[Form 4] Sionna Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Elena Ridloff, CFO & Head of Corporate Development of Sionna Therapeutics, Inc. (SION), reported sales of common stock on August 26-28, 2025 under a Rule 10b5-1 trading plan adopted May 20, 2025. The filings show sales of 3,700 shares on 08/26 at a weighted-average price of $25.13 (prices ranged $25.00–$25.28), 3,618 shares on 08/27 at $25.10 (range $25.00–$25.32), and 16,098 shares on 08/28 at $25.97 (range $25.01–$26.41). Post-transaction beneficial ownership is reported as 67,832 shares after 08/26, 64,214 after 08/27, and 48,116 after 08/28. The Form 4 was submitted by one reporting person and signed by an attorney-in-fact on 08/28/2025.

Positive

• Sales executed under a documented Rule 10b5-1 trading plan, adopted May 20, 2025, which supports procedural compliance
• Form 4 discloses weighted-average prices and price ranges for each day, enabling transparency about execution prices
• Filing includes post-transaction beneficial ownership counts for each reporting date (67,832; 64,214; 48,116 shares)

Negative

• Material reduction in insider holdings: cumulative sales reduced beneficial ownership to 48,116 shares as of 08/28/2025
• Multiple sizable sales over three days (total 23,416 shares sold) which may be viewed as significant by some investors

Insights

Securities Analyst

TL;DR: Insider sales under a pre-established 10b5-1 plan reduced the CFO's holdings by documented amounts over three days.

The transactions were executed pursuant to a Rule 10b5-1 trading plan adopted May 20, 2025, which indicates automatic scheduled sales rather than ad-hoc trades. The filing provides explicit share counts sold each day and weighted-average prices with disclosed price ranges. For investors, the key facts are the magnitude of the reductions (16,098 shares on the final day) and the declining beneficial ownership to 48,116 shares after 08/28/2025. The disclosure is complete regarding execution method and price ranges; no additional financial or strategic information about the company is contained in this Form 4.

Corporate Governance Expert

TL;DR: The reporting complies with Section 16 disclosure rules and cites a 10b5-1 plan; signatures and dates are provided.

The Form 4 lists the reporting person, title (CFO & Head of Corp. Dev.), issuer (Sionna Therapeutics, Inc., SION), and confirms the sales were executed under a 10b5-1 plan adopted May 20, 2025. The filing includes weighted-average prices and price ranges for each day and is signed by an attorney-in-fact, demonstrating procedural compliance. The document does not include any explanation of company-level impact or rationale beyond the trading plan reference.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Ridloff Elena

(Last) (First) (Middle)

C/O SIONNA THERAPEUTICS, INC.

21 HICKORY DRIVE, SUITE 500

(Street)

WALTHAM MA 02451

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Sionna Therapeutics, Inc. [ SION ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CFO & Head of Corp. Dev.

3. Date of Earliest Transaction (Month/Day/Year)
08/26/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/26/2025		S(1)		3,700	D	$25.13(2)	67,832	D
Common Stock	08/27/2025		S(1)		3,618	D	$25.1(3)	64,214	D
Common Stock	08/28/2025		S(1)		16,098	D	$25.97(4)	48,116	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

2. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.28, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

3. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.00 to $25.32, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

4. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $25.01 to $26.41, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price at which the transactions were effected.

	Jennifer Fitzpatrick, Attorney-in-Fact	08/28/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

Who reported the transactions on this Form 4 (SION)?

The reporting person is Elena Ridloff, identified as CFO & Head of Corporate Development at Sionna Therapeutics, Inc.

Were the sales executed under a Rule 10b5-1 plan?

Yes. The transactions were automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 20, 2025.

How many shares were sold and what were the prices?

Sales reported: 3,700 shares on 08/26/2025 at a weighted-average price of $25.13 (range $25.00–$25.28); 3,618 shares on 08/27/2025 at $25.10 (range $25.00–$25.32); and 16,098 shares on 08/28/2025 at $25.97 (range $25.01–$26.41).

What is the reporting person's beneficial ownership after these trades?

The Form 4 reports beneficial ownership of 67,832 shares after 08/26, 64,214 shares after 08/27, and 48,116 shares after 08/28, 2025.

Who signed the Form 4 and when?

The Form 4 was signed by Jennifer Fitzpatrick, Attorney-in-Fact on 08/28/2025.