Prothena's Late-Stage Study for AL Amyloidosis Fails, Stock Down

Shares of Prothena PRTA tumbled 22.5% in after-hours trading on May 23 after it announced the discontinuation of the development of the pipeline candidate, birtamimab.

The decision to discontinue comes after the late-stage AFFIRM-AL clinical study evaluating birtamimab in patients with AL amyloidosis did not meet its primary endpoint.

The company’s shares have lost 52.5% year to date compared with the industry’s decline of 5%.

More on PRTA’s Birtamimab

Birtamimab was a wholly-owned potential best-in-class anti-amyloid antibody for the treatment of AL amyloidosis.

The phase III AFFIRM-AL study was a global, double-blind, placebo-controlled, time-to-event clinical trial that enrolled 207 newly diagnosed, treatment naïve patients with Mayo Stage IV AL amyloidosis.

The patients in the active arm were given birtamimab every 28 days at a dose level of 24 mg/kg (maximum dose not to exceed 2500 mg). Patients in both the active and control arms received a bortezomib-containing chemotherapy regimen as standard of care and use of daratumumab was allowed.

However, the primary endpoint of time to all-cause mortality was not met for patients treated with birtamimab. In addition, neither of the secondary endpoints was met: 6-minute walk test distance and Short Form-36 version 2 Physical Component Score. Nonetheless, birtamimab was generally safe and well-tolerated, consistent with its established safety profile.

What Is Next for PRTA?

Due to the failure of the AFFIRM-AL study, PRTA will discontinue the development of birtamimab, including stopping the open label extension (OLE) of the AFFIRM-AL clinical study.

PRTA will also decrease ongoing operating expenses, including an expected substantial reduction in organizational size. Additional updates on the same is expected in June.

Updates on partnered programs with Roche RHHBY and Novo Nordisk NVO is expected in mid-2025 and the second half of 2025, respectively.

The company is also evaluating prasinezumab, in collaboration with Roche for the treatment of Parkinson’s disease (PD).

Roche had earlier reported that data from the phase IIb PADOVA study in patients with early-stage Parkinson’s disease showed that it missed the primary endpoint, but demonstrated a numerical delay in motor progression and positive trends on multiple secondary and exploratory endpoints, suggesting a possible clinical benefit.

Roche will continue to evaluate data from PADOVA. It will also collaborate with health authorities to determine the next steps by mid-year 2025.

Roche is currently conducting the OLEs of the phase II PASADENA and phase IIb PADOVA clinical studies.

Novo Nordisk is evalauting Coramitug (formerly PRX004), a potential first-in-class amyloid depleter antibody for the treatment of ATTR amyloidosis with cardiomyopathy.

NVO is conducting an ongoing phase II study in patients with ATTR cardiomyopathy.

PRTA is advancing an early-stage pipeline of programs for several potential neurological indications with Bristol Myers BMY.

BMS-986446 is a best-in-class anti-tau, MTBR-specific antibody for the is being investigated for the potential treatment of AD.
Bristol Myers continues to enroll patients with early AD in the ongoing phase II study on BMS-986446. The study is expected to be completed in 2027.

PRX019, a potential treatment for neurodegenerative diseases, is also being developed in collaboration with BMY.

PRTA has initiated a phase I first-in-human clinical trial on PRX019 to evaluate the safety, tolerability, immunogenicity, and pharmacokinetics of single ascending and multiple doses in healthy adults. The phase I study is expected to be completed in 2026.

With the discontinuation of birtamimab, the focus now shifts to above mentioned candidates in the pipeline.

PRTA currently carries a Zacks Rank #3 (Hold). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.

 

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