siRNA modified moiety |
siRNA chemical modification |
Example |
Functions/comments |
Ref. |
Sugar |
2ʹ-O-Me |
ALN-VSP02 (ASC-06), ALN-HBV, ONPATTRO (Patisiran),
ARO-HBV, ALN-HBV02, Atu027 |
Enhancing binding affinity, melting
temperature (Tm), and nuclease stability; reducing immune activation |
(CHIU & RANA, 2003; Weng, Xiao, Zhang, Liang, & Huang,
2019) |
|
2ʹ-O-MOE |
|
This alteration commonly has been employed in the
3ʹ-overhangs of siRNA (employed just in the sense strand); enhancing
melting temperature (Tm) and nuclease stability; reducing immune
activation |
(Behlke, 2008; Jackson et al., 2006) |
|
2ʹ-F |
ALN-HBV, ONPATTRO (Patisiran), ARO-HBV, ALN-HBV02 |
In every
part of both sense and antisense strands can be partially modified, and
there are studies of active siRNAs, which are completely changed with
2ʹF-RNA; enhancing binding affinity, melting temperature (Tm), and
nuclease stability; reducing immune activation |
(Weng et al.,
2019) |
|
2ʹ-O-cyanoethyl |
|
Improving interaction affinity and nuclease
resistance |
(Sekine, 2018) |
|
2ʹ-O-acetalester |
|
Can be employed to develop protected siRNA
molecules |
(Biscans et al., 2015) |
|
2ʹ-esterified units (levulinates) |
|
Can be employed to develop
protected siRNA molecules |
(Khvorova & Watts, 2017) |
|
2ʹ-O-DNP |
|
Improving interaction affinity and resistance to
nucleases while in some cases, somewhat reducing activity |
(Wu et al.,
2016) |
|
4ʹ-S |
|
Enhancing binding affinity and nuclease stability; is
compatible with siRNA activity when placed close to the terminal of
siRNA duplexes |
(Hoshika, Minakawa, Kamiya, Harashima, & Matsuda,
2005; Hoshika et al., 2007) |
|
Simultaneous application of 2ʹ-O-MOE with 4ʹS-RNA and 2ʹ-O-Me |
|
Improving potency and serum stability |
(Dong, Siegwart, & Anderson,
2019) |
|
2ʹF-ANA |
|
Can be tolerated in completely modified sense strands and
partially modified antisense strands siRNA; improving binding affinity
and nuclease resistance |
(Watts, Katolik, Viladoms, & Damha,
2009) |
|
4ʹS-2ʹF-ANA |
|
Does not hinder siRNA activity at different positions
in both strands. 2ʹF-ANA modifications in the sense strand are
synergistic with 4ʹS-2ʹF-ANA in the antisense strand; limited
modifications can be applied following the reduction of interaction
affinity. |
(Watts et al., 2007) |
|
LNA |
|
Improving binding affinity to RNA, which results from
conformational rigidity |
(Vester & Wengel, 2004) |
|
UNA |
|
Reducing binding affinity to RNA |
(Langkjær, Pasternak, &
Wengel, 2009) |
|
tc-DNA |
|
Can improve silencing activity when placed in the overhangs |
(Ittig, Schümperli, & Leumann, 2008) |
|
CeNA |
|
Can improve the potency of siRNA |
(Chernikov, Vlassov, &
Chernolovskaya, 2019) |
|
ANAs |
|
Can increase the potency and duration of silencing activity
when placed at the proper position |
(Chernikov et al.,
2019) |
|
HNAs |
|
Improving the potency of siRNA |
(Fisher et al.,
2009) |
|
Morpholino |
|
Can be employed in the sense strand and on the
overhangs; can suppress silencing activity in the antisense strand; can
eliminate backbone charges |
(P. Kumar et al., 2019) |
Backbone Linkage Modifications |
PS |
ALN-VSP02 (ASC-06), ALN-HBV,
ARO-HBV, ALN-HBV02 |
Enhancing nonspecific protein binding |
(Weng et
al., 2019) |
|
Amide-linked |
|
Enhancing thermodynamic stability and nuclease
resistance of siRNA duplex |
(Dong et al., 2019) |
|
Phosphonoacetate |
|
can eliminate backbone charges via esterification
leading to cellular uptake without transfection reagent |
(Sheehan et
al., 2003) |
|
Phosphorothioate |
|
Can increase potency of siRNA |
(Jahns et al.,
2015) |
|
PNA |
|
Enhancing thermodynamic stability, hydrophobicity, and
nuclease resistance of siRNA duplex; can eliminate backbone charges |
(Nielsen, Egholm, & Buchardt, 1994; Potenza et al.,
2008) |
|
2ʹ,5ʹ-linked |
|
Reducing the potency of siRNA |
(Prakash, Kraynack,
Baker, Swayze, & Bhat, 2006) |
Base Modifications |
5-Me-U |
|
Enhancing siRNA stability and effective
gene silencing by siRNA |
(Terrazas & Kool, 2008) |
|
5-Me-C |
|
Enhancing siRNA stability and effective gene silencing by
siRNA |
(Terrazas & Kool, 2008) |
|
GNA |
ALN-HBV02, ALN-AGT |
Improving thermal stability; enhancing
siRNA stability against snake venom phosphodiesterase; increasing siRNA
potencies |
(Schlegel et al., 2017; Weng et al., 2019) |
|
Diaminopurine |
|
Can improve the strength of A-U base pairs |
(Chiu
& Rana, 2002) |
|
2-thiouracil |
|
Improving binding affinity, potency, and specificity
of siRNA |
(Sipa et al., 2007) |
|
Pseudouracil |
|
Can improve the strength of A-U base pairs |
(Sipa et
al., 2007) |
|
2,4-difluorobenzene |
|
Can be tolerated in specific positions of
siRNA; in some cases, can increase the specificity of siRNA |
(Somoza,
Silverman, Miller, Chelliserrykattil, & Kool, 2008) |
|
2,4-dichlorobenzene |
|
Can be tolerated in specific positions of
siRNA; in some cases, can increase the specificity of siRNA |
(Somoza et
al., 2008) |
Terminal Conjugates |
Inverted abasic end cap |
ARO-HBV, AMG 890,
ARO-ANG3 |
Can improve exonuclease stability; can be used in
biophysical/biochemical studies as a result of biotin or fluorescent
dyes conjugation |
(Weng et al., 2019) |
|
Cholesterol conjugated |
|
Can protect siRNA duplex from HSV-2 after
intravaginal administration |
(Shmushkovich et al., 2018) |
Abbreviation: 2′-O-Me, 2′-methoxy group substitution; 2′-F, 2′-
fluoro substitution; 2ʹ-O-DNP, 2′-O-dinitrophenyl ethers; 2ʹF-ANA, HNAs,
hexitol nucleic acids; 2′-deoxy-2′- fluoroarabinonucleic acids; LNA,
locked nucleic acid; UNA, unlocked nucleic acid; CeNA, cyclohexenyl
nucleic acids; ANAs, altritol nucleic acids; PS, Phosphorothioate; PNA,
peptide nucleic acid; GNA, glycol nucleic acid; 2′-O-MOE,
2′-O-methoxyethyl; tc-DNA, tricyclo-DNA modification |
Abbreviation: 2′-O-Me, 2′-methoxy group substitution; 2′-F, 2′-
fluoro substitution; 2ʹ-O-DNP, 2′-O-dinitrophenyl ethers; 2ʹF-ANA, HNAs,
hexitol nucleic acids; 2′-deoxy-2′- fluoroarabinonucleic acids; LNA,
locked nucleic acid; UNA, unlocked nucleic acid; CeNA, cyclohexenyl
nucleic acids; ANAs, altritol nucleic acids; PS, Phosphorothioate; PNA,
peptide nucleic acid; GNA, glycol nucleic acid; 2′-O-MOE,
2′-O-methoxyethyl; tc-DNA, tricyclo-DNA modification |
Abbreviation: 2′-O-Me, 2′-methoxy group substitution; 2′-F, 2′-
fluoro substitution; 2ʹ-O-DNP, 2′-O-dinitrophenyl ethers; 2ʹF-ANA, HNAs,
hexitol nucleic acids; 2′-deoxy-2′- fluoroarabinonucleic acids; LNA,
locked nucleic acid; UNA, unlocked nucleic acid; CeNA, cyclohexenyl
nucleic acids; ANAs, altritol nucleic acids; PS, Phosphorothioate; PNA,
peptide nucleic acid; GNA, glycol nucleic acid; 2′-O-MOE,
2′-O-methoxyethyl; tc-DNA, tricyclo-DNA modification |
Abbreviation: 2′-O-Me, 2′-methoxy group substitution; 2′-F, 2′-
fluoro substitution; 2ʹ-O-DNP, 2′-O-dinitrophenyl ethers; 2ʹF-ANA, HNAs,
hexitol nucleic acids; 2′-deoxy-2′- fluoroarabinonucleic acids; LNA,
locked nucleic acid; UNA, unlocked nucleic acid; CeNA, cyclohexenyl
nucleic acids; ANAs, altritol nucleic acids; PS, Phosphorothioate; PNA,
peptide nucleic acid; GNA, glycol nucleic acid; 2′-O-MOE,
2′-O-methoxyethyl; tc-DNA, tricyclo-DNA modification |
Abbreviation: 2′-O-Me, 2′-methoxy group substitution; 2′-F, 2′-
fluoro substitution; 2ʹ-O-DNP, 2′-O-dinitrophenyl ethers; 2ʹF-ANA, HNAs,
hexitol nucleic acids; 2′-deoxy-2′- fluoroarabinonucleic acids; LNA,
locked nucleic acid; UNA, unlocked nucleic acid; CeNA, cyclohexenyl
nucleic acids; ANAs, altritol nucleic acids; PS, Phosphorothioate; PNA,
peptide nucleic acid; GNA, glycol nucleic acid; 2′-O-MOE,
2′-O-methoxyethyl; tc-DNA, tricyclo-DNA modification |