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Therapeutic siRNA: principles, challenges, and strategies.

Gavrilov K, Saltzman WM - Yale J Biol Med (2012)

Bottom Line: The major barrier to realizing the full medicinal potential of RNAi is the difficulty of delivering effector molecules, such as small interfering RNAs (siRNAs), in vivo.An effective delivery strategy for siRNAs must address limitations that include poor stability and non-targeted biodistribution, while protecting against the stimulation of an undesirable innate immune response.This article reviews the mechanistic principles of RNA interference, its potential, the greatest challenges for use in biomedical applications, and some of the work that has been done toward engineering delivery systems that overcome some of the hurdles facing siRNA-based therapeutics.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA. kseniya.gavrilov@yale.edu

ABSTRACT
RNA interference (RNAi) is a remarkable endogenous regulatory pathway that can bring about sequence-specific gene silencing. If harnessed effectively, RNAi could result in a potent targeted therapeutic modality with applications ranging from viral diseases to cancer. The major barrier to realizing the full medicinal potential of RNAi is the difficulty of delivering effector molecules, such as small interfering RNAs (siRNAs), in vivo. An effective delivery strategy for siRNAs must address limitations that include poor stability and non-targeted biodistribution, while protecting against the stimulation of an undesirable innate immune response. The design of such a system requires rigorous understanding of all mechanisms involved. This article reviews the mechanistic principles of RNA interference, its potential, the greatest challenges for use in biomedical applications, and some of the work that has been done toward engineering delivery systems that overcome some of the hurdles facing siRNA-based therapeutics.

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A) Common chemical modifications to siRNA sugars and backbone. B) Chemical modifications to nucleobases.
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Figure 3: A) Common chemical modifications to siRNA sugars and backbone. B) Chemical modifications to nucleobases.

Mentions: Chemical modifications can significantly enhance the stability and uptake of naked siRNAs [43]. Importantly, siRNAs can be directly modified without crippling their ability to silence their targets [43]. Chemical modifications have been rigorously investigated for virtually every part of siRNA molecules, from the termini and backbone to the sugars and bases, with the goal of engineering siRNA with prolonged half-life and increased cellular uptake. Most commonly, the sugar moiety is modified. For example, the incorporation of a 2’-fluoro (2’-F) [44], 2’-O-methyl [45], 2’-halogen, 2’-amine [46], or 2’-deoxy [47] can significantly increase the stability of siRNA in serum, as can the bridging of the sugar’s 2’- and 4’-positions with a –O-CH2 linker (producing what is called a “locked nucleic acid” or LNA) (Figure 3a) [48]. Among these, only the 2’-F can be introduced through endogenous transcription as opposed to chemical synthesis. Another caveat is that when the sugars of both strands of an siRNA duplex are replaced with 2’-O-methyl moieties, the duplex loses its silencing ability. However, 2’-O-methyl modification of only the sense strand leaves silencing activity intact as long as certain positions in the “seed” region of the sense strand are not modified [49]. Also, recent studies have shown that while heavy modification of siRNA duplexes with LNAs prolongs half-life in serum to as much as 90 hours, this is not without adverse affects on the gene-silencing activity, suggesting that the natural RNAi machinery can only accommodate moderate alterations of the chemical structure of siRNAs [50].


Therapeutic siRNA: principles, challenges, and strategies.

Gavrilov K, Saltzman WM - Yale J Biol Med (2012)

A) Common chemical modifications to siRNA sugars and backbone. B) Chemical modifications to nucleobases.
© Copyright Policy - open access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3375670&req=5

Figure 3: A) Common chemical modifications to siRNA sugars and backbone. B) Chemical modifications to nucleobases.
Mentions: Chemical modifications can significantly enhance the stability and uptake of naked siRNAs [43]. Importantly, siRNAs can be directly modified without crippling their ability to silence their targets [43]. Chemical modifications have been rigorously investigated for virtually every part of siRNA molecules, from the termini and backbone to the sugars and bases, with the goal of engineering siRNA with prolonged half-life and increased cellular uptake. Most commonly, the sugar moiety is modified. For example, the incorporation of a 2’-fluoro (2’-F) [44], 2’-O-methyl [45], 2’-halogen, 2’-amine [46], or 2’-deoxy [47] can significantly increase the stability of siRNA in serum, as can the bridging of the sugar’s 2’- and 4’-positions with a –O-CH2 linker (producing what is called a “locked nucleic acid” or LNA) (Figure 3a) [48]. Among these, only the 2’-F can be introduced through endogenous transcription as opposed to chemical synthesis. Another caveat is that when the sugars of both strands of an siRNA duplex are replaced with 2’-O-methyl moieties, the duplex loses its silencing ability. However, 2’-O-methyl modification of only the sense strand leaves silencing activity intact as long as certain positions in the “seed” region of the sense strand are not modified [49]. Also, recent studies have shown that while heavy modification of siRNA duplexes with LNAs prolongs half-life in serum to as much as 90 hours, this is not without adverse affects on the gene-silencing activity, suggesting that the natural RNAi machinery can only accommodate moderate alterations of the chemical structure of siRNAs [50].

Bottom Line: The major barrier to realizing the full medicinal potential of RNAi is the difficulty of delivering effector molecules, such as small interfering RNAs (siRNAs), in vivo.An effective delivery strategy for siRNAs must address limitations that include poor stability and non-targeted biodistribution, while protecting against the stimulation of an undesirable innate immune response.This article reviews the mechanistic principles of RNA interference, its potential, the greatest challenges for use in biomedical applications, and some of the work that has been done toward engineering delivery systems that overcome some of the hurdles facing siRNA-based therapeutics.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA. kseniya.gavrilov@yale.edu

ABSTRACT
RNA interference (RNAi) is a remarkable endogenous regulatory pathway that can bring about sequence-specific gene silencing. If harnessed effectively, RNAi could result in a potent targeted therapeutic modality with applications ranging from viral diseases to cancer. The major barrier to realizing the full medicinal potential of RNAi is the difficulty of delivering effector molecules, such as small interfering RNAs (siRNAs), in vivo. An effective delivery strategy for siRNAs must address limitations that include poor stability and non-targeted biodistribution, while protecting against the stimulation of an undesirable innate immune response. The design of such a system requires rigorous understanding of all mechanisms involved. This article reviews the mechanistic principles of RNA interference, its potential, the greatest challenges for use in biomedical applications, and some of the work that has been done toward engineering delivery systems that overcome some of the hurdles facing siRNA-based therapeutics.

Show MeSH
Related in: MedlinePlus