Nose-to-brain delivery of a SOD1-stabilizing small molecule ameliorates pathology in an ALS mouse model

Exposure of a pathogenic β6/β7 loop neo-epitope has been proposed to contribute to the pathogenesis of misfolded Cu/Zn superoxide dismutase (SOD1) in amyotrophic lateral sclerosis (ALS) by mediating early events in its noxious structural transformation and prion-like activity. Antibody-mediated blockade of this epitope was shown to ameliorate disease phenotype in an ALS animal model. Here, as an alternative strategy, we sought to block this epitope using a small molecule designed to occupy the inter-subunit cavity framed by the two β6/β7 loops. Using a structure-based virtual screen targeting this cavity, we identified a small molecule, N-[3-(3-methylimidazo[2,1-b][1,3]thiazol-6-yl)phenyl]-4-sulfamoylbenzamide (C7), that preferentially bound the native-like conformation of SOD1, reduced β6/β7 loop epitope accessibility, and inhibited irreversible apo-SOD1 misfolding in vitro. Delivered to presymptomatic hSOD1^G93A mice via a nanoparticle-based nose-to-brain delivery system, C7 significantly delayed the onset of motor abnormalities and modestly extended survival. At disease onset, spinal cord analysis revealed reduced misfolded SOD1 inclusions and attenuated astro- and microgliosis. Analysis of C7 concentrations in combined brain and spinal cord tissue indicated rapid but saturable nose-to-CNS uptake and slow clearance. Our findings demonstrate that targeting the surface cavity shaped by the β6/β7 loops of SOD1 with a reversibly-binding small molecule can ameliorate ALS-like disease in vivo, potentially by counteracting early misfolding events and/or limiting prion-like propagation of molecular pathology. However, saturable nose-to-CNS uptake of C7 restricts CNS exposure and likely constrains therapeutic efficacy, underscoring the need to define the rate-limiting pharmacokinetic step and to optimize the nanoparticle formulation and/or physicochemical properties of the C7 scaffold.