Sionna Therapeutics (SION) Form 144: 33,000 Shares Proposed Sale

Sionna Therapeutics (SION) Form 144 notice reports a proposed sale of 33,000 shares of common stock through Morgan Stanley Smith Barney, with an aggregate market value of $793,980 and an approximate sale date of 08/26/2025 on NASDAQ.

Rhea-AI Filing Summary

Sionna Therapeutics (SION) Form 144 notice reports a proposed sale of 33,000 shares of common stock through Morgan Stanley Smith Barney, with an aggregate market value of $793,980 and an approximate sale date of 08/26/2025 on NASDAQ. The shares were acquired on 06/15/2023 upon exercise of stock options and paid in cash. The filer also disclosed recent Rule 10b5-1 sales by the same account: 17,500 shares sold on 08/20/2025 for $397,152 and 34,500 shares sold on 08/19/2025 for $727,112.80. The filing includes the standard representation that the seller is not aware of undisclosed material adverse information and references a possible 10b5-1 plan adoption date field (not populated in the text provided).

Positive

• None.

Negative

• Insider sale disclosed: Proposed Rule 144 sale of 33,000 shares (aggregate market value $793,980) scheduled for 08/26/2025.
• Recent insider selling: Two 10b5-1 sales in August 2025 totaling 52,000 shares for gross proceeds of $1,124,264.80.

Insights

Securities Analyst

TL;DR: Insiders are executing Rule 144 and 10b5-1 sales totaling 85,000 shares recently; proposed sale is 33,000 shares (approx. $794k).

The filing documents a routine Rule 144 notice for sale of 33,000 common shares acquired via exercised options on 06/15/2023. The broker listed is Morgan Stanley Smith Barney and the transaction is slated for NASDAQ on 08/26/2025. The filing also discloses two recent 10b5-1-plan sales totaling 52,000 shares with combined gross proceeds of $1,124,264.80. For investors, these are insider liquidity events rather than company operational disclosures; they do not, by themselves, provide information about company performance or governance changes.

Corporate Governance Expert

TL;DR: The filing reflects compliance with Rule 144 and 10b5-1 procedures; no disclosure of material undisclosed information is claimed.

The signer makes the standard representation about lack of undisclosed material adverse information and references a 10b5-1 plan date field (not filled in the provided content). The presence of executed 10b5-1 sales suggests prearranged trading instructions, which typically reduce the likelihood that these trades signal undisclosed insider knowledge. There is no indication in this filing of unusual timing, related-party transactions, or other governance red flags based solely on the presented data.

FAQ

What does SION Form 144 report?

The filing reports a proposed sale of 33,000 common shares through Morgan Stanley Smith Barney with aggregate market value $793,980, approximate sale date 08/26/2025.

How were the 33,000 shares acquired?

The shares were acquired on 06/15/2023 through previously exercised stock options and payment was in cash.

Were there other recent sales by the same person?

Yes. Two 10b5-1 sales: 34,500 shares sold on 08/19/2025 for $727,112.80 and 17,500 shares sold on 08/20/2025 for $397,152.00.

Which broker is handling the proposed sale?

The broker listed is Morgan Stanley Smith Barney LLC, address: Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004.

Does the filing state the seller has undisclosed material information?

The filing includes the standard seller representation that they do not know any material adverse information about the issuer that has not been publicly disclosed.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 08/26/2025 - 04:28 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001772518
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	SIONNA THERAPEUTICS INC
SEC File Number	001-42504
Address of Issuer	21 Hickory Drive, Suite 500 Waltham MASSACHUSETTS 02451
Phone	6178192020
Name of Person for Whose Account the Securities are To Be Sold	ELENA RIDLOFF
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Officer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004	33000	793980.00	44139823	08/26/2025	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	06/15/2023	Previously Exercised Stock Options	Issuer			33000	06/15/2023	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
10b5-1 Sales for ELENA RIDLOFF 21 Hickory Drive, Suite 500 Waltham MA 02451	Common	08/20/2025	17500	397152.00
10b5-1 Sales for ELENA RIDLOFF 21 Hickory Drive, Suite 500 Waltham MA 02451	Common	08/19/2025	34500	727112.80

144: Remarks and Signature

Remarks	The securities to be sold were acquired upon the vesting of previously exercised options during the period of 06/15/2023 through 04/01/2024.
Date of Notice	08/26/2025
Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1	05/20/2025
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Elena Ridloff
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)