Site-targeted proximal complement C3 inhibition, but not C5 blockade, attenuates neurodegeneration in a mouse model of amyotrophic lateral sclerosis: Implications for failed clinical trials
Year: 2026
Type: article
Abstract: Complement activation contributes to amyotrophic lateral sclerosis (ALS) neuropathology, but whether motor neuron degeneration is driven by proximal or terminal activation products remains unresolved. Failed trials of C5 inhibition - ravulizumab (CHAMPION-ALS) and zilucoplan (ATHLEET/HEALEY ALS Trial), and of systemic C3 inhibition (pegcetacoplan, MERIDIAN) underscore this mechanistic gap. We compared two pharmacologically distinct inhibitors in hSOD1 G93A mice. CR2Crry blocks complement at C3 and localizes to sites of active deposition. BB5.1, functionally equivalent to ravulizumab, selectively blocks C5a generation and membrane attack complex (MAC) assembly. Treatment began at symptom onset and continued to humane endpoint. Both agents achieved robust target engagement across spinal cord, sciatic nerve, and neuromuscular junction (NMJ). Only CR2Crry extended survival, preserved motor function, and attenuated weight loss. CR2Crry reduced microglial activation and C3 opsonization in the ventral horn, diminished macrophage infiltration, preserved sciatic nerve axonal integrity, and maintained NMJ innervation. BB5.1 failed to modify any functional or neurodegenerative pathology despite confirmed MAC suppression. Proximal C3 activation products, not C5a or MAC, are the dominant drivers of complement-mediated neurodegeneration in the hSOD1 G93A model of ALS. Site-targeted C3 inhibition may address the mechanistic limitation underlying recent clinical trial failures and represents a translationally justified therapeutic strategy.
Source: Neurotherapeutics
Language: English
Subfield: Neurology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $3,900
OpenAlex ID: W7170192263