Provided herein are compositions and kits comprising a therapeutic agent linked to a cleavable substrate, wherein the cleavable substrate is capable of being cleaved by cathepsin E. Also provided are methods of treating one or more symptoms of a disease or disorder characterized by expression of cathepsin E in a subject and methods of eliminating a cancer cell characterized by expression of cathepsin E using the provided compositions and kits. Further provided herein are methods of detecting the presence of a cancer cell or detecting a cathepsin E expressing cell using a photosensitizer linked to a cleavable substrate, wherein the cleavable substrate is capable of being cleaved by cathepsin E.