FDA Hits Avidity's AOC for Myotonic Dystrophy Type 1 with Partial Hold

Sarah Silbiger/Getty Images

The FDA ordered Avidity Biosciences to halt clinical trial enrollment in a Phase I/II trial of AOC 1001 in myotonic dystrophy type 1 after a patient suffered a "serious adverse event", the company reported Tuesday. 

The company's stock price plummeted more than 20% before recovering slightly after it disclosed the FDA's partial hold.

The nearly 40 patients already enrolled in the trial can continue their current dosing cohort, which includes a placebo arm. The company said it is "taking all necessary steps" to resolve the partial hold and resume enrollment.  

"We are doing a thorough analysis and will work diligently with the FDA and the trial investigator to follow the progress of this participant and to resume new participant enrollment as soon as we can," said Sarah Boyce, chief executive officer at Avidity in a statement.  

Avidity noted it "remains on track" to report preliminary results for safety, tolerability and key biomarkers by the end of the year. 

AOC 1001 is an RNA-based antibody oligonucleotide conjugate molecule. Myotonic dystrophy type 1 is a progressive and often fatal genetic muscle disorder. It is caused by a triplet-repeat in the DMPK gene, resulting in a toxic gain of mRNA.  

AOC 1001 is "silencing RNA" and aims to reduce the expression of the toxic RNA buildup in DM1 patients. 

There are currently no treatments available for DM1, which effects fewer than 40,000 patients in the United States.  

DM1 primarily affects skeletal and cardiac muscle, but patients can suffer from a wide range of symptoms, including muscle weakness, respiratory problems, fatigue, hypersomnia, cardiac abnormalities, severe gastrointestinal complications and cognitive and behavioral impairment. 

Boyce noted the FDA recently authorized clinical trials to test two similar antibody oligonucleotide conjugates: AOC 1020 for facioscapulohumeral muscular dystrophy and AOC 1044 for Duchenne muscular dystrophy. 

Evercore ISI analyst Josh Schimmer, who follows the company, said in a research note to clients that he expects the partial hold to be "transient". He attributed this to the aforementioned FDA authorizations. 

Another analyst who tracks Avidity cited the FDA's willingness to allow dosing of AOC 1001 to continue as a good sign. 

"We think it is promising that the FDA is allowing enrolled patients who already initiated dosing to continue receiving drug or placebo and roll into the open-label extension study," said SVB Securities analyst Joseph Schwartz in a client report. 

Schwartz called the partial hold an "incremental setback."

In late-morning trading, Avidity's share price fell $3.25, or 17.33%, to $15.50 on heavier-than-usual trading. Avidity went public in June 2020 at an offer price of $18 per share, raising $259.2 million.