Increased cathepsin B activity in human lung tumors.

The occurrence and levels of cathepsin B activity were investigated in primary human lung tumors and lung metastases of renal, colorectal and urinary bladder carcinomas as well as in the associated apparently normal lung parenchyma using a continuous rate enzyme assay with Ac-Leu-Arg-Arg-NHMec (7-(N-acetyl-L-leucyl-L-arginyl-L-arginylamido)-4-methylcoumarin) as the fluorogenic substrate. The inhibition studies of the enzymic hydrolysis of the substrate provided evidence for the catalytic action of the cysteine proteinase cathepsin B (CB) in the lung tumor tissues and the lung parenchyma under the assay conditions used. In the studied group of twenty-four patients with primary lung tumors of all major histological types, the level of CB activity in the tumor tissue was increased twofold and more over that in the associated lung parenchyma in 83% and 75% of cases, when expressed on the basis of wet tissue weight and tissue DNA, respectively. In patients with primary lung adenocarcinoma, the activity of the enzyme in the tumor tissue was elevated over that in the lung parenchyma in all cases studied. In both subgroups of patients with squamous cell lung carcinoma and adenocarcinoma, the mean cathepsin B activity was significantly higher in the tumor tissue than in the lung parenchyma. No obvious correlation was found between the tissue level of cathepsin B activity and the stage of primary lung tumor disease. In a limited number of patients with lung metastases, the level of cathepsin B activity was also higher in the tumor tissue than in the lung parenchyma.