Discovery and Preliminary SAR of Arylpiperazines as Novel, Brainpenetrant Antiprion Compounds

Prion diseases are a group of fatal neurodegenerative disorders that include Creutzfeldt-Jakob disease (CJD) and kuru in humans, BSE in cattle, and scrapie in sheep. Such illnesses are caused by the conversion and accumulation of a misfolded pathogenic isoform (termed PrP^Sc) of a normally benign, host cellular protein, denoted PrP^C. We employed high-throughput screening (HTS) ELISAs to evaluate compounds for their ability to reduce the level of PrP^Sc in Rocky Mountain Laboratory (RML) prion-infected mouse neuroblastoma cells (ScN2a-cl3). Arylpiperazines were among the active compounds identified but the initial hits suffered from low potency and poor drug-likeness. The best of those hits, such as 1, 7, 13, and 19, displayed moderate antiprion activity with EC₅₀ values in the micromolar range. Key analogs were designed and synthesized based on the SAR, with analogs 41, 44, 46, and 47 found to have sub-micromolar potency. Analogs 41 and 44 were able to penetrate the blood-brain barrier (BBB) and achieved excellent drug concentrations in the brains of mice after oral dosing. These compounds represent good starting points for further lead optimization in our pursuit of potential drug candidates for the treatment of prion diseases.