Estuary Biotherapeutics Launches With $103 Million for ADPKD Gene Therapy

Estuary Biotherapeutics (Estuary) launched October 16, 2026, with $103 million in total committed financing, including a $93 million Series A led by RA Capital Management, to advance 2 gene therapy programs targeting the genetic root cause of autosomal dominant polycystic kidney disease (ADPKD).¹ The Series A included participation from Deep Track Capital, Biogen New Ventures, UPMC Enterprises, Pivotal bioVenture Partners, the National Kidney Foundation Innovation Fund, and a family office connected to an individual living with ADPKD, along with 4BIO Capital and GV, which co-led the company’s earlier $10 million seed financing.¹

“ADPKD is one of the world’s most common genetic diseases, yet patients are still awaiting a therapy that can transform the course of their disease,” said Wayne Sackett, co-founder and CEO of Estuary, in a company press release.¹ “We paired our scientific co-founders’ landmark breakthroughs in disease biology with a dedicated and passionate team focused on solving the most crucial remaining barrier to kidney gene therapy: delivery. By pioneering fit-for-purpose local administration and an efficient global development strategy, our team is moving with urgency to bring these important medicines into the clinic.”

What are EST-201 and EST-101, and how do they work?

Proceeds will advance Estuary’s 2 lead programs, EST-201 and EST-101, through clinical proof of concept.¹ EST-201 is a full-length polycystic kidney disease 2 (PKD2) gene therapy delivered through an adeno-associated virus (AAV) vector, designed for patients with ADPKD caused by a PKD2 mutation and anticipated to enter the clinic in 2027.¹ EST-101 delivers a compact, functional region of the polycystin-1 (PC1) protein using the same AAV vector, designed for patients with a PKD1 mutation and anticipated to enter the clinic in 2028.¹

Both programs are delivered locally to the kidney and are designed to transduce individual kidney epithelial cells, restoring polycystin protein levels across the nephron, rather than targeting pathways downstream of the disease’s underlying genetic cause as other ADPKD therapies do.¹ In the United States, Estuary estimates there are 10,000 to 15,000 patients with rapidly progressing ADPKD caused by a PKD2 mutation and 100,000 to 140,000 with rapidly progressing ADPKD caused by a PKD1 mutation, representing the initial treatment populations for EST-201 and EST-101, respectively.¹

What scientific evidence supports this approach?

Estuary’s approach builds on research from its scientific co-founders, Stefan Somlo, MD, and Michael Caplan, MD, PhD, of Yale School of Medicine.¹ In mice with established cystic disease, restoring polycystin expression reversed both the structural and functional hallmarks of disease, including shrinking kidneys, resolving cysts, and reducing inflammation and fibrosis.¹^,² Dr Caplan separately showed that a compact functional region of PC1 is sufficient to suppress cystic disease in mice, providing the scientific basis for an AAV-based approach to ADPKD caused by PKD1 mutations.¹^,³ “The differentiated approach pairs a known gene therapy modality with focal, kidney-directed delivery designed to reach the nephron directly,” said Emily Minkow, managing director, RA Capital Management.¹

What are the limitations?

EST-201 and EST-101 are both preclinical, investigational programs; neither has entered clinical testing, and the mouse-model reversal findings underlying the approach have not yet been replicated in humans.¹^,² The company has not disclosed data from its own kidney-targeting delivery platform, so how well the AAV vector transduces kidney cells in humans, as opposed to mice, remains unproven.¹ ADPKD affects more than 8 million people worldwide and is caused by PKD1 or PKD2 mutations in more than 90% of patients,⁴ but current standard-of-care therapy has been shown only to slow kidney growth and function decline, not halt or reverse it, which is the problem Estuary said its approach is designed to address.¹

References

1. Estuary Biotherapeutics. Estuary Biotherapeutics launches with $103 million to develop targeted gene therapies for kidney disease. Press release. Published October 16, 2026. Accessed October 16, 2026. https://estuarybio.com/news/estuary-series-a
2. Dong K, Zhang C, Tian X, et al. Renal plasticity revealed through reversal of polycystic kidney disease in mice. Nat Genet. 2021;53(12):1649-1663. doi:10.1038/s41588-021-00946-4
3. Onuchic L, Padovano V, Schena G, et al. The C-terminal tail of polycystin-1 suppresses cystic disease in a mitochondrial enzyme-dependent fashion. Nat Commun. 2023;14(1):1790. doi:10.1038/s41467-023-37449-1
4. Torres VE, Ahn C, Barten TRM, et al. KDIGO 2025 clinical practice guideline for the evaluation, management, and treatment of autosomal dominant polycystic kidney disease (ADPKD): executive summary. Kidney Int. 2025;107(2):234-254. doi:10.1016/j.kint.2024.07.010