Synthetic prions were produced in our laboratory by using recombinant mouse prion protein (MoPrP) composed of residues 89-230. The first mouse synthetic prion strain (MoSP1) was inoculated into transgenic (Tg) 9949 mice expressing N-terminally truncated MoPrP(Delta23-88) and WT FVB mice expressing full-length MoPrP. On first and second passage in Tg9949 mice, MoSP1 prions caused disease in 516 +/- 27 and 258 +/- 25 days, respectively; numerous, large vacuoles were found in the brainstem and gray matter of the cerebellum. MoSP1 prions passaged in Tg9949 mice were inoculated into FVB mice; on first and second passage, the FVB mice exhibited incubation times of 154 +/- 4 and 130 +/- 3 days, respectively. In FVB mice, vacuolation was less intense but more widely distributed, with numerous lesions in the hippocampus and cerebellar white matter. This constellation of widespread neuropathologic changes was similar to that found in FVB mice inoculated with Rocky Mountain Laboratory (RML) prions, a strain derived from a sheep with scrapie. Conformational stability studies showed that the half-maximal GdnHCl (Gdn(1/2)) concentration for denaturation of MoSP1 prions passaged in Tg9949 mice was approximate to4.2 M; passage in FVB mice reduced the Gdn(1/2) value to approximate to1.7 M. RML prions passaged in either Tg9949 or FVB mice exhibited Gdn(1/2) values of approximate to1.8 M. The incubation times, neuropathological lesion profiles, and Gdn(1/2) values indicate that MoSP1 prions differ from RML and many other prion strains derived from sheep with scrapie and cattle with bovine spongiform encephalopathy.

Background: Prion diseases are caused by the accumulation of an aberrantly folded isoform of the prion protein, designated PrPSc. In a cell-based assay, quinacrine inhibits the conversion of normal host prion protein (PrPC) to PrPSc at a half-maximal concentration of 300 nM. While these data suggest that quinacrine may be beneficial in the treatment of prion disease, its penetration into brain tissue has not been extensively studied. If quinacrine penetrates brain tissue in concentrations exceeding that demonstrated for in vitro inhibition of PrPSc, it may be useful in the treatment of prion disease. Methods: Oral quinacrine at doses of 37.5 mg/kg/D and 75 mg/kg/D was administered to mice for 4 consecutive weeks. Plasma and tissue ( brain, liver, spleen) samples were taken over 8 weeks: 4 weeks with treatment, and 4 weeks after treatment ended. Results: Quinacrine was demonstrated to penetrate rapidly into brain tissue, achieving concentrations up to 1500 ng/g, which is several-fold greater than that demonstrated to inhibit formation of PrPSc in cell culture. Particularly extensive distribution was observed in spleen (maximum of 100 mug/g) and liver (maximum of 400 mug/g) tissue. Conclusions: The documented extensive brain tissue penetration is encouraging suggesting quinacrine might be useful in the treatment of prion disease. However, further clarification of the distribution of both intracellular and extracellular unbound quinacrine is needed. The relative importance of free quinacrine in these compartments upon the conversion of normal host prion protein (PrPC) to PrPSc will be critical toward its potential benefit.