Extracellular Cathepsin B Is a Potential Therapeutic Target in Hepatocellular Carcinoma

ABSTRACT Hepatocellular carcinoma (HCC) is a major cause of cancer‐related deaths worldwide. Therapeutic options are limited, and therefore new therapeutic targets are needed. Cathepsins, lysosomal proteases, are implicated in various types of cancer. While intracellular cathepsins have various physiological functions, their extracellular secretion can lead to pathological effects. Cathepsin B (CTSB) stays active at neutral pH and contributes to several liver pathologies, including HCC. However, the mechanisms by which extracellular CTSB contributes to HCC remain unclear. Hence, this study aimed to investigate the role of extracellular CTSB in HCC. Cell and spheroid viability of HepG2 and Huh‐7 cells was assessed after treatment with extracellular and intracellular CTSB inhibitors. A chorioallantoic membrane HCC xenograft model was used to study the effect of combined extracellular CTSB inhibitor and chemotherapy treatment on tumour growth, apoptosis, proliferation and angiogenesis. The UK Biobank proteomics data was used to determine the potential role of CTSB in HCC patients. Inhibition of extracellular CTSB significantly decreased the viability of HepG2 and Huh‐7 cells in both monolayers and spheroids compared to intracellular CTSB inhibition. The chorioallantoic membrane model demonstrated that extracellular CTSB inhibition decreased the ratio of proliferation‐apoptosis and, in the presence of paclitaxel, tumour angiogenesis, which resulted in a smaller tumour mass. Furthermore, compared to healthy controls, HCC patients demonstrated higher plasma levels of CTSB which were associated with a higher mortality risk. In conclusion, targeting extracellular CTSB could be a promising therapeutic strategy for HCC, since it decreases angiogenesis and proliferation, while it increases apoptosis.