10H-phenothiazine exerts beneficial effects in spinal muscular atrophy in vitro and in vivo models.

Spinal Muscular Atrophy (SMA) is a neurodegenerative disorder affecting lower motor neurons (MNs) and leading to muscle atrophy, due to mutation of the SMN1 gene, which encodes SMN protein. Experimental studies also demonstrated the upper MN impairment. The available approved drugs for SMA increase the SMN protein production. Although effective, outcomes are dependent upon treatment timing and disease severity. Drug repositioning may represent a valid strategy to identify new treatments by repurposing FDA/EMA-approved drugs that, combined with the available ones, could delay neurodegeneration. To this aim, for the first time we used primary cortical neurons derived from the SMNΔ7 mice as defective in vitro disease model, to preliminary assess drug efficacy on neuronal survival and morphology. Under basal conditions, SMA cortical neurons showed significantly reduced vitality and altered morphology compared to WT neurons. All the parameters were rescued after treatment with known compounds (Valproic Acid, 4-aminopyridine and N-acetylcysteine), already tested in either preclinical or clinical context for SMA. We then investigated for the first time in SMA pathology the efficacy of 10H-phenothiazine (10H-PTZ), known to exert neuroprotection and to target altered mechanisms in Parkinson's and Alzheimer's disease. Its administration to SMA cortical neurons induced significant protective effects on both neuronal survival and morphology that were further confirmed in vivo, in a C. elegans SMA model. Overall, our results provide valuable insights, both in vitro and in vivo, into the potential of 10 H-PTZ repurposing for SMA, although additional functional studies will be required.