Sionna Therapeutics to Cut 46% of Staff, Pivots CF Drug Strategy After Trial Setback

Sionna Therapeutics Inc. (NASDAQ:SION) shares fell 3% in after-hours trading Monday after the company announced a significant strategic shift, including a 46% reduction in its workforce. The clinical-stage biopharmaceutical firm is pivoting its development focus to a new cystic fibrosis (CF) drug combination following disappointing clinical trial results for a prior candidate.

Strategic Restructuring

Sionna will now advance SION-451 + SION-2222, a proprietary dual-drug combination, into a Phase 2a trial. The company stated this new trial, named AscenSION CF, is expected to begin in the first quarter of 2027. The open-label study will evaluate the combination's effect on sweat chloride levels, safety, and pharmacokinetics in adults with CF who are homozygous for the F508del mutation.

To support this new focus, Sionna's board approved cost-saving measures, including the staff reduction. The company anticipates incurring approximately $6.4 million in restructuring charges. These changes are expected to extend its cash runway into the second half of 2029, based on its second-quarter 2026 cash position of approximately $268.3 million.

Rationale for the Pivot

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The decision follows a review of data from the PreciSION CF Phase 2a trial for its previous drug candidate, SION-719. According to the company, the trial, which tested SION-719 as an add-on to the standard-of-care treatment Trikafta, failed to achieve its key activity endpoint.

While a post hoc analysis showed a mean placebo-adjusted sweat chloride reduction of up to -8.6 mmol/L in a subset of participants, Sionna identified several issues that may have compromised the overall results:

• Drug exposure outliers in three participants, which were consistent with non-adherence to the treatment regimen.
• Lower exposures to Trikafta's components during the SION-719 treatment periods.
• Potential interactions between SION-719 and another drug component that may have blunted the therapeutic benefits.