Decreasing the intrinsically disordered protein -synuclein levels by targeting its structured mRNA with a ribonuclease- targeting chimera

alpha-Synuclein is an important drug target for the treatment of Parkinson's disease (PD), but it is an intrinsically disordered protein lacking typical small-molecule binding pockets. In contrast, the encoding SNCA mRNA has regions of ordered structure in its 5 ' untranslated region (UTR). Here, we present an integrated approach to identify small molecules that bind this structured region and inhibit alpha-synuclein translation. A drug-like, RNA-focused compound collection was studied for binding to the 5 ' UTR of SNCA mRNA, affording Synucleozid-2.0, a drug-like small molecule that decreases alpha-synuclein levels by inhibiting ribosomes from assembling onto SNCA mRNA. This RNA-binding small molecule was converted into a ribonuclease-targeting chimera (RiboTAC) to degrade cellular SNCA mRNA. RNA-seq and proteomics studies demonstrated that the RiboTAC (Syn-RiboTAC) selectively degraded SNCA mRNA to reduce its protein levels, affording a fivefold enhancement of cytoprotective effects as compared to Synucleozid-2.0. As observed in many diseases, transcriptome-wide changes in RNA expression are observed in PD. Syn-RiboTAC also rescued the expression of similar to 50% of genes that were abnormally expressed in dopaminergic neurons differentiated from PD patient-derived iPSCs. These studies demonstrate that the druggability of the proteome can be expanded greatly by targeting the encoding mRNAs with both small molecule binders and RiboTAC degraders.