R1 Therapeutics, a clinical-stage biopharmaceutical company developing first-in-class therapies for patients with kidney disease, has expanded its Series A financing to US$80.5 million. The expanded round includes a new investment from Samsara BioCapital, a leading biotech investor active across private and public markets. The capital will support AP306, a first-in-class pan phosphate transporter inhibitor in development for hyperphosphatemia in patients on dialysis, with Phase 2b topline data expected in the first half of 2027.
Expanded Syndicate Brings Total Funding to US$80.5 Million
Samsara BioCapital joins an investor syndicate that includes Abingworth, DaVita Venture Group, F-Prime, Curie.Bio, SNMA Capital, and U.S. Renal Care. The original Series A round closed at US$77.5 million in March 2026 and was oversubscribed, reflecting significant demand from life sciences investors. With the latest commitment, the total financing rises to US$80.5 million and further strengthens the company's clinical development position.
AP306 Targets a Longstanding Unmet Need in Dialysis Care
AP306 is being evaluated as a monotherapy in a global Phase 2b trial for hyperphosphatemia in patients with chronic kidney disease who are on dialysis. The investigational therapy is a pan phosphate transporter inhibitor that aims to block active phosphate transport, offering a differentiated alternative to conventional phosphate binders. Phosphate binders have remained the standard of care for roughly six decades, underscoring the need for new mechanisms of action.
Leadership Sees Validation Ahead of Phase 2b Readout
Krishna Polu, M.D., Co-Founder, President and CEO of R1 Therapeutics, said Samsara BioCapital brings rare scientific depth and a track record of investing in kidney companies across private and public markets. He noted that joining ahead of the Phase 2b readout strongly endorses the company's novel approach to hyperphosphatemia. Polu added that the expanded syndicate strengthens R1's ability to generate clinical data needed to bring AP306 to patients.
Abe Bassan, Partner at Samsara BioCapital, said managing phosphate levels remains one of the greatest challenges in dialysis care, with limited innovation for patients over the past several decades. He explained that AP306 uses a novel mechanism of action to inhibit active phosphate transport, offering a differentiated alternative to traditional phosphate binders. Bassan added that Samsara is pleased to join the syndicate and looks forward to supporting the team through Phase 2b and beyond.
Global Phase 2b Trial Is Underway
The multicenter, randomized, double-blind, placebo-controlled Phase 2b study is identified by the clinical trial number NCT06712654. It is being conducted at clinical sites across the United States and in China through R1's global partnership with Alebund Pharmaceuticals (Jiangsu) Limited, which trades on the Hong Kong Stock Exchange under the symbol 09637. This international footprint is expected to broaden the evidence base for AP306 in diverse patient populations.
Proceeds Support Clinical Development and Future Growth
Proceeds from the expanded financing will support the continued development of AP306 as R1 Therapeutics advances its lead asset through late-stage global clinical testing. The company is focused on generating robust Phase 2b data that could inform future registration strategy and broader development plans. With topline results expected in the first half of 2027, the funding positions R1 to execute on key clinical and operational milestones.
R1 Therapeutics is advancing a clinical pipeline built around first-in-class therapies for kidney disease, with AP306 positioned to address a significant unmet need in dialysis care. The expanded Series A financing and the addition of Samsara BioCapital provide both capital and strategic expertise ahead of an important clinical milestone. With a global Phase 2b trial underway and topline results expected in the first half of 2027, the company is focused on generating evidence that could support a new treatment approach for patients with hyperphosphatemia.