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Dual Emissive Ir(III) Complexes for Photodynamic Therapy and Bioimaging
Marta Redrado1, Andrea Benedi2, Isabel Marzo2
1Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain.
Abstract:
Photodynamic therapy (PDT) is a cancer treatment still bearing enormous prospects of improvement. Within the toolbox of PDT, developing photosensitizers (PSs) that can specifically reach tumor cells and promote the generation of high concentration of reactive oxygen species (ROS) is a constant research goal. Mitochondria is known as a highly appealing target for PSs, thus being able to assess the biodistribution of the PSs prior to its light activation would be crucial for therapeutic maximization. Bifunctional Ir(III) complexes of the type [Ir(C^N)2(N^N-R)]+, where N^C is either phenylpyridine (ppy) or benzoquinoline (bzq), N^N is 2,2'-dipyridylamine (dpa) and R either anthracene (1 and 3) or acridine (2 and 4), have been developed as novel trackable PSs agents. Activation of the tracking or therapeutic function could be achieved specifically by irradiating the complex with a different light wavelength (405 nm vs. 470 nm respectively). Only complex 4 ([Ir(bzq)2(dpa-acr)]+) clearly showed dual emissive pattern, acridine based emission between 407-450 nm vs. Ir(III) based emission between 521 and 547 nm. The sensitivity of A549 lung cancer cells to 4 evidenced the importance of involving the metal center within the activation process of the PS, reaching values of photosensitivity over 110 times higher than in dark conditions. Moreover, complex 4 promoted apoptotic cell death and possibly the paraptotic pathway, as well as higher ROS generation under irradiation than in dark conditions. Complexes 2-4 accumulated in the mitochondria but species 2 and 4 also localizes in other subcellular organelles.
Insights
Researchers developed novel iridium(III) complexes as trackable photosensitizers for cancer therapy. Complex 4 demonstrated dual emission and enhanced photodynamic therapy (PDT) efficacy by generating reactive oxygen species (ROS) and inducing cancer cell death.
Area of Science:
- Inorganic Chemistry
- Photochemistry
- Cancer Therapeutics
Background:
- Photodynamic therapy (PDT) requires photosensitizers (PSs) that target cancer cells and produce reactive oxygen species (ROS).
- Mitochondria are attractive targets for PSs, necessitating methods to assess biodistribution before light activation.
- Developing trackable PSs with tunable activation wavelengths is crucial for optimizing PDT.
Purpose of the Study:
- To design and synthesize novel bifunctional iridium(III) complexes as trackable photosensitizers for cancer treatment.
- To investigate the dual-emission properties and wavelength-specific activation of these complexes.
- To evaluate the efficacy of complex 4 in inducing cancer cell death and ROS generation.
Main Methods:
- Synthesis of bifunctional iridium(III) complexes [Ir(C^N)2(N^N-R)]+ with varying ligands.
- Spectroscopic analysis to determine dual emissive patterns and emission wavelengths.
- Cell viability assays on A549 lung cancer cells under different irradiation conditions.
- Assessment of reactive oxygen species (ROS) generation and cellular localization.
Main Results:
- Complex 4, [Ir(bzq)2(dpa-acr)]+, exhibited a dual emissive pattern with distinct emission bands for acridine and Ir(III) centers.
- Complex 4 showed significantly enhanced photosensitivity (over 110-fold increase) compared to dark conditions.
- Irradiation of complex 4 induced apoptotic and possibly paraptotic cell death and increased ROS generation in A549 cells.
- Complexes 2 and 4 accumulated in mitochondria, with 2 and 4 also localizing in other organelles.
Conclusions:
- Bifunctional iridium(III) complexes can serve as trackable photosensitizers with wavelength-dependent activation.
- Complex 4 demonstrates potent photodynamic efficacy against lung cancer cells, highlighting the role of the metal center in activation.
- The dual-emission and subcellular localization properties of these complexes offer potential for improved cancer therapy and diagnostics.
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