Drug library screen identifies inhibitors of toxic astrogliosis

Objective: Multiple sclerosis is a chronic neuroinflammatory disorder, in which activated immune cells directly or indirectly induce demyelination and axonal degradation. Inflammatory stimuli also change the phenotype of astrocytes, making them neurotoxic. The resulting toxic astrocyte phenotype has been observed in animal models of neuroinflammation and in multiple sclerosis lesions. Proteins secreted by toxic astrocytes are elevated in the cerebrospinal fluid of multiple sclerosis patients and reproducibly correlate with the rates of accumulation of neurological disability and brain atrophy. This suggests a pathogenic role for neurotoxic astrocytes in multiple sclerosis. Methods: Here, we applied a commercially available library of small molecules that are either Food and Drug Administration-approved or in clinical development to an in vitro model of toxic astrogliosis to identify drugs and signaling pathways that inhibit inflammatory transformation of astrocytes to a neurotoxic phenotype. Results: Inhibitors of three pathways related to the endoplasmic reticulum stress: 1) proteasome, 2) heat shock protein 90 and 3) mammalian target of rapamycin reproducibly decreased inflammation-induced conversion of astrocytes to toxic phenotype. Dantrolene, an anti-spasticity drug that inhibits calcium release through ryanodine receptors expressed in the endoplasmic reticulum of central nervous system cells, also exerted inhibitory effect at in vivo achievable concentrations. Finally, we established cerebrospinal fluid SERPINA3 as a relevant pharmacodynamic marker for inhibiting toxic astrocytes in clinical trials. Interpretation: Drug library screening provides mechanistic insight into the generation of toxic astrocytes and identifies candidates for immediate proof-of-principle clinical trial(s).