Photocatalytic arylterpyridine iridium(III) complexes trigger oncosis in 2D and 3D cancer cell models via NADH oxidation

Abstract

Eight novel arylterpyridine iridium(III) complexes [Ir(N^N^N)(C^N)Cl]PF6 (Ir1-Ir8), incorporating diverse para-substituents and extended aromatic groups, were synthesized and fully characterized. Upon exposure to biocompatible blue light, all complexes demonstrated potent antiproliferative effects in both 2D and 3D cancer cell models, with minimal toxicity toward non-cancerous cells. Complexes Ir2, Ir3, and Ir8 -those containing 9-anthracenyl-, 1,3benzodioxole-5-yl substituents, and 1,4-benzodioxan-6-yl, respectively -displayed the highest phototoxic indices and were further investigated. Ir2 and Ir3 preferentially localized in the cytoplasm of HCT116 cells, inducing oncotic-like cell death upon irradiation, characterized by distinct cellular morphological changes, adenosine triphosphate (ATP) depletion, and porimin upregulation. Mechanistic studies revealed that photoactivated Ir2 and Ir3 catalyzed nicotinamide adenine dinucleotide (NADH) oxidation with high turnover frequencies, accompanied by the generation of reactive oxygen species (ROS). Molecular dynamics and hybrid QM/MM simulations supported the formation of non-covalent Ir-NADH heterodimers, with Mulliken charge analysis indicating NADH→Ir charge transfer stabilized triplet states and identifying Ir8 as the most efficient NADH photocatalyst, in agreement with experimental evidence obtained by intracellular NAD⁺/NADH assays. Collectively, these findings establish a mechanistic framework for a novel class of photoactivated iridium complexes that exert synergistic phototoxic and photocatalytic effects, offering a promising alternative to conventional ROS-driven photodynamic therapy.