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mRNA therapeutics hold great potential for treating a variety of diseases through protein-replacement, immunomodulation, and gene editing. However, much like siRNA therapy the majority of progress in mRNA delivery has been confined to the liver. Previously, we demonstrated that poly(β-amino esters), a class of degradable polymers, are capable of systemic mRNA delivery to the lungs in mice when formulated into nanoparticles with poly(ethylene glycol)–lipid conjugates. Using experimental design, a statistical approach to optimization that reduces experimental burden, we demonstrate herein that these degradable polymer–lipid nanoparticles can be optimized in terms of polymer synthesis and nanoparticle formulation to achieve a multiple order-of-magnitude increase in potency. Furthermore, using genetically engineered Cre reporter mice, we demonstrate that mRNA is functionally delivered to both the lung endothelium and pulmonary immune cells, expanding the potential utility of these nanoparticles.

Autophagy is a homeostatic process critical for cellular survival, and its malfunction is implicated in human diseases including neurodegeneration. Loss of autophagy contributes to cytotoxicity and tissue degeneration, but the mechanistic understanding of this phenomenon remains elusive. Here, we generated autophagy-deficient (ATG5−/−) human embryonic stem cells (hESCs), from which we established a human neuronal platform to investigate how loss of autophagy affects neuronal survival. ATG5−/−neurons exhibit basal cytotoxicity accompanied by metabolic defects. Depletion of nicotinamide adenine dinucleotide (NAD) due to hyperactivation of NAD-consuming enzymes is found to trigger cell death via mitochondrial depolarization in ATG5−/−neurons. Boosting intracellular NAD levels improves cell viability by restoring mitochondrial bioenergetics and proteostasis in ATG5−/−neurons. Our findings elucidate a mechanistic link between autophagy deficiency and neuronal cell death that can be targeted for therapeutic interventions in neurodegenerative and lysosomal storage diseases associated with autophagic defect.

With the recent development of CRISPR technology, it is becoming increasingly easy to engineer the genome. Genome-editing systems based on CRISPR, as well as transcription activator-like effector nucleases (TALENs) and zinc-finger nucleases (ZFNs), are becoming valuable tools for biomedical research, drug discovery and development, and even gene therapy. However, for each of these systems to effectively enter cells of interest and perform their function, efficient and safe delivery technologies are needed. This Review discusses the principles of biomacromolecule delivery and gene editing, examines recent advances and challenges in non-viral and viral delivery methods, and highlights the status of related clinical trials.

I'd been a heavy guy my entire life. But after turning 21 and being able to drink, my habits got even worse. I would eat so much junk food and [...]

Small interfering RNAs (siRNAs) can specifically inhibit gene expression. As a result, they have tremendous scientific and clinical potential. However, the use of these molecules in patients and animal models has been limited by challenges with delivery. Intracellular RNA delivery is difficult; it requires a system that protects the siRNA from degradative nucleases in the bloodstream, minimizes clearance by the reticuloendothelial system, maximizes delivery to the target tissue, and promotes entry into, and out of, an endocytic vesicle. Despite these barriers, recent data suggest that RNA may be targeted to cells of interest in vivo. Herein we outline strategies for targeted siRNA delivery, and describe how these strategies may be improved.

In the field of drug delivery, pH-sensitive polymeric microparticles can be used to release therapeutic payloads slowly in extracellular conditions (pH 7.4) and faster in more acidic areas in vivo, such as sites of inflammation, tumors, or intracellular conditions. Our group currently uses and is further developing the pH-sensitive polymer acetalated dextran (Ac-DEX), which is a biodegradable polymer with highly tunable degradation kinetics. Ac-DEX has displayed enhanced delivery of vaccine and drug components to immune and other cells, making it an extremely desirable polymer for immune applications. Currently, one of the degradation products of Ac-DEX is methanol, which may cause toxicity issues if applied at high concentrations with repeated doses. Therefore, in this manuscript we report the first synthesis and characterization of an Ac-DEX analog which, instead of a methanol degradation product, has a much safer ethanol degradation product. We abbreviate this ethoxy acetal derivatized acetalated dextran polymer as Ace-DEX, with the ‘e’ to indicate an ethanol degradation product. Like Ac-DEX, Ace-DEX microparticles have tunable degradation rates at pH 5 (intracellular). These rates range from hours to several days and are controlled simply by reaction time. Ace-DEX microparticles also show minimal cytotoxicity compared to commonly used poly(lactic-co-glycolic acid) (PLGA) microparticles when incubated with macrophages. This study aims to enhance the biocompatibility of acetalated dextran-type polymers to allow their use in high volume clinical applications such as multiple dosing and tissue engineering.

We propose the use of a new biopolymer, acetalated dextran (Ac-DEX), to synthesize porous microparticles for pulmonary drug delivery. Ac-DEX is derived from the polysaccharide dextran and, unlike polyesters, has tunable degradation from days to months and pH neutral degradation products. Ac-DEX microparticles fabricated through emulsion techniques were optimized using a variety of postprocessing techniques to enhance the respirable fraction for pulmonary delivery. Tangential flow filtration resulted in a maximum 37% respirable fraction for Ac-DEX porous microparticles, compared to a 10% respirable fraction for poly(lactic-co-glycolic acid) (PLGA) porous microparticles. Ac-DEX microparticles were of an optimum diameter to minimize macrophage clearance but had a low enough theoretical density for deep lung penetration. Transepithelial electrical resistance (TEER) measurements showed that the particles did not impinge on a monolayer of lung epithelial cells in either air or liquid conditions. Also, the release of the chemotherapeutic camptothecin was shown to be tunable depending on Ac-DEX degradation time and molecular weight, and drug release was shown to be bioactive over a range of concentrations. Our results indicate that both release kinetics and fraction of burst release of drug from Ac-DEX porous microparticles can be tuned by simply changing the Ac-DEX polymer properties, affording a large range of formulation options for drug delivery to the pulmonary cavity. Overall, Ac-DEX porous microparticles show promise as an emerging carrier for pulmonary delivery of drugs to the alveolar region of the lung, particularly for the treatment of lung diseases.

Nanoparticles deliver siRNA for multigene silencing of endothelial cell adhesion molecules, which dampens leukocyte recruitment in atherosclerosis and myocardial infarction in mice.

Several letters to the editor are presented in response to articles in the September 29, 2008 issue, including "Are You Ready for a Howling, Pagan, YouTube, Oktoberfiesta?" by Gary Smith, a photograph by Chuck Solomon of former Yankee catcher Yogi Berra, and "Just My Type," by Dan Patrick.