Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 123

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 123
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 potential advancement of our selected dual combination of an NBD1 stabilizer and complementary modulator; |

| • |     | approximately $95.0 million to initiate and progress a dual combination Phase 2b dose-ranging clinical trial of our                                
 selected NBD1 stabilizer and complementary modulator and to continue manufacturing scale-up to supply drug product for late stage clinical trials; |

| • |     | approximately $15.0 million on other research and development activities; and |

| • |     | the remainder for working capital and other general corporate purposes, including the costs to operate our business, such 
 as our employee and facility costs and costs associated with being a public company.                                      |

We may also use a portion of the remaining net proceeds and our existing cash, cash equivalents and investments in marketable securities to in-license,acquire or invest in complementary businesses, technologies, products or assets. However, we have no current commitments, agreements, understandings or obligations to do so. We believe, based on our current operating plan, that the net proceeds from this offering, together with our existing cash, cash equivalents and investments in marketable securities, will be sufficient to fund our operations into 2028. Our expected use of proceeds from this offering described above represents our current intentions based on our present plans and business condition. As of the date of this prospectus, we 86

cannot predict with certainty all of the particular uses for the net proceeds to be received upon the completion of this offering or the actual amounts that we will spend on the uses set forth
above. We expect that we will require additional funds in order to fully accomplish the specified uses of the proceeds of this offering. Moreover, certain of our anticipated clinical activities are cross-program. For example, we intend to conduct
dual combination trials of our lead NBD1 stabilizer with one or more of our complementary modulators. The specific allocation and timing of our actual expenditures will depend on numerous factors, including progress of our research and development
efforts, the status of and results from preclinical studies and ongoing and future clinical trials, the timing and outcome of regulatory submissions, and other factors described in “Risk Factors” in this prospectus, as well as the
amount of cash used in our operations and any unforeseen cash needs. Therefore, our actual expenditures may differ materially from the estimates described above. We may find it necessary or advisable to use the net proceeds for other purposes.

We will have broad discretion over how to use the net proceeds to us from this