1. ¹Alnylam Pharmaceuticals, Inc., Cambridge, Massachusetts, USA
2. ²Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
3. ³Roche Kulmbach GmbH, Kulmbach, Germany
4. ⁴David H. Koch Institute of Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Correspondence: Akin Akinc, Alnylam Pharmaceuticals, Inc., 300 Third Street, Cambridge, Massachusetts 02142, USA. E-mail: aakinc@alnylam.com or; Daniel G Anderson, David H. Koch Institute of Integrative Cancer Research, Massachusetts Institute of Technology, 45 Carleton Street, Building E25-342, Cambridge, Massachusetts 02142, USA. E-mail: dgander@mit.edu

Received 5 December 2008; Accepted 6 February 2009; Published online 3 March 2009.

Abstract

RNA interference therapeutics afford the potential to silence target gene expression specifically, thereby blocking production of disease-causing proteins. The development of safe and effective systemic small interfering RNA (siRNA) delivery systems is of central importance to the therapeutic application of siRNA. Lipid and lipid-like materials are currently the most well-studied siRNA delivery systems for liver delivery, having been utilized in several animal models, including nonhuman primates. Here, we describe the development of a multicomponent, systemic siRNA delivery system, based on the novel lipid-like material 98N₁₂-5(1). We show that in vivo delivery efficacy is affected by many parameters, including the formulation composition, nature of particle PEGylation, degree of drug loading, and biophysical parameters such as particle size. In particular, small changes in the anchor chain length of poly(ethylene glycol) (PEG) lipids can result in significant effects on in vivo efficacy. The lead formulation developed is liver targeted (>90% injected dose distributes to liver) and can induce fully reversible, long-duration gene silencing without loss of activity following repeat administration.