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

The conversion of cellular prion protein (PrPC) to the protease resistant isoform (PrPSc) is considered essential for the progression of transmissible spongiform encephalopathies (TSEs). A potential therapeutic strategy for preventing the accumulation of PrPSc is to stabilize PrPC 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 PrPC immobilized on a sensor chip. In this paper we report some problems associated with the immobilization of PrPC onto the sensor surface for conducting drug screening and how these problems were overcome. We demonstrated that the conformational change of PrPC 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 PrPC (huPrPC, t-huPrPC and moPrPC). These results show the usefulness of this technique for the identification of PrPC binding ligands and to gain some insight as to their potential mode of action.