Novel compounds lowering the cellular isoform of the human prion protein in cultured human cells.

PURPOSE: Previous studies showed that lowering PrP(C) concomitantly reduced PrP(Sc) in the brains of mice inoculated with prions. We aimed to develop assays that measure PrP(C) on the surface of human T98G glioblastoma and IMR32 neuroblastoma cells. Using these assays, we sought to identify chemical hits, confirmed hits, and scaffolds that potently lowered PrP(C) levels in human brains cells, without lethality, and that could achieve drug concentrations in the brain after oral or intraperitoneal dosing in mice.
METHODS: We utilized HTS ELISA assays to identify small molecules that lower PrP(C) levels by ≥30% on the cell surface of human glioblastoma (T98G) and neuroblastoma (IMR32) cells.
RESULTS: From 44,578 diverse chemical compounds tested, 138 hits were identified by single point confirmation (SPC) representing 7 chemical scaffolds in T98G cells, and 114 SPC hits representing 6 scaffolds found in IMR32 cells. When the confirmed SPC hits were combined with structurally related analogs, >300 compounds (representing 6 distinct chemical scaffolds) were tested for dose-response (EC₅₀) in both cell lines, only studies in T98G cells identified compounds that reduced PrP(C) without killing the cells. EC₅₀ values from 32 hits ranged from 65 nM to 4.1 μM. Twenty-eight were evaluated in vivo in pharmacokinetic studies after a single 10 mg/kg oral or intraperitoneal dose in mice. Our results showed brain concentrations as high as 16.2 μM, but only after intraperitoneal dosing.
CONCLUSIONS: Our studies identified leads for future studies to determine which compounds might lower PrP(C) levels in rodent brain, and provide the basis of a therapeutic for fatal disorders caused by PrP prions.