REGENXBIO Inc ( RGNX ) reported additional interim safety and efficacy data in the Phase 1/2 AFFINITY DUCHENNE trial of RGX-202 in patients with Duchenne muscular dystrophy (Duchenne) ages 4 to11 years old.

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 at dose level 1 (1×1014 genome copies (GC)/kg body weight) and dose level 2 (2×1014 GC/kg body weight). 

In new data from the first patient, aged 12.1 years, who received RGX-202 at dose level 2, RGX-202 microdystrophin expression was measured to be 75.7% compared to control at three months. A reduction in serum creatinine kinase (CK) levels of 77% was observed at ten weeks from baseline.

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All four patients, across both dose levels, who completed three-month trial assessments indicate encouraging increases in expression of RGX-202 microdystrophin and reduction from baseline in serum CK levels, supporting evidence of clinical improvement.

Elevated CK levels are associated with muscle injury and are uniformly elevated in Duchenne patients. 

Among patients aged 8 to 11 at screening, RGX-202 microdystrophin expression levels (change from baseline) at three months following RGX-202 administration were higher in dose level 2. 

In addition, new recordings of the AFFINITY DUCHENNE trial clinic assessments and home videos shared with trial investigators by caregivers illustrate that patients treated with RGX-202 demonstrate initial evidence of strength and functional improvement.

REGENXBIO ( RGNX ) 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 filing using the accelerated approval pathway.

Price Action: RGNX shares are up 17.90% at $25.34 on the last check Tuesday.