The protease cathepsin K can debulk the cancer glycocalyx

The cancer glycocalyx is characterized by the overexpression of large glycoconjugates, including mucins, proteoglycans, and polysialic acid, which collectively increase glycocalyx thickness and stiffness to promote tumor survival, metastasis, and progression. Previous work demonstrated that enzymatic degradation of cancer cell-surface mucins reduced tumor burden and metastasis in mouse models of breast cancer, thus validating glycocalyx remodeling as a therapeutic strategy. However, this work relied on an engineered bacterial mucin-selective protease, or mucinase, which does not degrade other bulky glycoconjugates and raises immunogenicity concerns because of its bacterial origin. A human enzyme that can degrade cell-surface mucins and other bulky glycoconjugates would address both limitations. We screened all 15 human cathepsins for their ability to degrade purified and cell-surface mucins, since multiple cathepsins have previously been shown to degrade mucins within regions of dense glycosylation. We found that cathepsin K (CTSK) uniquely degrades cell-surface mucins, proteoglycans, and polysialylated glycoproteins, and we demonstrated that CTSK reduces total glycocalyx thickness. These findings establish CTSK as a promising starting point for the development of a glycocalyx-debulking enzyme for cancer therapeutics.