R1 Therapeutics is debuting with an oversubscribed $77.5 million series A financing aimed at advancing its first-in-class therapy for chronic kidney disease (CKD) patients on dialysis with high phosphate levels.
The funding was co-led by Abingworth, F-Prime Capital and DaVita Venture Group, with participation from Curie.Bio, SymBiosis and U.S. Renal Care, according to a March 17 release.
The financing arrives alongside the new company obtaining an exclusive global license to develop and commercialize an asset called AP306 from China-based Alebund Pharmaceuticals. The candidate is a pan-phosphate transporter inhibitor in development as a monotherapy for hyperphosphatemia, a condition characterized by elevated phosphorus levels in the blood that can cause muscle cramps, itchy skin, bone pain and rashes.
Hyperphosphatemia is common among the roughly 500,000 patients in the U.S. and 4 million people worldwide who are on dialysis, and the condition can lead to bone and cardiovascular disease.
AP306 was originally developed by Chugai Pharmaceutical, which later licensed it to Alebund, and is expected to enter a phase 2b study later this year. Alebund published phase 2a data on the asset in January 2025, demonstrating a significant reduction in serum phosphate levels along with favorable safety and tolerability.
According to the release, AP306 is the only agent that blocks the “active” transport of phosphate for the treatment of CKD, whereas approved therapies inhibit the “passive” transport of phosphate through binding.
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R1 notes that patients who take available phosphate binders, which were developed about 60 years ago, suffer from poor adherence due to high pill burdens and gastrointestinal tolerability issues, limiting their effectiveness.
The biotech is led by co-founder and CEO Krishna Polu, M.D., a nephrologist who has served as an advisor to Abingworth since April and has more than 20 years of experience in the biopharma industry. Polu highlighted the support of global kidney care providers DaVita and U.S. Renal Care and said, “AP306 represents a fundamentally new approach to treating hyperphosphatemia.”
R1’s AP306 will look to avoid the fate of two hyperphosphatemia treatment predecessors. Unicycive Therapeutics received a complete response letter (CRL) from the FDA last year as it advanced its hyperphosphatemia treatment candidate for CKD patients on dialysis. The FDA cited issues at a third-party manufacturing vendor that were flagged during an inspection. Unicycive resubmitted its new drug application and the FDA is expected to make an approval decision by or before June 29, 2026.
In 2021, Ardelyx also fell short of the FDA’s standards when its hyperphosphatemia candidate received a complete response letter stating the treatment effect was “small and of unclear clinical significance.” However, the treatment, designed to treat an electrolyte disorder that affects patients on dialysis by inhibiting the sodium-proton exchanger NHE3, was eventually approved in 2023 and is now sold as Xphozah.
R1’s lead investors bring deep pockets and expertise. Abingworth was acquired by the Carlyle Group and its $477 billion assets under management in 2022, and DaVita Venture Group has experience in renal biotechs, including joining kidney-focused Pathalys Pharma’s $105 million raise in 2024. Fidelity Biosciences rebranded as F-Prime in 2015 and has been responsible for 51 IPOs throughout its history, according to its website.
