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

Rhea-AI Filing Summary

Michael Cloonan, President & CEO and Director of Sionna Therapeutics (SION), reported transactions on 08/20/2025 executed under a Rule 10b5-1 plan. On that date he exercised a non-qualified stock option to acquire 25,000 shares at $6.11 per share, increasing his option-derived common stock to 25,000 shares exercisable and leaving him with 572,343 shares beneficially owned immediately after the acquisition. The option vests monthly in 48 installments following 02/02/2022 and has an expiration in 2032.

Simultaneously, Mr. Cloonan sold 25,000 common shares in multiple transactions at a weighted average price of $22.75 per share (individual sale prices ranged $21.07 to $23.99). After the sale his reported beneficial ownership was 547,343 shares. The filing states these trades were made pursuant to the 10b5-1 plan adopted 05/21/2025 and was signed via attorney-in-fact on 08/21/2025.

Positive

• Trades executed under a Rule 10b5-1 plan, providing a pre-arranged, documented framework for insider transactions.
• Option exercise at $6.11 demonstrates continued use of long-term compensation instruments and increased vested holdings derived from options.

Negative

• Sale of 25,000 shares reduced reported beneficial ownership from 572,343 to 547,343 shares.
• Insider liquidity event (sale at weighted average $22.75) could be viewed as management selling shares, which some investors monitor for signaling.

Insights

Financial Analyst

TL;DR: CEO exercised options at $6.11 and sold the same number of shares under a 10b5-1 plan; net ownership declined modestly.

These paired transactions—an exercise of 25,000 option shares and a contemporaneous sale of 25,000 common shares—are executed under an established 10b5-1 plan, which indicates pre-arranged trading rather than opportunistic insider timing. The exercise price of $6.11 is materially lower than the weighted average sale price of $22.75, generating a cash difference before taxes and fees. Reported beneficial ownership after the sale is 547,343 common shares with 228,142 shares underlying outstanding options. For investors, this filing documents insider liquidity but not a change in strategic control; the magnitude (25,000 shares) should be assessed relative to total outstanding shares for materiality.

Corporate Governance Expert

TL;DR: Transactions followed a documented 10b5-1 plan; filing includes standard disclosures and vesting schedule for options.

The Form 4 discloses that the trading activity was implemented under a 10b5-1 plan adopted on 05/21/2025, which provides the reporting person with an affirmative defense under Rule 10b5-1(c). The filing also supplies vesting terms for the exercised option (forty-eight equal monthly installments beginning 02/02/2022) and provides a weighted-average sale price range for the disposed shares. Signature via attorney-in-fact and the explanatory note about providing per-price sale details comply with common disclosure practices. No other governance concerns or departures are stated in the document.

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^*

Cloonan Michael

(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)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
08/20/2025

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	08/20/2025		M(1)		25,000	A	$6.11	572,343	D
Common Stock	08/20/2025		S(1)		25,000	D	$22.75(2)	547,343	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
Non-Qualified Stock Option (right to buy)	$6.11	08/20/2025		M(1)			25,000	(3)	03/01/2032	Common Stock	25,000	$0.0	228,142	D

Explanation of Responses:

1. This transaction was automatically executed pursuant to a Rule 10b5-1 trading plan adopted on May 21, 2025.

2. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $21.0700 to $23.99, 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 shares underlying this option vest in forty-eight equal monthly installments following February 2, 2022, subject to the Reporting Person's continued service on each such vesting date.

	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).
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FAQ

What did Sionna Therapeutics CEO Michael Cloonan report on Form 4 (SION)?

He reported the exercise of 25,000 option shares at $6.11 and the sale of 25,000 common shares at a weighted average price of $22.75 on 08/20/2025.

Were these transactions prearranged or opportunistic?

The filing states the transactions were executed pursuant to a Rule 10b5-1 trading plan adopted on 05/21/2025.

How many shares does Michael Cloonan beneficially own after these transactions?

The Form 4 reports 547,343 shares beneficially owned following the reported sale.

What are the terms of the option exercised by the reporting person?

A non-qualified stock option with exercise price $6.11, 25,000 underlying shares exercised on 08/20/2025, with vesting in 48 equal monthly installments beginning 02/02/2022 and an expiration in 2032.

At what prices were the sold shares executed?

Shares were sold in multiple transactions at prices ranging from $21.07 to $23.99, with a reported weighted average of $22.75.