R1 Therapeutics, a clinical-stage biopharmaceutical company developing therapies for kidney disease, has expanded its Series A financing to $80.5 million with a new investment from Samsara BioCapital.
The investment follows R1’s previously announced $77.5 million Series A, which was oversubscribed and announced in March 2026.
Samsara BioCapital joins investors including Abingworth, DaVita Venture Group, F-Prime, Curie.Bio, SNMA Capital and U.S. Renal Care.
R1 Therapeutics will use the new funding to continue developing AP306, its lead drug candidate for hyperphosphatemia in patients with chronic kidney disease (CKD) who are receiving dialysis.
AP306 is being evaluated as a monotherapy in a global Phase 2b clinical trial.
The company expects to report topline results from the trial in the first half of 2027.
Hyperphosphatemia occurs when phosphate levels in the blood become too high. It is a common complication among people with advanced kidney disease and dialysis.
R1 says phosphate binders have been the standard treatment for approximately 60 years, but more than 70% of U.S. dialysis patients do not achieve normal phosphate levels, according to the company.
Uncontrolled phosphate levels have been associated with cardiovascular and bone complications and increased mortality.
AP306 is designed to take a different approach by blocking the active transport of phosphate in the gut.
According to R1, AP306 is a first-in-class pan phosphate transporter inhibitor designed to block three key phosphate transporters in the gut.
The company believes this approach could provide rapid phosphate lowering while reducing the treatment burden for patients.
AP306 is currently being studied in a multi-center, randomized, double-blind, placebo-controlled Phase 2b trial, registered as NCT06712654.
The study is being conducted at clinical sites across the United States and China through R1’s partnership with Alebund Pharmaceuticals (Jiangsu) Limited.
R1 Therapeutics launched in March 2026 with its oversubscribed $77.5 million Series A financing.
The company holds exclusive global rights outside Greater China to AP306 from Alebund Pharmaceuticals.
AP306 was originally discovered by Chugai Pharmaceutical Co., Ltd. and was later licensed to Alebund Pharmaceuticals in 2021.
With the Series A now expanded to $80.5 million, R1 Therapeutics will continue advancing the global Phase 2b program and preparing for the next stages of development of AP306.
