Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 350

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 350
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 equivalents and restricted cash at end of period                           |     | $                               |   36,711 |   |     | $    |  39,807 |   |
| Supplemental cash flow information:                                                   |     |                                 |          |   |     |      |         |   |
| Right-of use asset obtained in exchange for new operating lease                       
 liability                                                                             |     | $                               |        — |   |     | $    |   9,516 |   |
| Deferred offering costs in accrued expenses                                           |     |                                 |      851 |   |     |      |       — |   |
| Reconciliation of cash, cash equivalents and restricted cash:                         |     |                                 |          |   |     |      |         |   |
| Cash and cash equivalents                                                             |     | $                               |   35,749 |   |     | $    |  38,845 |   |
| Restricted cash                                                                       |     |                                 |      962 |   |     |      |     962 |   |
| Total cash, cash equivalents, and restricted cash                                     |     | $                               |   36,711 |   |     | $    |  39,807 |   |

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements. F-34

SIONNA THERAPEUTICS, INC.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(Unaudited)

1. Nature of the Business

Organization

Sionna Therapeutics, Inc. (the
“Company”), formerly known as Sling Therapeutics, Inc., is a clinical-stage biopharmaceutical company dedicated to researching and developing novel medicines for cystic fibrosis. The Company was incorporated in Delaware in August 2019 and
is headquartered in Waltham, Massachusetts.

Risks and Uncertainties

The Company is subject to a number of risks common to other companies in the biotechnology industry, including but not limited to, development by
competitors of new technological innovations, risks of failure of preclinical studies and clinical trials, development and manufacturing of product candidates, obtaining regulatory approval for product candidates, competition from substitute
products, the need to successfully commercialize and gain market acceptance of its product candidates, protection of proprietary technology, dependence on key personnel, the ability to attract and retain qualified employees, reliance on third party
organizations’ compliance with government regulations, and the need to obtain additional financing. Product candidates currently