Company: SION
Filing Date: 2025-02-06
Form Type: S-1MEF
Source: 0001193125-25-021938
Chunk: 0

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-06
Form: S-1MEF
Chunk 0
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As filed with the Securities and Exchange Commission on February 6, 2025. Registration No. 333– UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 Sionna Therapeutics, Inc. (Exact name of registrant as specified in its charter)

| Delaware                        |     |                         2834 |     | 84-2801521         |
| (State or other jurisdiction of 
 incorporation or organization)  |     | -Primary Standard Industrial 
   Classification Code Number |     | -I.R.S. Employer   
 Identification No. |

21 Hickory Drive, Suite 500 Waltham, MA 02451 (617) 819-2020 (Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices) Michael Cloonan President and Chief Executive Officer Sionna Therapeutics, Inc. 21 Hickory Drive, Suite 500 Waltham, MA 02451 (617) 819-2020 (Name, address, including zip code, and telephone number, including area code, of agent for service) Copies to:

| Gabriela Morales-Rivera         
 William D. Collins Janet        
 Hsueh Goodwin Procter LLP       
 100 Northern Avenue             
 Boston, MA 02210 (617) 570-1000 |     | Jennifer Fitzpatrick                   
 Senior Vice President, General Counsel 
 21 Hickory Drive, Suite 500            
 Waltham, MA 02451 (617) 819-2020       |     | Tara Fisher                     
 Thomas J. Danielski             
 Ropes & Gray LLP                
 800 Boylston Street             
 Boston, MA 02199 (617) 951-7000 |

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this registration statement. If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☐ If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☒ 333-284352 If this Form is a post-effective amendment filed pursuant to Rule