Mimicking dominant negative inhibition of prion replication through structure-based drug design

Recent progress determining the structure of the host-encoded prion protein (PrPC) and the role of auxiliary molecules in prion replication permits a more rational approach in the development of therapeutic interventions. Our objective is to identify a new class of lead compounds that mimic the domi nant negative PrPC mutants, which inhibit an abnormal isoform (PrPSc) forma tion. A computational search was conducted on the Available Chemicals Direc tory for molecules that mimic both the spatial orientation and basic polymo rphism of PrP residues 168, 172, 215, and 219, which confer dominant negati ve inhibition. The search revealed 1,000 potential candidates that were vis ually analyzed with respect to the structure of this four-residue epitope o n PrPC. Sixty-three compounds were tested for inhibition of PrPSc formation in scrapie-infected mouse neuroblastoma cells (ScN2a), Two compounds, Cp-6 0 (2-amino-6-[(2-aminophenyl)thio]-4-(2-furyl)pyridine-3,5-dicarbonitrile) and Cp-62 (N'1-({5-[(4,5-dichloro-1H-imidazol-1-yl)methyl]-2-furyl}carbonyl )-4 methoxybenzene-1-sulfonohydrazide), inhibited PrPSc formation in a dose -dependent manner and demonstrated low levels of toxicity. A substructure s earch of the Available Chemicals Directory based on Cp-60 identified five r elated molecules, three of which exhibited activities comparable to Cp-60, Mimicking dominant negative inhibition in the design of drugs that inhibit prion replication may provide a more general approach to developing therape utics for deleterious protein-protein interactions.