# Novel Heteroleptic Iridium(III) Complexes Containing COUBPY Ligands for Effective Photoinduction of Ferroptosis for Cancer Therapy

## TL;DR

This study introduces new iridium complexes that effectively induce cancer cell death through light-activated ferroptosis, a non-apoptotic cell death mechanism.

## Contribution

The paper presents novel Ir-COUBPY complexes as photosensitizers that induce ferroptosis via dual ROS pathways and mitochondrial targeting.

## Key findings

- Ir-COUBPY complexes generate both superoxide and singlet oxygen upon light exposure.
- Nanoencapsulated Ir4a significantly enhances phototoxicity in cancer cells.
- Ferroptosis is confirmed as the primary cell death pathway induced by these complexes.

## Abstract

Ferroptosis, a recently described form of regulated,
nonapoptotic
cell death mechanism, presents significant potential for cancer treatment,
particularly when combined with photodynamic therapy (PDT). In this
study, we report the synthesis and biological evaluation of a series
of Ir-COUBPY complexes as novel photosensitizers (PSs) for effective
cancer phototherapy. These complexes exhibit high stability under
both dark and light conditions and are capable of photogenerating
Type I and Type II reactive oxygen species (ROS), as well as photo-oxidizing
NADH. Electron paramagnetic resonance (EPR) spectroscopy provided
direct evidence of light-induced superoxide and singlet oxygen generation,
confirming dual ROS pathways. Moreover, the Ir-COUBPY complexes preferentially
accumulated in the mitochondria of cancer cells, leading to the photogeneration
of hydroxyl radicals and hydrogen peroxide. Photocytotoxicity studies
on HeLa and A375 cancer cells underscored the role of the COUBPY ligand
in enhancing PDT efficiency upon irradiation with both green and red
light. Among the Ir-COUBPY complexes, the most effective PS, Ir4a, was encapsulated in polyurethane–polyurea hybrid
nanocapsules (NC-Ir4a), resulting in a significant increase
in phototoxic index values (e.g., from 64 to 179.6 in A375 cells).
Mechanistic studies confirmed ferroptosis as the primary cell death
pathway induced by Ir4a, supported by light-dependent
lipid peroxidation, glutathione oxidation and depletion, intracellular
ATP photodepletion, and the viability-restoring effect of Fer-1. These
effects were more pronounced upon nanoencapsulation. Photobiological
studies with 3D tumor spheroids of A375 cells further confirmed higher
cellular uptake of NC-Ir4a, contributing to improved
phototoxic efficiency. Overall, these findings highlight the potential
of coumarin-based COUBPY ligands in the design of new Ir­(III)-based
PSs that can be activated with light within the phototherapeutic window,
operating through nonconventional cell death mechanisms such as ferroptosis.