Background and Introduction: Increased expression and altered localisation of cathepsins in tumor microenvironment are often implicated in cancer invasion and metastasis. However the role of lysosomal cysteine protease cathepsin B (CTSB) in gallbladder cancer (GBC) remains unknown.
Methods: Gallbladder (GB) tissues obtained from GBC patients who underwent curative surgical resection (n=45) and control GB (n=70) were used to measure enzyme activity of CTSB by spectroflurometry. Protein and mRNA levels were analysed by western blotting, immunohistochemistry and qRT-PCR respectively. Expression of this cysteine protease was then correlated with clinicopathological parameters and disease free survival. Serum levels of CTSB in GBC (n=65), chronic cholecystitis (n=35) and healthy controls (n=20) was also evaluated by ELISA. Concomitantly the diagnostic potential of CTSB with already established tumor markers CA 19-9 and CEA was also assessed. Finally the effect of CTSB knockdown on cell proliferation, wound healing and invasion of GBC cells (OCUG-1 and NOZ) was evaluated.
Results: Significantly elevated levels of CTSB activity, protein and mRNA was detected in tissues of GBC patients as compared to controls (p<0.0001). CTSB activity exhibited a significant association with tumor stage, TNM staging and lymph node involvement (p <0.001). A reduced overall survival was noted with higher CTSB activity values in GBC patients (Hazard ratio 3.39, p = 0.001).Serum CTSB exhibited highest diagnostic sensitivity alone (84%) and in combination with CA 19-9 in distinguishing GBC patients from controls. Depleting endogenous CTSB activity in OCUG-1 and NOZ cells lead to significant reduction in proliferation, migratory and invasive potential of GBC cells (p<0.001).
Conclusion: This study demonstrates clinical significance of CTSB overexpression in gallbladder carcinogenesis and suggests its potential use as a novel therapeutic target in clinical management of GBC.