TDP-43 Gymnastics: It Takes a Machine to Move Complex Disease-Associated Proteins to Their Proper Subcellular Location and Assembly State
Prosetta has applied its platform to the devastating neurodegenerative disease amyotrophic lateral schlerosis (ALS) with very promising results. The neurodegeneration involved in ALS manifests as the nuclear protein TDP-43 entering the cytoplasm and aggregating within stress granules. Thus, ALS therapeutics need to both prevent the aggregation of mislocalized TDP-43 in the cytoplasm in response to stress, as well as relocalize TPD-43 to the nucleus where it belongs.
Prosetta has established cellular models that recreate both the mis-localization of TDP-43 from nucleus to cytoplasm and stress-induced aggregation of the cytoplasmically mislocalized TDP-43. We have used these models to screen our Hitfinder Collection and and have identified a number of Hitfinder compounds that prevent aggregate formation in stress granules and yet others that confer dramatic relocalization of TDP-43 to the nucleus. These results with cellular models are complemented by the ability of both classes of compounds to relieve the motor paralysis displayed by a TDP43-based transgenic C. elegans animal model.
The drug target appears not to be a single protein, but rather, a multi-protein complex – what Prosetta terms an “assembly machine”. Remarkably, the proteins that make up these multi-protein complexes are almost all proteins that have been implicated in ALS. What Prosetta has discovered is that these gene products are physically together in assembly machines that are excellent drug targets.
In addition to the promise of compounds with these activities, this work illustrates the power of Prosetta’s Hitfinder Collection. Prosetta had to screen less than three hundred (300) compounds – rather than hundreds of thousands - to identify these hits.
In addition to its success in identifying compounds that modify the causative molecular events of ALS, Prosetta is uniquely positioned to fulfill several additional requirements that will have to be met in order to advance an ALS compound to the clinic. The first is a method for guiding SAR that is target engagement-based rather than phenotypic. Prosetta’s successfully demonstrated SAR using its proprietary Drug Resin Affinity Chromatography tools is well suited to provide this. Second, a peripheral biomarker is needed with which to stratify ALS patients based on the specific molecular lesion that is causing their disease. A body of evidence suggests this can be achieved from peripheral blood mononuclear cells (PBMCs, or white blood cells), which have been shown to have distinctive signatures of ALS-associated aberrant assembly machines. Prosetta has demonstrated that PBMCs from healthy individuals contain the normal forms of assembly machines that are modified by ALS in brain cells. We expect to soon answer the question of whether PBMCs from ALS patients show the distinctive signatures of ALS-associated aberrant assembly machines. If so, this would set the stage for rapid and effective patient stratification and monitoring during a clinical trial.
With reasonable support to build on these promising advances we believe our novel ALS program could generate a clinical candidate in 12-24 months.