David B. Rozema

Dynamic PolyConjugates for targeted in vivo delivery of siRNA to hepatocytes

Achieving efficient in vivo delivery of siRNA to the appropriate target cell would be a major advance in the use of RNAi in gene function studies and as a therapeutic modality. Hepatocytes, the key parenchymal cells of the liver, are a particularly attractive target cell type for siRNA delivery given their central role in several infectious and metabolic disorders. We have developed a vehicle for the delivery of siRNA to hepatocytes both in vitro and in vivo, which we have named siRNA Dynamic PolyConjugates. Key features of the Dynamic PolyConjugate technology include a membrane-active polymer, the ability to reversibly mask the activity of this polymer until it reaches the acidic environment of endosomes, and the ability to target this modified polymer and its siRNA cargo specifically to hepatocytes in vivo after simple, low-pressure i.v. injection. Using this delivery technology, we demonstrate effective knockdown of two endogenous genes in mouse liver: apolipoprotein B (apoB) and peroxisome proliferator-activated receptor alpha (ppara). Knockdown of apoB resulted in clear phenotypic changes that included a significant reduction in serum cholesterol and increased fat accumulation in the liver, consistent with the known functions of apoB. Knockdown of ppara also resulted in a phenotype consistent with its known function, although with less penetrance than observed in apoB knockdown mice. Analyses of serum liver enzyme and cytokine levels in treated mice indicated that the siRNA Dynamic PolyConjugate was nontoxic and well tolerated.

Hepatocyte-targeted RNAi Therapeutics for the Treatment of Chronic Hepatitis B Virus Infection

RNA interference (RNAi)-based therapeutics have the potential to treat chronic hepatitis B virus (HBV) infection in a fundamentally different manner than current therapies. Using RNAi, it is possible to knock down expression of viral RNAs including the pregenomic RNA from which the replicative intermediates are derived, thus reducing viral load, and the viral proteins that result in disease and impact the immune systems ability to eliminate the virus. We previously described the use of polymer-based Dynamic PolyConjugate (DPC) for the targeted delivery of siRNAs to hepatocytes. Here, we first show in proof-of-concept studies that simple coinjection of a hepatocyte-targeted, N-acetylgalactosamine-conjugated melittin-like peptide (NAG-MLP) with a liver-tropic cholesterol-conjugated siRNA (chol-siRNA) targeting coagulation factor VII (F7) results in efficient F7 knockdown in mice and nonhuman primates without changes in clinical chemistry or induction of cytokines. Using transient and transgenic mouse models of HBV infection, we show that a single coinjection of NAG-MLP with potent chol-siRNAs targeting conserved HBV sequences resulted in multilog repression of viral RNA, proteins, and viral DNA with long duration of effect. These results suggest that coinjection of NAG-MLP and chol-siHBVs holds great promise as a new therapeutic for patients chronically infected with HBV.

Co-Injection of a Targeted, Reversibly Masked Endosomolytic Polymer Dramatically Improves the Efficacy of Cholesterol-Conjugated Small Interfering RNAs In Vivo

Effective in vivo delivery of small interfering (siRNA) has been a major obstacle in the development of RNA interference therapeutics. One of the first attempts to overcome this obstacle utilized intravenous injection of cholesterol-conjugated siRNA (chol-siRNA). Although studies in mice revealed target gene knockdown in the liver, delivery was relatively inefficient, requiring 3 daily injections of 50 mg/kg of chol-siRNA to obtain measurable reduction in gene expression. Here we present a new delivery approach that increases the efficacy of the chol-siRNA over 500-fold and allows over 90% reduction in target gene expression in mice and, for the first time, high levels of gene knockdown in non-human primates. This improved efficacy is achieved by the co-injection of a hepatocyte-targeted and reversibly masked endosomolytic polymer. We show that knockdown is absolutely dependent on the presence of hepatocyte-targeting ligand on the polymer, the cognate hepatocyte receptor, and the cholesterol moiety of the siRNA. Importantly, we provide evidence that this increase in efficacy is not dependent on interactions between the chol-siRNA with the polymer prior to injection or in the bloodstream. The simplicity of the formulation and efficacy of this mode of siRNA delivery should prove beneficial in the use of siRNA as a therapeutic.

siRNA delivery technologies for mammalian systems

Abstract Inhibition of gene expression using the RNA interference (RNAi) pathway is rapidly becoming the method of choice for studying gene function in mammalian cells. However, successful knockdown of the target gene requires efficient delivery of short interfering RNAs (siRNAs). Several technologies have been developed that enable effective delivery of siRNAs to both cells in culture and whole animals. These technologies will allow the use of RNAi to study gene function in mammalian model systems in which classical methods are often limited and costly.

Protease-triggered siRNA delivery vehicles.

The safe and efficacious delivery of membrane impermeable therapeutics requires cytoplasmic access without the toxicity of nonspecific cytoplasmic membrane lysis. We have developed a mechanism for control of cytoplasmic release which utilizes endogenous proteases as a trigger and results in functional delivery of small interfering RNA (siRNA). The delivery approach is based on reversible inhibition of membrane disruptive polymers with protease-sensitive substrates. Proteolytic hydrolysis upon endocytosis restores the membrane destabilizing activity of the polymers thereby allowing cytoplasmic access of the co-delivered siRNA. Protease-sensitive polymer masking reagents derived from polyethylene glycol (PEG), which inhibit membrane interactions, and N-acetylgalactosamine, which targets asialoglycoprotein receptors on hepatocytes, were synthesized and used to formulate masked polymer-siRNA delivery vehicles. The size, charge and stability of the vehicles enable functional delivery of siRNA after subcutaneous administration and, with modification of the targeting ligand, have the potential for extrahepatic targeting.

Phosphorylation-specific status of RNAi triggers in pharmacokinetic and biodistribution analyses

Abstract The RNA interference (RNAi)-based therapeutic ARC-520 for chronic hepatitis B virus (HBV) infection consists of a melittin-derived peptide conjugated to N-acetylgalactosamine for hepatocyte targeting and endosomal escape, and cholesterol-conjugated RNAi triggers, which together result in HBV gene silencing. To characterize the kinetics of RNAi trigger delivery and 5΄-phosphorylation of guide strands correlating with gene knockdown, we employed a peptide-nucleic acid (PNA) hybridization assay. A fluorescent sense strand PNA probe binding to RNAi duplex guide strands was coupled with anion exchange high performance liquid chromatography to quantitate guide strands and metabolites. Compared to PCR- or ELISA-based methods, this assay enables separate quantitation of non-phosphorylated full-length guide strands from 5΄-phosphorylated forms that may associate with RNA-induced silencing complexes (RISC). Biodistribution studies in mice indicated that ARC-520 guide strands predominantly accumulated in liver. 5΄-phosphorylation of guide strands was observed within 5 min after ARC-520 injection, and was detected for at least 4 weeks corresponding to the duration of HBV mRNA silencing. Guide strands detected in RISC by AGO2 immuno-isolation represented 16% of total 5΄-phosphorylated guide strands in liver, correlating with a 2.7 log10 reduction of HBsAg. The PNA method enables pharmacokinetic analysis of RNAi triggers, elucidates potential metabolic processing events and defines pharmacokinetic-pharmacodynamic relationships.

HIF2α targeted RNAi therapeutic inhibits clear cell renal cell carcinoma

Targeted therapy against VEGF and mTOR pathways has been established as the standard-of-care for metastatic clear cell renal cell carcinoma (ccRCC); however, these treatments frequently fail and most patients become refractory requiring subsequent alternative therapeutic options. Therefore, development of innovative and effective treatments is imperative. About 80%–90% of ccRCC tumors express an inactive mutant form of the von Hippel-Lindau protein (pVHL), an E3 ubiquitin ligase that promotes target protein degradation. Strong genetic and experimental evidence supports the correlate that pVHL functional loss leads to the accumulation of the transcription factor hypoxia-inducible factor 2α (HIF2α) and that an overabundance of HIF2α functions as a tumorigenic driver of ccRCC. In this report, we describe an RNAi therapeutic for HIF2α that utilizes a targeting ligand that selectively binds to integrins αvβ3 and αvβ5 frequently overexpressed in ccRCC. We demonstrate that functional delivery of a HIF2α-specific RNAi trigger resulted in HIF2α gene silencing and subsequent tumor growth inhibition and degeneration in an established orthotopic ccRCC xenograft model. Mol Cancer Ther; 17(1); 140–9. ©2017 AACR.

Sa1015 Long Duration of Effect From RNAI Therapeutic to Treat Chronic Hepatitis B Virus Infection Correlates With Persistence of the Phosphorylated Guide Strand

Chronic hepatitis B virus (HBV) infection is a major disease for which there remains an unmet medical need. Current therapies for chronic hepatitis B include reverse transcriptase inhibitors and interferon. These therapies either require life-long administration or have significant side effects and limited efficacy. We have taken a novel approach toward the treatment of chronic hepatitis B by developing an siRNA-based therapeutic. In contrast to current therapies, our approach has the promise of significantly decreasing viral protein load which is primarily responsible for disease progression. In our formulation, liver-tropic cholesterol-conjugated siRNAs against HBV (chol-siHBVs) are co-injected intravenously with a reversibly masked, hepatocyte-targeted melittin-like peptide (NAG-MLP). Co-injection of chol-siHBVs and NAG-MLP results in multi-log repression of viral RNA, proteins and viral DNA with long duration of effect in transient and transgenic mouse models of chronic HBV infection, without toxicity. Using a hybridization/HPLC-based method of detection, we are able to correlate the degree of repression of the virus with the amount of the active form of the siRNA guide strand in the liver. In addition, this form of the guide strand can be detected up to one month after a single administration, correlating with the duration of effect. High efficacy, a long duration of effect and establishment of a robust pharmacokinetic/ pharmacodynamic relationship in the liver suggest co-injection of NAG-MLP and cholsiHBVs holds great promise as a novel therapeutic for chronically HBV infected patients.