Use of a 2-aminothiazole to Treat Chronic Wasting Disease in Transgenic Mice

Abstract

Treatment with the 2-aminothiazole IND24 extended the survival of mice infected with mouse-adapted scrapie but also resulted in the emergence of a drug-resistant prion strain. Here, we determined whether IND24 extended the survival of transgenic mice infected with prions that caused scrapie in sheep or prions that caused chronic wasting disease (CWD; hereafter "CWD prions") in deer, using 2 isolates for each disease. IND24 doubled the incubation times for mice infected with CWD prions but had no effect on the survival of those infected with scrapie prions. Biochemical, neuropathologic, and cell culture analyses were used to characterize prion strain properties following treatment, and results indicated that the CWD prions were not altered by IND24, regardless of survival extension. These results suggest that IND24 may be a viable candidate for treating CWD in infected captive cervid populations and raise questions about why some prion strains develop drug resistance whereas others do not.

Keywords: chronic wasting disease; prion disease; survival extension; therapeutic; transgenic mice.

Figure 1.

Incubation periods of transgenic (Tg) mice inoculated with natural prion isolates and treated with vehicle (V; red) or IND24 (green). Kaplan–Meier survival curves of Tg mice expressing ovine prion protein that were inoculated with the sheep scrapie isolate SSBP/1 (IND24, n = 9; V, n = 9; A) or the sheep scrapie isolate CH1641 (IND24, n = 7; V, n = 8; C) and of Tg mice expressing elk prion protein that were inoculated with white-tailed deer (WTD) CWD prions (IND24, n = 8; V, n = 8; E). Immunoblots show proteinase K–resistant prion protein in the brains of animals with terminal disease that were infected with SSBP/1 (B), CH1641 (D), or WTD CWD prions (F) and treated with vehicle or IND24. PrP^Sc was probed using horseradish peroxidase–conjugated HuM-P Fab. Molecular weight markers of migrated protein standards represent 30 and 20 kDa.

Figure 2.

Biochemical and neuropathologic characterization of transgenic (Tg) mice inoculated with elk chronic wasting disease (CWD) prions and treated with IND24. A, Kaplan–Meier survival curves of Tg mice expressing elk prion protein (Tg[ElkPrP]) that were inoculated with elk CWD prions and treated with 3 different dosing regimens of IND24: 210 mg/kg/day from day 1 (dashed green; n = 8), as previously reported [10]; 210 mg/kg/day for 138 days, followed by 50 mg/kg/day (solid green; n = 9); or 50 mg/kg/day (dotted green; n = 8). Survival for mice treated with (V; solid red; n = 9), as previously reported [10], is also shown. B, Proteinase K–resistant PrP from the brains of terminal animals that were infected with elk CWD prions and treated with IND24 (green) or vehicle (red), as indicated. PrP^Sc was probed using horseradish peroxidase–conjugated HuM-P Fab. Molecular weight markers of migrated protein standards represent 30 and 20 kDa. C–H, Neuropathologic analysis of brain sections from terminal animals that were infected with elk CWD prions and treated with IND24 (C–E) or V (F–H). Immunohistochemical staining for PrP^Sc was performed using HuM-P Fab. Regions are caudate nucleus/septum (CN/S; C and F), hippocampus/thalamus (Hp/Th; D and G), and pons/cerebellum (P/Cb; E and H). Black bars represent 50 µM and also apply to the respective micrograph below each image. I, Quantification of plaque intensity (arbitrary units [AU]) in brain slices of Tg(ElkPrP) mice inoculated with elk CWD prions and treated with IND24 (green) or vehicle (red).

Figure 3.

Infected RK13 cells expressing elk prion protein (RK21) and treated with IND24. Proteinase K–resistant PrP from RK13-ElkPrP cells infected with elk chronic wasting disease (CWD) prions (top) [20] and with CWD prions from the brains of transgenic mice expressing ElkPrP and treated with vehicle (V; middle) or IND24 (bottom). Doses of IND24 are indicated in µM. PrP^Sc was probed using horseradish peroxidase–conjugated HuM-P Fab. Molecular weight markers of migrated protein standards represent 30 and 20 kDa for each blot.

Figure 4.

Passage of CWD[IND24]. A, Kaplan–Meier survival curves of transgenic mice expressing elk prion protein that were inoculated with CWD[V] (pink; n = 8) or CWD[IND24] (light green; n = 8) and given no treatment, compared with findings from the previously reported CWD[V] experiment (red; n = 9; [10]) and CWD[IND24] (dark green; n = 9). The circles indicate the incubation periods of animals used to derive the inocula. B, Proteinase K–resistant prion protein from the brains of terminal animals infected with CWD[V] or CWD[IND24]. PrP^Sc was probed using horseradish peroxidase–conjugated HuM-P Fab. Molecular weight markers of migrated protein standards represent 30 and 20 kDa.