New PET tracer helps scientists ‘see’ Parkinson’s toxic protein clumps
Partnership will use FD4 tracer to track potential disease-modifying therapy
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A new PET tracer, FD4, will visualize toxic alpha-synuclein clumps in Parkinson's disease trials.
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FD4 will track risvodetinib, a potential therapy aiming to slow Parkinson's progression by inhibiting Abelson tyrosine kinase.
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Upcoming clinical trials will use FD4 to assess risvodetinib's effect on protein accumulation.
A new high-tech imaging tool that can “see” the toxic protein clumps thought responsible for Parkinson’s disease is heading into clinical trials to help determine if an experimental therapy can slow the disease. Synusight Biotech has licensed its specialized positron emission tomography (PET) tracer ¹⁸F-FD4 to Abli Therapeutics and Xingimaging to track the effects of risvodetinib, a potential disease-modifying treatment for Parkinson’s disease.
By using this tracer, researchers can visualize alpha-synuclein aggregates — the hallmark “toxic clumps” of Parkinson’s — inside the living brain. This partnership will support two upcoming clinical trials, one in the U.S. and one in China, both of which are slated to begin later this year. Xingimaging will manufacture the tracer for use with the NeuroEXPLORER, a next-generation PET imager, at its newly established imaging facility in New Haven, Connecticut.
“This collaboration represents a key milestone in the global development of FD4,” Roger Fan, Synusight’s CEO, said in a company press release. “By integrating molecular imaging technologies with rigorously designed clinical trials and longitudinal follow-up, the partnership aims to directly interrogate the disease-modifying potential at the pathological level.”
Targeting the root cause of Parkinson’s
Parkinson’s disease is caused by the progressive dysfunction and loss of dopaminergic neurons, or the nerve cells that produce the signaling molecule dopamine, leading to the disease’s symptoms. The accumulation of toxic clumps of alpha-synuclein is thought to drive nerve cell dysfunction and death, and may begin before symptoms develop.
Although several treatments can help manage symptoms, there are no disease-modifying therapies that can slow or reverse the progression of Parkinson’s. Risvodetinib is designed to inhibit Abelson tyrosine kinase, an enzyme involved in multiple cell processes and a known target for Parkinson’s treatment. By blocking the activity of this enzyme, risvodetinib aims to reduce dopaminergic neuron loss and has the potential to slow disease progression.
In the Phase 2 201 study (NCT05424276), which enrolled patients with Parkinson’s who experienced bradykinesia, or slowness of movement, risvodetinib led to improvements in clinical tests that measure symptom severity and how the disease limits functional independence.
Now, Abli plans to re-enroll the 120 participants from that trial, which was completed in 2024, for a new ABILITY-PD trial. The new one-year study will use the FD4 tracer and the NeuroEXPLORER PET system to evaluate the effect of risvodetinib on the accumulation of toxic alpha-synuclein clumps.
The study will also collect motor, nonmotor, and dopamine transporter-specific functional data to evaluate how changes in these biomarkers correlate with functional outcomes in response to treatment.
A second, larger Phase 2b/3 trial — the CAMPD trial — is also in the works. It will compare risvodetinib to a placebo in up to 500 participants who have not yet started other Parkinson’s treatments.
“Abli has been expanding its portfolio of disease-related biomarkers, with both blood-borne and tissue measures of alpha-synuclein pathology and is excited to add alpha-synuclein PET imaging to this panel to expand our understanding of the potential disease-modifying effect of risvodetinib in [Parkinson’s],” said Milton Werner, PhD, Abli’s chairman and CEO.
In 2025, FD4 received a $3.84-million research grant from the Michael J. Fox Foundation, supporting its U.S. clinical registration and development.
Under the new collaboration, a non-exclusive clinical use license agreement, Synusight will receive an upfront payment and subsequent license-related fees from Abli. The values were not disclosed.
“This represents a pivotal opportunity to advance one of the most promising alpha-synuclein PET tracers in humans with the potential disease-modifying effect of risvodetinib in [Parkinson’s],” said Gilles Tamagnan, PhD, CEO of Xingimaging.
