Fig. 2.

Mechanism and targeting of activatable cell-penetrating peptide (ACPP) uptake. (a) The uptake of ACPP-L-EGFP was inhibited in A549 cells treated with heparin, but not by endocytosis inhibitors [50 µM amiloride (EIPA), 5 mM methyl-β-cyclodextrin (MβCD) and chlorpromazine]. (b) The uptake of ACPP-L-EGFP by A549 cells was not inhibited at 4 °C. (c) The uptake of ACPP-L-EGFP in A549 cells was significantly inhibited by weaken the potential difference across the cell membrane [PBS (K⁺)]. (d) The uptake of ACPP-L-EGFP was higher by tumour cells with high expression of MMP-2 (A549, SW480, Huh7 and U251) than by normal cells without MMP-2 expression (BEAS-2B). EGFP, enhanced green fluorescent protein; MMP-2, matrix metalloproteinase-2.