siRNA Design
RNAsDashboard

Chemistry

The evolution of chemical modifications that turned siRNA into a stable, potent and well-tolerated drug modality.

Evolution

  1. Endo-light
  2. STC (standard template chemistry)
  3. ESC (enhanced stabilization chemistry) Nair, J. K. et al. Impact of enhanced metabolic stability on pharmacokinetics and pharmacodynamics of GalNAc–siRNA conjugates. Nucleic Acids Res. 45, 10969–10977 (2017).
  4. Advanced ESC (Ikaria) Foster, D. J. et al. Advanced siRNA designs further improve in vivo performance of GalNAc–siRNA conjugates. Mol. Ther. 26, 708–717 (2018).
  5. ESC+ (enhanced stabilization chemistry plus)
  6. Targeted RNAi molecule (TRiM)
  7. GalXC DICER substrate
  8. Self-delivering, asymmetric siRNA (sd-rxRNA)

Key findings

  • Selective incorporation of 2′-OMe suppresses immunostimulatory activity of siRNAs Judge, A. D., Bola, G., Lee, A. C. & MacLachlan, I. Design of noninflammatory synthetic siRNA mediating potent gene silencing in vivo. Mol. Ther. 13, 494–505 (2006).
  • Fully chemically modified siRNA can still retain activity with improved stability Allerson, C. R. et al. Fully 2′-modified oligonucleotide duplexes with improved in vitro potency and stability compared to unmodified small interfering RNA. J. Med. Chem. 48, 901–904 (2005). Morrissey, D. V. et al. Activity of stabilized short interfering RNA in a mouse model of hepatitis B virus replication. Hepatology 41, 1349–1356 (2005).
  • ALN-TTR02 (patisiran) uses an endo-light design formulated in MC3-containing 2nd-gen LNPs, approved in 2018 for the treatment of hATTR amyloidosis with polyneuropathy Coelho, T. et al. Safety and efficacy of RNAi therapy for transthyretin amyloidosis. N. Engl. J. Med. 369, 819–829 (2013). Adams, D. et al. Patisiran, an RNAi therapeutic, for hereditary transthyretin amyloidosis. N. Engl. J. Med. 379, 11–21 (2018).
  • Revusiran & vutrisiran share the same sequence but differ in chemical modifications. Revusiran required 28,000 mg cumulative annual dosing vs vutrisiran's annual dosing of 100 mg (280-fold lower) at quarterly dosing of 25 mg.
  • Thermally destabilizing modifications, e.g. glycol nucleic acid (GNA) in the seed position, improve specificity by reducing seed-mediated off-target effects Janas, M. M. et al. Selection of GalNAc-conjugated siRNAs with limited off-target-driven rat hepatotoxicity. Nat. Commun. 9, 723 (2018).
  • 5′-phosphate analog (5′-(E)-vinylphosphonate) enhances RISC loading Prakash, T. P. et al. Identification of metabolically stable 5′-phosphate analogs that support single-stranded siRNA activity. Nucleic Acids Res. 43, 2993–3011 (2015). Parmar, R. et al. 5′-(E)-Vinylphosphonate: a stable phosphate mimic can improve the RNAi activity of siRNA-GalNAc conjugates. ChemBioChem 17, 985–989 (2016).

Building blocks

Browse the modification building blocks used across these designs: bases and sugars.