Tau-0N4R-IN-1 (Compound 6T) is a brain-penetrant inhibitor of tau0N4R oligomerization. It effectively inhibits the fibrillization of tau 0N4R, 2N3R, and 2N4R, showcasing potent anti-seeding effects against tau in vitro, and can dose-dependently reduce α-syn oligomerization while preventing the formation of α-syn inclusions. Tau-0N4R-IN-1 demonstrates stability in mouse microsomes and reduces Aβ plaques derived from the brain tissue of AD patients. Moreover, it exhibits favorable pharmacokinetic properties in mice.

Tau-0N4R-IN-1 inhibits the formation of α-syn oligomers across concentrations of 12.5-100 μM over 2500 minutes, and delays the lag time in the ThT assay at 100 μM, indicating a reduced increase in fluorescence intensity. It also inhibits α-syn aggregation at concentrations ranging from 12.5 to 50 μM in the PICUP assay. At a concentration of 100 μM, Tau-0N4R-IN-1 causes a reduction in tau 2N3R and 2N4R fibrils (at 10 μM). It slightly reduces tau 0N4R oligomerization at doses of 100 and 200 μM. Additionally, Tau-0N4R-IN-1 (50 μM, 5 days) diminishes Aβ plaques extracted from AD patients, and prevents the formation of α-syn inclusions in M17D neuroblastoma cells expressing fusion protein αS-3K::YFP at 40 μM over 96 hours. Moreover, Tau-0N4R-IN-1 demonstrates an anti-seeding effect in TauRD P301S FRET biosensor cells at concentrations between 5 and 20 μM over 48 hours, and remains stable in murine microsomes with 74% remaining after 30 minutes at 3 μM.

Administered via a single intravenous injection at a dose of 1 mg/kg, tau-0N4R-IN-1 exhibits high systemic exposure and a large volume of distribution in the plasma of CD1 male mice, and is capable of penetrating the blood-brain barrier (plasma:brain ≥1).