Repurposing immunomodulatory drugs targeting microglia for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that progressively affects upper and lower motor neurons, leading to symptoms including dysarthria, muscle weakness, and paralysis. The disease is multifactorial, with a variety of contributing pathways, including excitotoxicity, oxidative stress, and neuroinflammation. Current treatments target only two of these pathways with limited efficacy, highlighting the need for alternative approaches. Increasing evidence highlights the involvement of immune dysregulation, particularly microglial-mediated neuroinflammation, in ALS pathology. Fortunately, many immunomodulatory drugs acting on microglia are already available for other diseases, indicating promising opportunities for drug repurposing. This literature review provides an overview of existing drugs under investigation for ALS, including those that have failed, and highlights microglia-targeting compounds with emerging repurposing potential. Compounds such as ibudilast, fingolimod, and modafinil have shown encouraging initial clinical results, whereas others were well-tolerated but underpowered or failed to demonstrate efficacy. New candidates, such as azithromycin, montelukast, doxycycline, tofacitinib, quercetin, belinostat, propranolol, and several kinase inhibitors, have demonstrated positive preclinical results, supporting their advancement toward clinical evaluation. Overall, these findings emphasize the potential of microglia-targeting therapies for ALS. To realize this potential, future studies must include larger cohorts, assess effects across different disease stages and patient subgroups, and examine sex differences. This is essential to address patient heterogeneity and improve personalized treatments for ALS patients.