Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 2

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 2
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 to this offering, there has been no public market for our common stock. It is currently estimated that the initial public offering price per share will be between $16.00 and $18.00. We have applied to list our common stock on The Nasdaq Global Market (“Nasdaq”) under the symbol “SION.” We believe that upon the completion of this offering, we will meet the standards for listing on Nasdaq, and the completion of this offering is contingent upon such listing. We are an “emerging growth company” and “smaller reporting company” as defined under the United States (“U.S.”) federal securities laws and, as such, we have elected to comply with certain reduced reporting requirements. See the section titled “ Risk Factors” beginning on page 17 to read about factors that you should consider before deciding to invest in shares of our common stock.

|                                           |     | Per Share |     | Total |
|:------------------------------------------|:----|:----------|:----|:------|
| Initial public offering price             |     | $         |     | $     |
| Underwriting discounts and commissions(1) |     | $         |     | $     |
| Proceeds, before expenses, to us          |     | $         |     | $     |

| (1) | See the section titled “Underwriting” for additional information regarding compensation payable to the 
 underwriters.                                                                                          |

We have granted the underwriters the option to purchase up to an additional 1,323,529 shares of common stock from us, at the initial public offering price, less the underwriting discounts and commissions. The underwriters expect to deliver the shares of common stock on or about , 2025. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

| Goldman Sachs & Co. LLC |     | TD Cowen |     | Stifel |     | Guggenheim Securities |

, 2025

TABLE OF CONTENTS

|                                                                                       |     | Page |     |
| Contents                                                                              |     |      |     |
| PROSPECTUS SUMMARY                                                                    |     |      |   1 |
| RISK FACTORS                                                                          |     |      |  17 |
| CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS                                  |     |      |  84 |
| USE OF PROCEEDS                                                                       |