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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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Related in: MedlinePlus

Schematic of siRNA nanocarriers. A) Liposomes. B) Polymeric nanoparticles. C) Metallic core nanoparticles. D) Dendrimers. E) Polymeric micelles.
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Figure 4: Schematic of siRNA nanocarriers. A) Liposomes. B) Polymeric nanoparticles. C) Metallic core nanoparticles. D) Dendrimers. E) Polymeric micelles.

Mentions: Loading siRNA cargo into liposomes — vesicles consisting of a phospholid bilayer that circumscribes an inner aqueous compartment — is a prominent strategy for delivery to target cells (Figure 4a). Developed early on in the pursuit of an efficient non-viral delivery approach, these vectors have since been rigorously explored and characterized [59]. Liposomes facilitate efficient internalization of their siRNA cargo via membrane fusion with the host cell [42]. Lipid encapsulation is an attractive delivery approach because of the biocompatibility of the constituents and facile assembly of the complexes, which requires only mixing and incubation of components [35]. In addition, these complexes can be engineered for specific delivery through conjugation of targeting moieties directly to the lipid molecules prior to liposome production. Neutral lipids are highly non-toxic and do not activate an immune response. 1,2-Oleoyl-sn-Glycero-3-phosphocholine (DOPC) and 1,2-Dioleoyl-sn-Glycero-3-phosphoethanolamine (DOPE) are among the most widely used neutral lipids. Simply mixing siRNA with DOPC results in more than 65 percent encapsulation, and these complexes have been shown to bring about siRNA-mediated silencing in cancer cells in vivo [60]. Generally, however, neutral liposomes yield relatively low transfection efficiency. Cationic lipids, such as 1-oleoyl-2-[6-[(7-nitro-2-1,3-benzoxadiazol-4-yl) amino]hexanoyl]-3-trimethylammonium propane (DOTAP), can complex electrostatically with siRNAs and be used to create a more effective liposome as the positively charged lipids provide enhanced cell entry and increased protection against serum enzymes [61]. But incorporation of positive charge to increase transfection efficiency must be carefully balanced against inflammatory effects that the polycations create in vivo, as well as unwanted interaction with negatively charged serum proteins, which can lead to opsonization and clearance of the lipocomplex [62].


Therapeutic siRNA: principles, challenges, and strategies.

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

Schematic of siRNA nanocarriers. A) Liposomes. B) Polymeric nanoparticles. C) Metallic core nanoparticles. D) Dendrimers. E) Polymeric micelles.
© Copyright Policy - open access
Related In: Results  -  Collection

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

Figure 4: Schematic of siRNA nanocarriers. A) Liposomes. B) Polymeric nanoparticles. C) Metallic core nanoparticles. D) Dendrimers. E) Polymeric micelles.
Mentions: Loading siRNA cargo into liposomes — vesicles consisting of a phospholid bilayer that circumscribes an inner aqueous compartment — is a prominent strategy for delivery to target cells (Figure 4a). Developed early on in the pursuit of an efficient non-viral delivery approach, these vectors have since been rigorously explored and characterized [59]. Liposomes facilitate efficient internalization of their siRNA cargo via membrane fusion with the host cell [42]. Lipid encapsulation is an attractive delivery approach because of the biocompatibility of the constituents and facile assembly of the complexes, which requires only mixing and incubation of components [35]. In addition, these complexes can be engineered for specific delivery through conjugation of targeting moieties directly to the lipid molecules prior to liposome production. Neutral lipids are highly non-toxic and do not activate an immune response. 1,2-Oleoyl-sn-Glycero-3-phosphocholine (DOPC) and 1,2-Dioleoyl-sn-Glycero-3-phosphoethanolamine (DOPE) are among the most widely used neutral lipids. Simply mixing siRNA with DOPC results in more than 65 percent encapsulation, and these complexes have been shown to bring about siRNA-mediated silencing in cancer cells in vivo [60]. Generally, however, neutral liposomes yield relatively low transfection efficiency. Cationic lipids, such as 1-oleoyl-2-[6-[(7-nitro-2-1,3-benzoxadiazol-4-yl) amino]hexanoyl]-3-trimethylammonium propane (DOTAP), can complex electrostatically with siRNAs and be used to create a more effective liposome as the positively charged lipids provide enhanced cell entry and increased protection against serum enzymes [61]. But incorporation of positive charge to increase transfection efficiency must be carefully balanced against inflammatory effects that the polycations create in vivo, as well as unwanted interaction with negatively charged serum proteins, which can lead to opsonization and clearance of the lipocomplex [62].

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