Chondroitinase ABC enhances trastuzumab activity via cell-surface chondroitin sulfate cleavage in pancreatic cancer cells.

Pancreatic ductal adenocarcinoma (PDAC) has a glycan-rich microenvironment that hampers therapeutic antibody access to a cell-surface target antigen. The poor outcomes of a clinical trial involving enzymatic degradation of the hyaluronan suggest additional glycan-dependent resistance mechanisms. In this study, we investigated whether chondroitin sulfate (CS) proteoglycans (CSPGs) enriched in PDAC act as glycan decoy receptors that impair trastuzumab (Tmab) engagement with human epidermal growth factor receptor 2 (HER2). Using a monoclonal IgM antibody-based high-sensitivity immunoblot platform, we found that CS-A-bearing CSPGs were more abundant in PDAC-derived cell lines and tissues than in their normal counterparts. Chondroitinase ABC (ChABC) cleaved the CS-A chains attached to CSPG core proteins, a major component of which turned out to be CD44, a HER2-masking receptor implicated in reduced Tmab binding. CS-A directly bound to Tmab and dose-dependently inhibited the antibody binding to HER2. Furthermore, CS-A, a CS subtype enriched in PDAC cells, but not CS-C, stabilized the higher-temperature transition of Tmab, consistent with interactions at the Fab and/or Fc-CH3 domains. In HER2-expressing Capan-1 cells, ChABC and Tmab cooperated to inhibit migration under conditions in which each agent alone had little effect, and ChABC pretreatment increased intracellular Tmab uptake. These findings support a model in which CS-A-bearing CSPGs on the surface of PDAC cells sequester Tmab and limit its productive engagement with HER2. Thus, enzymatic CS cleavage emerges as a glycan-editing strategy to potentiate Tmab activity in CS-A-rich tumors.