The blood-brain barrier (BBB) is by far the most important target in developing new approaches to improve delivery of drugs and diagnostic tools into the Central Nervous System (CNS). Here we report the engineering of pH- sensitive polymersomes (synthetic vesicles formed by amphiphilic copolymers) that exploit endogenous transport mechanisms to traverse the BBB, enabling delivery of large macromolecules into both the CNS parenchyma and CNS cells. We achieve this by targeting the Low Density Lipoprotein Receptor-Related Protein 1 (LRP-1) receptor. We show that LRP-1 is associated with endothelial transcytosis that does not involve acidification of cargo in membrane-trafficking organelles. By contrast, this receptor is also associated with traditional endocytosis in CNS cells, thus aiding the delivery of relevant cargo within their cytosol. We prove this using IgG as a model cargo, thus demonstrating that the combination of appropriate targeting combined with pH-sensitive polymersomes enables the efficient delivery of macromolecules into CNS cells.

The human SOD1G93A transgenic mouse has been used extensively since its development in 1994 as a model for amyotrophic lateral sclerosis (ALS). In that time, a great many insights into the toxicity of mutant SOD1 have been gained using this and other mutant SOD transgenic mouse models. They all demonstrate a selective toxicity towards motor neurons and in some cases features of the pathology seen in the human disease. These models have two major drawbacks. Firstly the generation of robust preclinical data in these models has been highlighted as an area for concern. Secondly, the amount of time required for a single preclinical experiment in these models (3–4 months) is a hurdle to the development of new therapies. We have developed an inbred C57BL/6 mouse line from the original mixed background (SJLxC57BL/6) SOD1G93A transgenic line and show here that the disease course is remarkably consistent and much less prone to background noise, enabling reduced numbers of mice for testing of therapeutics. Secondly we have identified very early readouts showing a large decline in motor function compared to normal mice. This loss of motor function has allowed us to develop an early, sensitive and rapid screening protocol for the initial phases of denervation of muscle fibers, observed in this model. We describe multiple, quantitative readouts of motor function that can be used to interrogate this early mechanism. Such an approach will increase throughput for reduced costs, whilst reducing the severity of the experimental procedures involved.

Duchenne muscular dystrophy is a fatal muscle-wasting disorder. Lack of dystrophin compromises the integrity of the sarcolemma and results in myofibers that are highly prone to contraction-induced injury. Recombinant adeno-associated virus (rAAV)-mediated dystrophin gene transfer strategies to muscle for the treatment of Duchenne muscular dystrophy (DMD) have been limited by the small cloning capacity of rAAV vectors and high titers necessary to achieve efficient systemic gene transfer. In this study, we assess the impact of codon optimization on microdystrophin (DeltaAB/R3-R18/DeltaCT) expression and function in the mdx mouse and compare the function of two different configurations of codon-optimized microdystrophin genes (DeltaAB/R3-R18/DeltaCT and DeltaR4-R23/DeltaCT) under the control of a muscle-restrictive promoter (Spc5-12). Codon optimization of microdystrophin significantly increases levels of microdystrophin mRNA and protein after intramuscular and systemic administration of plasmid DNA or rAAV2/8. Physiological assessment demonstrates that codon optimization of DeltaAB/R3-R18/DeltaCT results in significant improvement in specific force, but does not improve resistance to eccentric contractions compared with noncodon-optimized DeltaAB/R3-R18/DeltaCT. However, codon-optimized microdystrophin DeltaR4-R23/DeltaCT completely restored specific force generation and provided substantial protection from contraction-induced injury. These results demonstrate that codon optimization of microdystrophin under the control of a muscle-specific promoter can significantly improve expression levels such that reduced titers of rAAV vectors will be required for efficient systemic administration.

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