R1 Therapeutics has expanded its Series A financing to $80.5 million, adding new investment from Samsara BioCapital to support development of its lead kidney disease candidate, AP306. Samsara joins an investor group that includes Abingworth, DaVita Venture Group, F-Prime, Curie.Bio, SNMA Capital and U.S. Renal Care.
The financing expands an oversubscribed $77.5 million Series A announced in March 2026.
AP306 is a first-in-class pan phosphate transporter inhibitor being evaluated as a monotherapy for hyperphosphatemia in patients with chronic kidney disease who are on dialysis.
The candidate is being studied in a global Phase 2b trial, with topline results expected in the first half of 2027.
AP306 is designed to block three key active phosphate transporters in the gut. R1 said more than 70% of U.S. dialysis patients fail to achieve normal phosphate levels using current treatments.
KEY QUOTES:
“Samsara brings a rare combination of scientific depth and a track record of investing in kidney companies across the private and public markets. Their decision to join ahead of the Phase 2b readout is a strong endorsement of our novel approach to addressing hyperphosphatemia. With our global trial underway, their support, alongside that of our existing syndicate, further strengthens our ability to generate the clinical data needed to bring AP306 to patients.”
Krishna Polu, M.D., Co-Founder, President and CEO of R1 Therapeutics
“Managing phosphate levels remains one of the greatest challenges in dialysis care, with limited innovation for patients over the past several decades. With AP306, R1 is pursuing a novel mechanism of action that inhibits active phosphate transport, offering a differentiated alternative to traditional phosphate binders. We are pleased to join the investor syndicate and look forward to supporting the team as they advance AP306 through Phase 2b and beyond.”
Abe Bassan, Partner at Samsara BioCapital
