Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 275

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 275
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 Atlas Venture. Entities affiliated with Atlas Ventures beneficially own more than 5% of our outstanding capital stock. Bruce Booth, D.Phil., a member of our board of directors, is a general partner at Atlas Venture. |

| (3) | OrbiMed Private Investments VIII, LP (“OrbiMed”) beneficially owns more than 5% of our outstanding capital 
 stock. Peter A. Thompson, M.D., a member of our board of directors, is a member at OrbiMed.                |

| (4) | Consists of (i) 2,155,469 shares of Series B preferred stock held by RA Capital Nexus Fund, L.P. and (ii) 923,773 shares                                                                                                                               
 of Series B preferred stock held by RA Capital Healthcare Fund, L.P. Entities affiliated with RA Capital beneficially own more than 5% of our outstanding capital stock. Joshua Resnick, M.D., M.B.A., a member of our board of directors, is a senior 
 managing director at RA Capital.                                                                                                                                                                                                                       |

| (5) | Consists of 2,275,528 shares of Series B preferred stock held by The Rise Fund Sling, L.P. Entities affiliated with TPG                                                   
 Growth beneficially owns more than 5% of our outstanding capital stock. Lucian Iancovici, M.D., a member of our board of directors, is a managing director at TPG Growth. |

198

Series C Preferred Stock Financing On March 4, 2024, in an initial closing and a subsequent closing, we issued and sold 17,717,162 and 911,808 shares of our Series C convertible preferred stock, par value $0.001 per share (“Series C preferred stock”), respectively, representing an aggregate of 18,628,970 shares of Series C preferred stock, at a purchase price of $9.762 per share, for an aggregate purchase price of approximately $181.9 million. Each outstanding share of Series C preferred stock will convert into one share of common stock immediately prior to the completion of this offering. The following table summarizes the shares of our Series C preferred stock issued to our related parties:

| Purchasers(1)                                           |     | Shares of Series C 
 Preferred Stock    |           |     | Total Purchase Price |            |
|:--------------------------------------------------------|:----|:-------------------|----------:|:----|:---------------------|-----------:|
| Entities affiliated with Atlas Venture(2)