Update on [18F]ACI‐12589: a novel and promising PET tracer for a‐synuclein

Abstract

AbstractBackgroundParkinson’s disease (PD) and other synucleinopathies, such as Multiple System Atrophy (MSA), involve a progressive accumulation of a‐synuclein (a‐syn) inclusions which correlate well with clinical manifestations. A PET agent capable of imaging specifically and selectively a‐syn inclusions could significantly improve differential diagnosis and clinical trials for drug candidates targeting a‐syn. Here, we report the preclinical and initial clinical characterization of [18F]ACI‐12589 in patients with different synucleinopathies.MethodLeveraging AC Immune’s proprietary small molecule Morphomer® library, compounds were optimized for affinity and specificity for pathological a‐syn as well as for selectivity versus frequent co‐pathologies, using autoradiography and radiobinding techniques. Based on these results [18F]ACI‐12589, was selected for initial clinical evaluation. PET scans were acquired for approximately 50 participants including idiopathic and genetic PD, MSA, Dementia with Lewy bodies (DLB) in addition to controls and cases from other neurodegenerative disorders (NDDs). Initial participants underwent 0‐90 min dynamic scans with arterial blood sampling allowing full kinetic modeling, while following scans were acquired as 60‐90 min static scans.ResultWhen tested on tissue sections, ACI‐12589 demonstrated a specific signal matching the distribution of pathological a‐syn. This target engagement was observed across a range of cases with different synucleinopathy diagnoses, but also in tissues from other NDDs, when a‐syn inclusions were present as co‐pathology. ACI‐12589 is selective in vitro versus frequent co‐pathologies such as amyloid‐b and Tau and has a clean off‐target profile, including for MAO‐A and B. Initial clinical data indicate that [18F]ACI‐12589 displayed substantial retention in MSA cases in expected disease‐affected brain areas based on clinical manifestations. When quantified, the signal in the cerebellar peduncles was clearly discriminating the MSA group from controls, synucleinopathy cases and other NDDs. In addition, this signal could not be blocked in vivo by the MAO‐B inhibitor Selegiline. Although to a lower level than in MSA cases, some signal retention was observed in different NDDs.Conclusion[18F]ACI‐12589 displays the preclinical and clinical characteristics deemed necessary to become a reliable and accurate PET radiotracer for the detection of a‐syn pathology in MSA. Additional evaluations of this tracer will focus on the longitudinal and early disease stage assessments.