Stabilizing the CHI3L1-Gal3BP complex remodels the glioblastoma immune microenvironment and synergizes with PD-1 blockade

CHI3L1 (YKL-40) is associated with mesenchymal, treatment-resistant glioblastoma (GBM) and shapes macrophage programs through interactions with galectin-3 or galectin-3-binding protein (Gal3BP). However, the CHI3L1-Gal3BP interaction has not been previously targeted. A surface plasmon resonance screen identified LZ6. Ternary complex formation was assessed by fluorescence-based, biophysical, and mass spectrometry methods. Activity was evaluated in five patient-derived GBM lines, myeloid cultures from eight donors, CRISPR interference with guide-resistant rescue, and a four-arm factorial study of orthotopic GL261 tumors. LZ6 increased Gal3BP engagement 3.4-fold while reducing galectin-3 in vitro. In GBM-conditioned cultures, LZ6 raised phagocytosis 22% to 44% and MHC class II 24% to 39% and lowered CD206 45% to 31% and IL-10 105 to 67 pg/mL, with concordant transcripts. Gal3BP knockdown reduced the response 41%; guide-resistant rescue restored it. Oral LZ6 raised the intratumoral Gal3BP:galectin-3 ratio from 1.02 to 1.56 at unchanged CHI3L1. In tumor tissue LZ6 shifted 20 of 24 immune endpoints, lowering CD206 and IL-10 and raising MHC class II and CD8 effector function. Median survival with LZ6 was 52.4 versus 26.3 days (P = 0.0012), and in combination with anti-PD-1 most animals survived to the end of follow-up (median not reached), with a significant factorial interaction (hazard ratio 0.24, 95% CI 0.10-0.57, P = 0.0014). LZ6 is a molecular glue of the CHI3L1-Gal3BP complex that engages its target in brain tumor after oral dosing and extends survival alone and synergistically with PD-1 blockade.