A promising anti-prion trimethoxychalcone binds to the globular domain of PrPC and changes its cellular location [PublishAheadOfPrint]

The search for anti-prion compounds has been encouraged by the fact that transmissible spongiform encephalopathies (TSEs) share molecular mechanisms with more prevalent neurodegenerative pathologies, such as Parkinson's and Alzheimer's diseases. Cellular prion protein conversion into protease-resistant forms (PrP^Res or PrP^Sc) is a critical step in the development of TSEs, thus being one of the main targets in the screening for anti-prion compounds. In this work, three trimethoxychalcones (J1, J8, J20) and one oxadiazole (Y17), previously identified in vitro as potential anti-prion compounds, were evaluated through different approaches in order to gain inferences about their mechanism of action. None of them changed PrP^C mRNA levels in N2a cells as shown by RT-qPCR. Among them, J8 and Y17 were effective in RT-QuIC reactions using rodent rPrP^23--231 as substrate and PrP^Sc seeds from hamster and human brain. However, when rPrP^90--231, which lacks the N-terminal domain, was used as substrate, only J8 remained effective, indicating that this region is important for Y17 activity, while J8 seems to interact with PrP^C globular domain. J8 also reduced the fibrillation of mouse rPrP^23--231 seeded with in vitro-produced fibrils. Furthermore, most of the compounds decreased the amount of PrP^C on N2a cell surface by trapping this protein in the endoplasmic reticulum. Based on these results, we hypothesize that J8, a non-toxic promising anti-prion compound as previously shown, may act by different mechanisms, since its efficacy is attributable not only to the PrP conversion inhibition, but also to reduction of PrP^C content on the cell surface.

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