Developing Photoaffinity Probes for Dopamine Receptor D2 to Determine Targets of Parkinson’s Disease Drugs

Dopaminergic pathways control highly consequential aspects of physiology and behavior. One of the most therapeutically important and best-studied receptors in these pathways is dopamine receptor D2 (DRD2). Unfortunately, DRD2 is challenging to study with traditional molecular biological techniques, and most drugs designed to target DRD2 are ligands for many other receptors. Here, we developed probes able to both covalently bind to DRD2 using photoaffinity labeling as well as provide a chemical handle for detection or affinity purification. These probes behaved like good DRD2 agonists in traditional biochemical assays and were able to perform in chemical biological assays of cell and receptor labeling. Rat whole brain labeling and affinity enrichment using the probe permitted proteomic analysis of the probes’ interacting proteins. Bioinformatic study of the hits revealed that the probes bound non-canonically targeted proteins in the Parkinson’s disease network as well as the retrograde endocannabinoid signaling, neuronal nitric oxide synthase, muscarinic acetylcholine receptor M1, GABA receptor, and dopamine receptor D1 (DRD1) signaling networks. Follow-up analysis may yield insights into how this pathway relates specifically to Parkinson’s disease symptoms or provide new targets for treatments. This work reinforces the notion that the combination of chemical biology and omics-based approaches provide a broad picture of a molecule’s “interactome,” and may also give insight into the pleiotropy of effects observed for a drug, or perhaps indicate new applications.