Preparation of NIR-Responsive Gold Nanocages as Efficient Carrier for Controlling Release of EGCG in Anticancer Application

Abstract

Hepatocellular carcinoma (HCC) is a type of cancer that has a restricted therapy option. Epigallocatechin gallate (EGCG) is one of the main biologically active ingredients in tea. A large number of studies have shown that EGCG has preventive and therapeutic effects on various tumors. In addition, the development of near-infrared (NIR)-responsive nano-platforms has been attracting cancer treatment. In this work, we designed and synthesized a strategy of gold nanocages (AuNCs) as an efficient carrier for controlling release of EGCG for anti-tumor to achieve the synergistic functions of NIR-response and inhibited tumor cell proliferation. The diameter of AuNCs is about 50 nm and has a hollow porous (8 nm) structure. Thermal imaging-graphic studies proved that the AuNCs-EGCG obtained have photothermal response to laser irradiation under near-infrared light and still maintain light stability after multiple cycles of laser irradiation. The resulted AuNCs-EGCG reduced the proliferation rate of HepG2 cells to 50% at 48 h. Western blot analysis showed that NIR-responsive AuNCs-EGCG can promote the expression of HepG2 cell apoptosis-related proteins HSP70, Cytochrome C, Caspase-9, Caspase-3, and Bax, while the expression of Bcl-2 is inhibited. Cell confocal microscopy analysis proved that AuNCs-EGCG irradiated by NIR significantly upregulates Caspase-3 by nearly 2-fold and downregulates Bcl-2 by nearly 0.33-fold, which is beneficial to promote HepG2 cell apoptosis. This study provides useful information for the NIR-responsive AuNCs-EGCG as a new type of nanomedicine for HCC.

Keywords: NIR responsive; epigallocatechin gallate; gold nanocages; hepatocellular carcinoma; photothermal therapy.

SCHEME 1

Schematic diagram of the synthesis of AuNCs-EGCG and its effect on cells under near-infrared radiation. AuNCs-EGCG can promote tumor cell apoptosis.

FIGURE 1

Characterization of AuNCs and EGCG-AuNCs. (A) TEM images and (B) DLS size distribution of AuNCs. (C) FTIR spectra, (D) XRD, (E) UV-vis and (F) fluorescence emission (λex = 400 nm) of samples. (G) Temperature rise curves of AuNCs-EGCG at different concentrations within 10 min. (H) Temperature rise curves of three groups of samples within 10 min. (I) The thermal curves of AuNCs and EGCG-AuNCs after repeated laser irradiation (n = 3). (J) Infrared thermography images of samples under 808 nm laser irradiation for 5 min.

FIGURE 2

Drug release from AuNCs-EGCG. (A) The release of EGCG from AuNCs-EGCG with or without laser irradiation. (B) The drug release curve of AuNCs-EGCG.

FIGURE 3

UV spectra of ABDA solution in control group and AuNCs-EGCG group.

FIGURE 4

NIR-responsive AuNCs-EGCG inhibited proliferation of HepG2 cells. (A) Effects of NIR-responsive AuNCs-EGCG at different times on the proliferation of HepG2 cells observed by MTT method. The mean and standard deviation (SD) of the data (n = 3) are shown. Statistical analysis: ^∗∗∗ p < 0.001. (B) Fluorescent images of Live/Dead-stained HepG2 cells after different treatments. Green: live cell staining, Red: dead cell staining. Scale bars are 25 μm.

FIGURE 5

NIR-responsive AuNCs-EGCG promoted HepG2 apoptosis. (A–G) The effect of NIR-responsive AuNCs-EGCG on the expression of HepG2 apoptosis-related proteins was detected by western blot and semi-quantitative analysis. The mean and standard deviation (SD) of the data (n = 3) are shown. Statistical analysis: ^∗∗∗ p < 0.001.

FIGURE 6

NIR-responsive AuNCs-EGCG promoted the expression level of Caspase-3 protein in HepG2 cells (A,B). Confocal microscopy immunofluorescence analysis of Caspase-3 protein expression and its semi-quantification analysis. Scale bars are 25 μm. The mean and standard deviation (SD) of the data (n = 3) are shown. Statistical analysis: ^∗∗∗ p < 0.001.

FIGURE 7

NIR-responsive AuNCs-EGCG inhibited the expression level of Bcl-2 protein in HepG2 cells (A,B). Confocal microscopy immunofluorescence analysis of Bcl-2 protein expression and its semi-quantification analysis. Scale bars are 25 μm. The mean and standard deviation (SD) of the data (n = 3) are shown. Statistical analysis: ^∗∗∗ p < 0.001.