Regenxbio stock dropped 25% to $8.05 on Monday after the FDA placed a clinical hold on RGX-121, its investigational gene therapy for Hunter syndrome. Trading was briefly halted ahead of the news.
The hold came after an expanded MRI monitoring program turned up asymptomatic findings in five patients. Each had a small nodule or cystic mass on their spine. All five had received injections of RGX-121 roughly three to six years earlier.
Researchers classified the findings as non-serious. Radiologists assessed them as likely benign, and there is no clinical or pathological evidence linking them directly to the therapy.
Still, the FDA moved to place a clinical hold on the program, and Regenxbio said it no longer expects to resubmit its Biologics License Application for RGX-121 anytime soon.
As recently as June, the FDA had told Regenxbio no additional studies were needed before resubmitting the BLA in the third quarter. That timeline is now off the table.
This is the second Regenxbio program to be paused by the FDA in recent months. RGX-111, a separate candidate, was placed on clinical hold earlier this year, just weeks before a key approval decision. The hold was extended to RGX-121 at the time due to similarities between the two therapies.
CEO Curran Simpson said the findings appear “unique and limited” to the Hunter syndrome program, but acknowledged they “require longer-term follow-up and additional data analysis” before the company can fully assess the benefit-risk profile of RGX-121.
All five patients continue to show overall stability or improvement on neurocognitive and neurobehavioral assessments.
Hunter syndrome is a rare genetic disorder where the body cannot break down complex sugar molecules. It mostly affects boys and is life-limiting, with patients typically surviving into their 20s.
Regenxbio says its Duchenne muscular dystrophy and wet age-related macular degeneration programs use a different capsid and routes of administration and are not affected by the hold.
The company plans to submit a BLA for its Duchenne candidate in the current quarter.
Topline data for its wet AMD candidate, co-developed with AbbVie, is expected in Q4. Analysts have flagged this readout as a key stock catalyst for Regenxbio.
Other companies in adjacent spaces felt a knock-on effect. Sarepta Therapeutics fell 3.3% and EyePoint dropped 4.3% on the day.
Earlier this month, Barclays analyst Eliana Merle downgraded Regenxbio to Equal Weight from Overweight, citing an unclear regulatory environment and rising competition as risks to both programs.
The company said it is working with partner NS Pharma to evaluate additional patient imaging and longer-term follow-up data, and will incorporate FDA feedback into next steps for RGX-121.
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