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

Rhea-AI Filing Summary

Sionna Therapeutics CFO Elena Ridloff reported sales of common stock under a pre-established Rule 10b5-1 trading plan. On 08/19/2025 she sold 34,500 shares at a weighted average price of $21.08 (individual trade prices ranged $20.67 to $21.57), reducing her beneficial ownership to 89,032 shares. On 08/20/2025 she sold an additional 17,500 shares at a weighted average price of $22.69 (individual trade prices ranged $22.00 to $23.355), reducing her beneficial ownership to 71,532 shares. The Form 4 notes the transactions were executed automatically under a plan adopted May 20, 2025, and the report was signed by an attorney-in-fact on 08/21/2025.

Positive

• Transactions executed under a Rule 10b5-1 plan, indicating the sales were pre-arranged and not ad hoc
• Detailed disclosure of weighted-average prices and price ranges, and an undertaking to provide per-trade details upon request

Negative

• Insider sold a total of 52,000 shares (34,500 on 08/19/2025 and 17,500 on 08/20/2025), reducing beneficial ownership from 89,032 to 71,532 shares
• Filing lacks context on proportion of insider holdings versus total shares outstanding, so investor impact cannot be fully assessed from this form alone

Insights

Financial Analyst

TL;DR: Insider sales totaling 52,000 shares executed under a 10b5-1 plan; disclosure is routine and lacks additional context.

These trades represent voluntary, pre-arranged dispositions by the CFO rather than ad hoc sales. Total shares sold were 52,000 across two dates with weighted average prices of $21.08 and $22.69. The filing discloses post-sale beneficial ownership levels of 89,032 and then 71,532 shares. From a financial perspective, the disclosure is transparent but does not provide company-specific operational or financial signals; impact on valuation depends on the size of these holdings relative to total outstanding shares, which is not provided here.

Corporate Governance Expert

TL;DR: Use of a formally adopted 10b5-1 plan and detailed price ranges indicate adherence to governance and disclosure practices.

The Form 4 explicitly states the sales were executed pursuant to a Rule 10b5-1 trading plan adopted May 20, 2025, and provides weighted-average prices plus ranges for the multiple transactions. The reporting includes an undertaking to provide detailed per-trade quantities upon request, which supports transparency. There is no indication of other contemporaneous transactions or amendments in this filing.

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)
08/19/2025

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	08/19/2025		S(1)		34,500	D	$21.08(2)	89,032	D
Common Stock	08/20/2025		S(1)		17,500	D	$22.69(3)	71,532	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 $20.6700 to $21.5700, 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 $22.0000 to $23.355, 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	08/21/2025
	** 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

What did SION insider Elena Ridloff report on Form 4?

She reported sales of 34,500 shares on 08/19/2025 and 17,500 shares on 08/20/2025, executed under a Rule 10b5-1 plan.

Were the SION sales part of a prearranged trading plan?

Yes. The Form 4 states the trades were automatically executed pursuant to a 10b5-1 trading plan adopted May 20, 2025.

At what prices were the SION shares sold?

The weighted average prices were $21.08 for the 08/19 sales (individual prices ranged $20.67 to $21.57) and $22.69 for the 08/20 sales (individual prices ranged $22.00 to $23.355).

How many SION shares does the reporting person own after the transactions?

The filing reports beneficial ownership of 89,032 shares after the 08/19 transactions and 71,532 shares after the 08/20 transactions.

Who signed the Form 4 for Elena Ridloff?

The Form 4 was signed by Jennifer Fitzpatrick, Attorney-in-Fact on 08/21/2025.