Anti-Prion Screening for Acridine, Dextran, and Tannic Acid using Real Time–Quaking Induced Conversion: A Comparison with PrP(Sc)-Infected Cell Screening

Prion propagation is mediated by the structural alteration of normal prion protein (PrP(C)) to generate pathogenic prion protein (PrP(Sc)). To date, compounds for the inhibition of prion propagation have mainly been screened using PrP(Sc)-infected cells. Real time–quaking-induced conversion (RT-QuIC) is one alternative screening method. In this study, we assessed the propagation inhibition effects of known anti-prion compounds using RT-QuIC and compared the results with those from a PrP(Sc)-infected cell assay. Compounds were applied to RT-QuIC reactions at 0 h or 22 h after prion propagation to determine whether they inhibited propagation or reduced amplified aggregates. RT-QuIC reactions in presence of acridine, dextran sulfate sodium (DSS), and tannic acid inhibited seeded aggregation with sporadic Creutzfeldt-Jakob disease at 0 h. After treatment at 22 h, amplified fluorescence was decreased in wells treated with either acridine or tannic acid. Compound activities were verified by western blot of RT-QuIC products and in a dye-independent conversion assay, the Multimer Detection System. Protease K-resistant PrP(Sc) fragments (PrP(res)) were reduced by DSS and tannic acid in the PrP(Sc)-infected cell assay. Importantly, these inhibitory effects were similar despite different treatment times (0 h versus 3 days). Consequentially, RT-QuIC enabled the more specific classification of compounds according to action (i.e., inhibition of prion propagation versus reduction of amplified aggregates). RT-QuIC addresses the limitations of cell-based screening methods and can be used to further aid our understanding of the mechanisms of action of anti-prion compounds.