Cathepsin B and Cysteine Protease Inhibitors in Human Tongue Cancer: Correlation with Tumor Staging and In Vitro Inhibition of Cathepsin B by Chicken Cystatin

AIM: The study is aimed to investigate if the sera and the tumor tissues of tongue cancer patients demonstrate elevated cathepsin B activity during cancer progression and in vitro inhibition of the activity of cathepsin B by chicken cystatin. METHODS: Pro-cathepsin B and cathepsin B activities and cystatins as antipapain activity were measured using a fluorogenic substrate in 47 sera from patients and compared with 40 control subjects. Peroxidase method was used for immunohistochemical staining. RESULTS: The activities of pro-cathepsin B and cathepsin B were found to be significantly increased and their endogenous inhibitor cystatin C decreased in the sera of patients with tongue cancer. Patients with advanced stages had higher serum activities of pro-cathepsin B, cathepsin B and cysteine protease inhibitors if compared with the patients with stage I disease. However, the levels of cysteine protease inhibitors were not comparable to those of cathepsin B. The serum activity of cathepsin B from tongue cancer patients could be decreased by 2.4-fold after treatment with 5 nM purified egg white cystatin. Immunohistochemical staining showed significantly increased expression of cystatin C and cathepsin B in tongue tumor tissues, while negative staining was observed with the non-tumor parts. CONCLUSION: Elevated cathepsin B level was closely correlated with the invasion and progression of tongue cancer. The incomparable levels between cathepsin B and its natural inhibitors could contribute to the uncontrolled proteolysis and thus the malignant progression of tongue cancer. Chicken cystatin was able to effectively inhibit patients' cathepsin B activities in sera.