Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 276

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 276
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 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. |

199

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 shares of common stock at a ratio of 1-for-1.4611 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)               |     |                    | 1,153,967 |     | $                    | 11,265,026 |
| OrbiMed Private Investments VIII, LP(3)                 |     |                    | 2,048,760 |     | $                    | 19,999,995 |
| Entities affiliated with RA Capital(4)                  |     |                    | 5,456,093 |     | $                    | 53,262,380 |
| Sionna Aggregator, LP(5)                                |     |                    | 2,817,045 |     | $                    | 27,499,993 |
| Entities affiliated with TPG Growth(6)                  |     |                    | 1,765,541 |     | $                    | 17,235,211 |
| Entities affiliated with Viking Global Opportunities(7) |     |                    | 2,560,950 |     | $                    | 24,999,994 |

| (1) | Additional details regarding these stockholders and their equity holdings are included in this prospectus under the 
 section “Principal Stockholders.”