aibioBristol Myers Squibb drops Prothena's PRX019, ending up to $617.5 million in milestones
Tickers PRTA
Bristol Myers Squibb will end its PRX019 license on January 28, 2027, dropping up to $617.5 million in milestones it could have owed. The 8-K cites an internal strategic review and gives no further reason.
Key facts
- Company
- Prothena Corporation plc (NASDAQ: PRTA)
- News type
- Distress
- Primary source
- Prothena Corporation plc 8-K (2026-10-29)
The termination
Prothena Corporation plc (Nasdaq: PRTA) disclosed in a Form 8-K filed October 29, 2026 under Item 1.02 that Bristol Myers Squibb told it on October 28, 2026 that it "has decided not to advance PRX019 further in the clinic." The decision followed what the filing calls an internal strategic review. The PRX019 Global License Agreement, signed in May 2024 by a Prothena subsidiary, will terminate on January 28, 2027.
Money received and money dropped
The subsidiary received an upfront payment of $80 million under the 2024 agreement. Prothena was also eligible for development, regulatory and sales milestones of up to $617.5 million, plus tiered royalties on worldwide net sales. With the termination, Bristol Myers Squibb will not owe any of those amounts. The filing does not say whether any milestone had been reached before the decision.
The Phase 1 description
The 8-K says Prothena completed the Phase 1 trial of PRX019 in the first half of 2026. It describes the trial as having "successfully demonstrated a benign safety and tolerability profile, no immunogenicity, and dose-dependent pharmacokinetics and pharmacodynamic effects, meeting the Company's prespecified pharmacodynamic targets."
That is Prothena's own summary. The 8-K gives no efficacy results, no patient numbers and no data tables, and the pharmacodynamic targets are the company's own. The only reason given for Bristol Myers Squibb's decision is the strategic review, so the filing does not show whether the trial results played a part in it.
The moponetug collaboration
PRX019 and moponetug, formerly PRX005, were both clinical-stage programs in a research and development collaboration signed in 2018. Bristol Myers Squibb continues to develop moponetug, an antibody targeting tau, in the Phase 2 TargetTau-1 trial in patients with early Alzheimer's disease (NCT06268886). Bristol Myers Squibb has paid Prothena $135 million in licensing payments for moponetug so far. Prothena remains eligible for up to $562.5 million in regulatory and sales milestones, plus tiered royalties. The 8-K gives no timing for the trial's results.
Prothena's financial position
The annual report on Form 10-K filed February 27, 2026 showed a 2025 net loss of $244.1 million, against $122.3 million in 2024. Cash used in operations was $163.6 million in 2025, against $150.1 million a year earlier. Research and development expense was $134.9 million in 2025, against $222.5 million in 2024.
At June 30, 2026, Prothena held cash and cash equivalents of $288.2 million, according to its 10-Q. Year-end cash and cash equivalents were $307.5 million for 2025, against $471.4 million for 2024. What the termination removes is the milestone and royalty stream the company could have earned from PRX019.
What the filing leaves out
The 8-K does not say what Prothena plans to do with PRX019 once the agreement ends. It gives no estimate of any charge or cost tied to the termination. It also gives no reason for the decision beyond the strategic review, and no information about Bristol Myers Squibb's next steps on PRX019 apart from the termination date.
What comes next
The license ends on January 28, 2027. Until then the filing gives no indication of any transition plan. The main remaining partnered value is the moponetug milestone pool of up to $562.5 million, which depends on a Phase 2 trial whose result and timing the filing does not state. Prothena has not said what it intends to do with PRX019, and the 8-K does not address it.