[144] Sionna Therapeutics, Inc. SEC Filing

Rhea-AI Filing Summary

Sionna Therapeutics (SION) filed a Form 144 notifying the proposed sale of 17,500 common shares through Morgan Stanley Smith Barney, with an aggregate market value of $375,900.00, and an approximate sale date of 08/20/2025 on NASDAQ. The shares were acquired on 09/20/2022 via previously exercised stock options and paid in cash. The filing shows 44,139,823 shares outstanding. The filing also discloses Rule 10b5-1 sales by Elena Ridloff totaling 34,500 common shares on 08/19/2025 for gross proceeds of $727,112.80. The notice includes the standard representation that the seller is unaware of undisclosed material adverse information.

Positive

• Full compliance with Rule 144 disclosure requirements, including acquisition details and broker information
• Use of a broker (Morgan Stanley Smith Barney) for the planned disposition, indicating an orderly execution channel
• Prior 10b5-1 sales disclosed with dates and gross proceeds, enhancing transparency

Negative

• Insider selling activity: proposed sale of 17,500 shares and recent 10b5-1 sales of 34,500 shares that add supply to the market
• Limited context on whether these sales are part of a broader plan or reflect any change in insider intent beyond the filings

Insights

Securities Analyst

TL;DR: Routine insider sale disclosure; no financials changed but adds supply to market.

The Form 144 documents a proposed insider sale of 17,500 shares via a broker and reports recent Rule 10b5-1 transactions of 34,500 shares producing $727,112.80. The shares to be sold were acquired by exercising options on 09/20/2022 and paid in cash, which is a common source for Rule 144 filings. From a market-impact perspective, the volumes disclosed are modest relative to the reported outstanding share count of 44,139,823 and do not, by themselves, indicate material change to capitalization or operations. The filing demonstrates compliance with SEC resale rules and confirms use of a brokerage channel for the disposition.

Corporate Governance Expert

TL;DR: Proper disclosure of planned insider sale and prior 10b5-1 execution; governance process appears followed.

The notice contains required details: acquisition date, nature of acquisition (previously exercised options), payment method (cash), and broker information. It also discloses recent aggregated sales by the same insider under a 10b5-1 plan, including dates and gross proceeds. These elements align with transparent insider reporting expectations and the certification that no undisclosed material adverse information is known at signature. The filing does not disclose any governance breaches or material adverse events.

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

144: Issuer Information

Name of Issuer

SEC File Number

Address of Issuer

Phone

Name of Person for Whose Account the Securities are To Be Sold

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

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	17500	375900.00	44139823	08/20/2025	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	09/20/2022	Previously Exercised Stock Options	Issuer			17500	09/20/2022	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	08/19/2025	34500	727112.80

144: Remarks and Signature

Remarks

Date of Notice

Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1

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

ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)

FAQ

What does the Form 144 filed by Sionna Therapeutics (SION) disclose?

The filing discloses a proposed sale of 17,500 common shares via Morgan Stanley Smith Barney with an aggregate market value of $375,900.00, and an approximate sale date of 08/20/2025.

How and when were the shares to be sold acquired?

The 17,500 shares were acquired on 09/20/2022 through previously exercised stock options and payment was made in cash.

Were there any recent insider sales disclosed in the filing?

Yes. The filing reports Rule 10b5-1 sales by Elena Ridloff of 34,500 common shares on 08/19/2025 for gross proceeds of $727,112.80.

How many Sionna Therapeutics shares are outstanding according to the filing?

The filing lists 44,139,823 shares outstanding.

What broker is handling the proposed sale?

The proposed sale is to be handled by Morgan Stanley Smith Barney LLC, located at 1 New York Plaza, 8th Floor, New York, NY 10004.