Insider Sale Filed for SION: 25,000 Shares via Morgan Stanley (09/26/2025)

Rhea-AI Filing Summary

Sionna Therapeutics (SION) insider sale notice: This Form 144 reports a proposed sale of 25,000 common shares by an insider through Morgan Stanley Smith Barney, valued at $687,500, with the sale target date of 09/26/2025 on NASDAQ. The securities were acquired on 09/26/2025 by exercise of stock options and paid in cash. The filing shows 44,139,823 shares outstanding, so the proposed sale equals approximately 0.0566% of outstanding shares. The filer also disclosed three 10b5-1 sales by Michael Cloonan in August 2025 totaling 50,000 shares for aggregate gross proceeds of $1,193,154.98. The notice includes the standard insider representation about absence of undisclosed material information and a 10b5-1 plan reference but does not provide plan adoption dates or signature details.

Positive

• Clear disclosure of broker, share count, market value, acquisition method, and payment
• Past 10b5-1 sales disclosed, enabling transparency on recent insider liquidity (50,000 shares for $1,193,154.98)

Negative

• Insider selling activity (proposed 25,000 shares plus 50,000 shares sold in August 2025) which may be viewed negatively by some investors
• Missing plan adoption and signature details in the provided excerpt, limiting verification of 10b5-1 procedural timing

Insights

Securities Analyst

TL;DR: Insider plans to sell 25,000 shares (about 0.0566% of float); recent 10b5-1 sales total 50,000 shares for $1.19M.

The filing documents a routine Rule 144 notice for an insider sale executed through Morgan Stanley Smith Barney with securities acquired by option exercise on the same date as the planned sale. The small size of the proposed transaction relative to total outstanding shares suggests limited direct dilution or market impact. The disclosure of multiple 10b5-1 sales in August 2025 totaling 50,000 shares and roughly $1.19 million in proceeds is material for tracking insider liquidity trends but, standing alone, does not indicate company-level operational changes. The form lacks explicit dates for any 10b5-1 plan adoption or a signature block in the provided content, which limits verification of procedural details.

Corporate Governance Expert

TL;DR: Filing shows compliant insider sale notice but omits plan adoption and signature details in the provided excerpt.

The Form 144 presents required information on the proposed sale, including broker, number of shares, market value, acquisition method, and payment. Disclosure that the shares were acquired by exercising stock options and paid in cash aligns with common insider liquidity events. The repeated use of 10b5-1 sale mechanics by the named insider indicates reliance on prearranged trading plans; however, the excerpt does not include the plan adoption date or explicit signature, which are important governance confirmations. From a governance perspective, the document is procedural rather than a substantive operational disclosure.

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

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	25000	687500.00	44139823	09/26/2025	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	09/26/2025	Exercise of Stock Options	Issuer			25000	09/26/2025	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 MICHAEL CLOONAN 21 Hickory Drive, Suite 500 Waltham MA 02451	Common	08/27/2025	7426	185713.86
10b5-1 Sales for MICHAEL CLOONAN 21 Hickory Drive, Suite 500 Waltham MA 02451	Common	08/26/2025	17574	438726.12
10b5-1 Sales for MICHAEL CLOONAN 21 Hickory Drive, Suite 500 Waltham MA 02451	Common	08/20/2025	25000	568715.00

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 this Form 144 for SION report?

It reports a proposed sale of 25,000 common shares valued at $687,500 to be sold on 09/26/2025 on NASDAQ, acquired by exercise of stock options and paid in cash.

Who is the broker handling the sale listed on the Form 144?

The broker is listed as Morgan Stanley Smith Barney LLC, Executive Financial Services, 1 New York Plaza, New York, NY.

Has the insider sold other SION shares recently?

Yes. The filing discloses three 10b5-1 sales in August 2025 totaling 50,000 shares for gross proceeds of $1,193,154.98.

What portion of outstanding shares does the proposed sale represent?

The proposed sale of 25,000 shares vs 44,139,823 outstanding equals approximately 0.0566% of outstanding shares.

Were the shares acquired or gifted before sale?

The securities to be sold were acquired on 09/26/2025 by exercise of stock options and paid in cash.