Prothena (NASDAQ: PRTA) okays $100M share buyback through 2026

Rhea-AI Filing Summary

Prothena Corporation plc announced that its board has authorized a share repurchase plan allowing the company to buy back up to $100.0 million of its outstanding ordinary shares. The plan runs through December 31, 2026, is fully discretionary, and can be suspended or ended at any time.

Prothena reported $308.4 million in cash, cash equivalents and restricted cash and no debt as of December 31, 2025, and expects to end 2026 with about $255 million in cash excluding any repurchases. The company also highlights potential to earn up to $105 million in 2026 clinical milestone payments from strategic partners Novo Nordisk and Bristol Myers Squibb.

Positive

• Board authorizes up to $100.0 million share repurchase, a sizable capital return alongside a reported $308.4 million cash balance and no debt as of December 31, 2025, plus potential $105 million of 2026 milestone payments from Novo Nordisk and Bristol Myers Squibb.

Negative

• None.

Insights

Biotech equity analyst

Prothena pairs a sizable buyback with a strong cash position.

Prothena’s board authorized a share repurchase plan of up to $100.0 million through December 31, 2026. For a late-stage biotech, this signals management’s willingness to return capital while maintaining funding for its development pipeline.

The company reported $308.4 million in cash, cash equivalents and restricted cash and no debt as of December 31, 2025, and projects about $255 million at year-end excluding repurchases. It also notes potential $105 million of clinical milestone payments in 2026 tied to partnered programs with Novo Nordisk and Bristol Myers Squibb.

The plan is discretionary and may be suspended or discontinued, so actual buybacks will depend on market conditions, capital needs, and clinical progress. Subsequent company filings and updates around 2026 milestones will clarify how much of the authorized amount is ultimately used.

0001559053FALSE00015590532026-02-272026-02-27

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

Date of Report (Date of earliest event reported): February 27, 2026

_______________________________________________________

PROTHENA CORPORATION PUBLIC LIMITED COMPANY

(Exact name of registrant as specified in its charter)

_______________________________________________________

Ireland

001-35676

98-1111119

(State or Other Jurisdiction of Incorporation)

(Commission File Number)

(IRS Employer Identification No.)

77 Sir John Rogerson's Quay, Block C

Grand Canal Docklands

Dublin 2,

D02 VK60,

Ireland

(Address of principal executive offices, including Zip Code)

Registrant’s telephone number, including area code: 011-353-1-236-2500

___________________________________________________

(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 (see General Instruction A.2. below):

☐ 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			Name of Each Exchange on Which Registered
Ordinary Shares, par value $0.01 per share			PRTA			The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in 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 7.01 Regulation FD.

On February 27, 2026, Prothena Corporation plc (the "Company") issued a press release announcing a share repurchase plan under which the Company may repurchase up to $100.0 million of the Company's outstanding ordinary shares, par value $0.01 per share. A copy of that press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information in Item 7.01 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section. It may only be incorporated by reference in another filing under the Exchange Act or the Securities Act of 1933, as amended, if such subsequent filing specifically incorporate by reference the information furnished pursuant to Item 7.01 (including Exhibit 99.1) of this Current Report.

Item 8.01 Other Events.

On February 27, 2026, the Company announced a share repurchase plan under which the Company may repurchase up to $100.0 million of the Company's outstanding ordinary shares, par value $0.01 per share. The share repurchase plan will expire on December 31, 2026, may be suspended or discontinued at any time, and does not obligate the company to acquire any amount of ordinary shares.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No.						Description
99.1						Press Release dated February 27, 2026
104						Cover Page Interactive Data File (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 hereunto duly authorized.

Date:

February 27, 2026

PROTHENA CORPORATION PLC

By:

/s/ Tran B. Nguyen

Name:

Tran B. Nguyen

Title:

Chief Strategy Officer and Chief Financial Officer

EXHIBIT 99.1

PRESS RELEASE

Prothena Announces up to $100 Million Share Repurchase Plan

DUBLIN, Ireland, February 27, 2026 -- Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today announced that its Board of Directors has authorized a Share Repurchase Plan under which the Company may repurchase up to $100.0 million of the Company’s outstanding ordinary shares, par value $0.01 per share.

Prothena had cash, cash equivalents and restricted cash of $308.4 million and no debt as of December 31, 2025. Excluding any potential purchases under this Share Repurchase Plan, Prothena expects to end the year with approximately $255 million in cash, cash equivalents, and restricted cash. This financial guidance does not include the potential to earn up to $105 million of aggregate clinical milestone payments from strategic partners in 2026 related to the advancement of both coramitug for ATTR amyloidosis with cardiomyopathy by Novo Nordisk and PRX019 for neurodegenerative diseases by Bristol Myers Squibb.

Prothena may repurchase the shares from time to time in open market transactions, which may be structured to occur in accordance with the requirements of Rule 10b-18 of the Securities Exchange Act of 1934, as amended. Prothena may also enter into Rule 10b5-1 plans to facilitate repurchases. The timing, number of shares repurchased, and prices paid for the shares under this program will depend on general business and market conditions as well as corporate and regulatory limitations, prevailing share prices, and other considerations. The Share Repurchase Plan will expire on December 31, 2026, may be suspended or discontinued at any time, and does not obligate the company to acquire any amount of ordinary shares. No amount or any amount of outstanding ordinary shares may be acquired by the expiration of the Share Repurchase Plan, at Prothena’s sole discretion.

About Prothena

Prothena Corporation plc is a late-stage clinical biotechnology company with expertise in protein dysregulation with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases. Fueled by its

deep scientific expertise built over decades of research, Prothena is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. Prothena’s pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of diseases including Parkinson’s disease, ATTR amyloidosis with cardiomyopathy, Alzheimer’s disease, Amyotrophic lateral sclerosis (ALS) and a number of other neurodegenerative diseases. Prothena is developing and applying its proprietary CYTOPE® technology to target a broad spectrum of intracellular disease pathways in the brain and periphery. For more information, please visit the Company’s website at www.prothena.com and follow the Company on X (formerly Twitter) @ProthenaCorp.

Forward-Looking Statements

This press release contains forward-looking statements. These statements relate to, among other things, our plans and expectations regarding the Share Repurchase Plan, capital allocation, and other objectives and expectations; our anticipated cash burn and projected year end cash, cash equivalents, and restricted cash; and the receipt of clinical milestone payments in 2026. These statements are based on estimates, projections and assumptions that may prove not to be accurate, and actual results could differ materially from those anticipated due to known and unknown risks, uncertainties and other factors, including but not limited to uncertainties related to the completion of operational and financial closing procedures, audit adjustments and other developments that may arise that would require adjustments to the preliminary financial results included in this press release, as well as those described in the “Risk Factors” sections of our Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 27, 2026, and discussions of potential risks, uncertainties, and other important factors in our subsequent filings with the SEC. We undertake no obligation to update publicly any forward-looking statements contained in this press release as a result of new information, future events, or changes in our expectations.

Contacts:

Mark Johnson, CFA, Vice President, Investor Relations

650-837-8550

IR@prothena.com

Media@prothena.com

FAQ

What did Prothena (PRTA) announce in its new share repurchase plan?

Prothena’s board authorized a Share Repurchase Plan to buy back up to $100.0 million of its outstanding ordinary shares. The plan offers flexibility in timing and amount of repurchases and can be suspended or discontinued at any time before its December 31, 2026 expiration.

How long will Prothena’s $100 million share repurchase plan last?

The Share Repurchase Plan is authorized through December 31, 2026. Prothena may repurchase shares at its discretion during this period, including via open market transactions and potential Rule 10b5-1 plans, but is not obligated to acquire any specific number of shares.

What is Prothena’s cash position and debt level supporting the buyback?

Prothena reported $308.4 million in cash, cash equivalents and restricted cash and no debt as of December 31, 2025. This balance underpins the authorized $100.0 million share repurchase plan and the company’s ongoing late-stage clinical development activities.

What year-end 2026 cash balance does Prothena expect excluding repurchases?

Prothena expects to end 2026 with approximately $255 million in cash, cash equivalents and restricted cash, excluding any purchases under the Share Repurchase Plan. This guidance reflects anticipated cash burn from operations but does not factor in the actual execution of buybacks.

What potential milestone payments does Prothena highlight for 2026?

Prothena notes potential to earn up to $105 million of aggregate clinical milestone payments in 2026. These relate to advancement of coramitug for ATTR amyloidosis with cardiomyopathy by Novo Nordisk and PRX019 for neurodegenerative diseases by Bristol Myers Squibb.

How will Prothena execute the share repurchases under the plan?

Prothena may repurchase shares from time to time in open market transactions, potentially structured to follow Rule 10b-18. The company may also use Rule 10b5-1 trading plans, with timing and volume influenced by business conditions, regulations and prevailing share prices.

Filing Exhibits & Attachments

4 documents

Press Releases

• EX-99.1 EX-99.1 10.5 KB

Other Documents

• EX-101 XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT 1.8 KB
• EX-101 XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT 22.7 KB
• EX-101 XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT 13.2 KB