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BREAKING: Ascidian’s RNA Exon Editor for Stargardt Disease Makes Historic First in Gene Therapy

The first clinical-stage RNA exon editor in the world – which is being applied first to eye care – just made major breakthroughs with IND and FDA Fast Track designations simultaneously. 

American biotechnology firm Ascidian Therapeutics (Boston, MA) announced today that the FDA has approved their Investigational New Drug (IND) application for groundbreaking Stargardt disease candidate ACDN-01. 

The drug candidate has also been granted the FDA’s Fast Track designation, which expedites FDA regulatory processes and communications for drugs that show potential for meeting high unmet needs in serious diseases.

In the spotlight is Ascidian Therapeutics’ proprietary exon editing technology, a novel approach to gene therapy that has bagged the company a litany of firsts in not only the ophthalmic world, but in all of medicine. 

The IND makes ACDN-01 the only clinical-stage therapeutic targeting the genetic cause of Stargardt disease, the world’s most common inherited single-gene retinal disease.1 But perhaps more significantly, ACDN-01 is also the first clinical-stage RNA exon editor in the world, a technology that could have effects far beyond the human eye. 

“By editing RNA and not DNA, the Ascidian approach brings unique advantages with potential to transform the lives of people living with Stargardt disease and, more broadly, to dramatically expand the reach of genetic medicine,” said Dr. Michael Ehlers, president and interim chief executive officer of Ascidian Therapeutics.

“The advancement of Ascidian’s first-of-its kind RNA exon editor from the lab to the clinic is a unique and novel therapeutic approach targeting the genetic cause of Stargardt disease,” said Dr. Byron Lam, director of the Mark J. Daily Inherited Retinal Disease Research Center at the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. 

“This is a critical step toward overcoming the challenges of Stargardt disease, such as the size of the ABCA4 gene and large number of mutations within the patient population, that have long kept Stargardt out of reach for conventional gene therapies. Stargardt patients deserve treatment options, and I am looking forward to the clinical evaluation of this promising approach.”

Enrollment in the company’s Phase 1/2 STELLAR trial to investigate the use of ACDN-01 in Stargardt disease and other retinopathies is slated to kick off in the first half of 2024. In an interview with Biotech TV, Dr. Ehlers indicated that the first patient dosing could take place as early as mid-2024.2 

Targeting RNA opens up galaxy of new possibilities

Ascidian’s proprietary exon editing platform involves manipulating malformed proteins at the root of diseases like Stargardt at the pre-mRNA level. The technology targets mutated exons, parts of the gene that eventually become mRNA, which are in turn transcribed into the body’s multitude of proteins. 

This approach, which targets RNA over DNA, affords exon editing a host of advantages over current gene editing technologies. 

“Currently-used technologies have limitations, which may include challenges with packaging and delivering in vivo, addressing large genes or genes with high mutational variance, maintaining native gene expression, or correcting disease-causing genetic changes without permanently altering our DNA with potentially immunogenic enzymes,” wrote Dr. Ehlers in a LinkedIn post accompanying the announcement.

Ascidian’s bold regulatory gambit pays off

The buzz surrounding the technology, the IND, and the Fast Track designation has also been amplified by Ascidian’s seemingly bold choice to file in the US without ex-US clinical data. Drugs that follow this path are few and far between, with many firms first heading to the clinic in less stringent regulatory environments. 

Dr. Ehlers explained that the company’s decision to first summit the FDA’s notoriously treacherous regulatory mountain speaks volumes about the drug’s breakthrough potential. 

“We chose to go to the FDA first because we have conviction in the rigor of our data,” said Dr.  Ehlers.

Dr. Ehlers credited the technology’s potential safety improvements, and especially with exon editing’s reduction of off-target editing and its dangerous consequences, as drivers of the FDA’s swift action.2


  1. Sahel JA, Marazova K, Audo I. Clinical characteristics and current therapies for inherited retinal degenerations. Cold Spring Harb Perspect Med. 2014;5(2):a017111.
  2. Biotech TV. The Science Behind the News: Ascidian Therapeutics’ IND is Cleared for an RNA Exon Editing Program Against Stargardt Disease. Available at: Accessed on 30 January 2024.
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