Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 139

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 139
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 development expenses:         |     |                     |        |     |      |        |     |        |        |   |
| IPR&D acquisition related costs                        |     |                     | 13,639 |     |      |      — |     |        | 13,639 |   |
| Personnel-related (including stock-based compensation) |     |                     |  6,521 |     |      |  6,123 |     |        |    398 |   |
| Facility, lab and depreciation                         |     |                     |  1,925 |     |      |  1,783 |     |        |    142 |   |
| Other R&D related costs                                |     |                     |  1,974 |     |      |  1,137 |     |        |    837 |   |
| Total research and development expenses                |     | $                   | 43,035 |     | $    | 30,736 |     | $      | 12,299 |   |

Research and development expenses increased by $12.3 million to $43.0 million for the nine months ended September 30, 2024 from $30.7 million for the nine months ended September 30, 2023. The increase in research and development expenses was primarily due to direct research and development expenses of:

| • |     | $4.3 million increase in complementary modulator programs cost due to the initiation of the SION-109 Phase 1 clinical trial in 2024 offset by a $7.0 million decrease in NBD1 program costs due to a decrease in manufacturing expenses; and |

| • |     | unallocated research and development expenses increased by $15.0 million due to                                                                                                          
 in-process research and development (“IPR&D”) costs incurred in connection with the AbbVie License Agreement of $13.6 million and other unallocated research and development expenses of 
 $1.4 million due to increased professional services and external research and development spend.                                                                                         |

101

General and Administrative Expenses The following table summarizes our general and administrative expenses (in thousands):

|                                                        | 2024 | Nine Months         
 Ended September 30, |       |     | 2023 |   |       |     | Change |       |
|:-------------------------------------------------------|:-----|:--------------------|------:|:----|:-----|:--|------:|:----|:-------|------:|