Protease-modulated cellular uptake of quantum dots

Abstract

Quantum dots (QDs) are often cell-impermeable and require transporters to facilitate crossing over cell membranes. Here we present a simple and versatile method that utilizes enzymes, matrix metalloprotease 2 (MMP-2) and MMP-7, to modulate the cellular uptake of QDs. QD-peptide conjugates could be efficiently taken up into cells after the MMP treatment. This enzyme-modulated cellular uptake of QDs may be applied to other nanoparticles for biological imaging and selective drug delivery into tumor cells.

Figure 1

(a) Fluorescence images of HT-1080 cells stained with QD@BRn conjugates (n = 9, 7, 5, 4, 3, 2, 1, 0 for A to H, respectively) and QD (I); (b) Fluorescence intensity of COS-7 cells in 96 microtiter plates incubated with QD@BRn (n as indicated for each column); (c) Fluorescence intensity of COS-7 cells incubated with QDs conjugated with a mixture of BR4 and BR at indicated ratios.

Figure 2

(a) HPLC analysis of the MMP-2 catalyzed cleavage of the substrate BR4XPLGVRGE4; (b–d) Overlaid fluorescence and differential interference contrast (DIC) images of HT-1080 cells stained with the conjugate QD@BR4XPLGVRGE4 (b), QD@BR4XPLG (formed with MMP-2 cleaved BR4XPLGVRGE4) (c), and MMP-2 treated conjugate QD@BR4XPLGVRGE4 (d), respectively. Display scale: 0–600.

Figure 3

Overlaid fluorescence and DIC images of HT-1080 cells incubated with QD conjugates with indicated peptides with and without MMP-2 treatment (A–F), and MMP-7 (G–H). Display scale: 0–1000 for A–D; 0–1200 for E, F and 0–500 for G, H.

Scheme 1

Schematic of QD conjugates that can be activated by MMPs for cellular uptake.