Prothena SEC Filings

Prothena Corporation plc filed its annual report describing a late-stage biotechnology company focused on diseases caused by protein misfolding, particularly neurodegenerative and rare amyloid disorders. Its pipeline spans wholly owned and partnered antibody, small‑molecule and vaccine programs.

Key partnered assets include prasinezumab with Roche for Parkinson’s disease, coramitug with Novo Nordisk for ATTR cardiomyopathy, and BMS-986446 and PRX019 with Bristol Myers Squibb for Alzheimer’s and other neurodegenerative diseases. Early programs feature the CYTOPE® intracellular targeting platform, Alzheimer’s candidates PRX012 and PRX012‑TfR, and dual Aβ‑tau vaccine PRX123.

The company discontinued development of birtamimab after the Phase 3 AFFIRM‑AL trial failed to meet its endpoints and implemented an approximate 63% workforce reduction in 2025 to lower operating costs while continuing to support key collaborations and selected wholly owned projects.

Prothena Corporation plc amends its shelf registration to permit the offer and issuance of up to $200,000,000 of ordinary shares from time to time. This Post-Effective Amendment notes the company will no longer qualify as a well-known seasoned issuer after filing its Annual Report for the year ended December 31, 2025.

The prospectus describes the general terms for future takedowns under the shelf, the requirement that each offering be accompanied by a prospectus supplement with specific amounts, prices and terms, and that offerings may be conducted through underwriters, dealers, agents or directly to purchasers.

Prothena Corporation plc reported significantly weaker 2025 financial results while highlighting progress across its partnered neurology pipeline. For 2025, the company posted a net loss of $244.1 million, nearly double the prior year’s $122.3 million, as revenue fell to $9.7 million from $135.2 million driven by lower collaboration payments.

Research and development expenses declined to $134.9 million and general and administrative expenses to $59.4 million, reflecting lower clinical, personnel, manufacturing, and consulting costs, though results included $30.1 million of restructuring charges and a $43.2 million non-cash tax expense. Prothena ended 2025 with $308.4 million in cash, cash equivalents and restricted cash and no debt, and had about 53.8 million ordinary shares outstanding as of February 12, 2026.

For 2026, Prothena expects net cash used in operating and investing activities of $50–$55 million and to finish the year with roughly $255 million in cash at the midpoint, excluding up to $105 million of potential clinical milestone receipts from partners. The company also secured shareholder and court approval to create distributable reserves, allowing its board to consider a share redemption program in 2026 at its discretion, and noted multiple late-stage trials with Roche, Novo Nordisk, and Bristol Myers Squibb targeting Parkinson’s, ATTR amyloidosis, and Alzheimer’s disease.

Rubric Capital Management LP and David Rosen disclosed beneficial ownership of Prothena Corporation plc’s ordinary shares. They report holding 3,677,331 ordinary shares, representing 6.83% of the outstanding class.

The percentage is calculated based on 53,829,982 ordinary shares outstanding as of October 31, 2025, as reported by Prothena. Rubric Capital Master Fund LP has the right to receive dividends or sale proceeds on more than 5% of the shares. The investors state that the shares are held in the ordinary course of business and not for the purpose of changing or influencing control of Prothena.

Prothena Corporation plc disclosed that director Paula Cobb has decided to resign from its Board of Directors, effective December 31, 2025. Until that date, she will continue serving on the Board as well as on the Compensation Committee and the Audit Committee.

The company stated that Ms. Cobb’s decision to step down was not because of any disagreement with Prothena on matters related to its operations, policies, or practices, suggesting this is a routine governance change rather than a dispute-driven departure.

Prothena Corporation plc reported the results of an extraordinary general meeting of shareholders held on November 19, 2025. Shareholders considered a single proposal to approve a reduction of the Company’s capital to create distributable reserves.

The proposal was approved with 37,779,052 votes in favor, 46,738 against, and 45,906 abstentions. Creating distributable reserves is an Irish corporate law mechanism that can give a company more flexibility to make future distributions, such as dividends or other returns of value, if its board later chooses to do so and other legal requirements are met. This update reflects a change in Prothena’s capital structure authorization rather than an immediate financial transaction.

Prothena (PRTA) reported Q3 2025 results showing modest collaboration revenue and lower operating spend amid an ongoing restructuring. Total revenue was $2.4 million for the quarter and $9.7 million year-to-date. Research and development expense declined to $28.9 million in Q3, with program spend led by PRX012 ($14.7 million), followed by birtamimab ($7.1 million) and PRX019 ($2.2 million). General and administrative expense was $13.2 million in Q3; restructuring costs totaled $33.1 million year-to-date.

The company recorded a Q3 net loss of $36.5 million and a year-to-date net loss of $222.5 million. Cash and cash equivalents were $330.8 million as of September 30, 2025, compared with $471.4 million at year-end 2024, reflecting $140.3 million used in operating activities year-to-date. Shareholders’ equity was $295.0 million, with total assets of $352.6 million.

Prothena’s collaboration with BMS continues to contribute deferred revenue tied to the PRX019 Phase 1 clinical trial obligation, with $2.4 million recognized in Q3 and $2.7 million remaining as of quarter end. Ordinary shares outstanding were 53,829,982 as of October 31, 2025.

Prothena Corporation plc furnished a press release announcing its financial results for the third quarter ended September 30, 2025. The press release is attached as Exhibit 99.1 to a current report on Form 8-K dated November 6, 2025. The company states that the information provided under Item 2.02 and Exhibit 99.1 is furnished and not deemed “filed” under Section 18 of the Exchange Act.

Prothena Corporation plc is asking shareholders to approve a reduction of capital to create distributable reserves at an Extraordinary General Meeting to be held on November 19, 2025 at 4:00 p.m. local time in Dublin. The Board unanimously recommends a FOR vote on Proposal No. 1, which would permit the company to convert a portion of its capital into distributable reserves that can be used for dividends, share repurchases or other corporate purposes consistent with Irish law.

The Proxy Statement will be made available primarily via the internet on or about October 7, 2025 to shareholders of record as of the September 24, 2025 Record Date. There were 53,829,928 ordinary shares outstanding as of the Record Date. Voting may be done in person, by signed proxy card, by internet, or by telephone (if printed materials are requested). Advance director nomination windows are set for October 29, 2025 through December 28, 2025, and universal proxy notices must comply by March 14, 2026. Voting results will be filed within four business days after the meeting.