CTSS and neoplasm: However, studies have indicated that cancer patients have higher levels of its protein and activity.146 The role of cathepsin B in cells is to drive caspase-dependent apoptosis and promote tumor invasion, metastasis and angiogenesis.147 According to earlier research, cathepsins are most active in an acidic environment and are released in an active state when the pH of the environment around the cell is below a certain level.148,149 This provides a direction for the design of intelligent nanoparticles with dual response of pH and enzyme.