Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 137

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 137
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 applicable regulatory authorities; |

| • |     | the development of commercial-scale manufacturing and distribution processes for our current any future product candidates; |

| • |     | our ability to obtain, maintain and protect patent, trade secret protection and regulatory exclusivity for our product 
 candidates, both in the U.S. and internationally;                                                                      |

| • |     | our ability to successfully recruit and retain additional employees; |

| • |     | the timing and amount of milestones, royalties or other payments we must make to our licensing partners; and |

| • |     | the commercialization of our product candidates, if and when approved. |

A change in the outcome of any of these variables with respect to the development of any current or future product candidate could mean a significant change in the costs and timing associated with the development of that product candidate. For example, if the FDA or another regulatory authority were to delay a planned start of a clinical trial or require us to conduct clinical trials beyond those that we currently anticipate would be required for the completion of clinical development of a product candidate, or if we experience significant delays in our clinical trials due to slower than expected patient enrollment or other reasons, we could be required to expend significant additional financial resources and time on the completion of clinical development of that product candidate. We do not 99

have control over many of these factors, including certain aspects of clinical development, the regulatory submissions process, potential threats to our intellectual property rights and general
political and economic conditions that may negatively impact our business in the future. We may never obtain regulatory approval for any of our product candidates, and, even if we do, drug commercialization takes several years and millions of
dollars in development costs.

General and Administrative Expenses

General and administrative expenses consist primarily of personnel-related costs, including salaries, payroll tax, bonuses, benefits and stock-based
compensation charges for those individuals in executive, legal, finance, human resources, information technology and other administrative functions. Other significant costs include legal fees relating to intellectual property and corporate matters,
professional fees for auditing, accounting, tax and consulting services, office and information technology costs, insurance costs and facilities, depreciation and other general and administrative expenses that are allocated. We recognize general and
administrative expenses in the periods in which they are incurred.

We anticipate that our general and administrative expenses will increase in the
future to support our increased research and development activities, pre-commercial preparation activities for our product candidates and any future product candidates and, if any product candidate receives
marketing approval, commercialization