REGENXBIO Releases Interim Data from RGX-202 Clinical Trial

REGENXBIO announced newinterim data from the Phase I/II AFFINITY DUCHENNE trial of RGX-202, a potential gene therapy for Duchenne muscular dystrophy. Trial investigator Carolina Tesi-Rocha, M.D., Clinical Professor, Neurology, Stanford School of Medicine, Stanford Children's Health, is presenting this data, including new functional, safety, biomarker, and cardiac MRI measures, at the Muscular Dystrophy Association Clinical and Scientific Conference. In the interim functional results from seven participants treated at the pivotal dose level, aged approximately 6 to 12 years at dosing, RGX-202 continues to demonstrate evidence of positively impacting disease trajectory on North Star Ambulatory Assessment and all timed function tests at one year. Functional outcomes were analyzed using multiple validated methods to estimate expected disease progression without treatment, including the cTAP disease progression model and external control comparisons using coarsened exact matching and propensity score weighting. Propensity score weighting is the primary analysis method specified in the SAP for the pivotal trial. The pivotal dose participants demonstrated improved performance across all timed function tests and NSAA when compared to external control using propensity score weighting. The 95% confidence interval demonstrates favorability to RGX-202. On NSAA, pivotal dose participants exceeded expected disease trajectory and external controls. Notably, five of the seven participants were aged 8+ at dosing, when functional decline is expected. At one year, participants improved an average of +4.9 points compared to cTAP. The older participants improved an average of +5.2 points compared to cTAP. Additionally, dose level 1 participants exceeded expected disease trajectory and improved an average of +5.6 points compared to cTAP at two years. Pivotal dose participants demonstrated cardiac stability at one year post-treatment as measured by MRI endpoints, including mean left ventricular ejection fraction, global circumferential strain, and fibrosis assessed by late gadolinium enhancement. Biomarker data from the Phase I/II study continues to support consistent, high expression and transduction of RGX-202 microdystrophin. New data from an additional patient, aged 3.6 at dosing, had a microdystrophin expression level of 51.2% at Week 12. The primary endpoint in the pivotal phase of AFFINITY DUCHENNE is the proportion of participants whose RGX-202 microdystrophin expression is greater than10% at Week 12. RGX-202 was appropriately localized to the sarcolemma, demonstrating that the differentiated construct with the inclusion of the C-Terminal domain is appropriately targeting the muscle. New interim safety data from all Phase I/II pivotal dose participants aged 1 to less than12 years at dosing show no evidence of liver injury across multiple measures. Mean gamma-glutamyl transferase and total bilirubin, recognized markers of liver inflammation in Duchenne, did not exceed the upper limit of normal up to two years post-treatment. A mean reduction in creatine kinase was observed at one year post-treatment and supported by mean reductions in ALT, AST, and LDH. RGX-202 was well tolerated with no serious adverse events and no AEs of special interest in the Phase I/II study as of the data cut date. Common drug-related AEs included vomiting, fatigue, and nausea. All are typically anticipated with gene therapy administration. A proactive, short-course immune modulation regimen in combination with a differentiated construct and industry-leading product purity levels of more than 80% full capsids may contribute to a favorable safety profile for RGX-202.