Sionna will test SION-451 + SION-2222 in Phase 2a cystic fibrosis trial after post hoc SION-719 analysis identified an exploratory -8.6 mmol/L sweat chloride reduction.
Written By: Rishabh Sonawane, BPharm
Reviewed By: Pharmacally Editorial Team
Sionna Therapeutics will advance its proprietary CFTR modulator combination, SION-451 and SION-2222, into a Phase 2a proof-of-concept trial. The strategic pivot follows a post hoc analysis of the Phase 2a PreciSION CF study, which identified pharmacokinetic (PK) and drug-interaction factors that obscured the activity signal of the nucleotide-binding domain 1 (NBD1) stabilizer SION-719 when added to standard-of-care Trikafta.
Post Hoc Analysis Reveals Hidden Signal
The randomized, double-blind, placebo-controlled Phase 2a PreciSION CF trial (NCT07108153) evaluated SION-719 as an add-on to Trikafta (elexacaftor/tezacaftor/ivacaftor) in 15 adults with cystic fibrosis (CF) homozygous for the F508del mutation. The study missed its primary activity endpoint, leading Sionna to halt development of SION-719 as a Trikafta add-on.
In the primary analysis of 14 evaluable participants, the placebo-adjusted mean change in sweat chloride was -1.0 mmol/L (-1.1 mmol/L using treatment-period baseline). However, a post hoc analysis identified three participants with drug-exposure patterns indicative of non-adherence. Excluding these three individuals yielded a mean placebo-adjusted sweat chloride reduction of -8.6 mmol/L. Sionna noted that the treatment-period baseline analysis provides a more representative view of period-to-period variability.
Mechanistic and Pharmacokinetic Caveats
The analysis revealed two major factors undermining SION-719’s efficacy in the combination setting:
- Exposure Reductions: ETI exposure fell by 25% to 30% during SION-719 co-administration.
- Pharmacodynamic Antagonism: Preclinical human bronchial epithelial (HBE) cell data indicated that ivacaftor blunts the additional benefit provided by NBD1 stabilization. Notably, this inhibitory interaction was not observed when combining NBD1 stabilizers with complementary correctors targeting transmembrane domain 1 (TMD1) or intracellular loop 4 (ICL4).
Phase 2a AscenSION CF Trial Planned for 2027
Sionna will pivot to testing its proprietary double-combination regimen: SION-451 (NBD1 stabilizer) and SION-2222 (ICL4 corrector). The Phase 2a AscenSION CF trial is slated to initiate in Q1 2027. The 28-day study will evaluate adults with F508del-homozygous CF who transition directly from Trikafta to SION-451 (twice daily) plus SION-2222 (once daily). Primary endpoints include safety, pharmacokinetics, and sweat chloride changes.
The progression is backed by Phase 1 clinical data demonstrating target exposure coverage and favorable overall tolerability for the doublet combination.
Restructuring Extends Cash Runway into 2029
To align resources with its updated pipeline priorities, Sionna is implementing a corporate restructuring that includes a workforce reduction of approximately 46%. The company expects to incur about $6.4 million in restructuring and related charges. Supported by $268.3 million in cash, cash equivalents, and marketable securities reported at the end of Q2 2026, Sionna expects its operating runway to extend into the second half of 2029.
Reference
Sionna Therapeutics Announces Plans to Advance SION-451 + SION-2222 Dual Combination into Phase 2a Proof-of-Concept Trial, Sionna Therapeutics, 14 September 2026
About the Writer
Rishabha Sonawane, B.Pharm (LinkedIn) is healthcare writer with a strong interest in medical writing, regulatory affairs, clinical research, and AI-driven drug discovery. He has completed specialized training from the NIH and ICMR in clinical pharmacology, clinical research, and scientific writing. Passionate about evidence-based healthcare communication, he focuses on translating complex scientific research into clear, accurate, and engaging medical content.