Sionna Therapeutics Stock Crashes 92% After SION-719 Cystic Fibrosis Trial Fails Key Endpoint

Sionna Therapeutics shares plunged roughly 92% to a record low on August 10, 2026, after the company announced that SION-719, its first-in-class NBD1 stabilizer, missed the primary endpoint in the PreciSION CF Phase 2a proof-of-concept trial. The study evaluated SION-719 as an add-on to Trikafta, Vertex Pharmaceuticals' standard of care, in adult cystic fibrosis patients homozygous for the F508del mutation, measuring changes in sweat chloride levels as a marker of CFTR function. Following the failure, Sionna said it is discontinuing the 719 program entirely.

Analysts moved swiftly: Stifel cut its rating on the stock and Raymond James downgraded shares as well, both citing the trial failure. Barron's noted the outcome could be a positive for Vertex Pharmaceuticals, whose dominant CF franchise faces less competitive pressure as a result. Law firm Johnson Fistel announced it is investigating potential violations of federal securities laws in connection with the collapse.

As of its most recent quarter, Sionna held approximately $268.3 million in cash, previously expected to fund operations into 2028, though the company's path forward is now significantly uncertain with its lead program abandoned.