Sionna Therapeutics — Third Quarter 2026 Earnings Summary

Financial Performance:

• Research and development expenses were $22.0 million for the quarter ended September 30, 2026, compared to $16.0 million in the same period of 2025.
• General and administrative expenses were $12.8 million for the quarter ended September 30, 2026, compared to $7.8 million in the same period of 2025.
• Net loss was $32.4 million for the quarter ended September 30, 2026, compared to a net loss of $20.3 million in the same period of 2025.
• Cash, cash equivalents, and marketable securities totaled $249.8 million as of September 30, 2026, down from $310.3 million as of December 31, 2025.
• Working capital was $212.1 million as of September 30, 2026, compared to $229.7 million as of December 31, 2025.
• Total stockholders' equity was $240.5 million as of September 30, 2026, compared to $306.8 million as of December 31, 2025.
• Net loss per share (basic and diluted) was $0.72 for the quarter ended September 30, 2026, compared to $0.46 in the same period of 2025.

Guidance and Future Outlook:

• The company expects its current cash position to fund operations into the second half of 2029.
• The AscenSION CF Phase 2 proof-of-concept trial for the SION-451 + SION-2222 dual combination is expected to initiate in the first quarter of 2027.

Business Segments and Product Lines:

• Sionna plans to advance the SION-451 + SION-2222 dual combination into the AscenSION CF Phase 2 proof-of-concept trial, selecting it based on clinical, PK, and nonclinical data including Phase 1 safety and tolerability results.
• The AscenSION CF trial will be an open-label study evaluating participants with CF homozygous for F508del treated with SION-451 + SION-2222 for 28 days after switching from Trikafta®, assessing sweat chloride, safety, and pharmacokinetics.
• Sionna is not advancing SION-719 as an add-on to standard of care following the PreciSION CF Phase 2a trial's failure to achieve its key activity endpoint.
• Post hoc analyses of the PreciSION CF trial excluding three participants with dosing non-adherence showed a mean placebo-adjusted sweat chloride reduction of up to -8.6 mmol/L for SION-719 added to Trikafta.
• Clinical and nonclinical data presented at the 2026 North American Cystic Fibrosis Conference (NACFC) indicated that NBD1 stabilizer-based combinations demonstrated improved CFTR trafficking and function up to wild-type levels in primary CF human bronchial epithelial cells.

Market and Competitive Landscape:

• Sionna's NBD1 stabilizer combinations showed potential to benefit a broad population of people with CF, including those with two copies of F508del or one copy of F508del and a null CFTR mutation.
• The competitive landscape includes existing CF therapies such as Trikafta, which serves as the standard of care in the planned AscenSION CF trial.

Risks and Challenges:

• The company faces risks related to the interpretation of PreciSION CF results, potential confounding factors, and the inherent limitations of post hoc analyses which may not reliably predict future outcomes.
• Risks include the possibility that in vitro and preclinical data may not translate to clinical benefit, and that results observed with one compound may not be predictive of results with a different compound or combination.
• Challenges include uncertainties in designing and conducting the AscenSION CF Phase 2 trial, the ability to demonstrate safety and efficacy of product candidates, and the ability to obtain regulatory feedback or approvals.
• The company faces risks regarding the ability to replicate positive results from earlier studies, retain key personnel following workforce reduction, and secure sufficient funding.

Management Commentary and Tone:

• CEO Mike Cloonan stated the company established a focused path forward centered on the SION-451 + SION-2222 dual combination, citing favorable Phase 1 results and PreciSION CF post hoc analyses as support for advancement.
• Management expressed confidence that with resources focused on the program and a cash runway into the second half of 2029, the company is well-positioned to execute its strategy.

Other Key Points:

• In September 2026, Sionna implemented a workforce reduction of approximately 46% and other cost-saving measures to focus resources on advancing SION-451 + SION-2222 and extend its operating runway.
• The increase in R&D and G&A expenses for the quarter was primarily driven by development expenses, personnel-related costs including stock-based compensation, and restructuring costs associated with the workforce reduction.