Antisense nucleic acid splice correction therapy for Duchenne muscular dystrophy and related disorders

Degenerative diseases cause increasing medical and social burdens in aging Western societies. Few of these diseases are treatable and therefore it is vital that new types of therapies are developed. In this research we will study Duchenne muscular dystrophy (DMD), a common, X-linked inherited, degenerative disease of muscle caused by lack of the protein dystrophin, and that is uniformly fatal and currently untreatable, typically leading to the deaths of affected boys in their 20s. We will investigate a new type of gene therapy for DMD, which has already shown promise in two preliminary clinical trials in DMD patients. The therapy, called exon skipping, uses small DNA patches known as antisense oligonucleotides (AOs) to correct the effects of mutations in the dystrophin gene, thereby producing new dystrophin protein of near-normal function and correcting the harmful effects of the disease. The recent clinical trials tested the application of this method in single muscles and therefore one of the major challenges in taking this therapy forward is to develop the means to deliver the AOs effectively to all muscle groups and also to the heart, given that all are affected by the disease. We have recently discovered that attaching small protein fragments known as peptides to the AO allows greatly improved delivery of the AO compounds to multiple muscle groups and heart. In this research we now also plan to test protein fragments that potentially allow the AO to be targeted specifically to muscle and /or heart, initially studying a recently discovered prototype compound known as B-MSP-PMO. We plan to test its long-term effectiveness in two mouse models of DMD, one mild and one severe, and also to attempt to understand better how this compound is targeted to muscle and to what extent it is likely to be safe to use. We also plan to evaluate improved versions of this AO as we are currently working to discover improved peptides that may target the AO to muscle and or heart with even greater efficiency. We will also investigate further recent exciting findings where we have discovered that the delivery of such drugs can be enhanced further by administering them together with a range of sugars. This work will therefore significantly advance the prospects for a disease-modifying therapy for DMD and also for other diseases where exon skipping or AO delivery would be a valuable therapy.

Experimental nucleic acid based therapies are being intensively investigated as novel strategies for currently untreatable human disease. This Programme aims to develop a detailed molecular understanding of the chemical biological requirements for long-term, targeted, functional and phenotypic antisense oligonucleotide (AO)-mediated splice correction in mouse models of Duchenne muscular dystrophy (DMD). DMD is a fatal muscle degenerative disease and AO mediated splice correction of the DMD pre-mRNA has the potential to treat approximately 75% of DMD patients and has been shown to be well tolerated with therapeutic efficacy in two recent Phase I clinical trials. A critical challenge now in the development of this approach is the need for long-term, targeted, high efficiency systemic correction of the DMD phenotype. In this Programme beginning with state-of-the-art AO-peptide conjugates (B-PMO and B-MSP-PMO) we will study long-term correction of the muscle and cardiac physiological phenotypes following splice correction in dystrophin deficient mdx and dystrophin/utrophin deficient double knockout (DKO) mice. We will also discover and study novel transduction peptides for enhanced AO delivery and splice correction, and develop methods for targeted AO delivery to muscle and cardiac tissues including novel chimeric transduction/targeting peptides and study their mechanisms of action. AO conjugates incorporating these novel peptides will be studied over the long term in DMD animal models. Work will further include study of safety aspects including long term toxicology, tissue biodistribution/pharmacokinetics, and genome-wide off-target and splicing dysregulation effects. Finally, we will further investigate our striking recent findings related to GLUT transporter mediated AO delivery to muscle and cardiac tissues. This is a challenging and integrated programme of work with several streams of study moving from discovery and basic chemistry and chemical biology through to in vitro and in vivo studies in DMD animal models and clinical application via the PI?s participation in the UK MDEX Consortium. It will substantially advance our understanding of the requirements for successful systemic splice correction of the DMD phenotype and will have direct implications for the therapy of related neuromuscular disorders and other diseases where forced manipulation of pre-mRNA splicing and/or targeted AO delivery would be of therapeutic value.