Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 236

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 236
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�, and       and their                                                   
 terms will expire at our first annual meeting of stockholders following this offering, to be held in 2025; |

| • |     | the Class II directors will be      , and       and their                                                       
 terms will expire at our second annual meeting of stockholders following this offering, to be held in 2026; and |

| • |     | the Class III directors will be      , and       and their                                                 
 terms will expire at our third annual meeting of stockholders following this offering, to be held in 2027. |

172

We expect that any additional directorships resulting from an increase in the number of directors will
be distributed among the three classes so that, as nearly as possible, each class will consist of one third of the directors. The division of our board of directors into three classes with staggered three-year terms may delay or prevent a change of
our management or a change in control.

This classification of our board of directors may have the effect of delaying or preventing changes in
control of our company.

Director Independence

Under the
listing standards, requirements and rules of The Nasdaq Stock Market LLC (the “Nasdaq Listing Rules”), independent directors must comprise a majority of our board of directors as a listed company within one year of the listing date.

Our board of directors has undertaken a review of the independence of each director. Based on information provided by each director concerning his or
her background, employment and affiliations, including family relationships, our board of directors has determined that none of the members of our board of directors, except Mr. Cloonan, have relationships that would interfere with the exercise of
independent judgment in carrying out the responsibilities of a director and that each of the directors, except Mr. Cloonan, is “independent” as that term is defined under the Nasdaq Listing Rules. Our board of directors has determined that
Mr. Cloonan, by virtue of his position as our current Chief Executive Officer, is not independent under applicable rules and regulations of the SEC and the Nasdaq Listing Rules. In making these determinations, our board of directors considered
the current and prior relationships that each non-employee director has with our company and all other facts and circumstances our board of directors deemed relevant