Identification of compounds inhibiting prion replication and toxicity by removing PrP from the cell surface.

The vast majority of therapeutic approaches tested so far for prion diseases, transmissible neurodegenerative disorders of human and animals, tackled PrP , the aggregated and infectious isoform of the cellular prion protein (PrP ), with largely unsuccessful results. Conversely, targeting PrP expression, stability or cell surface localization are poorly explored strategies. We recently characterized the mode of action of chlorpromazine, an anti-psychotic drug known to inhibit prion replication and toxicity by inducing the re-localization of PrP from the plasma membrane. Unfortunately, chlorpromazine possesses pharmacokinetic properties unsuitable for chronic use in vivo, namely low specificity and high toxicity. Here, we employed HEK293 cells stably expressing EGFP-PrP to carry out a semi-automated high content screening (HCS) of a chemical library directed at identifying non-cytotoxic molecules capable of specifically relocalizing PrP from the plasma membrane as well as inhibiting prion replication in N2a cell cultures. We identified four candidate hits inducing a significant reduction in cell surface PrP , one of which also inhibited prion propagation and toxicity in cell cultures in a strain-independent fashion. This study defines a new screening method and novel anti-prion compounds supporting the notion that removing PrP from the cell surface could represent a viable therapeutic strategy for prion diseases.