Regenxbio Inc. (NASDAQ:RGNX) stock is trading lower on Monday after a regulatory update on its investigational gene therapy, RGX-121 (clemidsogene lanparvovec or Navsunli), for Mucopolysaccharidosis type II (MPS II), also known as Hunter Syndrome.
FDA Places Clinical Hold On RGX-121
The U.S. Food and Drug Administration (FDA) placed a clinical hold on RGX-121 following the discovery of asymptomatic spine MRI findings in five participants in the CAMPSIITE study.
The company said it does not expect to resubmit the RGX-121 Biologics License Application (BLA) in the near term.
Five Participants Show Asymptomatic Spine MRI Findings
All five participants continue to do well clinically and have demonstrated overall stability to improvement on neurocognitive and neurobehavioral assessments.
The findings were identified through an expanded MRI monitoring plan, implemented by Regenxbio a few months ago, following the clinical hold related to RGX-111.
The enhanced monitoring included both brain and spine MRI and identified asymptomatic findings of either a small nodule or a small cystic mass in spine MRIs of five participants who received intracisternal or intraventricular RGX-121 approximately three to six years ago.
Investigators deemed these findings to be nonserious, and radiologists believe they are likely benign.
There is no clinical or pathological evidence to confirm the nature or causation of the spine MRI findings.
No brain nodules or masses were identified on any brain MRIs.
Regenxbio To Continue Monitoring Patients
Because spine MRI is not normally conducted for MPS in clinical practice or trials, the underlying prevalence and clinical significance of these types of asymptomatic findings in this patient population are unknown.
Investigators plan to continue to observe these patients with periodic imaging only.
The company and its partner NS Pharma are evaluating additional patient imaging and longer-term follow-up data, and will incorporate FDA feedback, including the full clinical hold letter once received, into next steps for RGX-121.
RGX-121 Targets Rare Hunter Syndrome
MPS II is a rare, X-linked recessive disease caused by a deficiency in the lysosomal enzyme I2S, leading to an accumulation of glycosaminoglycans (GAGs), including heparan sulfate (HS), in tissues, which ultimately results in cell, tissue, and organ dysfunction, including in the CNS.
Approximately 2,000 patients worldwide are diagnosed with MPS II, with more than 500 babies born annually around the world with the disease.
RGX-121 is a one-time investigational gene therapy, designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system (CNS).
Delivery of the IDS gene within cells in the CNS could provide a permanent source of secreted iduronate-2-sulfatase (I2S) protein beyond the blood-brain barrier, allowing for long-term cross-correction of cells throughout the CNS.
RGX-121 expressed protein is structurally identical to normal I2S.
RGNX Stock Price Activity: Regenxbio shares were down 23.79% at $8.170 during premarket trading on Monday, according to Benzinga Pro data.
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