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REGENXBIO: Announces New Positive Initial Efficacy Data From AFFINITY DUCHENNE® Trial

March 5, 2024

REGENXBIO Inc. reported on March 4, 2024 additional interim safety and efficacy data in the Phase I/II AFFINITY DUCHENNE® trial of RGX-202 in patients with Duchenne muscular dystrophy (Duchenne) ages 4 to11 years old, including RGX-202 microdystrophin expression from dose level 2 and video of trial clinic assessments demonstrating initial evidence of strength and functional improvement.

Press release highlights:

  • New three-month assessment in first patient at dose level 2 demonstrates robust microdystrophin expression
  • Patient aged 12 years at dosing had expression level at 75.7% of control
  • Early evidence of strength and motor function improvement observed
  • On track to initiate pivotal trial in second half of 2024

“RGX-202 at dose level 2 is demonstrating significantly increased microdystrophin expression in a 12-year-old patient. We know there is an insufficient level of data available to the community for boys older than 7 years, and we are committed to being transparent with our data for a Duchenne community in need of new treatment options that can meaningfully impact disease. In addition, we are encouraged by the safety data at both dose levels and initial caregiver observations of strength and motor function improvement in boys treated with RGX-202.

We look forward to following these patients to establish durability and greater separation from baseline, which we hope will further establish RGX-202 as an important option among treatments in development.”

Kenneth T. Mills, President and CEO, REGENXBIO.

“There is a need for treatment options for boys with Duchenne that have the potential to alter the disease trajectory. I am very pleased with the new microdystrophin expression data from RGX-202 dose level 2. It is encouraging to see that patients are safely progressing through their trial protocol strength and motor function assessments with early observations of improvement, including in older boys.”

Aravindhan Veerapandiyan, M.D., Arkansas Children’s Hospital.

Safety Update
As of February 28, 2024, RGX-202 has been well tolerated with no drug-related serious adverse events in five patients, aged 4.4 to 12.1. Time of post-administration follow up ranges from approximately seven weeks to over eleven months. All patients who reached three-month follow-up have completed the immunosuppression regimen per study protocol.

Clinical Program Updates
REGENXBIO expects to make a pivotal dose determination in mid-2024. The Company also expects to share strength and functional assessment data for both dose levels and the initiation of a pivotal trial in the second half of 2024. The Company plans to use RGX-202 microdystrophin expression as a surrogate endpoint to support a Biologics License Application (BLA) filing using the accelerated approval pathway.

AFFINITY DUCHENNE Trial Design
RGX-202 has differentiated and important biology most similar to naturally occurring dystrophin that protects from the muscle degradation associated with Duchenne. RGX-202 is designed to deliver a transgene for a novel microdystrophin that includes the functional elements of the C-Terminal (CT) domain found in naturally occurring dystrophin. Presence of the CT domain has been shown in preclinical studies to recruit several key proteins to the muscle cell membrane, leading to improved muscle resistance to contraction-induced muscle damage in dystrophic mice. Additional design features, including codon optimization and reduction of CpG content, may potentially improve gene expression, increase translational efficiency and reduce immunogenicity. RGX-202 is designed to support the delivery and targeted expression of genes throughout skeletal and heart muscle using the NAV AAV8 vector, a vector used in numerous clinical trials, and a well-characterized muscle-specific promoter (Spc5-12).

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