(8-Hydroxyquinoline) Gallium(III) Complex with High Antineoplastic Efficacy for Treating Colon Cancer via Multiple Mechanisms

Abstract

A series of (8-hydroxyquinoline) gallium(III) complexes (CP-1-4) was synthesized and characterized by single X-ray crystallography and density functional theory (DFT) calculation. The cytotoxicity of the four gallium complexes toward a human nonsmall cell lung cancer cell line (A549), human colon cancer cell line (HCT116), and human normal hepatocyte cell line (LO2) was evaluated using MTT assays. CP-4 exhibited excellent cytotoxicity against HCT116 cancer cells (IC₅₀ = 1.2 ± 0.3 μM) and lower toxicity than cisplatin and oxaliplatin. We also evaluated the anticancer mechanism studies in cell uptake, reactive oxygen species analysis, cell cycle, wound-healing, and Western blotting assays. The results showed that CP-4 affected the expression of DNA-related proteins, which led to the apoptosis of cancer cells. Moreover, molecular docking tests of CP-4 were performed to predict other binding sites and to confirm its higher binding force to disulfide isomerase (PDI) proteins. The emissive properties of CP-4 suggest that this complex can be used for colon cancer diagnosis and treatment, as well as in vivo imaging. These results also provide a foundation for the development of gallium complexes as potent anticancer agents.

Scheme 1. Structures of Four Gallium(III) Complexes

Figure 1

Comparison of (a) DFT theoretical structures and (b) single-crystal structures of four gallium complexes.

Figure 2

DFT calculation of electrostatic potentials of four ligands and gallium(III) complexes (positively charged red area, negatively charged blue area).

Figure 3

Fluorescence intensities of four gallium(III) complexes (a) CP-1 (λ_ex = 400 nm), (b) CP-2 (λ_ex = 439 nm), (c) CP-3 (λ_ex = 450 nm), and (d) CP-4 (λ_ex = 421 nm) at different concentrations.

Figure 4

Electron (green) and cavity (blue) distributions of four gallium(III) complexes calculated by DFT.

Figure 5

Cell viability of (a) A549, (b) HCT116, and (c) LO2 cell line treated with four gallium(III) complexes at different concentrations for 72 h.

Figure 6

Comparative toxicity of CP-1, CP-3, and CP-4 against the tested different cell lines at 10 μM after 48 h of exposure.

Figure 7

Hoechst 33342 staining detected morphological changes in HCT116 cells after treatment by varied compounds at 10 μM for 24 h. All scale bars = 10 μm.

Figure 8

(a) CLSM of HCT116 cells interacted with CP-1, CP-3, and CP-4 at 10 μM for 5 h. (b) 2D intensity histogram of CPs’ fluorescence colocation and Pearson correlation coefficient (PCC). All scale bars = 50 μm.

Figure 9

(a) Generation of reactive oxygen species induced by different compounds in HCT116 cells at 10 uM for 24 h. (b) Mean fluorescence intensity of different complexes. All scale bars = 10 μm.

Figure 10

(a) Migration inhibition (wound-healing assay) of HCT116 untreated or treated with the tested compounds for 24 h at the 2 μM concentrations. (b) Different healing rates. All scale bars = 10 μm.

Figure 11

(a) Cell cycle distribution was tested by flow cytometric analysis of DNA content after treatment with 10 μM CPs and platinum compounds for 24 h in HCT116 cells. (b) Different cell cycle ratios.

Figure 12

Colon cancer cells were treated with CP-4 (2.5 and 5 μM) for 24 h, and the expression levels of related proteins were detected by WB method, with Tubulin used as an internal reference.

Figure 13

Interaction networks of CP-4 with (a) PDI and (b) GSK-3β in Docking Mod.