R1 Therapeutics announced on Mar. 18 that it has raised $77.5 million in an oversubscribed series A funding round to support the development of new treatments for kidney diseases. The California-based company said the funds will be used to advance AP306, a drug candidate aimed at lowering phosphate levels in patients with chronic kidney disease.
The announcement highlights growing interest and investment in therapies targeting kidney disease, an area with significant unmet medical need. R1's lead program, AP306, is described as a pan phosphate transporter inhibitor and is claimed by the company to be “the only agent that blocks the ‘active’ transport” of phosphate, whereas existing treatments only passively restrict its movement.
AP306 was originally developed by Chugai and later sublicensed to R1 from Alebund Pharmaceuticals, which retains rights to the drug in Greater China. Financial terms of this agreement were not disclosed. The drug has completed Phase 2a testing in China, with results from February 2025 showing a notable reduction in serum phosphate levels compared to baseline. According to R1, about 20% more patients treated with AP306 reached recommended phosphate levels than those taking Sanofi’s Renvela.
R1 plans to work with Alebund on a global Phase 2b study for AP306, expected to begin later this year. "AP306 has the potential to deliver superior efficacy with substantially lower pill burden compared to current phosphate binder therapies," Krishna Polu, CEO of R1 Therapeutics, said in a statement.
Other companies also reported fundraising successes on Tuesday. Mestag Therapeutics secured $40 million for its Phase 1 STARLYS study of a bispecific antibody for solid tumors, while iDEL Therapeutics closed a €9 million (about $10.4 million) seed round to advance programs focused on delivering cancer drugs directly into cells.
The influx of capital into these biopharma startups reflects ongoing momentum in early-stage life sciences investment and continued efforts toward developing innovative therapies.
