Screening a library of potential prion therapeutics against cellular prion proteins and insights into their mode of biological activities by surface plasmon resonance

Abstract The conversion of cellular prion protein (PrP C ) to the protease resistant isoform (PrP Sc ) is considered essential for the progression of transmissible spongiform encephalopathies (TSEs). A potential therapeutic strategy for preventing the accumulation of PrP Sc is to stabilize PrP C through the direct binding of a small molecule to make conversion less energetically favourable. Using surface plasmon resonance (SPR)-based technology we have developed a procedure, based on direct binding, for the screening of small molecules against PrP C immobilized on a sensor chip. In this paper we report some problems associated with the immobilization of PrP C onto the sensor surface for conducting drug screening and how these problems were overcome. We demonstrated that the conformational change of PrP C on the chip surface leads to increased exposure of the C-terminal which was observed by the increase in quinacrine binding over time, and loss of heparin binding to the N-terminal. In addition, we also report the results of the successful screening of a library of 47 compounds of known activity in cell line or cell free conversion studies for direct binding to three forms of PrP C (huPrP C , t-huPrP C and moPrP C ). These results show the usefulness of this technique for the identification of PrP C binding ligands and to gain some insight as to their potential mode of action.