Researchers in the Departments of Neurology at UCLA and the University of Washington have developed a novel AAV gene therapy that treats limb-girdle muscular dystrophy type R1/2A (LGMD2A), an as of yet unmet target.
BACKGROUND:
Muscular dystrophies are a group of muscle diseases caused by mutations in a persons’ genes. Mutations within the calpain3 gene (CAPN3) cause one of the most common limb-girdle muscular dystrophies, LGMD2A, a disease that affects skeletal muscle. The proximal skeletal muscle impairment induced is associated with elevated levels of serum creatine kinase. Patients develop dystrophic features including skeletal muscle degeneration/regeneration, variation in fiber size, mitochondrial abnormalities and inflammatory infiltrates: leading to wheelchair dependencies within a decade of diagnosis.
Gene therapy for LGMD2A is expected to be highly efficacious because it is a monogenic recessive disorder, thereby amenable to gene replacement strategies. Mutations within CAPN3 are primarily of a missense type, with greater than 100 known disease-causing mutations spread along the length of the cDNA. Notably, overexpression of CAPN3 is nontoxic to skeletal muscle, and the cDNA can be packaged within the 4.7 kilobase constraints of AAV without modification, providing a non-immunogenic treatment with long-term persistence of the transgene cassette: allowing high therapeutic potential.
Since the pathomechanism of LGMD2A appears different from other dystrophies, most disease-modifying therapies for other neuromuscular disorders will not be effective for LGMD2A patients. One such reason is that CAPN3 is not expressed in the heart and can be toxic if expressed at high levels. Furthermore, LGMD2A preferentially impacts slow fibers, leading to a slow oxidative phenotype. Therefore, it is critical that the therapeutic construct expresses in both fast and slow muscle fibers with minimal off-target expression in the heart.
INNOVATION:
Dr. Melissa Spencer and colleagues in the Department of Neurology at UCLA and Dr. Jeffery Chamberlain and colleagues in the Department of Neurology at the University of Washington have developed a safe, skeletal muscle-specific AAV gene therapy for the treatment of limb-girdle muscular dystrophy type R1/2A. This novel AAV vector contains a unique regulatory cassette combined with CAPN3 to effectively de-target the heart and express highly in both fast and slow skeletal muscle fibers. As a result, the invention addresses the treatment of LGMD2A, a currently unmet clinical need.
POTENTIAL APPLICATIONS:
• Gene Therapy for Limb Girdle Muscular Dystrophy
• Animal Research Studies
• Skeletal muscle restricted regulatory cassettes
ADVANTAGES:
• Specific for LGMD2A, but regulatory cassettes can be applied to other muscle diseases in cases where the transgene should not express in the heart
• Skeletal muscle specific expression
• Targets fast and slow skeletal muscle fibers
• Minimal off-target cardiotoxicity
• Packaged in AAV with no modifications
DEVELOPMENT-TO-DATE: Pilot analyses have been completed in Capn3 knockout mice and C57B6 mice to test preliminary toxicity of AAV-Capn3 vectors, levels of Capn3 needed for therapeutic rescue, and optimization of Capn3 in fast and slow skeletal muscle fibers.