REGENXBIO recently presented their interim clinical data from the Phase I/II AFFINITY DUCHENNE™ Trial of RGX-202 at the 28th Annual International Congress of the World Muscle Society. Highlights included:

• RGX-202, a potential one-time AAV Therapeutic for the treatment of Duchenne that includes an optimized transgene for a novel microdystrophin, continues to be well-tolerated in three patients from dose level 1 (1×1014 GC/kg).
• Initial biomarker data in two patients who completed a three-month assessment demonstrate robust microdystrophin expression with localization to the muscle cell membrane.
• Patient aged 4.4 years old had an expression level at 38.8% of control.
• Trial dose escalation is expected by the end of 2023.
• Pivotal dose determination and initiation of pivotal program anticipated in 2024.
• Plan to use RGX-202 microdystrophin as a surrogate endpoint to support a Biologics License Application filing using the accelerated approval pathway.
• RGX-202 development program uses commercial-ready cGMP material from the REGENXBIO Manufacturing Innovation Center.

“Duchenne is a rare degenerative disease, and without a functional dystrophin protein, muscles progressively weaken, leading to loss of mobility and declining respiratory and cardiac function. The unique construct of RGX-202, inclusive of the C-Terminal domain, has the potential to make a meaningful impact for patients and we are encouraged by these interim safety and efficacy results.”

livier Danos, Ph.D., Chief Scientific Officer of REGENXBIO

RGX-202 is an investigational one-time AAV therapeutic for Duchenne, using the NAV® AAV8 vector to deliver a transgene for a novel microdystrophin that includes the functional elements of the C-Terminal (CT) domain as well as a muscle-specific promoter to support a targeted therapy for improved resistance to muscle damage associated with Duchenne.

Safety Update

As of September 28, 2023, RGX-202 was reported to be well tolerated with no drug-related serious adverse events in three patients, aged 4.4, 10.6 and 6.3 years, dosed to date at dose level 1. Time of post-administration follow up ranges from three weeks to more than five months. The two patients who reached three-month follow-up have completed the immunosuppression regimen per study protocol.

Clinical Program Updates

REGENXBIO expects to dose patients at dose level 2 (2×1014 genome copies (GC)/kg body weight) in the Phase I/II AFFINITY DUCHENNE trial by the end of 2023. In addition, the trial protocol has been amended to accelerate the development of RGX-202, updating the dose expansion phase of the trial to begin after two patients from the previous three patients.

Today, REGENXBIO also provided an update on a newly completed preclinical efficacy study evaluating RGX-202 manufactured using REGENXBIO’s NAVXpress™ commercial-ready process at both dose levels. RGX-202 at dose level 2 showed improvement in functional performance, compared to dose level 1, as determined by forelimb muscle strength and treadmill exhaustion in mdx mice. This data further supports plans to immediately initiate dose escalation to dose level 2.

The Company expects to share initial strength and functional assessment data for both dose levels in 2024. Additionally, REGENXBIO expects to make a pivotal dose determination and initiate a pivotal program for RGX-202 in 2024.

Defeat Duchenne Canada continues to work with REGENXBIO to establish Canadian clinical trial sites.