SION Insider Ridloff Reduces Stake by 9,584 Shares via 10b5-1 Sales

Rhea-AI Filing Summary

Elena Ridloff, CFO & Head of Corporate Development of Sionna Therapeutics (SION), reported planned sales under a Rule 10b5-1 trading plan adopted May 20, 2025. The Form 4 shows sales executed on 08/29/2025 (748 shares) and 09/02/2025 (8,836 shares) at weighted-average prices of $25.18 and $25.08 respectively, for a total of 9,584 shares sold. After the 08/29 sale Ridloff held 47,368 shares; after the 09/02 sale she held 38,532 shares. The filings state the trades were automatic under the 10b5-1 plan and note the sales occurred in multiple transactions at prices within the disclosed ranges. The reporting person authorized Jennifer Fitzpatrick as attorney-in-fact to sign the Form.

Positive

• Sales executed under a Rule 10b5-1 trading plan, providing an affirmative defense and reducing potential insider-trading signaling concerns
• Detailed price-range disclosure and willingness to provide per-transaction quantities on request enhances transparency

Negative

• Insider reduced beneficial ownership from 47,368 shares to 38,532 shares following reported sales
• Material quantity sold (9,584 shares) represents a meaningful reduction in the reporting person’s stake

Insights

Corporate Governance Expert

TL;DR: Insider sales executed under a pre-established 10b5-1 plan reduce signaling risk but materially lower the officer's stake.

The transactions were explicitly executed pursuant to a Rule 10b5-1 plan adopted May 20, 2025, which provides an affirmative defense against insider trading claims and typically indicates prearranged, non-discretionary sales. The reporting shows 9,584 total shares sold across two dates at weighted-average prices near $25.10, reducing beneficial ownership from 47,368 to 38,532 shares. For governance assessment, the clear disclosure of the plan date and price ranges supports compliance transparency; however, the reduction in holdings is material relative to the officer's reported position and should be noted by stakeholders evaluating insider alignment with shareholders.

Securities Analyst

TL;DR: Pre-planned sales limit information asymmetry, but the disclosed reduction in shares is a concrete change in insider exposure.

From a market-signaling perspective, explicit identification of a 10b5-1 plan lowers the likelihood that the sales reflect undisclosed inside information. The sales occurred in multiple tranches at weighted-average prices of $25.18 and $25.08; total shares sold were 9,584. Reported beneficial ownership declined to 38,532 shares after the second reported sale. These are straightforward, routine disclosures of insider liquidity rather than corporate operational developments, so the investor impact is limited but measurable in terms of insider ownership percentage change.

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)
08/29/2025

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	08/29/2025		S(1)		748	D	$25.18(2)	47,368	D
Common Stock	09/02/2025		S(1)		8,836	D	$25.08(3)	38,532	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 $25.00 to $25.34, 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 $25.30, 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	09/03/2025
	** 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 trades did SION insider Elena Ridloff report on Form 4?

The Form 4 discloses sales of 748 shares on 08/29/2025 and 8,836 shares on 09/02/2025, totaling 9,584 shares sold.

Were the SION sales by the insider discretionary or preplanned?

The sales were executed pursuant to a Rule 10b5-1 trading plan adopted May 20, 2025, indicating preplanned, non-discretionary trades.

At what prices were the SION shares sold?

The Form reports weighted-average prices of $25.18 (08/29/2025) and $25.08 (09/02/2025); individual transactions ranged within disclosed bands.

How many SION shares did Ridloff beneficially own after the reported sales?

After the 08/29 sale she reported 47,368 shares beneficially owned; after the 09/02 sale she reported 38,532 shares.

Who signed the Form 4 on behalf of the reporting person?

The Form indicates it was signed by Jennifer Fitzpatrick, Attorney-in-Fact on 09/03/2025.