Novel Small‐Molecular Ligands for Prolyl Oligopeptidase to Combat Tauopathies

Background Tauopathies that include e.g. frontotemporal dementia and Alzheimer’s disease, are neurodegenerative diseases characterized by accumulation of hyperphosphorylated Tau in the brain. Tau is a tempting drug target for tauopathies but no Tau‐targeting therapies are in clinical use. We have recently shown that small‐molecular inhibitors of prolyl oligopeptidase (PREP) can activate protein phosphatase 2A (PP2A) by regulating PREP‐PP2A interaction. PP2A is the main phosphatase regulating Tau, and therefore, we decided to test the efficacy of a reference PREP inhibitor, KYP‐2047, and novel PREP ligands on cellular and animal models of tauopathies. Method The compounds, KYP‐2047 and HUP‐46, 55 and 59 (1, 5 and 10 μM), were first screened in the GFP‐2N4R‐Tau transfected HEK‐293 cells where the Tau aggregation was induced by small‐dose okadaic acid (OA; 10 nM), a PP2A inhibitor. The results were verified by using 2N4R‐Tau transfected HEK‐293 cells with 10 nM OA. After the treatment the cells were fractioned to RIPA soluble and SDS‐fractions, and total Tau and S262 phosphorylated Tau (pS262 Tau) levels were studied by Western blot (WB). Finally, KYP‐2047 and HUP‐46 were tested in PS19 Tau transgenic mouse. PS19 mice were treated with the ligands for 4 weeks (10 mg/kg/day, Alzet minipump i.p.) starting from 5.5 months old when the behavioral deficits were observed. After the treatment, the mice behavior was tested by Barnes Maze and locomotor activity assay, and total Tau, pS262 Tau and PP2A levels were studied. Result In the GFP‐Tau aggregation assay, all compounds decreased the GFP signal as an indicative of Tau aggregation with 10 mM concentration but HUP‐46 was the most effective (Fig. 1). WB that showed that PREP ligands had the most significant effect on total Tau and pS262 Tau in the SDS‐fraction. In the PS19 mice, KYP‐2047 restored normal behavior in Barnes maze and locomotor activity assay. HUP‐46 had similar effect but did not reach significance (Fig. 2). However, both compounds reduced significantly total Tau and pS262 Tau levels in mouse hippocampus and cortex, and activated PP2A (Fig. 3). Conclusion Small‐molecular PREP ligands, such as KYP‐2047 and HUP‐46 have disease‐modifying effects on cellular and animal models of tauopathies.