MMP2 and neoplasm: When the 2C5/peptide/TATp-Lip specifically targeted tumor cells, the long-chain PEG was released after the MMP2-cleavable linker was cleaved by the highly expressed extracellular MMP2, resulting in the exposure of the originally unexposed surface-attached cell-penetrating TATp, which facilitated the enhanced intracellular delivery of the system (Zhu et al., 2012).