Atrium Therapeutics CMO has 21K shares withheld

Atrium Therapeutics’ chief medical officer had shares withheld for taxes upon RSU vesting, reducing his direct holdings to 51,638 shares.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that Chief Medical Officer Steven George Hughes had 21,459 shares51,638 shares

Insider Trade Summary

Tax Withholding: 21,459 shares

Tax Withholding 1 txn

Insider Hughes Steven George

Role Chief Medical Officer

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	21,459	$8.95	$192K

Holdings After Transaction: Common Stock — 51,638 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 tax liability: 21,459 shares Price per share for tax-withholding transaction: $8.95 per share Shares held after transaction: 51,638 shares +1 more

4 metrics

Shares withheld for tax liability 21,459 shares Common stock withheld on September 18, 2026 to satisfy tax withholding obligations on RSU vesting

Price per share for tax-withholding transaction $8.95 per share Valuation used for the 21,459 shares withheld on September 18, 2026

Shares held after transaction 51,638 shares Direct holdings of Atrium Therapeutics common stock by Steven George Hughes after the September 18, 2026 transaction

Shares used for exercise price or tax liability 21,459 shares Total shares reported under code F for payment of tax liability by delivering or withholding securities

Key Terms

restricted stock units, tax withholding obligations, payment of tax liability by delivering or withholding securities

3 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"

payment of tax liability by delivering or withholding securities financial

"transaction was a payment of tax liability by delivering or withholding"

FAQ

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

What insider transaction did Atrium Therapeutics (RNA) report for Steven George Hughes?

Atrium Therapeutics reported that Chief Medical Officer Steven George Hughes had 21,459 shares

Was the Atrium Therapeutics (RNA) Form 4 transaction a market sale or tax withholding?

The Form 4 states the transaction was a payment of tax liability by delivering or withholding securities, and a footnote explains the 21,459 shares

How many Atrium Therapeutics (RNA) shares does Steven George Hughes hold after this transaction?

After the September 18, 2026 tax-withholding transaction, Steven George Hughes directly holds 51,638 shares

At what price were the Atrium Therapeutics (RNA) shares valued for the tax withholding?

The Form 4 reports that the 21,459 shares$8.95 per share in connection with the September 18, 2026 tax-withholding transaction.

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

No. The filing’s Rule 10b5-1 checkbox is not marked as affirming a plan, and the transaction is described instead as shares withheld to satisfy tax withholding obligations on restricted stock unit vesting.

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 - 04:25 PM Accepted by SEC EDGAR 09/22/2026 - 04:23 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^*

Hughes Steven George

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Medical Officer

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)		21,459	D	$8.95	51,638	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.

	/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)