Prothena Highlights Phase 2 Data for Coramitug (Formerly PRX004) Published in Circulation, Official Journal of AHA

• Novo Nordisk’s Phase 2 data for coramitug supports ongoing Phase 3 CLEOPATTRA clinical trial in patients with ATTR amyloidosis with cardiomyopathy
• Coramitug is being developed by Novo Nordisk as part of their up to $1.2 billion acquisition of Prothena’s ATTR amyloidosis business and pipeline

DUBLIN--(BUSINESS WIRE)--Prothena Corporation plc (NASDAQ:PRTA) announced the publication of Phase 2 clinical trial data for coramitug (formerly PRX004), a potential first-in-class amyloid depleter antibody, for the treatment of ATTR amyloidosis with cardiomyopathy (ATTR-CM), in the American Heart Association’s journal, Circulation.

A link to the online publication can be found here:

Coramitug, a Humanized Monoclonal Antibody for the Treatment of Transthyretin Amyloid Cardiomyopathy: a Phase 2, Randomized, Multicenter, Double-Blind, Placebo-Controlled Trial¹

The Phase 2 clinical trial results were presented during a late-breaking session at the American Heart Association (AHA) Scientific Sessions on November 10, 2025 and simultaneously published in AHA journal, Circulation. Novo Nordisk recently initiated the Phase 3 CLEOPATTRA clinical trial evaluating the effects of coramitug versus placebo on cardiovascular outcomes in participants with ATTR-CM (NCT07207811).

Novo Nordisk gained full worldwide rights to the intellectual property and related rights of the ATTR amyloidosis business and pipeline it acquired from Prothena in July 2021. Under the terms of the acquisition agreement, Prothena is eligible to receive up to $1.2 billion dollars upon achievement of clinical development and sales milestones, including $100 million earned to date. Prothena is eligible to earn a clinical milestone payment when prespecified enrollment criteria are met in the CLEOPATTRA Phase 3 clinical trial.

About Coramitug (formerly PRX004)

Coramitug (formerly PRX004) is an investigational antibody designed to deplete amyloid associated with disease pathology in hereditary and wild type ATTR amyloidosis, without affecting the native, normal tetrameric form of the protein^2-4. Coramitug’s proposed mechanism of action is to deplete both the deposited amyloid to improve organ function and circulating non-native TTR to prevent further organ deposition^2-4. This differentiated depleter mechanism of action could be developed as a monotherapy approach to ATTR amyloidosis and might also complement existing therapeutic approaches which either stabilize or reduce production of the native TTR tetramer⁴.

About Prothena

Prothena Corporation plc is a late-stage clinical biotechnology company with expertise in protein dysregulation and a pipeline of investigational therapeutics 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 ATTR amyloidosis with cardiomyopathy, Alzheimer’s disease, Parkinson’s disease and a number of other neurodegenerative diseases. 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, the treatment potential, design, and proposed mechanism of action coramitug; plans for ongoing and future clinical trials of coramitug; and amounts we might receive under our agreement with Novo Nordisk. 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 those described in the “Risk Factors” sections of our Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on November 6, 2025, 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.

References:

¹ www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.125.077304
² Preclinical studies of PRX004 (coramitug) – data on file
³ Higaki JN et al. Amyloid, 2016
⁴ Suhr OB et al. Amyloid, 2025