Estuary Biotherapeutics launched October 16 with a $93 million Series A led by RA Capital Management, aimed at the most common inherited kidney disorder. Roughly one person in every 400 to 1,000 carries ADPKD, autosomal dominant polycystic kidney disease. Mutations drive cysts that progressively destroy kidney tissue and often end in renal failure. Tolvaptan is the only specifically approved drug, and it slows the disease rather than reversing it.
Research from two Yale School of Medicine professors, Stefan Somlo and Michael Caplan, formed the company in 2022. In mice, Somlo’s team found that switching proteins known as polycystins back on shrank cysts and reversed kidney inflammation and scarring. Subsequent work showed only a fragment of the full polycystin protein is required, and that is what makes gene therapy plausible: a small payload fits inside standard viral vectors and can reach the kidney.
Two programs carry the thesis. The first, EST-201, carries a complete PKD2 gene. The second, EST-101, delivers only the portion of the PKD1 protein that does the work. Both are designed as one-time, locally administered treatments slated for human testing in 2027 and 2028.
Deep Track Capital, 4BIO Capital, Alphabet’s GV and Biogen’s early-stage arm joined the round. A $10 million seed had been co-led by two of those firms. Chief executive Wayne Sackett called delivery “the most crucial remaining barrier to kidney gene therapy.”
Competition is real. Novartis agreed last year to buy Regulus Therapeutics for $800 million to control an RNA-targeting ADPKD candidate.
