Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 11

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 11
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| • |     | The Preliminary Price Range assumes the conversion of all of the Company’s outstanding redeemable                                                                                                                                             
 convertible preferred stock. The Company’s redeemable convertible preferred stock currently has substantial economic rights and preferences over the Common Stock. Immediately prior to the closing of the IPO, all outstanding shares of the 
 Company’s redeemable convertible preferred stock will convert into Common Stock, thus eliminating the superior rights and preferences of the redeemable convertible preferred stock as compared to the Common Stock.                          |

FOIA CONFIDENTIAL TREATMENT REQUESTED BY SIONNA THERAPEUTICS, INC.

Division of Corporation Finance Office of Life Sciences U.S. Securities and Exchange Commission January 24, 2025 Page 8

| • |     | The valuations of comparable companies that have completed or launched IPOs from January 2024 to date, which                                       
 valuations reflected increases from the last rounds of private equity financing prior to such IPOs, i.e., reflecting step-up multiples in the IPO. |

| • |     | From December 2024 to January 2025, the Company conducted 65 “testing-the-waters” meetings with prospective investors, and as a result, the Company elected to continue to pursue an IPO. |

| • |     | The price that investors are willing to pay in the IPO, for which the Preliminary Price Range is intended to                                                                                                                                       
 serve as an estimate, may take into account other factors that have not been expressly considered in prior valuations of the Common Stock, but which the Company or the underwriters for the IPO believe are significant to investors in their own 
 subjective and qualitative assessment of the Company, and thus may not be objectively determinable or quantifiable under the above-described valuation models.                                                                                     |

| • |     | In determining the Preliminary Price Range, the underwriters utilized a number of valuation methodologies,                                                                    
 including a discounted cash flow analysis, factors likely to affect the Company’s revenues and profitability, and relevant trading multiples for comparable public companies. |

| • |     | The successful completion of the IPO would strengthen the Company’s balance sheet, provide access to public                          
 equity and provide enhanced operational flexibility, increasing the value of the Common Stock compared to that of a private company. |

| • |     | Recent market conditions used in the determination of the Preliminary Price Range after discussions with the                          
 underwriters, based on the current market environment and the supply and demand for such investment opportunities in the marketplace. |

The Company believes the