Different 2-Aminothiazole Therapeutics Produce Distinct Patterns of Scrapie Prion Neuropathology in Mouse Brains

Abstract

Because no drug exists that halts or even slows any neurodegenerative disease, developing effective therapeutics for any prion disorder is urgent. We recently reported two compounds (IND24 and IND81) with the 2-aminothiazole (2-AMT) chemical scaffold that almost doubled the incubation times in scrapie prion-infected, wild-type (wt) FVB mice when given in a liquid diet. Remarkably, oral prophylactic treatment with IND24 beginning 14 days prior to intracerebral prion inoculation extended survival from ∼120 days to over 450 days. In addition to IND24, we evaluated the pharmacokinetics and efficacy of five additional 2-AMTs; one was not followed further because its brain penetration was poor. Of the remaining four new 2-AMTs, IND114338 doubled and IND125 tripled the incubation times of RML-inoculated wt and Tg4053 mice overexpressing wt mouse prion protein (PrP), respectively. Neuropathological examination of the brains from untreated controls showed a widespread deposition of self-propagating, b-sheet-rich "scrapie" isoform (PrP Sc ) prions accompanied by a profound astrocytic gliosis. In contrast, mice treated with 2-AMTs had lower levels of PrP Sc and associated astrocytic gliosis, with each compound resulting in a distinct pattern of deposition. Notably, IND125 prevented both PrP Sc accumulation and astrocytic gliosis in the cerebrum. Progressive central nervous system dysfunction in the IND125-treated mice was presumably due to the PrP Sc that accumulated in their brainstems. Disappointingly, none of the four new 2-AMTs prolonged the lives of mice expressing a chimeric human/ mouse PrP transgene inoculated with Creutzfeldt-Jakob disease prions.

Optimization of Aryl Amides that Extend Survival in Prion-Infected Mice

“…Studies with IND24 showed unexpected effects on efficacy when dosing was started later and when the mouse models and prion strains were varied (Berry et al, 2013;Berry et al, 2015;Giles et al, 2015). In addition, prophylactic dosing with IND24 was more effective at extending survival than continuous dosing starting after inoculation .…”

“…Such compounds were extended to long-term efficacy studies. We have now reported efficacy for 10 compounds in RML-infected mice: six 2-AMTs (Berry et al, 2013;Giles et al, 2015) and the four aryl amides described here. Remarkably, all 10 extend the survival of prion-infected mice, many by 2-fold or more.…”

“…In addition to mouse-passaged prion strains, IND24 was effective against CWD prions from deer and elk but was ineffective against two isolates of sheep scrapie (Berry et al, 2013;Berry et al, 2015); however, IND24 and all other compounds tested to date failed to extend the survival of Tg mice expressing either human PrP or a chimeric human/ mouse PrP that were each infected with human CJD prions (Berry et al, 2013;Lu et al, 2013;Giles et al, 2015).…”

“…Aryl Amides Are Not Efficacious against CJD Prions. None of the compounds reported to date that extend survival of mice infected with mouse-passaged prion strains shows efficacy against mice inoculated with CJD prions (Berry et al, 2013;Lu et al, 2013;Giles et al, 2015). We therefore inoculated Tg1014 mice expressing a chimeric human/mouse PrP (Giles et al, 2010) with sCJD(MM1) prions and treated them with each of the aryl amides at the same dose shown to be effective against RML prions.…”

“…Using prion-infected cells for screening assays, multiple compounds have been identified that double the survival of mice inoculated with mouse-passaged prions, including Compound B (Kawasaki et al, 2007), Anle138b (Wagner et al, 2013), and a series with the 2-aminothiazole (2-AMT) chemical scaffold (Berry et al, 2013;Giles et al, 2015). When prions from the brains of mice treated with 2-AMT IND24 (Berry et al, 2013) were used to infect CAD5 cells, the resulting strain was resistant to IND24, raising the specter that small molecule intervention could lead to drug resistance, a concept that had been suggested by other studies (Ghaemmaghami et al, 2009;Oelschlegel and Weissmann, 2013).…”