CTSB and cancer: Therefore, using cancer-associatedenzymes to fabricate activable PSs has attracted great attention.In this section, we will discuss several typical examples of enzyme-activatable“smart” PSs, including those activated by nitroreductase(NTR), azoreductase, cathepsin B, β-galactosidase, alkalinephosphatases, tyrosinase, γ-glutamyl transpeptidase, and aminopeptidase.