Variety of antiprion compounds discovered through an in silico screen based on cellular-form prion protein structure: Correlation between antiprion activity and binding affinity

Transmissible spongiform encephalopathies are associated with the conformational conversion of the prion protein from the cellular form (PrP(C)) to the scrapie form. This process could be disrupted by stabilizing the PrP(C) conformation, using a specific ligand identified as a chemical chaperone. To discover such compounds, we employed an in silico screen that was based on the nuclear magnetic resonance structure of PrP(C). In combination, we performed ex vivo screening using the Fukuoka-1 strain-infected neuronal mouse cell line at a compound concentration of 10 microM and surface plasmon resonance. Initially, we selected 590 compounds according to the calculated docked energy and finally discovered 24 efficient antiprion compounds, whose chemical structures are quite diverse. Surface plasmon resonance studies showed that the binding affinities of compounds for PrP(C) roughly correlated with the compounds' antiprion activities, indicating that the identification of chemical chaperones that bind to the PrP(C) structure and stabilize it is one efficient strategy for antiprion drug discovery. However, some compounds possessed antiprion activities with low affinities for PrP(C), indicating a mechanism involving additional modulation factors. We classified the compounds roughly into five categories: (i) binding and effective, (ii) low binding and effective, (iii) binding and not effective, (iv) low binding and not effective, and (v) acceleration. In conclusion, we found a spectrum of compounds, many of which are able to modulate the pathogenic conversion reaction. The appropriate categorization of these diverse compounds would facilitate antiprion drug discovery and help to elucidate the pathogenic conversion mechanism.