Development of [$^18$F]ACI-19626 as a first-in-class brain PET tracer for imaging TDP-43 pathology

Aggregated TDP-43 is a hallmark of frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and limbic-predominant age-related TDP-43 encephalopathy (LATE), and a common co-pathology in other neurodegenerative diseases. Currently, no specific biomarkers exist to assess TDP-43 pathology in vivo. We developed two small-molecule radiopharmaceuticals, [F]ACI-19278 and [F]ACI-19626, for visualizing TDP-43 inclusions by positron emission tomography (PET). Both ligands bind with high affinity to aggregated, but not soluble, TDP-43 in patient brain samples from diverse TDP-43 proteinopathies, including frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP), ALS, and LATE, and in cell models. Both compounds display excellent selectivity for TDP-43 over Aβ, Tau, and α-synuclein aggregates. In non-human primates, [F]ACI-19278 and [F]ACI-19626 show a pharmacokinetic profile suitable for brain PET imaging (rapid brain uptake; fast and complete washout). ACI-19278 and ACI-19626 are promising first-in-class TDP-43 PET tracers with the potential to revolutionize the diagnosis and treatment of neurodegenerative proteinopathies, enabling a precision medicine approach.