Synthesis, Structure, and Function of Heparan Sulfate Glycopolymers to Investigate Glycosaminoglycan–Protein Interactions

ConspectusHeparan sulfate (HS), a highly sulfated glycosaminoglycan, varies in its disaccharide units, chain length, and sulfation patterns. HS structural diversity and its localization at cell surfaces and in the extracellular matrix enable HS interaction with a breadth of HS-binding proteins (HSBPs), HS thus being a co-receptor for other proteins and initiating various biological responses. Several designed and studied HS mimetics modulate HSBP activity implicated in various diseases. A key HSBP is heparanase (HPSE), which can cleave HS into smaller fragments, facilitating release of angiogenic growth factors, activating biological signals that may contribute to pathological conditions (promoting tumor development and metastasis), and enabling autoreactive immune cells to target insulin-producing β-cells. Thus, HPSE serves as a crucial target for disease therapy strategies. Several saccharide-based HS mimetics, designed as HSPE inhibitors, have advanced to clinical trials, but these sugar molecules were discontinued or suspended due to adverse effects from off-target HSBP interactions. Glycopolymers engineered to incorporate functionalized glycan residues into their polymeric backbones are a promising approach to retain endogenous HS' native biological activity, thereby enhancing therapeutic efficacy. Stereoselective formation of α-1,2-cis-glycosidic linkages that connect the glucosamine unit to the uronic acid disaccharide core is challenging during development of HS mimetics as HPSE inhibitors. Computational modeling and a stereoselective catalytic glycosylation method were used to design and synthesize glycopolymer-based HS mimetics with repeating units of the glucosamine-glucuronic acid disaccharide core and a controlled degree of polymerization and incorporate glycan residues with precisely tailored sulfation patterns. This strategy ensures targeted biological activity and maintains structural specificity toward its intended HSBP. Glycopolymers were synthesized using ring-opening metathesis polymerization with the third-generation Grubbs catalyst, enabling precise control over both the degree of polymerization and molecular weight by tuning the catalyst loading. The most potent glycopolymer displayed superior potency and selectivity compared to previously reported monovalent and polymeric HPSE inhibitors and demonstrated remarkable antimetastatic activity in models of mammary carcinoma and myeloma cancer. It also protected pancreatic β-cells and human islets from HPSE-induced damage, suggesting a possible diabetes therapeutic agent. Prioritizing multivalency and precise structural control in polymeric HS mimetics facilitates targeted interactions with specific HSBPs and enhances their potential for precision therapeutic applications.