Protein Assembly Modulation: A New Approach to ALS Therapeutics

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease with a complex, multifactorial pathophysiology, most commonly manifest as loss of motor neurons. We introduce a new mechanism of ALS pathogenesis via a novel drug-like small molecule series that targets protein disulfide isomerase (PDI) within a previously unappreciated transient and energy-dependent multi-protein complex. This novel drug was found to have activity in cellular models for both familial and sporadic ALS, as well as in transgenic worms, flies, and mice bearing a diversity of human genes with ALS-associated mutations. These compounds were initially identified as modulators of human immunodeficiency virus (HIV) capsid assembly in cell-free protein synthesis and assembly (CFPSA) systems, with demonstrated antiviral activity in cell culture. Their advancement as ALS-therapeutics, and the subsequent separation of activity against HIV and ALS in chemical subseries through structure-activity-relationship optimization, may provide insights into the molecular mechanisms governing pathophysiology of disordered homeostasis relevant to ALS.

An ALS Therapeutic Assembly Modulator Target in Peripheral Blood Mononuclear Cells: Implications for ALS Pathophysiology, Therapeutics, and Diagnostics

“…However when PBMC extracts were applied to the ALS-active drug resin described previously 10 versus control resin (lacking the drug ligand), washed and bound material analyzed, a distinctive subset of proteins was observed, also largely shared between healthy individuals and ALS patients, but with a few possible differences (black arrows in Figure 1B ).…”

“…This target multi-protein complex is relevant to ALS for three reasons. First, the drug that served as the ligand to bind and isolate the target is therapeutic in a wide range of ALS cellular and animal models 10 . Second, the composition of the target multi-protein complex includes a number of proteins of the ALS interactome.…”

“…Regardless of their natural history and role in the pathophysiology of ALS, the presence of TDP-43 aggregates are pathognomonic for the disease 8,9 . Recently we presented our studies on the role of a newly appreciated dimension of gene expression, termed protein assembly, in pathophysiology of diverse diseases, including ALS 10 .…”

“…We have identified several structurally unrelated small molecule chemotypes termed assembly modulators, that are strikingly efficacious, including at both preventing neurodegeneration and correcting TDP-43 pathology, in various cellular and animal models of ALS 10 . The compounds are broadly efficacious at reversing both TDP-43 mislocalization and stress-induced TDP-43 aggregation, in both familial and sporadic ALS cellular models 10 . Efficacy was also demonstrated in various transgenic animals expressing human ALS-causing mutations including in TDP-43, FUS, c9orf72, and SOD1 10 .…”

“…The compounds are broadly efficacious at reversing both TDP-43 mislocalization and stress-induced TDP-43 aggregation, in both familial and sporadic ALS cellular models 10 . Efficacy was also demonstrated in various transgenic animals expressing human ALS-causing mutations including in TDP-43, FUS, c9orf72, and SOD1 10 . In view of this breadth of efficacy, we hypothesized the mechanism of action of the assembly modulator drug to target a step common to most, if not all, ALS.…”