A copper chaperone-mimetic polytherapy for SOD1-associated amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease in which motor neurons progressively and rapidly degenerate, eventually leading to death. The first protein found to contain ALS-associated mutations was copper/zinc superoxide dismutase 1 (SOD1), which is conformationally stable when it contains its metal ligands and has formed its native intramolecular disulfide. Mutations in SOD1 reduce protein folding stability via disruption of metal binding and/or disulfide formation, resulting in misfolding, aggregation, and ultimately cellular toxicity. A great deal of effort has focused on preventing the misfolding and aggregation of SOD1 as a potential therapy for ALS; however, the results have been mixed. Here, we utilize a small-molecule polytherapy of diacetylbis(N(4)-methylthiosemicarbazonato)copper(II) (CuATSM) and ebselen to mimic the metal delivery and disulfide bond promoting activity of the cellular chaperone of SOD1, the “copper chaperone for SOD1.” Using microscopy with automated image analysis, we find that polytherapy using CuATSM and ebselen is highly effective and acts in synergy to reduce inclusion formation in a cell model of SOD1 aggregation for multiple ALS-associated mutants. Polytherapy reduces mutant SOD1-associated cell death, as measured by live-cell microscopy. Measuring dismutase activity via zymography and immunoblotting for disulfide formation showed that polytherapy promoted more effective maturation of transfected SOD1 variants beyond either compound alone. Our data suggest that a polytherapy of CuATSM and ebselen may merit more study as an effective method of treating SOD1-associated ALS.

X-ray crystallography and computational docking for the detection and development of protein-ligand interactions

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterised by the selective dysfunction and death of the upper and lower motor neurons. Median survival rates are between 3 and 5 years after diagnosis. Mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) have been linked to a subset of familial forms of ALS (fALS). Herein, we describe a fragment- based drug discovery (FBDD) approach for the investigation of small molecule binding sites in SOD1. X-ray crystallography has been used as the primary screening method and has been shown to directly detect protein-ligand interactions which cannot be unambiguously identified using other biophysical methods. The structural requirements for effective binding at Trp32 are detailed for a series of quinazoline-containing compounds. The investigation of an additional site that binds a range of catecholamines and the use of computational modelling to assist fragment evolution is discussed. This study also highlights the importance of ligand solubility for successful Xray crystallographic campaigns in lead compound design.