R1 Therapeutics, a Redwood City, California-based clinical-stage biopharmaceutical company developing therapies for kidney disease, has expanded its Series A financing to $80.5 million following a new investment from Samsara BioCapital. The extension increases the financing by $3 million from the $77.5 million Series A announced in March 2026.
Samsara BioCapital joins an investor syndicate that includes Abingworth, DaVita Venture Group, F-Prime, Curie.Bio, SNMA Capital, formerly SymBiosis Capital Management, and U.S. Renal Care. The original $77.5 million financing was co-led by Abingworth, DaVita Venture Group and F-Prime.
R1 said the proceeds will support the continued clinical development of AP306, a pan phosphate transporter inhibitor being evaluated as a monotherapy for hyperphosphatemia in patients with chronic kidney disease who are on dialysis. AP306 is currently being studied in a global Phase 2b trial, with topline data expected in the first half of 2027.
The company began the global Phase 2b program in 2026, with the first patient randomized in July. The study is being conducted in partnership with Alebund Pharmaceuticals in the United States and China.
R1 launched in March 2026 and was co-founded by Krishna Polu, M.D., its President and CEO, and L. Mary Smith, Ph.D., its Chief Operating Officer. The company is focused on developing treatments for kidney disease, with AP306 serving as its lead clinical program.
