Consortium to Develop an Alpha-Synuclein Imaging Agent
9th International Symposium on Functional Neuroreceptor Mapping of the Living Brain - Baltimore
The Michael J. Fox Foundation (MJFF) is supporting a consortium with the goal of developing a PET radiotracer to image the distribution of alpha-synuclein in the brain. The accumulation of aggregated alpha-synuclein in the brain is the pathological hallmark of Parkinsonís disease and is a frequent target for drugs being developed to treat PD. The ability to visualize alpha-synuclein in the brain could be useful both as a biomarker of the presence of disease and disease progression and as a tool for drug development.†
Four groups have been selected by MJFF to participate in the consortium including three academic groups and a contract research organization (BioFocus). These groups are working to identify and test compounds that can ultimately be radiolabeled and used as PET imaging agents.
Two approaches were pursued to identify compounds that bind to aggregated alpha-synuclein. The first approach utilized a competition binding assay using either the fluorescent ligand Thioflavin T or the radioligand [3H]-Chrysamine G. Following assay optimization, approximately 100,000 compounds selected from the BioFocus libraries were screened in both assay formats at a single concentration of 10 micromolar. From the Thioflavin T screen, approximately 2,000 compounds showing >45% inhibition of binding were selected for hit confirmation at 10 micromolar in duplicate, and 263 of these compounds proceeded to IC50 potency determination. Selectivity of these compounds was determined against aggregated beta-amyloid and tau using Thioflavin T and Thioflavin S assays respectively. The second approach utilized a Surface Plasmon Resonance (SPR) based Biacore assay developed to investigate the direct binding of compounds to monomeric alpha-synuclein, aggregated alpha-synuclein and aggregated beta-amyloid, immobilized to Biacore CM5 chips via amine coupling reactions. Following the screening of approximately 3,500 compounds against these three protein targets, 120 compounds were selected for KD determination.
Further characterization of interesting compounds identified from these approaches is ongoing, including binding studies in PD brains with Lewy body pathology.
Authors:†Jamie L. Eberling, Andrew D. Medhurst, Kevin Nash, Andrew Gill, Scott Pollack, David Cronk, Brian Bacskai, Chet Mathis, Robert Mach