Atrium Therapeutics corrects post-offering shares to 21.6M

The post-offering share count includes shares issued in connection with settlement of make-whole equity awards tied to Atrium’s spin-off from Avidity Biosciences.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. amended its earlier 8-K to correct the post-offering count to 21,571,507 common shares outstanding. On October 7, 2026, the company entered into a securities purchase agreement with selected accredited investors to sell 5,170,384 common shares and pre-funded warrants to purchase up to 1,134,930 shares.

The post-offering count includes shares issued in connection with settlement of make-whole equity awards made in connection with the company’s spin-off from Avidity Biosciences. Atrium described the offering’s closing as expected and cited closing conditions and timing as risks.

8-K Event Classification

Item 8.01 — Other Events

1 item

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

Key Figures

Common shares in the offering: 5,170,384 shares Shares purchasable under pre-funded warrants: Up to 1,134,930 shares Common shares outstanding following the offering: 21,571,507 shares

3 metrics

Common shares in the offering 5,170,384 shares Securities purchase agreement entered into on October 7, 2026

Shares purchasable under pre-funded warrants Up to 1,134,930 shares Securities purchase agreement entered into on October 7, 2026

Common shares outstanding following the offering 21,571,507 shares Includes shares issued in connection with settlement of make-whole equity awards

Key Terms

pre-funded warrants, accredited investors, make whole equity awards, Regulation D

4 terms

pre-funded warrants financial

"pre-funded warrants to purchase up to 1,134,930 shares"

Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.

accredited investors regulatory

"selected investors that qualify as “accredited investors”"

Accredited investors are individuals or entities considered to have enough financial knowledge and resources to understand and handle more complex and risky investments. They are often allowed to participate in private investment opportunities that are not available to the general public, similar to how experienced players might access exclusive clubs or events. This status helps ensure that investors can manage potential risks and rewards appropriately.

make whole equity awards financial

"settlement of the make whole equity awards"

Regulation D regulatory

"Rule 501(a) of Regulation D"

Regulation D is a set of rules that govern how companies can raise money from investors without going through the full process required for public stock offerings. It provides simplified options for private placements, making it easier for companies to seek investments from a smaller group of investors. For investors, it offers opportunities to invest in private companies, often with fewer restrictions, but also with different levels of risk and disclosure.

FAQ

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

What securities did RNA agree to sell in the October 2026 PIPE?

On October 7, 2026, Atrium agreed to sell 5,170,384 common shares and pre-funded warrants to purchase up to 1,134,930 shares to selected investors that qualify as accredited investors.

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

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true 0002093101 0002093101 2026-10-07 2026-10-07

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 7, 2026

Atrium Therapeutics, Inc.

(Exact name of registrant as specified in its charter)

Delaware		001-43008		39-4639499
(State or other jurisdiction of incorporation)		(Commission File Number)		(IRS Employer Identification No.)

10578 Science Center Drive, Suite 125
San Diego, California				92121
(Address of principal executive offices)				(Zip Code)

Registrant’s telephone number, including area code: (619) 876-0700

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common stock, par value $0.001 per share		RNA		The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Explanatory Note

This Form 8-K/A is being filed as an amendment (“Amendment No. 1”) to the current report on Form 8-K filed by Atrium Therapeutics, Inc. (the “Company”) with the Securities and Exchange Commission on October 8, 2026 (the “Original Form 8-K”) to correct the previously disclosed number of shares outstanding after the offering. No other information has been revised.

Item 8.01 Other Events.

As previously disclosed in the Original Form 8-K, on October 7, 2026, the Company entered into a securities purchase agreement with selected investors that qualify as “accredited investors” (collectively, the “PIPE Investors”), as defined in Rule 501(a) of Regulation D promulgated under the United States Securities Act of 1933, as amended, to sell to the PIPE Investors an aggregate of (i) 5,170,384 shares of the Company’s common stock, par value $0.001 per share (the “Common Stock”), and (ii) pre-funded warrants to purchase up to 1,134,930 shares of Common Stock (the “Offering”). Following the Offering, the Company will have 21,571,507 shares of Common Stock outstanding, which includes shares issued in connection with the settlement of the make whole equity awards that were made in connection with its spin-off from Avidity Biosciences, Inc.

Forward-Looking Statements

This Amendment No. 1 contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including, without limitation, express or implied statements regarding the expected closing of the Offering. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “would,” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including risks relating to the Company’s inability, or the inability of the PIPE Investors, to satisfy the conditions to closing for the Offering; the timing of the closing of the Offering; and other risks and uncertainties described under the caption “Risk Factors” in the Company’s Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2026 and June 30, 2026 and in subsequent filings and furnishings, which are on file with the SEC; and risks described in other filings that the Company makes with the SEC in the future. Any forward-looking statements contained in this Amendment No. 1 speak only as of the date hereof, and the Company expressly disclaims any obligation to update any forward-looking statements, whether because of new information, future events or otherwise.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

						ATRIUM THERAPEUTICS, INC.
Date: October 9, 2026				By:		/s/ Kathleen Gallagher
						Name: Kathleen Gallagher Title: Chief Executive Officer

Filing Exhibits & Attachments

3 documents

Other Documents

• EX-101 XBRL TAXONOMY EXTENSION SCHEMA 3.1 KB
• EX-101 XBRL TAXONOMY EXTENSION LABEL LINKBASE 18.3 KB
• EX-101 XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE 11.4 KB