Identification of a nanomolar affinity α-synuclein fibril imaging probe by ultra-high throughput in silico screening

Small molecules that bind with high affinity and specificity to fibrils of the alpha-synuclein (alpha S) protein have the potential to serve as positron emission tomography (PET) imaging probes to aid in the diagnosis of Parkinson's disease and related synucleinopathies. To identify such molecules, we employed an ultra-high throughput in silico screening strategy using idealized pseudo-ligands termed exemplars to identify compounds for experimental binding studies. For the top hit from this screen, we used photo-crosslinking to confirm its binding site and studied the structure-activity relationship of its analogs to develop multiple molecules with nanomolar affinity for alpha S fibrils and moderate specificity for alpha S over A beta fibrils. Lastly, we demonstrated the potential of the lead analog as an imaging probe by measuring binding to alpha S-enriched homogenates from mouse brain tissue using a radiolabeled analog of the identified molecule. This study demonstrates the validity of our powerful new approach to the discovery of PET probes for challenging molecular targets.