Knocking down disease: a progress report on sirna therapeutics

KEY POINTS * The key bottlenecks for small RNA drugs that harness RNA interference (RNAi) for selective gene knockdown _in vivo_ include their delivery across the plasma membrane and their

release from endosomes into the cytosol. * Small interfering RNA (siRNA)-based drugs can now be delivered into the cytosol of hepatocytes to suppress gene expression in the liver. * Recent

siRNA clinical trials show durable and potent gene silencing in the liver, with manageable toxicity for a handful of disease targets. * The most effective strategies for gene knockdown in

the liver use second-generation lipid nanoparticles or GalNAc-conjugated siRNAs that are taken up by the asialoglycoprotein receptor, which is exclusively expressed by hepatocytes. *

Achieving gene knockdown outside the liver is still clinically unproven. The most attractive strategies use topical administration of siRNAs to accessible tissue sites, such as the skin, eye

or mucosa, or use siRNAs that are covalently linked to an RNA aptamer that binds with high affinity to a cell surface receptor selectively expressed on cells being targeted for gene

knockdown. * Methods that are being developed to deliver siRNAs therapeutically may eventually prove to be useful for delivering other nucleic acid therapeutics, including antisense

oligonucleotides, mRNAs for gene expression, or CRISPR–Cas9 (clustered regularly interspaced short palindromic repeats–CRISPR-associated 9) for gene editing. ABSTRACT Small interfering RNAs

(siRNAs), which downregulate gene expression guided by sequence complementarity, can be used therapeutically to block the synthesis of disease-causing proteins. The main obstacle to siRNA

drugs — their delivery into the target cell cytosol — has been overcome to allow suppression of liver gene expression. Here, we review the results of recent clinical trials of siRNA

therapeutics, which show efficient and durable gene knockdown in the liver, with signs of promising clinical outcomes and little toxicity. We also discuss the barriers to more widespread

applications that target tissues besides the liver and the most promising avenues to overcome them. Access through your institution Buy or subscribe This is a preview of subscription

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AND FUTURE DIRECTIONS Article 03 April 2024 RNA INTERFERENCE IN THE ERA OF NUCLEIC ACID THERAPEUTICS Article 26 February 2024 THERAPEUTIC SIRNA: STATE OF THE ART Article Open access 19 June

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ACKNOWLEDGEMENTS This work was supported by the Swedish Research Council (A.W.) and the US National Institutes of Health (NIH) grant CA139444 (to J.L.). AUTHOR INFORMATION AUTHORS AND

AFFILIATIONS * Boston Children's Hospital and Department of Pediatrics, Program in Cellular and Molecular Medicine, Harvard Medical School, Boston, 02115, Massachusetts, USA Anders

Wittrup & Judy Lieberman * Department of Clinical Sciences, Section for Oncology and Pathology, Lund University, 221 85, Lund, Sweden Anders Wittrup Authors * Anders Wittrup View author

publications You can also search for this author inPubMed Google Scholar * Judy Lieberman View author publications You can also search for this author inPubMed Google Scholar CORRESPONDING

AUTHOR Correspondence to Judy Lieberman. ETHICS DECLARATIONS COMPETING INTERESTS J.L. is on the Scientific Advisory Board of Alnylam Pharmaceuticals. A.W. declares no competing interests.

POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR TABLE 1 GLOSSARY * RNA interference (RNAi). An endogenous gene silencing mechanism, present in virtually all eukaryotic

cells, by which short double-stranded RNA molecules induce translational inhibition and/or degradation of mRNAs containing partially complementary sequences. * Gene knockdown An experimental

technique used to reduce gene expression using sequence-specific oligonucleotides, typically by RNA interference (RNAi) or antisense mechanisms. * RNA-induced silencing complex (RISC). The

catalytic effector complex of RNA interference (RNAi)-mediated gene silencing. The RISC is a multiprotein complex that incorporates one strand of a small interfering RNA (siRNA) or microRNA.

* Aptamers Oligonucleotides (DNA or RNA) selected to bind with high affinity to defined structures. * MicroRNAs (miRNAs). Endogenous, ~21-nucleotide-long, imperfectly paired double-stranded

RNA molecules present in both plants and animals that guide the silencing of a multitude of genes bearing partially complementary sequences. * Endosomal escape The process of cytosolic

entry of small interfering RNAs (siRNAs) from a vesicular compartment, following initial endocytosis of the siRNA (and delivery vehicle) into the target cell. RIGHTS AND PERMISSIONS Reprints

and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Wittrup, A., Lieberman, J. Knocking down disease: a progress report on siRNA therapeutics. _Nat Rev Genet_ 16, 543–552 (2015).

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