update 2013-01-31: this post has been deprecated; please see Fluphenazine, trimipramine and two styryl compounds for a more complete treatment of this subject.

@s just noticed today this study from late 2011.  Thomas Wisniewski’s lab at NYU tested two already FDA-approved drugs, trimiprimine (an antidepressant) and fluphenazine (an antipsychotic) in mice and found significant delays (about 20%) in disease onset as well as reduction in severity.     Since they’re both psychiatric-indicated drugs, they obviously both know how to cross the blood-brain barrier.  The mouse model was scrapie mice infected via intraperitoneal injection.

The study in PLoS ONE:

Chung E, Prelli F, Dealler S, Lee WS, Chang Y-T, et al. (2011) Styryl-Based and Tricyclic Compounds as Potential Anti-Prion Agents. PLoS ONE 6(9): e24844. doi:10.1371/journal.pone.0024844

And see also the NYU press release.