Sionna's SION-451 combination trial heads to a safety readout this half
The Phase 1 healthy-volunteer study testing SION-451 alongside two other CFTR correctors is built to show whether the triple combination is tolerable, not whether it works in cystic fibrosis.
Executive Summary
- Sionna Therapeutics is running a healthy-volunteer safety and pharmacokinetics study to test whether its CFTR stabilizer can be combined with two other correctors without added toxicity, a tolerability question that gates the drug's path into cystic fibrosis patients.
- The trial has enrolled toward its original target without amendment to its endpoints, population, or completion date, indicating an operationally uneventful run heading into readout.
- Because the study is early-phase and non-registrational, its consequence is internal: a clean tolerability signal would support moving the three-way combination into patients, while a safety signal would narrow which pairing advances.
- Sionna has guided topline data for the second half of 2026, consistent with a registered primary completion date in June 2026, giving the readout a defined near-term window rather than an open-ended timeline.
The trial
The study, registered as NCT07035990, is a randomized, placebo-controlled Phase 1 trial enrolling 144 healthy adults in Australia to test SION-451 in two separate dual combinations, one with SION-2222 (galicaftor), a transmembrane domain 1-directed CFTR corrector, and one with SION-109, an intracellular loop 4-directed CFTR corrector. Its two primary endpoints track the incidence of treatment-emergent adverse events for each pairing, with twelve secondary endpoints capturing pharmacokinetic measures including AUC, Cmax, and half-life for each combination. There is no efficacy endpoint: this is a tolerability and exposure study, not a test of CFTR function. NCT07035990Safety, Tolerability, and Pharmacokinetics of Multiple Dose Combinations of SION-451 and Complementary Modulators SION-2222 and SION-109 in Healthy Participants.NCT07035990
Probability of SuccessBased on the AppliedXL Probability of Success model. For more information about the methodology, read the research here.
Why it matters
Sionna's cystic fibrosis strategy rests on NBD1 stabilizers, and SION-451 is one of two clinical-stage stabilizers in that class alongside SION-719, which separately completed enrollment in a Phase 2a proof-of-concept trial in April 2026. Chief Executive Officer Mike Cloonan said the company entered 2026 "with both of our clinical stage NBD1 stabilizer programs on track for topline readouts this summer," tying SION-451's combination data to the same near-term window as the patient-facing SION-719 study. Whether SION-451 can be paired with a second corrector without compounding toxicity determines which combination advances toward a patient trial. SionnaSionna Therapeutics Reports First Quarter 2026 Financial ResultsMay 12, 2026
Operational read
The trial dosed its first subjects on August 25, 2025 and moved from Not yet recruiting to Recruiting on September 2, 2025. Its enrollment target of 144 has not changed since the study was first registered, and no amendments have touched its endpoints, eligibility criteria, or primary completion date, which remains June 1, 2026. That stability means the readout's timing risk sits with disclosure rather than execution: the study is not showing signs of a delayed or troubled run, and the open question is when Sionna reports out, not whether the trial finished cleanly. NCT07035990Safety, Tolerability, and Pharmacokinetics of Multiple Dose Combinations of SION-451 and Complementary Modulators SION-2222 and SION-109 in Healthy Participants.NCT07035990
The competitive frame
No competing trial shares SION-451's specific combination of NBD1 stabilization with dual CFTR correctors in this dataset, so the study sits without a direct comparator on mechanism. The broader field of early-phase healthy-volunteer safety studies spans unrelated targets, including a polycystic kidney disease program and a spinal muscular atrophy antisense trial, none of which bear on CFTR modulation. The nearest points of reference are Sionna's own pipeline: SION-719's parallel Phase 2a readout in cystic fibrosis patients, expected on the same summer 2026 timeline, will test the NBD1-stabilizer approach directly in disease rather than in healthy volunteers. SionnaSionna Therapeutics Reports First Quarter 2026 Financial ResultsMay 12, 2026
This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.