The role of heat shock proteins in Amyotrophic Lateral Sclerosis: The therapeutic potential of Arimoclomol

Arimoclomol is a hydroxylamine derivative, a group of compounds which have unique properties as co-inducers of heat shock protein expression, but only under conditions of cellular stress. Arimoclomol has been found to be neuroprotective in a number of neurodegenerative disease models, including Amyotrophic Lateral Sclerosis (ALS), and in mutant Superoxide Dismutase 1 (SOD1) mice that model ALS, Arimoclomol rescues motor neurons, improves neuromuscular function and extends lifespan. The therapeutic potential of Arimoclomol is currently under investigation in a Phase II clinical trial for ALS patients with SOD1 mutations. In this review we summarize the evidence for the neuroprotective effects of enhanced heat shock protein expression by Arimoclomol and other inducers of the Heat Shock Response. ALS is a complex, multifactorial disease affecting a number of cell types and intracellular pathways. Cells and pathways affected by ALS pathology and which may be targeted by a heat shock protein-based therapy are also discussed in this review. For example, protein aggregation is a characteristic pathological feature of neurodegenerative diseases including ALS. Enhanced heat shock protein expression not only affects protein aggregation directly, but can also lead to more effective clearance of protein aggregates via the unfolded protein response, the proteasome–ubiquitin system or by autophagy. However, compounds such as Arimoclomol have effects beyond targeting protein mis-handling and can also affect additional pathological mechanisms such as oxidative stress. Therefore, by targeting multiple pathological mechanisms, compounds such as Arimoclomol may be particularly effective in the development of a disease-modifying therapy for ALS and other neurodegenerative disorders.