Intracellular Fenton reaction based on mitochondria-targeted copper(ii)–peptide complex for induced apoptosis

Abstract

Hydrogen peroxide (H₂O₂) induces apoptosis in cancer cells; however, the conversion of H₂O₂ into the highly toxic hydroxyl radical (˙OH) directly by Fenton reaction in mitochondria to induce cancer cell apoptosis has rarely been achieved in biomedical systems. Herein, we designed a metal–peptide complex comprised of a copper-binding GGH (Gly-Gly-His) domain and the mitochondria-penetrating peptide (MPP) FrFKFrFK-CONH₂ (Phe-r-Phe-Lys-Phe-r-Phe-Lys-CONH₂, where r = D-arginine). GGH is a motif that can form coordination complexes with copper(II), where the MPP with alternating cationic and hydrophobic residues can transport copper(II) into mitochondria. The copper(II)–MPP complex in the presence of ascorbate (Asc) exhibited strong cytotoxicity to the investigated cell lines, especially HeLa cells, due to the selective intracellular uptake ability of copper(II). In mitochondria, the copper(II)–MPP complex induced Fenton reaction with endogenous H₂O₂ to produce the highly reactive ˙OH radical. Meanwhile, the continuous production of ˙OH is toxic to cells because it depolarizes the mitochondrial membrane potential (Δψ_m), blocking the cell cycle and inducing apoptosis in cancer cells. These results establish a new system for Cu-mediated ˙OH generation via intra-mitochondrial Fenton reaction between the copper(II)–MPP complex, Asc and H₂O₂ in response to the microenvironment of cancer cells, which opens a promising treatment in cancer therapy.