CuATSM protects against the in vitro cytotoxicity of wild type-like SOD1 mutants but not mutants that disrupt metal binding.

Mutations in the SOD1 gene are associated with some forms of familial ALS (fALS). There are over 150 different mutations in the SOD1 gene which cause various effects to the SOD1 enzyme structure, including loss of metal binding and a decrease in dimer affinity. The copper-based therapeutic CuATSM has been proven to be effective at rescuing neuronal cells from SOD1 mutant toxicity, and has also increased the life expectancy of mice expressing the human transgenes SOD1G93A and SOD1G37R. Furthermore, CuATSM is currently the subject of a phase I/II clinical trial in Australia as a treatment for ALS. In order to determine if CuATSM protects against a broad variety of SOD1 mutations, we used a well-established cell culture model of SOD1-fALS. NSC-34 cells expressing SOD1-EGFP constructs were treated with CuATSM and examined by time lapse microscopy. Our results show a concentration dependent protection of cells expressing mutant SOD1A4V over the experimental time period. We tested the efficacy of CuATSM on ten SOD1-fALS mutants and found that while protection was observed in cells expressing pathogenic wild type-like mutants, cells expressing a truncation mutant or metal binding region mutants were not. We also show that CuATSM rescue is associated with an increase in human SOD1 activity and a decrease in SOD1 aggregation in vitro. In conclusion, CuATSM has shown to be a promising therapeutic for SOD1-associated ALS, however, our in vitro results suggest that the protection afforded varies depending on the SOD1 variant, including negligible protection to mutants with deficient copper binding.