Targeted Therapy against Metastatic Melanoma Based on Self-Assembled Metal-Phenolic Nanocomplexes Comprised of Green Tea Catechin

Abstract

The targeted therapy of metastatic melanoma is an important yet challenging goal that has received only limited attention to date. Herein, green tea polyphenols, (-)-epigallocatechin-3-gallate (EGCG), and lanthanide metal ions (Sm³⁺) are used as building blocks to engineer self-assembled Sm^III-EGCG nanocomplexes with synergistically enhanced tumor inhibitory properties. These nanocomplexes have negligible systemic toxic effects on healthy cells but cause a significant reduction in the viability of melanoma cells by efficiently regulating their metabolic pathways. Moreover, the wound-induced migration of melanoma cells can be efficiently inhibited by Sm^III-EGCG, which is a key criterion for metastatic melanoma therapy. In a mouse melanoma tumor model, Sm^III-EGCG is directly compared with a clinical anticancer drug, 5-fluorouracil and shows remarkable tumor inhibition. Moreover, the targeted therapy of Sm^III-EGCG is shown to prevent metastatic lung melanoma from spreading to main organs with no adverse side effects on the body weight or organs. These in vivo results demonstrate significant advantages of Sm^III-EGCG over its clinical counterpart. The results suggest that these green tea-based, self-assembled nanocomplexes possess all of the key traits of a clinically promising candidate to address the challenges associated with the treatment of advanced stage metastatic melanoma.

Keywords: metal‐phenolic network; metastatic melanoma; polyphenols; self‐assembly; targeted therapy.

Figure 1

Green tea polyphenol‐based nanocomplexes and their therapeutic effects on metastatic melanoma. a) Facile synthesis of Sm^III‐EGCG nanocomplexes through self‐assembly. b) SEM image of narrowly dispersed Sm^III‐EGCG nanocomplexes with near‐spherical morphology. Scale bar is 100 nm. c) ¹H NMR spectra of EGCG molecules and Sm^III‐EGCG nanocomplexes demonstrate coordination complexation between the galloyl groups of EGCG and Sm³⁺ ions. d) HAADF‐TEM and EDS mapping images of Sm^III‐EGCG nanocomplexes. Scale bars are 50 nm. e) Schematic illustration of the developments of metastatic melanoma, which transforms from primary melanoma and migrates to invade other organs. The administration of Sm^III‐EGCG nanocomplexes can effectively inhibit the developments of metastatic melanoma through three main targeted therapeutic effects (green boxes). f) Internalization of Sm^III‐EGCG into the melanoma cells, disassembly of green tea catechin and Sm³⁺ ions, and mitochondria‐associated apoptosis.

Figure 2

Selective toxicity of Sm^III‐EGCG nanocomplexes on melanoma cells. a) Cell viability of a melanoma cell line (B16F10 cells) was determined by CCK‐8 assay after 24 h incubation with different concentrations of Sm^III‐EGCG, EGCG, and Sm³⁺ ions individually. b) Cell viability of Sm^III‐EGCG nanocomplexes on normal healthy cells (NIH/3T3 and HLECs cells) compared with B16F10 cells. c) Western‐blot analysis of mitochondria‐associated apoptotic protein expression after incubation with Sm^III‐EGCG at different concentrations. d) Sm^III‐EGCG‐induced apoptosis in B16F10 cells counted by using flow cytometry. The variation is represented by the standard deviation of three independent replicates in all graphs, ^*** (p‐value < 0.05). e) Fluorescence microscopy images of generation of mitochondrial dysfunction. MitoTracker (red) probe indicates the change of mitochondrial membrane potential changes in B16F10 cells. 4′,6‐diamidino‐2‐phenylindole (DAPI) stain (blue) represents the cell nuclei. Scale bars are 20 and 10 µm in inset.

Figure 3

Wound‐induced migration assays indicated the inhibition of migration of B16F10 melanoma cells in the presence of Sm^III‐EGCG nanocomplexes. In the control group, B16F10 melanoma cells expanded to the center area (yellow dashed lines) after 16 h due to the their migration capacity, which represents the most challenging point for the therapy of metastatic melanoma. After treatment with Sm^III‐EGCG nanocomplexes, the presence of Sm^III‐EGCG effectively inhibited the growth of B16F10 melanoma cells where the yellow dashed lines of 16 h migration were similar with the white solid lines of right after the wound was inflicted (0 h).

Figure 4

In vivo tumor therapy of Sm^III‐EGCG nanocomplexes in a melanoma tumor model. a) Schematic of tumor formation and injection of Sm^III‐EGCG nanocomplexes into the tumor. Mice were subcutaneously injected with 1.0 × 10⁶ B16F10 cells and the antitumor effects of 50 mg kg⁻¹ Sm^III‐EGCG or 5‐fluorouracil (30 mg kg⁻¹) was evaluated. Saline was used as the control. b–d) Morphological changes in tumor size. c) Panel: Photographic images of mice bearing B16F10 tumors with treatments of PBS, 5‐fluorouracil, and Sm^III‐EGCG. d) Panel: Photographic images of postmortem tumors. e) Tumor growth monitored at different time‐points and calculated tumor volume. The variation is represented by the standard deviation of three independent replicates in all graphs, ^*** (p‐value < 0.05). f) Body weight per experimental group at the indicated time points. The variation is represented by the standard deviation of three independent replicates in all graphs.

Figure 5

Sm^III‐EGCG nanocomplexes were successful in treating a metastatic lung melanoma model. a) Schematic of metastatic melanoma formation and inhibition by Sm^III‐EGCG nanocomplexes. b) Morphological changes in lungs at 0 and 24 d. In the control and 5‐fluorouracil‐treated groups, black dots can be seen on the lung, while no obvious black dots can be observed in the Sm^III‐EGCG‐treated group. c) Static numbers of metastatic nodules in different groups. The variation is represented by the standard deviation of three independent replicates in all graphs, ^*** (p‐value < 0.05). d) Histopathology of the heart, liver, and kidney from mice. The main organs were collected and processed for histological analysis. The sections were stained with hematoxylineosin. Images are representative of three independent experiments. The scale bar is 100 µm.