Despite efforts to understand the interactions between nanoparticles and cells, the cellular processes that determine the efficiency of intracellular drug delivery remain unclear. Here we examine ...cellular uptake of short interfering RNA (siRNA) delivered in lipid nanoparticles (LNPs) using cellular trafficking probes in combination with automated high-throughput confocal microscopy. We also employed defined perturbations of cellular pathways paired with systems biology approaches to uncover protein-protein and protein-small molecule interactions. We show that multiple cell signaling effectors are required for initial cellular entry of LNPs through macropinocytosis, including proton pumps, mTOR and cathepsins. siRNA delivery is substantially reduced as ≅70% of the internalized siRNA undergoes exocytosis through egress of LNPs from late endosomes/lysosomes. Niemann-Pick type C1 (NPC1) is shown to be an important regulator of the major recycling pathways of LNP-delivered siRNAs. NPC1-deficient cells show enhanced cellular retention of LNPs inside late endosomes and lysosomes, and increased gene silencing of the target gene. Our data suggest that siRNA delivery efficiency might be improved by designing delivery vehicles that can escape the recycling pathways.
Induction of delta aminolevulinic acid synthase 1 ( ALAS1) gene expression and accumulation of neurotoxic intermediates result in neurovisceral attacks and disease manifestations in patients with ...acute intermittent porphyria, a rare inherited disease of heme biosynthesis. Givosiran is an investigational RNA interference therapeutic agent that inhibits hepatic ALAS1 synthesis.
We conducted a phase 1 trial of givosiran in patients with acute intermittent porphyria. In part A of the trial, patients without recent porphyria attacks (i.e., no attacks in the 6 months before baseline) were randomly assigned to receive a single subcutaneous injection of one of five ascending doses of givosiran (0.035, 0.10, 0.35, 1.0, or 2.5 mg per kilogram of body weight) or placebo. In part B, patients without recent attacks were randomly assigned to receive once-monthly injections of one of two doses of givosiran (0.35 or 1.0 mg per kilogram) or placebo (total of two injections 28 days apart). In part C, patients who had recurrent attacks were randomly assigned to receive injections of one of two doses of givosiran (2.5 or 5.0 mg per kilogram) or placebo once monthly (total of four injections) or once quarterly (total of two injections) during a 12-week period, starting on day 0. Safety, pharmacokinetic, pharmacodynamic, and exploratory efficacy outcomes were evaluated.
A total of 23 patients in parts A and B and 17 patients in part C underwent randomization. Common adverse events included nasopharyngitis, abdominal pain, and diarrhea. Serious adverse events occurred in 6 patients who received givosiran in parts A through C combined. In part C, all 6 patients who were assigned to receive once-monthly injections of givosiran had sustained reductions in ALAS1 messenger RNA (mRNA), delta aminolevulinic acid, and porphobilinogen levels to near normal. These reductions were associated with a 79% lower mean annualized attack rate than that observed with placebo (exploratory efficacy end point).
Once-monthly injections of givosiran in patients who had recurrent porphyria attacks resulted in mainly low-grade adverse events, reductions in induced ALAS1 mRNA levels, nearly normalized levels of the neurotoxic intermediates delta aminolevulinic acid and porphobilinogen, and a lower attack rate than that observed with placebo. (Funded by Alnylam Pharmaceuticals; ClinicalTrials.gov number, NCT02452372 .).
Delivery of short interfering RNAs (siRNAs) remains a key challenge in the development of RNA interference (RNAi) therapeutics. A better understanding of the mechanisms of siRNA cellular uptake, ...intracellular transport and endosomal release could critically contribute to the improvement of delivery methods. Here we monitored the uptake of lipid nanoparticles (LNPs) loaded with traceable siRNAs in different cell types in vitro and in mouse liver by quantitative fluorescence imaging and electron microscopy. We found that LNPs enter cells by both constitutive and inducible pathways in a cell type-specific manner using clathrin-mediated endocytosis as well as macropinocytosis. By directly detecting colloidal-gold particles conjugated to siRNAs, we estimated that escape of siRNAs from endosomes into the cytosol occurs at low efficiency (1-2%) and only during a limited window of time when the LNPs reside in a specific compartment sharing early and late endosomal characteristics. Our results provide insights into LNP-mediated siRNA delivery that can guide development of the next generation of delivery systems for RNAi therapeutics.
Primary hyperoxaluria type 1 (PH1), an inherited rare disease of glyoxylate metabolism, arises from mutations in the enzyme alanine-glyoxylate aminotransferase. The resulting deficiency in this ...enzyme leads to abnormally high oxalate production resulting in calcium oxalate crystal formation and deposition in the kidney and many other tissues, with systemic oxalosis and ESRD being a common outcome. Although a small subset of patients manages the disease with vitamin B6 treatments, the only effective treatment for most is a combined liver-kidney transplant, which requires life-long immune suppression and carries significant mortality risk. In this report, we discuss the development of ALN-GO1, an investigational RNA interference (RNAi) therapeutic targeting glycolate oxidase, to deplete the substrate for oxalate synthesis. Subcutaneous administration of ALN-GO1 resulted in potent, dose-dependent, and durable silencing of the mRNA encoding glycolate oxidase and increased serum glycolate concentrations in wild-type mice, rats, and nonhuman primates. ALN-GO1 also increased urinary glycolate concentrations in normal nonhuman primates and in a genetic mouse model of PH1. Notably, ALN-GO1 reduced urinary oxalate concentration up to 50% after a single dose in the genetic mouse model of PH1, and up to 98% after multiple doses in a rat model of hyperoxaluria. These data demonstrate the ability of ALN-GO1 to reduce oxalate production in preclinical models of PH1 across multiple species and provide a clear rationale for clinical trials with this compound.
siRNA therapeutics have promise for the treatment of a wide range of genetic disorders. Motivated by lipoproteins, we report lipopeptide nanoparticles as potent and selective siRNA carriers with a ...wide therapeutic index. Lead material cKK-E12 showed potent silencing effects in mice (ED50 ∼ 0.002 mg/kg), rats (ED50 < 0.01 mg/kg), and nonhuman primates (over 95% silencing at 0.3 mg/kg). Apolipoprotein E plays a significant role in the potency of cKK-E12 both in vitro and in vivo. cKK-E12 was highly selective toward liver parenchymal cell in vivo, with orders of magnitude lower doses needed to silence in hepatocytes compared with endothelial cells and immune cells in different organs. Toxicity studies showed that cKK-E12 was well tolerated in rats at a dose of 1 mg/kg (over 100-fold higher than the ED50). To our knowledge, this is the most efficacious and selective nonviral siRNA delivery system for gene silencing in hepatocytes reported to date.
Significant effort has been applied to discover and develop vehicles which can guide small interfering RNAs (siRNA) through the many barriers guarding the interior of target cells. While studies have ...demonstrated the potential of gene silencing in vivo, improvements in delivery efficacy are required to fulfill the broadest potential of RNA interference therapeutics. Through the combinatorial synthesis and screening of a different class of materials, a formulation has been identified that enables siRNA-directed liver gene silencing in mice at doses below 0.01 mg/kg. This formulation was also shown to specifically inhibit expression of five hepatic genes simultaneously, after a single injection. The potential of this formulation was further validated in nonhuman primates, where high levels of knockdown of the clinically relevant gene transthyretin was observed at doses as low as 0.03 mg/kg. To our knowledge, this formulation facilitates gene silencing at orders-of-magnitude lower doses than required by any previously described siRNA liver delivery system.
The acute hepatic porphyrias are inherited disorders of heme biosynthesis characterized by life-threatening acute neurovisceral attacks. Factors that induce the expression of hepatic 5-aminolevulinic ...acid synthase 1 (ALAS1) result in the accumulation of the neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), which recent studies indicate are primarily responsible for the acute attacks. Current treatment of these attacks involves i.v. administration of hemin, but a faster-acting, more effective, and safer therapy is needed. Here, we describe preclinical studies of liver-directed small interfering RNAs (siRNAs) targeting Alas1 (Alas1-siRNAs) in a mouse model of acute intermittent porphyria, the most common acute hepatic porphyria. A single i.v. dose of Alas1-siRNA prevented the phenobarbital-induced biochemical acute attacks for approximately 2 wk. Injection of Alas1-siRNA during an induced acute attack significantly decreased plasma ALA and PBG levels within 8 h, more rapidly and effectively than a single hemin infusion. Alas1-siRNA was well tolerated and a therapeutic dose did not cause hepatic heme deficiency. These studies provide proof-of-concept for the clinical development of RNA interference therapy for the prevention and treatment of the acute attacks of the acute hepatic porphyrias.
We recently demonstrated that siRNAs conjugated to triantennary N‐acetylgalactosamine (GalNAc) induce robust RNAi‐mediated gene silencing in the liver, owing to uptake mediated by the ...asialoglycoprotein receptor (ASGPR). Novel monovalent GalNAc units, based on a non‐nucleosidic linker, were developed to yield simplified trivalent GalNAc‐conjugated oligonucleotides under solid‐phase synthesis conditions. Synthesis of oligonucleotide conjugates using monovalent GalNAc building blocks required fewer synthetic steps compared to the previously optimized triantennary GalNAc construct. The redesigned trivalent GalNAc ligand maintained optimal valency, spatial orientation, and distance between the sugar moieties for proper recognition by ASGPR. siRNA conjugates were synthesized by sequential covalent attachment of the trivalent GalNAc to the 3′‐end of the sense strand and resulted in a conjugate with in vitro and in vivo potency similar to that of the parent trivalent GalNAc conjugate design.
Sugar goes straight to the liver: An siRNA conjugate bearing three N‐acetylgalactosamine moieties, each sequentially attached by a non‐nucleosidic linker, was recognized by the asialoglycoprotein receptor with high affinity. The resulting liver‐specific delivery of the conjugate for robust RNAi‐mediated gene silencing in vivo shows potential for delivery of oligonucleotide therapeutics into hepatocytes.
Asialoglycoprotein receptor (ASGPR) mediated delivery of triantennary N-acetylgalactosamine (GalNAc) conjugated short interfering RNAs (siRNAs) to hepatocytes is a promising paradigm for RNAi ...therapeutics. Robust and durable gene silencing upon subcutaneous administration at therapeutically acceptable dose levels resulted in the advancement of GalNAc-conjugated oligonucleotide-based drugs into preclinical and clinical developments. To systematically evaluate the effect of display and positioning of the GalNAc moiety within the siRNA duplex on ASGPR binding and RNAi activity, nucleotides carrying monovalent GalNAc were designed. Evaluation of clustered and dispersed incorporation of GalNAc units to the sense (S) strand indicated that sugar proximity is critical for ASGPR recognition, and location of the clustered ligand impacts the intrinsic potency of the siRNA. An array of nucleosidic GalNAc monomers resembling a trivalent ligand at or near the 3′ end of the S strand retained in vitro and in vivo siRNA activity, similar to the parent conjugate design. This work demonstrates the utility of simple, nucleotide-based, cost-effective siRNA–GalNAc conjugation strategies.
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