ABSTRACT
The opportunity to harness the RNA interference (RNAi) pathway to silence disease-causing genes holds great promise for the development of therapeutics directed against targets that are otherwise not addressable with current medicines. Although there are numerous examples of in vivo silencing of target genes after local delivery of small interfering RNAs (siRNAs), there remain only a few reports of RNAi-mediated silencing in response to systemic delivery of siRNA, and there are no reports of systemic efficacy in non-rodent species. Here we show that siRNAs, when delivered systemically in a liposomal formulation, can silence the disease target apolipoprotein B (ApoB) in non-human primates. APOB-specific siRNAs were encapsulated in stable nucleic acid lipid particles (SNALP) and administered by intravenous injection to cynomolgus monkeys at doses of 1 or 2.5 mg kg(-1). A single siRNA injection resulted in dose-dependent silencing of APOB messenger RNA expression in the liver 48 h after administration, with maximal silencing of >90%. This silencing effect occurred as a result of APOB mRNA cleavage at precisely the site predicted for the RNAi mechanism. Significant reductions in ApoB protein, serum cholesterol and low-density lipoprotein levels were observed as early as 24 h after treatment and lasted for 11 days at the highest siRNA dose, thus demonstrating an immediate, potent and lasting biological effect of siRNA treatment. Our findings show clinically relevant RNAi-mediated gene silencing in non-human primates, supporting RNAi therapeutics as a potential new class of drugs.
Subject(s)
Primates/genetics , RNA Interference/drug effects , RNA, Small Interfering/pharmacology , Animals , Apolipoproteins B/deficiency , Apolipoproteins B/genetics , Apolipoproteins B/metabolism , Phenotype , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Small Interfering/administration & dosage , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolismABSTRACT
A series of novel cationic lipids was designed and synthesized in an effort to understand the importance of the various structural features with respect to transfection efficiency. Particular attention has been paid to the hydrophobic domain and the cationic headgroup. An efficient method of synthesizing asymmetric diether lipids is described, using alkyl chains ranging from C(12) to C(18) and the unsaturated oleyl group. The ternary formulations including the diether lipid 3beta-[N-(N',N'-dimethylaminoethyl)carbamoyl]cholesterol (DC-Chol) and dioleoyl phosphatidylethanolamine (DOPE) were up to 10-fold more efficacious in in vitro assays than the DC-Chol/DOPE control. The shorter and most asymmetric diether lipids performed the best. The chemical nature and basicity of the headgroups have been varied by the coupling of the four naturally occurring amino acids with cationic side chains-arginine, histidine, lysine, and tryptophan. Transfection efficiency was highest for arginine/lysine derivatives, with binary formulations containing the amino acid derivative alone and DOPE proving superior.
