Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 46

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 46
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 inspection or other appropriate means. In addition, while these clinical trials are subject to the applicable local laws, acceptance of the data by the FDA will be dependent upon its determination that the trials were conducted consistent with all applicable U.S. laws and regulations. There can be no assurance that the FDA will accept data from trials conducted outside of the U.S. as adequate support of a marketing application. Similarly, any data submitted to foreign regulatory authorities may not adhere to their standards and requirements for clinical trials and data from trials conducted outside of such jurisdiction may not be accepted. If the FDA or any comparable foreign regulatory authority does not accept such data, it would result in the need for additional trials, which could be costly and time-consuming, and which may result in current or future product candidates that we may develop not receiving approval for commercialization in the applicable jurisdiction. In addition, such foreign trials would be subject to the applicable local laws of the foreign jurisdictions where the trials are conducted, which may increase costs or time required to complete the clinical trial. Conducting clinical trials outside the U.S. also exposes us to additional risks, including risks associated with:

| • |     | additional foreign regulatory requirements; |

| • |     | foreign exchange fluctuations; |

| • |     | compliance with foreign manufacturing, customs, shipment and storage requirements; |

| • |     | inconsistent standards for reporting and evaluating clinical data and AEs; |

| • |     | varying standards or availability of CF care, resulting in data that may differ from patients who have received the U.S. 
 standard of care therapy;                                                                                                |

| • |     | any pandemic, epidemic or public health emergencies; |

| • |     | diminished protection of intellectual property in some countries; and |

| • |     | political instability, civil unrest, war or similar events that may jeopardize our ability to commence, conduct or complete 
 a clinical trial and evaluate resulting data.                                                                               |

35

If any third-party manufacturer of our product candidates is unable to increase the scale of its production of our product candidates or increase the product yield of its manufacturing, then our manufacturing costs may increase and commercialization may be delayed.

In order to produce sufficient quantities to meet the demand for clinical trials and, if approved, subsequent commercialization of our product
candidates, our third-party manufacturers will be required to increase their production and optimize their manufacturing processes while maintaining the quality of our product candidates. The transition to larger scale production could prove
difficult. In addition, if our third-party manufacturers are not able to