Identification of novel fluorescent probes preventing PrP^Sc replication in prion diseases

Prion diseases are serious, not curable neurodegenerative disorders caused by the accumulation of the misfolded protein PrP^Sc that represents the pathological variant of the normally folded cellular protein PrP^C. Molecules that bind the cellular isoform PrP^C preventing its misfolding, could arrest the progression of pathological conditions related to the abnormal PrP protein. In this context, by combining 3D-QSAR model, derived from pharmacophore-based alignment, with molecular docking procedures and physico-chemical properties prediction we have developed a virtual screening protocol to find novel chemicals able to prevent PrP^C misfolding. We identified different hits characterized by low toxicity and able to inhibit PrP^Sc accumulation in vitro in prion-infected neuroblastoma cell lines (ScN2a). In this assay, the pyrroloquinoxaline hydrazone 96 showed the higest potency with an IC₅₀ value of 1.6 μM. Pyrroloquinoxaline 96 was demonstrated also to bind PrP^Sc aggregates in infected ScN2a cells with a fluorescence pattern comparable to that found for Thioflavin-T. In consideration of its satisfactory physico-chemical properties, including predicted blood brain barrier permeability, 96 could represent an interesting prototypic hit for the development of diagnostic and therapeutic probes for prion diseases.