UK-based R1 Therapeutics, Inc. expanded its Series A financing to USD 80.5 million with the addition of Samsara BioCapital, giving the kidney disease biotech further backing as its lead hyperphosphatemia drug AP306 approaches a Phase IIb readout expected in the first half of 2027.
Samsara joined a syndicate co-led by Abingworth, DaVita Venture Group, and F-Prime after R1 launched in March 2026 with an oversubscribed USD 77.5 million Series A. Existing investors include Curie.Bio, SNMA Capital, formerly SymBiosis Capital Management, and US Renal Care. The expanded financing remains focused on advancing AP306 as a standalone treatment for elevated phosphate levels in patients on dialysis.
AP306 is currently being evaluated in a global Phase IIb trial in patients with chronic kidney disease on dialysis. The multicenter, randomized, double-blind, placebo-controlled study is enrolling approximately 168 patients across the US and China and is evaluating a range of fixed doses, with topline data expected in the first half of 2027.
R1 describes AP306 as a first-in-class pan phosphate transporter inhibitor designed to block the three sodium-dependent phosphate transporters NaPi-IIb, PiT-1, and PiT-2 in the gut, thereby inhibiting active phosphate absorption. The company licensed exclusive development and commercialization rights outside Greater China from Alebund Pharmaceuticals, which is partnering on the Phase IIb study. AP306 was originally discovered by Chugai Pharmaceutical and licensed to Alebund in 2021.