ability and the potency of siRNAs. Our findings provide information on incorporating chemically modified nucleotides into siRNAs for potent, durable therapeutics and also inform on methods used to select siRNAs for therapeutic and research purposes.
Strapps
Walter R
WR
Sirna Therapeutics Inc., A Wholly Owned Subsidiary of Merck & Co., Inc., San Francisco, CA 94158, USA. walter_strapps@merck.com
Pickering
Victoria
V
Muiru
Gladys T
GT
Rice
Julie
J
Orsborn
Stacey
S
Polisky
Barry A
BA
Sachs
Alan
A
Bartz
Steven R
SR
D000818:Animals; D045744:Cell Line, Tumor; D016207:Cytokines / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000737:chemistry*; D058727:RNA, Small Untranslated
D016207:Cytokines; D034741:RNA, Small Interfering; D058727:RNA, Small Untranslated