Cathepsins K, L, and S activity profiles in human lung cancer. A) Different stages (I, II, and III) of lung cancer and normal lung tissues were obtained and prepared as described. 10 μg of protein were loaded for multiplex cathepsin zymography, and a representative zymogram is shown and cropped for clarity. B) Cathepsin K, L, and S activities were quantified by densitometry. Cathepsin activity from 24 samples (18 cancer and 6 normal) comparing normal to tumor is shown. C) Comparisons of cathepsins K, L, and S activity changes at different stages of tumor progression (n = 4-6, *p < 0.05).