Centennial Honors College Western Illinois University Undergraduate Research Day 2012 Poster Presentation Cathepsin B Enzymatic Activity and Inhibition In Vitro and in MCF-7 Breast Cancer Cells Jennifer Tournear Faculty Mentors: Lisa Wen and Jenq-Kuen Huang Chemistry Cathepsins are an enzyme family of lysosomal proteases. Lysosomal proteases travel within the lysosomes of the cell and assist in the degradation of protein. The enzymes are thought to be released into the cytosol of cells through lysosomal leakage. The cathepsins have been widely studied and are associated with many human diseases including cancer, osteoporosis, inflammatory airway diseases and acute pancreatitis. The focus of this study is on cathepsin B and its activity in breast cancer cells. It is a cysteine cathepsin endopeptidase and is an essential part of many biological processes. It is when the proteolytic activity becomes unregulated that it is correlated with human disease. This project observes the enzymatic activity of human cathepsin B in vitro and in MCF-7 breast cancer cells. Inhibitors that have been previously synthesized are also used in this project to determine the inhibition potency. The results of an inhibition screening showed encouraging inhibition percentages and IC50 results of the top inhibitor were also promising. These results lead to an in progress protocol of a determining the cathepsin B activity in the MCF-7 cells by tissue culturing, inducing apoptosis, and implementing the Magic Red® protocol for the cathepsin B assay. Studying the activity in MCF-7 breast cancer cells and the inhibition of, could be a positive step in understanding cancer and the possibility of developing therapeutic agents for such diseases.