Sionna Therapeutics Reports Fourth Quarter and Full Year 2025 Financial Results (Form 8-K)

Sionna Therapeutics Reports Fourth Quarter and Full Year 2025 Financial Results

Ongoing PreciSION CF Phase 2a proof-of-concept trial evaluating NBD1 stabilizer SION-719 as an add-on to standard of care in participants with cystic fibrosis is on track with topline data anticipated in mid-2026

Ongoing Phase 1 trial evaluating NBD1 stabilizer SION-451 in proprietary dual combinations with SION-2222 and with SION-109 in healthy volunteers is on track with topline data anticipated in mid-2026

Maintained strong cash position with approximately $310.3 million in cash and cash equivalents, expected to fund operations into 2028

WALTHAM, Mass., March 2, 2026 (GLOBE NEWSWIRE) - Sionna Therapeutics, Inc. (Nasdaq: SION), a clinical-stage biopharmaceutical company on a mission to revolutionize the current treatment paradigm for cystic fibrosis (CF) by developing novel medicines that normalize the function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, today reported financial results for the fourth quarter and full year ended December 31, 2025, and provided a business update.

"2025 was a remarkable and transformative year for Sionna. Propelled by the momentum of our upsized IPO in February, we have been steadily executing across our pipeline and strengthening the capabilities of our team. We delivered positive results from the two Phase 1 trials of our first-in-class NBD1 stabilizers SION-719 and SION-451 and expeditiously advanced these candidates into the next stages of development," said Mike Cloonan, President and Chief Executive Officer of Sionna. "With topline readouts from both of our ongoing trials anticipated this year, along with the capital to support us into 2028, Sionna is making meaningful progress toward our goal to deliver additional options for those living with CF."

Pipeline Updates

NBD1 Stabilizers

•Ongoing PreciSION CF Phase 2a Proof-of-Concept Trial with SION-719 On Track: In October 2025, Sionna announced the initiation of the PreciSION CF Phase 2a proof-of-concept (POC) trial (NCT07108153) evaluating SION-719 as an add-on to standard of care (SOC) in CF patients. The trial is evaluating the safety, tolerability, and pharmacokinetics (PK) of SION-719 when administered with SOC and assessing change in CFTR function as measured by sweat chloride levels. Topline data from this trial are anticipated in mid-2026.

•Ongoing Phase 1 Dual Combination Trial with SION-451 and Complementary Modulators On Track: In August 2025, Sionna announced the initiation of the Phase 1 trial (NCT07035990) evaluating SION-451 in proprietary dual combinations with SION-2222 (galicaftor), a transmembrane domain 1 (TMD1)-directed CFTR corrector, and with SION-109, an intracellular loop 4 (ICL4)-directed CFTR corrector, in healthy volunteers. The trial is ongoing, with topline data anticipated in mid-2026.

•Data Presented at 2025 North American Cystic Fibrosis Conference: In October 2025, Sionna presented data at the 2025 North American Cystic Fibrosis Conference (NACFC). An oral presentation highlighted data from the two single agent healthy volunteer Phase 1 clinical trials of novel NBD1 stabilizers, SION-719 and SION-451. As previously disclosed, in these Phase 1 trials, both SION-719 and SION-451 were generally well tolerated and exceeded target exposure levels. A poster presentation included new preclinical data that show the impact of SION-719 and SION-451 on the half-life of F508del-CFTR protein. In preclinical studies, NBD1 stabilizers SION-719 and SION-451 increased the half-life of mature F508del-CFTR protein up to levels seen in wild-type. This effect was

apparent when NBD1 stabilizers were used as single agents or when combined with complementary modulators. These data reinforce the differentiation of the NBD1 mechanism of action.

Financial Results for the Quarter and Year Ended December 31, 2025

Research and Development Expenses: Research and development expenses were $15.2 million for the fourth quarter of 2025 and $60.3 million for the year ended December 31, 2025, compared to $14.3 million and $57.3 million, respectively, for the same periods of 2024. These increases were mainly driven by development expenses to support the advancement of Sionna's clinical pipeline.

General and Administrative Expenses: General and administrative expenses were $8.4 million for the fourth quarter of 2025 and $28.7 million for the year ended December 31, 2025, compared to $3.9 million and $13.3 million, respectively, for the same periods of 2024. These increases were primarily due to personnel-related costs, professional fees, and stock-based compensation expenses to support the Company's continued growth and operational activities.

Net Loss: Net loss was $20.4 million for the fourth quarter of 2025 and $75.3 million for the year ended December 31, 2025, compared to a net loss of $15.8 million and $61.7 million, respectively, for the same periods of 2024.

Cash and Cash Equivalents: Cash, cash equivalents and marketable securities totaled $310.3 million as of December 31, 2025. Sionna expects its current cash position to fund operations into 2028.

About Sionna Therapeutics
Sionna Therapeutics is a clinical-stage biopharmaceutical company on a mission to revolutionize the current treatment paradigm for cystic fibrosis (CF) by developing novel medicines that normalize the function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Sionna's goal is to deliver differentiated medicines for people living with CF that can restore their CFTR function to as close to normal as possible by directly stabilizing CFTR's nucleotide binding domain 1 (NBD1), which Sionna believes is central to potentially unlocking dramatic improvements in clinical outcomes and quality of life for people with CF. Leveraging more than a decade of the co-founders' research on NBD1, Sionna is advancing a pipeline of small molecules engineered to correct the defects caused by the F508del genetic mutation, which occurs in NBD1. Sionna is also developing a portfolio of complementary CFTR modulators that are designed to work synergistically with its NBD1 stabilizers to improve CFTR function. For more information about Sionna, visit www.sionnatx.com.

Sionna intends to use its Investor Relations website as a means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Sionna's Investor Relations website, in addition to following Sionna's press releases, SEC filings, public conference calls, presentations, and webcasts.