To further simulate the real situation of HA-BPY-GEF-NPs after entering into tumor cells, HA-BPY-GEF-NPs were incubated in mild acidic solution (pH 5.4) since the cathepsin B was localized in endosomes and lysosomes and was more active in these acidic milieus (28). Here, CTSB is linked to neoplasm.