Structure-Guided Optimization of CHI3L1 Modulators Reveals G721-0377 as a Lead Compound for Restoring Astrocyte Function in Alzheimer's Disease.

Alzheimer's disease (AD) involves astrocytic dysfunction characterized by impaired lysosomal activity, defective amyloid clearance, and neuroinflammation, processes strongly regulated by the inflammatory effector CHI3L1. G721-0282, a reported CHI3L1-binding small molecule with demonstrated modulation of downstream signaling pathways including MAPK and STAT3, provides a validated chemical starting point for targeting CHI3L1-driven astrocytic pathology in AD, but it exhibits suboptimal potency and drug-like properties that limit its translational potential. We therefore performed a virtual screening of commercially available analogues of G721-0282 to enable structure-guided optimization, generating a detailed structure-activity map, and prioritizing 24 derivatives. Biophysical analyses identified compound G721-0377 as the most promising candidate, with optimized substitutions resulting in enhanced CHI3L1-binding affinity (K d = 45 μM), representing a ∼3-5-fold improvement over related analogs (K d = 65-236 μM). Compound G721-0377 also exhibited favorable physicochemical and pharmacokinetic properties, including improved solubility, balanced permeability, reduced microsomal clearance, and an enhanced cardiac safety margin. Given their micromolar potency, all functional studies were conducted in vitro. Functionally, G721-0377 uniquely reversed CHI3L1-induced astrocytic dysfunction, restoring amyloid uptake, lysosomal proteolysis and acidification, suppressing CHI3L1 and IL-6 secretion, and inhibiting NF-κB activation to levels comparable to a neutralizing anti-CHI3L1 antibody. Collectively, these findings establish G721-0377 as a promising early stage lead compound with improved affinity, safety, and robust functional efficacy, supporting its further development as a disease-modifying therapeutic for AD.