Bis(thiosemicarbazide)gallium(III) Complexes as Potent Anticancer Agents by ROS Induction and Mitochondrial Pathway Activation

A series of bis(thiosemicarbazide)gallium (III) complexes were synthesized and characterized by infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, single-crystal x-ray crystallography, and density functional theory (DFT) calculation. The cytotoxicity of these gallium(III) complexes (CP 1–4) was subsequently evaluated against HCT-116, HeLa, MDA-MB-231, and A549 cancer cell lines, as well as the normal cell line LO2, by MTT assays. The results indicated that CP-1 displayed potent inhibitory effects against human colorectal cancer cells (HCT-116) (IC₅₀ = 0.03 ± 0.01) and human breast cancer cells (MDA-MB-231) (IC₅₀ = 0.02 ± 0.01), significantly outperforming cisplatin. Moreover, CP-2 exhibited notable selectivity towards MDA-MB-231 cells (IC₅₀ = 5.01 ± 0.40) with minimal toxicity towards normal cells. Mechanistic studies revealed that treatment with CP 1–2 led to elevated intracellular reactive oxygen species (ROS) levels, resulting in cell cycle arrest at different phases. Specifically, CP-1 induced G2/M phase arrest, inhibiting cancer cell proliferation, whereas CP-2 hindered DNA synthesis (S phase) to impede cell proliferation. Furthermore, both CP-1 and CP-2 caused a reduction in mitochondrial membrane potential, activating the mitochondrial apoptotic pathway and inducing apoptosis in cancer cells. Molecular docking experiments demonstrated strong interactions between CP 1–2 and protein disulfide isomerase (PDI) at the molecular level. These findings suggest that CP-1 and CP-2 serve as potential anticancer agents, particularly showing promising potential in the treatment of breast cancer.