Prothena Reports First Quarter 2019 Financial Results and Provides R&D Update Net cash used in operating and investing activities was $17.6 million in the first quarter; quarter-end cash and restricted cash position of $

Prothena Reports First Quarter 2019 Financial Results and Provides R&D Update

DUBLIN, Ireland, May 7, 2019 -- Prothena Corporation plc (NASDAQ:PRTA), a clinical-stage neuroscience company, today reported financial results for the first quarter of 2019. In addition, the Company provided an update on its R&D programs and 2019 financial guidance.

"We continue to advance our neuroscience pipeline of investigational therapies, and are progressing several programs towards key milestones," said Gene Kinney, Ph.D., President and Chief Executive Officer of Prothena. "We have initiated cell line development of a lead candidate for our tau program under our collaboration with Celgene. Enrollment in our Phase 1 study of PRX004 in ATTR amyloidosis is progressing and we now anticipate that the fourth quarter update on this program will include data from cohorts 1 through 4. Data from Part 1 of the Phase 2 PASADENA study of prasinezumab in Parkinson's disease, which is being run by Roche, are expected in 2020. We also recently reported results from the Phase 3 VITAL study of NEOD001 in AL amyloidosis and are exploring business development opportunities that could result in further clinical investigation of NEOD001."

First Quarter 2019 and Recent Development

NEOD001 (birtamimab) is an investigational humanized immunoglobulin G1 designed to directly neutralize soluble toxic aggregates and promote clearance of amyloid via phagocytosis to remove organ-deposited amyloid thought to cause organ dysfunction in patients with AL amyloidosis.

Upcoming Research and Development Milestones

Prothena is advancing a pipeline of therapeutic candidates for a number of indications and novel targets.

Prasinezumab (PRX002/RG7935), a potential treatment for Parkinson's disease, is a monoclonal antibody designed to target alpha-synuclein and is the focus of a worldwide collaboration with Roche.

PRX004, a potential treatment for ATTR amyloidosis, is a monoclonal antibody designed to target and clear the pathogenic, misfolded forms of the TTR protein.

Tau is a protein implicated in diseases including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), frontotemporal dementia (FTD) and chronic traumatic encephalopathy (CTE). Prothena's internally discovered tau antibody targets a novel epitope on the protein.

First Quarter 2019 Financial Results and Updated 2019 Guidance

Prothena reported a net loss of $20.9 million for the first quarter of 2019, as compared to a net loss of $48.7 million for the first quarter of 2018. Net loss per share for the first quarter of 2019 was $0.52, as compared to a net loss per share of $1.26 for the first quarter of 2018.

Prothena reported total revenue from its collaboration with Roche of $0.2 million for the first quarter of 2019 as compared to total revenue of $0.2 million for the first quarter of 2018.

Research and development (R&D) expenses totaled $13.3 million for the first of 2019, as compared to $34.7 million for the first quarter 2018. The decrease in R&D expenses compared to the first quarter of 2018 was primarily due to lower clinical trial costs, lower consulting and personnel costs and lower product manufacturing expenses. R&D expenses included non-cash share-based compensation expense of $2.1 million for the first quarter 2019 as compared to $2.3 million for the first quarter of 2018.

General and administrative (G&A) expenses totaled $9.9 million for the first quarter of 2019, as compared to $14.2 million for the first quarter of 2018. The decrease in G&A expenses compared to the first quarter of 2018 was primarily due to lower personnel costs and consulting expenses. G&A expenses included non-cash share-based compensation expense of $4.1 million for the first quarter of 2019, as compared to $4.6 million for the first quarter of 2018.

Total non-cash share-based compensation expense was $6.2 million for the first quarter of 2019, as compared to $6.9 million for the first quarter 2018.

As of March 31, 2019, Prothena had $414.2 million in cash, cash equivalents and restricted cash and no debt.

As of April 30, 2019, Prothena had approximately 39.9 million ordinary shares outstanding.

The Company is updating its full year 2019 net cash burn from operating and investing activities, and expects it to be $57-65 million, representing a decrease of approximately $7 million, and expects to end the year with approximately $371 million in cash, cash equivalents and restricted cash (midpoint). The Company had planned on initiating cell line development of a lead candidate for an Amyloid beta discovery program this year but will not be making additional investments in this program at this time based on the recent discontinuation of Biogen's aducanumab program. The updated estimated full year 2019 cash burn from operating and investing activities is primarily driven by an updated estimated net loss of $83-94 million, which includes an estimated $24 million of non-cash shared-based compensation expense.

Forward-looking Statements

This press release contains forward-looking statements. These statements relate to, among other things: the sufficiency of our funding to advance our neuroscience pipeline; the progress of our neuroscience pipeline of investigational therapies towards key milestones; our expected timing of reporting data from the Phase 2 PASADENA study of prasinezumab; our expected timing of reporting data from the Phase 1 study of PRX004 and the expected scope of that data; our exploration of business development opportunities that could result in further clinical investigation of NEOD001; the design and proposed mechanisms of action of NEOD001 and its potential as a treatment for AL amyloidosis; the results of post hoc analyses that reveal a potential survival benefit favoring NEOD001; the design of prasinezumab and its potential as a treatment for Parkinson's disease; the design of PRX004 and its potential as a treatment for ATTR amyloidosis; our goal of advancing a research pipeline of novel targets for a number of potential indications; our expected net cash burn from operating and investing activities in 2019 and cash balance at the end of 2019; and our estimated net loss and non-cash share-based compensation expense for 2019. 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 the risks, uncertainties and other factors described in the "Risk Factors" sections of our Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) March 15, 2019 and our subsequent Quarterly Reports on Form 10-Q filed with the SEC. Prothena undertakes 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 Prothena's expectations.

PROTHENA CORPORATION PLC

CONSOLIDATED STATEMENTS OF OPERATIONS

(unaudited - amounts in thousands except per share data)

PROTHENA CORPORATION PLC

CONSOLIDATED BALANCE SHEETS

(unaudited - amounts in thousands)

Media and Investor Contact:

Ellen Rose, Head of Communications

650-922-2405, ellen.rose@prothena.com