Atrium Therapeutics insider has 11,632 shares withheld

Atrium Therapeutics’ CEO had shares withheld for RSU tax obligations and remains a significant common stock holder.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that Chief Executive Officer, President and director Kathleen P. Gallagher had 11,632 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations related to vesting restricted stock units. These shares were not sold in the market, and she continued to hold 119,729 shares of common stock directly afterward.

Insider Trade Summary

Tax Withholding: 11,632 shares

Tax Withholding 1 txn

Insider Gallagher Kathleen P.

Role See Remarks

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	11,632	$8.95	$104K

Holdings After Transaction: Common Stock — 119,729 shares (Direct)

Footnotes (1)

1. F1. Represents shares withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting of restricted stock units.

Key Figures

Shares withheld for taxes: 11,632 shares Per-share value used for withholding: $8.95 per share Direct holdings after transaction: 119,729 shares

3 metrics

Shares withheld for taxes 11,632 shares Common stock withheld on September 18, 2026 to satisfy tax withholding obligations on RSU vesting

Per-share value used for withholding $8.95 per share Value applied to the 11,632 withheld shares for tax withholding related to RSU vesting

Direct holdings after transaction 119,729 shares Common stock directly held by Kathleen P. Gallagher after the September 18, 2026 withholding

Key Terms

restricted stock units, tax withholding obligations

2 terms

restricted stock units financial

"in connection with the vesting of restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

tax withholding obligations financial

"to satisfy tax withholding obligations in connection with the vesting"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did Atrium Therapeutics (RNA) report for Kathleen P. Gallagher?

Atrium Therapeutics reported that Kathleen P. Gallagher had 11,632 shares of common stock withheld on September 18, 2026 to cover tax withholding obligations from vesting restricted stock units.

Did the Atrium Therapeutics (RNA) CEO sell shares in the open market?

No. The 11,632 shares of Atrium Therapeutics common stock were withheld by the company to satisfy tax withholding obligations tied to vesting restricted stock units, rather than sold in open-market transactions.

How many Atrium Therapeutics (RNA) shares does Kathleen P. Gallagher hold after the transaction?

After the tax-related withholding of 11,632 shares, Kathleen P. Gallagher directly held 119,729 shares of Atrium Therapeutics common stock.

At what value were the withheld Atrium Therapeutics (RNA) shares recorded?

The 11,632 withheld shares were valued at $8.95 per share for the purpose of satisfying tax withholding obligations in connection with vesting restricted stock units.

Was the Atrium Therapeutics (RNA) insider transaction under a Rule 10b5-1 trading plan?

No. The filing indicates that the transaction involving 11,632 withheld shares to cover RSU-related taxes was not made under a Rule 10b5-1 trading plan.

AI-generated analysis. How Rhea-AI works. Not financial advice.

Form 4 Insider Transactions: What Each Field Means →

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Available on EDGAR 09/22/2026 - 04:18 PM Accepted by SEC EDGAR 09/22/2026 - 04:17 PM Learn about SEC filing dates

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).

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^*

Gallagher Kathleen P.

(Last) (First) (Middle)

C/O ATRIUM THERAPEUTICS, INC.

10578 SCIENCE CENTER DRIVE, SUITE 125

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Atrium Therapeutics, Inc. [ RNA ]

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

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	See Remarks

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/18/2026

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

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

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

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	09/18/2026		F(1)		11,632	D	$8.95	119,729	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. Represents shares withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting of restricted stock units.

Remarks:

Chief Executive Officer and President

	/s/ Brendan Winslow, Attorney-in-Fact	09/22/2026
	** 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.
* Form 4: SEC 1474 (03-26)