Financial Performance Overview

Prothena, a late-stage clinical biotechnology company, has reported its financial results for the three and six months ended June 30, 2026. The company’s revenue recognition, shareholders’ equity, share-based compensation, income taxes, and restructuring activities are the key highlights from the report.

Revenue Recognition

During the six months ended June 30, 2026, Prothena recognized $50.0 million in revenue related to a development milestone payment for the continued advancement of its drug candidate coramitug in the Phase 3 CLEOPATTRA clinical trial. In contrast, no revenue was recognized during the three and six months ended June 30, 2025. There are no remaining performance obligations under the share purchase agreement with Novo Nordisk, and Prothena had no outstanding accounts receivable from Novo Nordisk as of June 30, 2026, and December 31, 2025.

Shareholders’ Equity

As of June 30, 2026, Prothena had 100,000,000 ordinary shares authorized for issuance, with a par value of $0.01 per share, and 51,744,327 ordinary shares issued and outstanding. Each ordinary share is entitled to one vote and, on a pro rata basis, to dividends when declared and the remaining assets of the company in the event of a winding up.

The company also had 10,000 Euro Deferred Shares authorized for issuance with a nominal value of €22 per share, but no Euro Deferred Shares were outstanding as of June 30, 2026.

Share Repurchase Plan

On February 27, 2026, Prothena announced a share repurchase plan under which the company may repurchase up to $100.0 million of its outstanding ordinary shares. During the three and six months ended June 30, 2026, the company repurchased 1,454,898 shares and 2,243,888 shares, respectively, at an average repurchase price of approximately $10.30 and $9.93 per share, respectively, for an aggregate amount of approximately $15.0 million and $22.3 million, respectively, excluding commissions.

Share-Based Compensation

Prothena’s equity incentive plans, including the 2018 Long Term Incentive Plan, 2020 Employment Inducement Incentive Plan, and the previously Amended and Restated 2012 Long Term Incentive Plan, reserve ordinary shares for the issuance of stock options, stock appreciation rights, restricted shares, RSUs, and other share-based awards.

As of June 30, 2026, the number of ordinary shares authorized under the 2018 LTIP was 18,641,433, and the number of ordinary shares authorized under the 2020 EIIP was 1,485,000, with 696,163 ordinary shares remaining available for future awards.

The company’s option awards generally vest over four years, while RSU awards generally vest over either two or three years. As of June 30, 2026, 3,196,732 ordinary shares remained available for grant under the company’s equity incentive plans.

The table below summarizes the share-based compensation expense for the periods presented:

	Three Months Ended June 30		Six Months Ended June 30
	2026	2025	2026
Research and development	$1,668	$4,674	$3,661
General and administrative	$4,467	$5,663	$9,389
Restructuring costs	$1,743	$2,081	$1,743
Total share-based compensation expense	$7,878	$12,418	$14,793

The amount of unearned share-based compensation related to unvested stock options at June 30, 2026, is $32.9 million, with a weighted-average period of 2.96 years over which this unearned compensation is expected to be recognized.

Income Taxes

Prothena recorded an income tax expense of $2,000 and $3,000 for the three and six months ended June 30, 2026, respectively, compared to an income tax expense of $44.8 million and $43.6 million for the same periods in 2025. The decrease in income tax expense was primarily due to the company recording a valuation allowance for its federal deferred tax assets during the three and six months ended June 30, 2025.

As of June 30, 2026, Prothena had a full valuation allowance against its federal, state, and Irish deferred tax assets, as the company believes it is not more likely than not that these assets will be realized.

Restructuring

In June 2025, Prothena commenced a restructuring plan following the company’s decision to discontinue further development of its drug candidate birtamimab. The restructuring charges primarily consisted of employee termination benefits and contract termination costs associated with the discontinuation of birtamimab.

For the three and six months ended June 30, 2026, Prothena recorded a net reduction in the restructuring liability of approximately $8.2 million and $13.0 million, respectively, as the company concluded its restructuring activities. The total amount expected to be incurred at inception in connection with the restructuring plan was $32.6 million, and the cumulative amount incurred to date as of June 30, 2026, was $28.3 million.

Key Programs and Collaborations

Prothena’s pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of various neurodegenerative and rare peripheral amyloid diseases.

Prasinezumab for Parkinson’s Disease

Prasinezumab is an investigational humanized monoclonal antibody that targets alpha-synuclein, a protein implicated in Parkinson’s disease and other synucleinopathies. Prasinezumab is the focus of Prothena’s worldwide collaboration with Roche.

In the fourth quarter of 2025, Roche initiated the Phase 3 PARAISO clinical trial evaluating prasinezumab as a potential treatment for early Parkinson’s disease. The trial is designed to evaluate the efficacy and safety of prasinezumab in approximately 900 participants.

In December 2024, Roche announced topline results from the Phase 2b PADOVA clinical trial, which showed a potential clinical effect of prasinezumab in slowing motor progression in people with early-stage Parkinson’s disease. The results informed the initiation of the Phase 3 PARAISO study.

Prothena and Roche also continue to explore the observed effects in the Phase 2 PASADENA and Phase 2b PADOVA open-label extension studies.

Coramitug for ATTR Amyloidosis

Coramitug is an investigational antibody designed to deplete amyloid associated with disease pathology in hereditary and wild-type ATTR amyloidosis. In July 2021, Prothena’s ATTR amyloidosis business, including coramitug, was acquired by Novo Nordisk.

In the fourth quarter of 2025, Novo Nordisk initiated the Phase 3 CLEOPATTRA clinical trial evaluating coramitug as a potential treatment for ATTR amyloidosis with cardiomyopathy (ATTR-CM). The trial is designed to evaluate the efficacy and safety of coramitug in approximately 1,280 participants.

Moponetug for Alzheimer’s Disease

Moponetug is an investigational antibody designed to target tau, a protein implicated in Alzheimer’s disease. Moponetug is being developed by Bristol Myers Squibb (BMS) under an exclusive global license agreement with Prothena.

In October 2025, BMS obtained Fast Track designation from the FDA for moponetug for the treatment of Alzheimer’s disease. BMS is currently evaluating moponetug in a Phase 2 clinical trial.

Early-Stage Programs

Prothena is also advancing several early-stage programs for neurological diseases, including a TDP-43 CYTOPE® program for the potential treatment of amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease programs, such as PRX012 and PRX012-TfR.

The company is developing a new technology, CYTOPE®, which incorporates a cell-internalizing domain to enable precise targeting of intracellular disease pathways in the brain and periphery. Prothena is exploring potential strategic collaborations and licensing deals to further advance its early-stage programs.

Outlook and Analysis

Prothena’s financial performance for the three and six months ended June 30, 2026, was driven by the recognition of a $50.0 million milestone payment from Novo Nordisk for the continued advancement of coramitug in the Phase 3 CLEOPATTRA trial. This milestone payment, along with the company’s ongoing collaborations and partnerships, has provided Prothena with the necessary funding to advance its pipeline of investigational therapies for various neurodegenerative and rare peripheral amyloid diseases.

The company’s focus on developing novel therapies targeting protein dysregulation, a key driver of many devastating neurological disorders, has positioned Prothena as a leader in this field. The progress of its lead programs, such as prasinezumab for Parkinson’s disease and coramitug for ATTR amyloidosis, as well as the advancement of its early-stage pipeline, including the promising TDP-43 CYTOPE® program, suggest that Prothena is well-positioned to continue delivering value to its shareholders.

However, the company’s reliance on collaborations and partnerships, as well as the inherent risks associated with drug development, could pose challenges in the future. Prothena’s ability to successfully navigate the regulatory landscape, secure additional partnerships, and manage its operating expenses will be crucial in determining the company’s long-term success.

Overall, Prothena’s financial report highlights the company’s strong execution in advancing its pipeline and leveraging its scientific expertise to address significant unmet medical needs in the field of neurodegenerative diseases. As Prothena continues to make progress with its late-stage and early-stage programs, investors will be closely watching the company’s ability to translate its scientific advancements into commercial success.