Diverse lipid conjugates for functional extra-hepatic siRNA delivery in vivo.

Small interfering RNA (siRNA)-based therapies are proving to be efficient for treating liver-associated disorders. However, extra-hepatic delivery remains challenging, limiting therapeutic siRNA utility. We synthesized a panel of fifteen lipid-conjugated siRNAs and systematically evaluated the impact of conjugate on siRNA tissue distribution and efficacy. Generally, conjugate hydrophobicity defines the degree of clearance and the liver-to-kidney distribution profile. In addition to primary clearance tissues, several conjugates achieve significant siRNA accumulation in muscle, lung, heart, adrenal glands and fat. Oligonucleotide distribution to extra-hepatic tissues with some conjugates was significantly higher than with cholesterol, a well studied conjugate, suggesting that altering conjugate structure can enhance extra-hepatic delivery. These conjugated siRNAs enable functional gene silencing in lung, muscle, fat, heart and adrenal gland. Required levels for productive silencing vary (5-200 µg/g) per tissue, suggesting that the chemical nature of conjugates impacts tissue-dependent cellular/intracellular trafficking mechanisms. The collection of conjugated siRNA described here enables functional gene modulation in vivo in several extra-hepatic tissues opening these tissues for gene expression modulation. A systemic evaluation of a panel of conjugated siRNA, as reported here, has not previously been investigated and shows that chemical engineering of lipid siRNAs is essential to advance the RNA therapeutic field.

Hydrophobicity drives the systemic distribution of lipid-conjugated siRNAs via lipid transport pathways.

Efficient delivery of therapeutic RNA beyond the liver is the fundamental obstacle preventing its clinical utility. Lipid conjugation increases plasma half-life and enhances tissue accumulation and cellular uptake of small interfering RNAs (siRNAs). However, the mechanism relating lipid hydrophobicity, structure, and siRNA pharmacokinetics is unclear. Here, using a diverse panel of biologically occurring lipids, we show that lipid conjugation directly modulates siRNA hydrophobicity. When administered in vivo, highly hydrophobic lipid-siRNAs preferentially and spontaneously associate with circulating low-density lipoprotein (LDL), while less lipophilic lipid-siRNAs bind to high-density lipoprotein (HDL). Lipid-siRNAs are targeted to lipoprotein receptor-enriched tissues, eliciting significant mRNA silencing in liver (65%), adrenal gland (37%), ovary (35%), and kidney (78%). Interestingly, siRNA internalization may not be completely driven by lipoprotein endocytosis, but the extent of siRNA phosphorothioate modifications may also be a factor. Although biomimetic lipoprotein nanoparticles have been explored for the enhancement of siRNA delivery, our findings suggest that hydrophobic modifications can be leveraged to incorporate therapeutic siRNA into endogenous lipid transport pathways without the requirement for synthetic formulation.

Comparison of partially and fully chemically-modified siRNA in conjugate-mediated delivery in vivo.

Small interfering RNA (siRNA)-based drugs require chemical modifications or formulation to promote stability, minimize innate immunity, and enable delivery to target tissues. Partially modified siRNAs (up to 70% of the nucleotides) provide significant stabilization in vitro and are commercially available; thus are commonly used to evaluate efficacy of bio-conjugates for in vivo delivery. In contrast, most clinically-advanced non-formulated compounds, using conjugation as a delivery strategy, are fully chemically modified (100% of nucleotides). Here, we compare partially and fully chemically modified siRNAs in conjugate mediated delivery. We show that fully modified siRNAs are retained at 100x greater levels in various tissues, independently of the nature of the conjugate or siRNA sequence, and support productive mRNA silencing. Thus, fully chemically stabilized siRNAs may provide a better platform to identify novel moieties (peptides, aptamers, small molecules) for targeted RNAi delivery.

Extracellular vesicles from mice with alcoholic liver disease carry a distinct protein cargo and induce macrophage activation through heat shock protein 90.

A salient feature of alcoholic liver disease (ALD) is Kupffer cell (KC) activation and recruitment of inflammatory monocytes and macrophages (MØs). These key cellular events of ALD pathogenesis may be mediated by extracellular vesicles (EVs). EVs transfer biomaterials, including proteins and microRNAs, and have recently emerged as important effectors of intercellular communication. We hypothesized that circulating EVs from mice with ALD have a protein cargo characteristic of the disease and mediate biological effects by activating immune cells. The total number of circulating EVs was increased in mice with ALD compared to pair-fed controls. Mass spectrometric analysis of circulating EVs revealed a distinct signature for proteins involved in inflammatory responses, cellular development, and cellular movement between ALD EVs and control EVs. We also identified uniquely important proteins in ALD EVs that were not present in control EVs. When ALD EVs were injected intravenously into alcohol-naive mice, we found evidence of uptake of ALD EVs in recipient livers in hepatocytes and MØs. Hepatocytes isolated from mice after transfer of ALD EVs, but not control EVs, showed increased monocyte chemoattractant protein 1 mRNA and protein expression, suggesting a biological effect of ALD EVs. Compared to control EV recipient mice, ALD EV recipient mice had increased numbers of F4/80hi cluster of differentiation 11b (CD11b)lo KCs and increased percentages of tumor necrosis factor alpha-positive/interleukin 12/23-positive (inflammatory/M1) KCs and infiltrating monocytes (F4/80int CD11bhi ), while the percentage of CD206+ CD163+ (anti-inflammatory/M2) KCs was decreased. In vitro, ALD EVs increased tumor necrosis factor alpha and interleukin-1ß production in MØs and reduced CD163 and CD206 expression. We identified heat shock protein 90 in ALD EVs as the mediator of ALD-EV-induced MØ activation. CONCLUSION: Our study indicates a specific protein signature of ALD EVs and demonstrates a functional role of circulating EVs containing heat shock protein 90 in mediating KC/MØ activation in the liver. (Hepatology 2018;67:1986-2000).

Hydrophobicity of Lipid-Conjugated siRNAs Predicts Productive Loading to Small Extracellular Vesicles.

Small extracellular vesicles (sEVs) show promise as natural nano-devices for delivery of therapeutic RNA, but efficient loading of therapeutic RNA remains a challenge. We have recently shown that the attachment of cholesterol to small interfering RNAs (siRNAs) enables efficient and productive loading into sEVs. Here, we systematically explore the ability of lipid conjugates-fatty acids, sterols, and vitamins-to load siRNAs into sEVs and support gene silencing in primary neurons. Hydrophobicity of the conjugated siRNAs defined loading efficiency and the silencing activity of siRNA-sEVs complexes. Vitamin-E-conjugated siRNA supported the best loading into sEVs and productive RNA delivery to neurons.

Optimized Cholesterol-siRNA Chemistry Improves Productive Loading onto Extracellular Vesicles.

Extracellular vesicles are promising delivery vesicles for therapeutic RNAs. Small interfering RNA (siRNA) conjugation to cholesterol enables efficient and reproducible loading of extracellular vesicles with the therapeutic cargo. siRNAs are typically chemically modified to fit an application. However, siRNA chemical modification pattern has not been specifically optimized for extracellular vesicle-mediated delivery. Here we used cholesterol-conjugated, hydrophobically modified asymmetric siRNAs (hsiRNAs) to evaluate the effect of backbone, 5'-phosphate, and linker chemical modifications on productive hsiRNA loading onto extracellular vesicles. hsiRNAs with a combination of 5'-(E)-vinylphosphonate and alternating 2'-fluoro and 2'-O-methyl backbone modifications outperformed previously used partially modified siRNAs in extracellular vesicle-mediated Huntingtin silencing in neurons. Between two commercially available linkers (triethyl glycol [TEG] and 2-aminobutyl-1-3-propanediol [C7]) widely used to attach cholesterol to siRNAs, TEG is preferred compared to C7 for productive exosomal loading. Destabilization of the linker completely abolished silencing activity of loaded extracellular vesicles. The loading of cholesterol-conjugated siRNAs was saturated at ∼3,000 siRNA copies per extracellular vesicle. Overloading impaired the silencing activity of extracellular vesicles. The data reported here provide an optimization scheme for the successful use of hydrophobic modification as a strategy for productive loading of RNA cargo onto extracellular vesicles.

Transvascular Delivery of Hydrophobically Modified siRNAs: Gene Silencing in the Rat Brain upon Disruption of the Blood-Brain Barrier.

Effective transvascular delivery of therapeutic oligonucleotides to the brain presents a major hurdle to the development of gene silencing technologies for treatment of genetically defined neurological disorders. Distribution to the brain after systemic administrations is hampered by the low permeability of the blood-brain barrier (BBB) and the rapid clearance kinetics of these drugs from the blood. Here we show that transient osmotic disruption of the BBB enables transvascular delivery of hydrophobically modified small interfering RNA (hsiRNA) to the rat brain. Intracarotid administration of 25% mannitol and hsiRNA conjugated to phosphocholine-docosahexanoic acid (PC-DHA) resulted in broad ipsilateral distribution of PC-DHA-hsiRNAs in the brain. PC-DHA conjugation enables hsiRNA retention in the parenchyma proximal to the brain vasculature and enabled active internalization by neurons and astrocytes. Moreover, transvascular delivery of PC-DHA-hsiRNAs effected Htt mRNA silencing in the striatum (55%), hippocampus (51%), somatosensory cortex (52%), motor cortex (37%), and thalamus (33%) 1 week after administration. Aside from mild gliosis induced by osmotic disruption of the BBB, transvascular delivery of PC-DHA-hsiRNAs was not associated with neurotoxicity. Together, these findings provide proof-of-concept that temporary disruption of the BBB is an effective strategy for the delivery of therapeutic oligonucleotides to the brain.

Exosomes Produced from 3D Cultures of MSCs by Tangential Flow Filtration Show Higher Yield and Improved Activity.

Exosomes can deliver therapeutic RNAs to neurons. The composition and the safety profile of exosomes depend on the type of the exosome-producing cell. Mesenchymal stem cells are considered to be an attractive cell type for therapeutic exosome production. However, scalable methods to isolate and manufacture exosomes from mesenchymal stem cells are lacking, a limitation to the clinical translation of exosome technology. We evaluate mesenchymal stem cells from different sources and find that umbilical cord-derived mesenchymal stem cells produce the highest exosome yield. To optimize exosome production, we cultivate umbilical cord-derived mesenchymal stem cells in scalable microcarrier-based three-dimensional (3D) cultures. In combination with the conventional differential ultracentrifugation, 3D culture yields 20-fold more exosomes (3D-UC-exosomes) than two-dimensional cultures (2D-UC-exosomes). Tangential flow filtration (TFF) in combination with 3D mesenchymal stem cell cultures further improves the yield of exosomes (3D-TFF-exosomes) 7-fold over 3D-UC-exosomes. 3D-TFF-exosomes are seven times more potent in small interfering RNA (siRNA) transfer to neurons compared with 2D-UC-exosomes. Microcarrier-based 3D culture and TFF allow scalable production of biologically active exosomes from mesenchymal stem cells. These findings lift a major roadblock for the clinical utility of mesenchymal stem cell exosomes.

5΄-Vinylphosphonate improves tissue accumulation and efficacy of conjugated siRNAs in vivo.

5΄-Vinylphosphonate modification of siRNAs protects them from phosphatases, and improves silencing activity. Here, we show that 5΄-vinylphosphonate confers novel properties to siRNAs. Specifically, 5΄-vinylphosphonate (i) increases siRNA accumulation in tissues, (ii) extends duration of silencing in multiple organs and (iii) protects siRNAs from 5΄-to-3΄ exonucleases. Delivery of conjugated siRNAs requires extensive chemical modifications to achieve stability in vivo. Because chemically modified siRNAs are poor substrates for phosphorylation by kinases, and 5΄-phosphate is required for loading into RNA-induced silencing complex, the synthetic addition of a 5΄-phosphate on a fully modified siRNA guide strand is expected to be beneficial. Here, we show that synthetic phosphorylation of fully modified cholesterol-conjugated siRNAs increases their potency and efficacy in vitro, but when delivered systemically to mice, the 5΄-phosphate is removed within 2 hours. The 5΄-phosphate mimic 5΄-(E)-vinylphosphonate stabilizes the 5΄ end of the guide strand by protecting it from phosphatases and 5΄-to-3΄ exonucleases. The improved stability increases guide strand accumulation and retention in tissues, which significantly enhances the efficacy of cholesterol-conjugated siRNAs and the duration of silencing in vivo. Moreover, we show that 5΄-(E)-vinylphosphonate stabilizes 5΄ phosphate, thereby enabling systemic delivery to and silencing in kidney and heart.

Chitosan-Mangafodipir nanoparticles designed for intranasal delivery of siRNA and DNA to brain.

The overall objective of the present research was to develop a nanocarrier system for non-invasive delivery to brain of molecules useful for gene therapy. Manganese-containing nanoparticles (mNPs) carrying anti-eGFP siRNA were tested in cell cultures of eGFP-expressing cell line of mouse fibroblasts (NIH3T3). The optimal mNPs were then tested in vivo in mice. Following intranasal instillation, mNPs were visualized by 7T MRI throughout brain at 24 and 48 hrs. mNPs were effective in significantly reducing GFP mRNA expression in Tg GFP+ mice in olfactory bulb, striatum, hippocampus and cortex. Intranasal instillation of mNPS loaded with dsDNA encoding RFP also resulted in expression of the RFP in multiple brain regions. In conclusion, mNPs carrying siRNA, or dsDNA were capable of delivering the payload from nose to brain. This approach for delivery of gene therapies to humans, if successful, will have a significant impact on disease-modifying therapeutics of neurodegenerative diseases.

Synthesis and Evaluation of Parenchymal Retention and Efficacy of a Metabolically Stable O-Phosphocholine-N-docosahexaenoyl-l-serine siRNA Conjugate in Mouse Brain.

Ligand-conjugated siRNAs have the potential to achieve targeted delivery and efficient silencing in neurons following local administration in the central nervous system (CNS). We recently described the activity and safety profile of a docosahexaenoic acid (DHA)-conjugated, hydrophobic siRNA (DHA-hsiRNA) targeting Huntingtin (Htt) mRNA in mouse brain. Here, we report the synthesis of an amide-modified, phosphocholine-containing DHA-hsiRNA conjugate (PC-DHA-hsiRNA), which closely resembles the endogenously esterified biological structure of DHA. We hypothesized that this modification may enhance neuronal delivery in vivo. We demonstrate that PC-DHA-hsiRNA silences Htt in mouse primary cortical neurons and astrocytes. After intrastriatal delivery, Htt-targeting PC-DHA-hsiRNA induces ∼80% mRNA silencing and 71% protein silencing after 1 week. However, PC-DHA-hsiRNA did not substantially outperform DHA-hsiRNA under the conditions tested. Moreover, at the highest locally administered dose (4 nmol, 50 µg), we observe evidence of PC-DHA-hsiRNA-mediated reactive astrogliosis. Lipophilic ligand conjugation enables siRNA delivery to neural tissues, but rational design of functional, nontoxic siRNA conjugates for CNS delivery remains challenging.

Exosome-mediated Delivery of Hydrophobically Modified siRNA for Huntingtin mRNA Silencing.

Delivery represents a significant barrier to the clinical advancement of oligonucleotide therapeutics for the treatment of neurological disorders, such as Huntington's disease. Small, endogenous vesicles known as exosomes have the potential to act as oligonucleotide delivery vehicles, but robust and scalable methods for loading RNA therapeutic cargo into exosomes are lacking. Here, we show that hydrophobically modified small interfering RNAs (hsiRNAs) efficiently load into exosomes upon co-incubation, without altering vesicle size distribution or integrity. Exosomes loaded with hsiRNAs targeting Huntingtin mRNA were efficiently internalized by mouse primary cortical neurons and promoted dose-dependent silencing of Huntingtin mRNA and protein. Unilateral infusion of hsiRNA-loaded exosomes, but not hsiRNAs alone, into mouse striatum resulted in bilateral oligonucleotide distribution and statistically significant bilateral silencing of up to 35% of Huntingtin mRNA. The broad distribution and efficacy of hsiRNA-loaded exosomes delivered to brain is expected to advance the development of therapies for the treatment of Huntington's disease and other neurodegenerative disorders.

RNA Therapeutics for Improving CAR T-cell Safety and Efficacy.

Autologous chimeric antigen receptor (CAR) T cells have recently emerged as potent tools in the fight against cancer, with promising therapeutic efficacy against hematological malignancies. However, several limitations hamper their widespread clinical use, including availability of target antigen, severe toxic effects, primary and secondary resistance, heterogeneous quality of autologous T cells, variable persistence, and low activity against solid tumors. Development of allogeneic off-the-shelf CAR T cells could help address some of these limitations but is impeded by alloimmunity with either rejection and limited expansion of allo-CAR T cells or CAR T cells versus host reactions. RNA therapeutics, such as small interfering RNAs, microRNAs, and antisense oligonucleotides, are able to silence transcripts in a sequence-specific and proliferation-sensitive way, which may offer a way to overcome some of the challenges facing CAR T-cell development and clinical utility. Here, we review how different RNA therapeutics or a combination of RNA therapeutics and genetic engineering could be harnessed to improve the safety and efficacy of autologous and allogeneic CAR T-cell therapy.

PK-modifying anchors significantly alter clearance kinetics, tissue distribution, and efficacy of therapeutics siRNAs.

Effective systemic delivery of small interfering RNAs (siRNAs) to tissues other than liver remains a challenge. siRNAs are small (∼15 kDa) and therefore rapidly cleared by the kidneys, resulting in limited blood residence times and tissue exposure. Current strategies to improve the unfavorable pharmacokinetic (PK) properties of siRNAs rely on enhancing binding to serum proteins through extensive phosphorothioate modifications or by conjugation of targeting ligands. Here, we describe an alternative strategy for enhancing blood and tissue PK based on dynamic modulation of the overall size of the siRNA. We engineered a high-affinity universal oligonucleotide anchor conjugated to a high-molecular-weight moiety, which binds to the 3' end of the guide strand of an asymmetric siRNA. Data showed a strong correlation between the size of the PK-modifying anchor and clearance kinetics. Large 40-kDa PK-modifying anchors reduced renal clearance by ∼23-fold and improved tissue exposure area under the curve (AUC) by ∼26-fold, resulting in increased extrahepatic tissue retention (∼3- to 5-fold). Furthermore, PK-modifying oligonucleotide anchors allowed for straightforward and versatile modulation of blood residence times and biodistribution of a panel of chemically distinct ligands. The effects were more pronounced for conjugates with low lipophilicity (e.g., N-Acetylgalactosamine [GalNAc]), where significant improvement in uptake by hepatocytes and dose-dependent silencing in the liver was observed.

Comparative route of administration studies using therapeutic siRNAs show widespread gene modulation in Dorset sheep.

siRNAs comprise a class of drugs that can be programmed to silence any target gene. Chemical engineering efforts resulted in development of divalent siRNAs (di-siRNAs), which support robust and long-term efficacy in rodent and nonhuman primate brains upon direct cerebrospinal fluid (CSF) administration. Oligonucleotide distribution in the CNS is nonuniform, limiting clinical applications. The contribution of CSF infusion placement and dosing regimen on relative accumulation, specifically in the context of large animals, is not well characterized. To our knowledge, we report the first systemic, comparative study investigating the effects of 3 routes of administration - intrastriatal (i.s.), i.c.v., and intrathecal catheter to the cisterna magna (ITC) - and 2 dosing regimens - single and repetitive via an implanted reservoir device - on di-siRNA distribution and accumulation in the CNS of Dorset sheep. CSF injections (i.c.v. and ITC) resulted in similar distribution and accumulation across brain regions. Repeated dosing increased homogeneity, with greater relative deep brain accumulation. Conversely, i.s. administration supported region-specific delivery. These results suggest that dosing regimen, not CSF infusion placement, may equalize siRNA accumulation and efficacy throughout the brain. These findings inform the planning and execution of preclinical and clinical studies using siRNA therapeutics in the CNS.

Comparative Colocalization Single-Molecule Spectroscopy (CoSMoS) with Multiple RNA Species.

Colocalization single-molecule spectroscopy (CoSMoS) allows studying RNA-protein complexes in the full complexity of their cellular environment at single-molecule resolution. Conventionally, the interaction between a single RNA species and multiple proteins is monitored in real time. However, comparing interactions of the same proteins with different RNA species in the same cell extract promises unique insights into RNA biology. Here, we describe an approach to monitor multiple RNA species simultaneously to enable direct comparison. This approach represents a technological development to avoid conventional inter-experiment comparisons.

Preparation of SNAPf-Beads for Colocalization Single-Molecule Spectroscopy (CoSMoS) of RNA-Protein Complexes.

The SNAPf-tag is a chemical tag that allows rapid and highly specific covalent labeling of proteins even in the full complexity of the cellular environment. The SNAPf-tag has been instrumental to study native RNA-protein complexes at single-molecule resolution in their cellular environment as efficient labeling of the RNAs and proteins of interest is essential for this colocalization single-molecule spectroscopy (CoSMoS) technique. However, removal of excessive benzylguanine dye after the labeling reaction has remained challenging. Here, we describe a strategy to remove excessive benzylguanine dye using SNAPf-tag coated beads as sponges.

A divalent siRNA chemical scaffold for potent and sustained modulation of gene expression throughout the central nervous system.

Sustained silencing of gene expression throughout the brain using small interfering RNAs (siRNAs) has not been achieved. Here we describe an siRNA architecture, divalent siRNA (di-siRNA), that supports potent, sustained gene silencing in the central nervous system (CNS) of mice and nonhuman primates following a single injection into the cerebrospinal fluid. Di-siRNAs are composed of two fully chemically modified, phosphorothioate-containing siRNAs connected by a linker. In mice, di-siRNAs induced the potent silencing of huntingtin, the causative gene in Huntington's disease, reducing messenger RNA and protein throughout the brain. Silencing persisted for at least 6 months, with the degree of gene silencing correlating to levels of guide strand tissue accumulation. In cynomolgus macaques, a bolus injection of di-siRNA showed substantial distribution and robust silencing throughout the brain and spinal cord without detectable toxicity and with minimal off-target effects. This siRNA design may enable RNA interference-based gene silencing in the CNS for the treatment of neurological disorders.

Serum Deprivation of Mesenchymal Stem Cells Improves Exosome Activity and Alters Lipid and Protein Composition.

Exosomes can serve as delivery vehicles for advanced therapeutics. The components necessary and sufficient to support exosomal delivery have not been established. Here we connect biochemical composition and activity of exosomes to optimize exosome-mediated delivery of small interfering RNAs (siRNAs). This information is used to create effective artificial exosomes. We show that serum-deprived mesenchymal stem cells produce exosomes up to 22-fold more effective at delivering siRNAs to neurons than exosomes derived from control cells. Proteinase treatment of exosomes stops siRNA transfer, indicating that surface proteins on exosomes are involved in trafficking. Proteomic and lipidomic analyses show that exosomes derived in serum-deprived conditions are enriched in six protein pathways and one lipid class, dilysocardiolipin. Inspired by these findings, we engineer an "artificial exosome," in which the incorporation of one lipid (dilysocardiolipin) and three proteins (Rab7, Desmoplakin, and AHSG) into conventional neutral liposomes produces vesicles that mimic cargo delivering activity of natural exosomes.