Discovery and Preliminary Structure–Activity Relationship of Arylpiperazines as Novel, Brain-Penetrant Antiprion Compounds

Creutzfeldt-Jakob disease and kuru in humans, BSE in cattle, and scrapie in sheep are fatal neurodegenerative disorders. 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 enzyme-linked immunosorbent assays to evaluate compounds for their ability to reduce the level of PrP^Sc in Rocky Mountain Laboratory 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 <b>1</b>, <b>7</b>, <b>13</b>, and <b>19</b>, displayed moderate antiprion activity with EC₅₀ values in the micromolar range. Key analogues were designed and synthesized on the basis of the structure–activity relationship, with analogues <b>41</b>, <b>44</b>, <b>46</b>, and <b>47</b> found to have submicromolar potency. Analogues <b>41</b> and <b>44</b> were able to penetrate the blood–brain barrier 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

Towards Optimization of Arylamides As Novel, Potent, and Brain-Penetrant Antiprion Lead Compounds

The prion diseases caused by PrP^Sc, an alternatively folded form of the cellular prion protein (PrP^C), are rapidly progressive, fatal, and untreatable neurodegenerative disorders. We employed HTS ELISA assays to identify compounds that lower the level of PrP^Sc in prion-infected mouse neuroblastoma (ScN2a-cl3) cells and identified a series of arylamides. Structure–activity relationship (SAR) studies indicated that small amides with one aromatic or heteroaromatic ring on each side of the amide bond are of modest potency. Of note, benzamide (<b>7</b>), with an EC₅₀ of 2200 nM, was one of only a few arylamide hits with a piperazine group on its aniline moiety. The basic piperazine nitrogen can be protonated at physiologic pH, improving solubility, and therefore, we wanted to exploit this feature in our search for a drug candidate. An SAR campaign resulted in several key analogues, including a set with biaryl groups introduced on the carbonyl side for improved potency. Several of these biaryl analogues have submicromolar potency, with the most potent analogue <b>17</b> having an EC₅₀ = 22 nM. More importantly, <b>17</b> and several biarylamides (<b>20</b>, <b>24</b>, <b>26</b>, and <b>27</b>) were able to traverse the blood–brain barrier (BBB) and displayed excellent drug levels in the brains of mice following oral dosing. These biarylamides may represent good starting points for further lead optimization for the identification of potential drug candidates for the treatment of prion diseases