0000879407 FALSE 0000879407 2025-09-10 2025-09-10

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT
PURSUANT TO SECTION 13 OR 15(D) OF
THE SECURITIES EXCHANGE ACT OF 1934
September 10, 2025
Date of Report
(Date of earliest event reported)

Arrowhead Pharmaceuticals, Inc.
(Exact name of registrant as specified in its charter)

Delaware |  | 001-38042 |  | 46-0408024
(State or other jurisdiction of incorporation) |  | (Commission File Number) |  | (IRS Employer Identification No.)

177 E. Colorado Blvd, Suite 700, Pasadena, CA 91105
(Address of principal executive offices, including Zip Code)
(626) 304-3400
(Registrant’s telephone number, including area code)

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 |  | ARWR |  | 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. ☐

Item 8.01 Other Events
On September 10, 2025, Arrowhead Pharmaceuticals, Inc. (the “Company” or the “Plaintiff”) filed a Complaint for Declaratory Judgment in the United States District Court for the District of Delaware against Ionis Pharmaceuticals, Inc. (the “Defendant”) to declare that Ionis’s United States Patent Number 9,593,333 (“the ’333 patent”) is invalid and/or not infringed by the Company’s planned commercialization of investigational plozasiran. A copy of the complaint is attached hereto as Exhibit 99.1 (the “Complaint”).
The Company intends to vigorously pursue its claims in this litigation.
Forward-Looking Statements
This Current Report on Form 8-K contains forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995. Any statements contained in this report except for historical information may be deemed to be forward-looking statements. Without limiting the generality of the foregoing, words such as “may,” “will,” “expect,” “believe,” “anticipate,” “hope,” “intend,” “plan,” “project,” “could,” “estimate,” “continue,” “target,” “forecast” or “continue” or the negative of these words or other variations thereof or comparable terminology are intended to identify such forward-looking statements. These forward-looking statements include, but are not limited to, statements about our planned commercialization of investigational plozasiran and beliefs and expectations regarding the merit of the Ionis letter, the validity and enforceability of the ‘333 Patent, the Company’s patent portfolio, and the Company’s claims and lawsuit against the Defendant. These statements are based upon our current expectations and speak only as of the date hereof. Our actual results or outcomes may differ materially and adversely from those expressed in any forward-looking statements as a result of numerous factors and uncertainties, including the risks and uncertainties described in our most recent Annual Report on Form 10-K, subsequent Quarterly Reports on Form 10-Q and other documents filed with the Securities and Exchange Commission from time to time. We assume no obligation to update or revise forward-looking statements to reflect new events or circumstances.
Item 9.01. Financial Statements and Exhibits.
(d) Exhibits

Exhibit No. |  | Description
99.1 |  | Complaint for Declaratory Judgment dated September 10, 2025
99.2 |  | Press Release, dated September 11, 2025.
104 |  | Cover Page Interactive Data File (the cover page tags are embedded within the Inline XBRL document).

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 thereunto duly authorized.
Date: September 11, 2025

ARROWHEAD PHARMACEUTICALS, INC.
By: |  | /s/ Daniel Apel
|  | Daniel Apel
|  | Chief Financial Officer