Ascidian Therapeutics: $40 Million Closed To Treat Human Diseases

By Annie Baker • Nov 20, 2023

Ascidian Therapeutics – a biotechnology company focused on treating human diseases by rewriting RNA – recently announced $40 million in Series A extension funding committed by Apple Tree Partners (ATP). This funding round will advance Ascidian’s lead program, an RNA exon editor to halt the progression of Stargardt disease or other ABCA4 retinopathies, and additional programs in the company’s pipeline.

The company also revealed that its founding CEO Michael Ehlers, M.D., Ph.D., will return as interim President and Chief Executive Officer, effective immediately. Dr. Ehlers, who also chairs Ascidian’s Board of Directors and serves as Chief Scientific Officer at ATP and a venture partner at the firm, succeeds Romesh Subramanian, Ph.D., who is departing Ascidian.

Ascidian designs RNA editors to replace multiple mutated exons simultaneously. Using this platform, Ascidian can edit genes too large to package in viral vectors and genes with high mutational variance, thereby addressing underlying causes of complicated genetic diseases beyond the reach of current gene therapy and base editing approaches. And since Ascidian’s technique does not introduce exogenous enzymes, the risk of adverse immune reactions is reduced. And because it does not modify DNA, the risk of off-target effects is decreased.

Earlier this year, Ascidian presented at the American Society of Gene and Cell Therapy Annual Meeting (ASGCT) six-month data from their lead program, establishing the production of therapeutically relevant levels of full-length ABCA4 protein following a one-time treatment with a single AAV-delivered RNA exon editing development candidate in the non-human primate retina. And this data represented the most efficient and durable RNA exon editing via trans-splicing ever achieved in large animals.

Ascidian anticipates submitting an Investigational New Drug (IND) Application to the U.S. Food and Drug Administration (FDA) for its lead program in ABCA4 retinopathies early next year. Beyond the lead program, Ascidian is advancing programs with first-in-class potential in neurological and neuromuscular disorders.


“We thank Romesh for his contributions to Ascidian over the past 14 months, including his work to validate the company’s novel exon editing platform and progress its programs. Ascidian’s approach to edit RNA at kilobase scales has demonstrated its potential in non-human primate studies, and today we are poised to submit our plans for human trials of what we believe will be a one-time treatment to preserve sight in people with Stargardt disease. This is only the beginning. The potential reach of altering RNA at this scale is vast.”

– Dr. Ehlers

“ATP created and incubated Ascidian with Mike Ehlers as the framer of the vision and architect of its groundbreaking exon editing platform, which defines a new class of RNA therapeutics. Our renewed investment in Ascidian is a resounding vote of confidence in the originality and brilliance of the company’s approach, the promising data to date, and Mike’s proven leadership.”

– Seth Harrison, M.D., ATP founder and managing partner and a member of the Ascidian Board of Directors