Smart multifunctional nanostructure for targeted cancer chemotherapy and magnetic resonance imaging

Abstract

Targeted chemotherapy and magnetic resonance imaging of cancer cells in vitro has been achieved using a smart multifunctional nanostructure (SMN) constructed from a porous hollow magnetite nanoparticle (PHMNP), a heterobifunctional PEG ligand, and an aptamer. The PHMNPs were prepared through a three-step reaction and loaded with the anticancer drug doxorubicin while being functionalized with PEG ligands. Targeting aptamers were then introduced by reaction with the PEG ligands. The pores of the PHMNPs are stable at physiological pH, but they are subject to acid etching. Specific binding and uptake of the SMN to the target cancer cells induced by aptamers was observed. In addition, multiple aptamers on the surface of one single SMN led to enhanced binding and uptake to target cancer cells due to the multivalent effect. Upon reaching the lysosomes of target cancer cells through receptor-mediated endocytosis, the relatively low lysosomal pH level resulted in corrosion of the PHMNP pores, facilitating the release of doxorubicin to kill the target cancer cells. In addition, the potential of using SMN for magnetic resonance imaging was also investigated.

Figure 1

Synthesis and characterization of SMNs. (a) Schematic illustrating the synthesis of SMNs. TEM images of (b) IMNPs; (c) HMNPs; and (d) PHMNPs. Inset of (d) shows the zoomed image of a representative PHMNP. The scale bars are 100 nm (10 nm for the inset). (e) Dispersibility of PHMNPs (left) and PPHMNPs (right) in hexane and water. (f) Fluorescence intensity of PPHMNPs and SMNs (Excitation: 545 nm). (IMNP = iron-magnetite core-shell nanoparticle, HMNP = hollow magnetite nanoparticle, PHMNP = porous hollow magnetite nanoparticle, PPHMNP = PEGylated porous hollow magnetite nanoparticle, SMN = smart multifunctional

Figure 2

Flow cytometry histograms to monitor the binding of SMNs with (a) CEM cells (target cells), and (b) Ramos cells (control cells). Flow cytometry histograms to compare the binding of free sgc8 aptamer and SMNs with (c) CEM cells, and (d) Ramos cells.

Figure 3

Colocalization study of (a) sgc8 aptamer, and (b) SMNs with lysosensor in CEM cells (target cells).

Figure 4

Cytotoxicity assay of CEM cells (target cells) and Ramos cells (control cells) treated with (a) DOX only, and (b) DOX-SMNs.

Figure 5

The potential of using SMNs as T₂ contrast agents. (a) T₂ relaxation measurements, and (b) T₂*-weighted MRI images of SMNs, SMNs incubated with CEM cells (target cells), and SMNs incubated with Ramos cells (control cells). The concentration of SMNs in (a) is 10 μg/ml, while the concentrations of it in (b) are labeled on the right side of the figure.

Scheme 1

Mechanism of SMNs for targeted cancer chemotherapy. Due to surface coating of aptamers, DOX-SMNs specifically enter target cancer cells through receptor-mediated endocytosis and reside in acidic lysosomes. This leads to SMN pore size enlargement because of its acid-sensitivity, facilitating the release of entrapped DOX and the killing of target cancer cells. (SMN = smart multifunctional nanostructure, DOX-SMN = DOX-loaded SMN, DOX = doxorubicin)