The tumor-targeting ability and parent drug release were both taken into consideration for the design of compound 11, which contained a folate as a tumor-targeting moiety, due to the overexpression of folate receptors on the tumor surface, and a tetrapeptide Gly-Phe-Leu-Gly (GFLG) as an enzyme-responsive substrate, which was responsive to cathepsin B, which is highly expressed in tumor cells and beneficial for enhancement of water solubility. Here, CTSB is linked to neoplasm.