In vivo results showed an accumulation of these NPs in brainand GBM tissues, significantly reducing tumor size without severetoxicity to peripheral tissues.119 A differentapproach took advantage of the overexpression of matrix metalloproteinases.It developed poly(ethylene glycol)-poly(ε-caprolactone) (PEG–PCL)NPs modified with an activatable low-weight molecular protein (ALWMP).The positive charges of the LWMP peptide were concealed by the anionicpeptide E10, which was linked through an MMP-2 cleavable linker. Here, MMP2 is linked to glioblastoma.