Sionna Therapeutics Reports Fourth Quarter and Full Year 2024 Financial Results Phase 1 MAD dosing completed for SION-451 and final MAD cohort of SION-719 planned; Interim data in healthy volunteers show potential to pro

Sionna Therapeutics Reports Fourth Quarter and Full Year 2024 Financial Results

Phase 1 MAD dosing completed for SION-451 and final MAD cohort of

SION-719 planned; Interim data in healthy volunteers show potential to provide clinically meaningful benefit to CF patients. Topline data anticipated in first half of 2025

On track to initiate NBD1 Phase 2a proof-of-concept trial in

combination with SOC in CF patients and combination MAD trials of an NBD1 stabilizer with a complementary modulator in healthy volunteers in the second half of 2025, with topline data for both anticipated in

Completed upsized IPO with gross proceeds of approximately $219 million,

extending runway into 2028

Waltham, MA, March 20, 2025 (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, 2024, and provided a business update.

2024 was an excellent year for Sionna including strong clinical execution across multiple programs. Encouraging interim Phase 1 data for SION-719 and SION-451, our highly potent nucleotide-binding domain 1 (NBD1) stabilizers, showed that both candidates were generally well tolerated and achieved target

exposures reinforcing their potential to deliver meaningful clinical benefits for people with CF, said Mike Cloonan, President and Chief Executive Officer of Sionna. Building on this momentum, we successfully completed an upsized

IPO, a significant milestone that extends our cash runway into 2028 and provides financial and strategic flexibility. 2025 is off to a strong start with the consummation of the IPO and the progression of the Phase 1 single ascending dose (SAD) and

multiple ascending dose (MAD) trials for SION-719 and SION-451. We look forward to announcing topline data in the first half of this year and initiating our Phase 2a proof-of-concept (POC) trial and the combination MAD Phase 1 program later this year.

Complementary Modulators

Financial Results for the Quarter and Year Ended December 31, 2024

Research and Development Expenses: Research and development expenses were $14.3 million for the fourth quarter of 2024 and $57.3 million

for the year ended December 31, 2024, compared to $9.9 million and $40.6 million, respectively, for the same periods of 2023. These increases were mainly driven by direct program spend to support Sionna s clinical pipeline.

In 2024, Sionna licensed three clinical-stage assets, galicaftor (SION-2222), navocaftor (SION-3067) and SION-2851, from AbbVie Global Enterprises LTD, which resulted in the recognition of in-process research

and development expenses of $13.6 million, which consisted of a $5.0 million upfront payment and $8.6 million of non-cash expense.

General and Administrative Expenses: General and administrative expenses were $3.9 million for the fourth quarter of 2024 and

$13.3 million for the year ended December 31, 2024, compared to $2.7 million and $9.7 million, respectively, for the same periods of 2023. The increase was primarily due to personnel-related costs, including stock-based

compensation, and professional fees.

Net Loss: Net loss was $15.8 million for the fourth quarter of 2024 and $61.7 million

for the year ended December 31, 2024, compared to a net loss of $11.9 million and $47.3 million, respectively, for the same periods of 2023.

Cash and Cash Equivalents: Cash, cash equivalents and marketable securities totaled $168.0 million as of December 31, 2024. This balance

excludes net proceeds from our IPO of $199.6 million after deducting underwriting discounts and commissions and other offering costs. With the net IPO proceeds, 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 CF by developing novel medicines that normalize the function of the 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 resides 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 the Company s Investor Relations website, in addition to following the Company s press releases, SEC filings, public

conference calls, presentations, and webcasts.

Cautionary Note Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including,

without limitation, implied and express statements about Sionna s beliefs and expectations regarding: the initiation, timing, progress and results of Sionna s research and development programs, preclinical studies and clinical trials,

including the timing of Phase 1 topline data for SION-719 and SION-451, and the planned initiation of combination MAD trials and a Phase 2a POC trial; the ability of

clinical trials to demonstrate safety and efficacy of Sionna s product candidates; the ability of Sionna s preclinical studies to predict later clinical trial results; financial projections and expectations regarding the time period in

which Sionna s capital resources will be sufficient to fund its anticipated operations, including cash runway, use of capital, expenses and other financial results; and other statements that are not historical facts. In some cases, the

forward-looking statements can be identified by terms such as may, will, should, would, expect, plan, anticipate, could, intend,

target, project, believe, estimate, predict, potential or continue or the negative of these terms or other similar expressions. Any forward-looking statements in

this press release are based on management s current expectations and beliefs and are subject to a number of risks, uncertainties and important factors that may cause actual events or results to differ materially from those expressed or implied

by the forward-looking statements contained in this press release. Factors that could cause actual results to differ include, but are not limited to, risks and

uncertainties inherent in the development of product candidates, including uncertainties concerning the initiation, timing, progress, and results of our planned and future clinical trials and

studies; our ability to replicate positive results from earlier preclinical studies or clinical trials in current or future clinical trials; our ability to demonstrate that our NBD1 stabilizers, complementary CFTR modulators, and any potential

future product candidates are safe and effective for their proposed indications; regulatory developments in the United States and foreign countries; and general economic, industry and market conditions. These risks and uncertainties are described in

the section entitled Risk Factors in Sionna s most recent Annual Report on Form 10-K as well as any subsequent filings with the Securities and Exchange Commission. The events and

circumstances reflected in the forward-looking statements may not be achieved or occur. In addition, any forward-looking statements represent Sionna s views only as of today and should not be relied upon as representing its views as of any

subsequent date. Sionna explicitly disclaims any obligation to update any forward-looking statements except as required by law. No representations or warranties (expressed or implied) are made about the accuracy of any such forward-looking

Sionna Therapeutics, Inc.

Consolidated Statements of Operations

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Sionna Therapeutics, Inc.

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