P.142 Improving FSHD RNAi gene therapy using myotropic MyoAAVs

Abstract

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant or digenic disorder affecting more than 870,000 people worldwide. FSHD is caused by de-repression of the toxic <i>DUX4</i> gene in skeletal muscle. There are currently no approved treatments for FSHD, but several promising <i>DUX4</i>-inhibition therapies are under development. Previously, our lab published pre-clinical efficacy and safety studies for a <i>DUX4</i>-targeted RNAi-based gene therapy using an artificial microRNA called mi405. In unpublished data, we performed dose-finding studies in FSHD animal models, demonstrated inhibition of human <i>DUX4</i>-associated biomarkers in xenografts, confirmed long-term expression in vivo, and characterized the biodistribution of two lead AAV vector serotypes (AAV6 & AAV9). In line with muscular dystrophy gene therapy studies now in clinical trials (e.g., micro-dystrophin), our dose-finding work demonstrated that sufficient muscle transduction required high dose systemic delivery of AAV9 (1e14vg/kg). Though high doses were non-pathogenic in our toxicology studies [WL1] and several systemic gene therapy studies used doses that exceeded our target range, serious adverse events and deaths in other programs raised concerns about the safety of first generation AAV vector doses exceeding 10^14 vg/kg. Here we seek to reduce potential perceived or real safety issues. We aim to boost muscle transduction and reduce vector doses required to provide therapeutic benefit using new, engineered MyoAAV serotypes. Here, we compare our first generation AAV9 system with MyoAAVs carrying the same mi405 genome and a GFP reporter, using intramuscular and systemic delivery. Consistent with published data, systemically delivered MyoAAVs provided drastically superior muscle transduction compared to AAV9. Specifically, we observed widespread muscle transduction following 3e13 vg/kg doses in mice. We are now performing dose finding efficacy and safety studies in FSHD mice to support a future clinical trial (9e12 vg/kg, 3e13 vg/kg, and 6e13 vg/kg). We expect that new muscle-enhanced vectors combined with the highly efficacious mi405 will enable lower AAV doses while preserving the therapeutic efficacy of high dose first generation vectors.