Lloyd Jeffs

RNAi-mediated gene silencing in non-human primates.

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.

Potent and persistent in vivo anti-HBV activity of chemically modified siRNAs

The efficacy of lipid-encapsulated, chemically modified short interfering RNA (siRNA) targeted to hepatitis B virus (HBV) was examined in an in vivo mouse model of HBV replication. Stabilized siRNA targeted to the HBV RNA was incorporated into a specialized liposome to form a stable nucleic-acid-lipid particle (SNALP) and administered by intravenous injection into mice carrying replicating HBV. The improved efficacy of siRNA-SNALP compared to unformulated siRNA correlates with a longer half-life in plasma and liver. Three daily intravenous injections of 3 mg/kg/day reduced serum HBV DNA >1.0 log10. The reduction in HBV DNA was specific, dose-dependent and lasted for up to 7 d after dosing. Furthermore, reductions were seen in serum HBV DNA for up to 6 weeks with weekly dosing. The advances demonstrated here, including persistence of in vivo activity, use of lower doses and reduced dosing frequency are important steps in making siRNA a clinically viable therapeutic approach.

Rational design of cationic lipids for siRNA delivery

We adopted a rational approach to design cationic lipids for use in formulations to deliver small interfering RNA (siRNA). Starting with the ionizable cationic lipid 1,2-dilinoleyloxy-3-dimethylaminopropane (DLinDMA), a key lipid component of stable nucleic acid lipid particles (SNALP) as a benchmark, we used the proposed in vivo mechanism of action of ionizable cationic lipids to guide the design of DLinDMA-based lipids with superior delivery capacity. The best-performing lipid recovered after screening (DLin-KC2-DMA) was formulated and characterized in SNALP and demonstrated to have in vivo activity at siRNA doses as low as 0.01 mg/kg in rodents and 0.1 mg/kg in nonhuman primates. To our knowledge, this represents a substantial improvement over previous reports of in vivo endogenous hepatic gene silencing.

Postexposure Protection of Guinea Pigs against a Lethal Ebola Virus Challenge Is Conferred by RNA Interference

Abstract BackgroundEbola virus (EBOV) infection causes a frequently fatal hemorrhagic fever (HF) that is refractory to treatment with currently available antiviral therapeutics. RNA interference represents a powerful, naturally occurring biological strategy for the inhibition of gene expression and has demonstrated utility in the inhibition of viral replication. Here, we describe the development of a potential therapy for EBOV infection that is based on small interfering RNAs (siRNAs) MethodsFour siRNAs targeting the polymerase (L) gene of the Zaire species of EBOV (ZEBOV) were either complexed with polyethylenimine (PEI) or formulated in stable nucleic acid–lipid particles (SNALPs). Guinea pigs were treated with these siRNAs either before or after lethal ZEBOV challenge ResultsTreatment of guinea pigs with a pool of the L gene–specific siRNAs delivered by PEI polyplexes reduced plasma viremia levels and partially protected the animals from death when administered shortly before the ZEBOV challenge. Evaluation of the same pool of siRNAs delivered using SNALPs proved that this system was more efficacious, as it completely protected guinea pigs against viremia and death when administered shortly after the ZEBOV challenge. Additional experiments showed that 1 of the 4 siRNAs alone could completely protect guinea pigs from a lethal ZEBOV challenge ConclusionsFurther development of this technology has the potential to yield effective treatments for EBOV HF as well as for diseases caused by other agents that are considered to be biological threats

A Scalable, Extrusion-Free Method for Efficient Liposomal Encapsulation of Plasmid DNA

No HeadingPurpose.A fully scalable and extrusion-free method was developed to prepare rapidly and reproducibly stabilized plasmid lipid particles (SPLP) for nonviral, systemic gene therapy.Methods.Liposomes encapsulating plasmid DNA were formed instantaneously by mixing lipids dissolved in ethanol with an aqueous solution of DNA in a controlled, stepwise manner. Combining DNA-buffer and lipid-ethanol flow streams in a T-shaped mixing chamber resulted in instantaneous dilution of ethanol below the concentration required to support lipid solubility. The resulting DNA-containing liposomes were further stabilized by a second stepwise dilution.Results.Using this method, monodisperse vesicles were prepared with particle sizes less than 200 nm and DNA encapsulation efficiencies greater than 80%. In mice possessing Neuro 2a tumors, SPLP demonstrated a 13 h circulation half-life in vivo, good tumor accumulation and gene expression profiles similar to SPLP previously prepared by detergent dialysis. Cryo transmission electron microscopy analysis showed that SPLP prepared by stepwise ethanol dilution were a mixed population of unilamellar, bilamellar, and oligolamellar vesicles. Vesicles of similar lipid composition, prepared without DNA, were also <200 nm but were predominantly bilamellar with unusual elongate d morphologies, suggesting that the plasmid particle affects the morphology of the encapsulating liposome. A similar approach was used to prepare neutral egg phosphatidylcholine:cholesterol (EPC:Chol) liposomes possessing a pH gradient, which was confirmed by the uptake of the lipophilic cation safranin O.Conclusions.This new method will enable the scale-up and manufacture of SPLP required for preclinical and clinical studies. Additionally, this method now allows for the acceleration of SPLP formulation development, enabling the rapid development and evaluation of novel carrier systems.

Abstract B204: Development of ALN‐VSP: An RNAi therapeutic for liver malignancies

Malignancies of the liver, including primary (hepatocellular carcinoma) and secondary (metastatic) tumors, represent a significant unmet medical need. We are developing a therapeutic for solid tumors involving the liver that is comprised of lipid particle‐formulated small interfering RNAs (siRNAs) targeting VEGF and the mitotic kinesin, KSP (Eg5). For each target, potent siRNA duplexes were selected following extensive screening in tissue culture cells. To assess efficacy in vivo , a stable nucleic acid lipid particle (SNALP) formulation was developed based on similar formulations previously shown to silence liver‐expressed genes via systemic administration in multiple species. A SNALP‐formulated combination of the KSP and VEGF siRNAs (referred to as ALN‐VSP) was tested in orthotopic liver tumor models in which human tumor cells are implanted directly into the livers of immunocompromised mice. We show that intravenous administration of ALN‐VSP leads to silencing of both KSP and VEGF expression in established liver tumors. This is accompanied by the formation of numerous aberrant mitotic figures (“monoasters”) in tumor cells indicative of the pharmacologic inhibition of KSP. In addition, we demonstrate that ALN‐VSP treatment provides a clear survival benefit even when treatment is initiated in animals with a significant tumor burden. A Phase 1 clinical trial of ALN‐VSP has recently been initiated. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B204.