Discovery of a CHI3L1-targeted small molecule modulating neuroinflammation in Alzheimer's disease via DNA-encoded library (DEL) screening.

Chitinase-3-like protein 1 (CHI3L1, also known as YKL-40) has emerged as a central effector of astrocyte-mediated neuroinflammation and a promising biomarker for Alzheimer's disease (AD). However, small molecule CHI3L1 inhibitors that modulate neuroinflammation are limited. Here, we report the discovery of a CHI3L1-targeted small molecule, DEL-C1, identified through DNA-encoded library (DEL) screening and validated using orthogonal biophysical, computational, and cellular approaches. DEL-C1 demonstrated direct CHI3L1 binding in microscale thermophoresis (MST) and surface plasmon resonance (SPR) assays, with reversible and concentration-dependent association. Molecular docking and 100 ns molecular dynamics simulations revealed a stable binding mode within the CHI3L1 substrate groove, anchored by Tyr206 and flanked by Trp99 and Trp352, supporting a thermodynamically favorable interaction. In vitro ADME profiling indicated a balanced physicochemical profile, permeability, and metabolic stability, consistent with CNS drug-like properties. Functionally, DEL-C1 reversed CHI3L1-induced astrocyte dysfunction by restoring Aβ uptake, lysosomal acidification, and proteolytic activity, while reducing CHI3L1 and IL-6 secretion. DEL-C1 also suppressed CHI3L1-driven NF-κB transcriptional activation, highlighting its anti-inflammatory potential. Collectively, this study establishes DEL-C1 as a promising small molecule modulator of CHI3L1 and a chemical tool to interrogate astrocyte-driven neuroinflammation in AD.