Uncaging Iridium(III) Complexes for Combined Photodynamic and Photoactivated Chemotherapy

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Medicinal Chemistry

Background:

• Photochemotherapy offers targeted cancer treatment with reduced systemic toxicity.
• Iridium(III) complexes are explored for their photophysical properties and potential as anticancer agents.
• Developing light-activatable prodrugs requires precise control over drug release and activation mechanisms.

Purpose of the Study:

• To develop novel iridium(III) complexes as light-activatable anticancer prodrugs.
• To investigate the role of sulfur- and selenium-based "caging" groups in modulating photoreactivity.
• To evaluate the photocytotoxicity and underlying mechanisms of these complexes.

Main Methods:

• Synthesis and characterization of two iridium(III) complexes: [Ir(cys)(ppy)(terpy)]PF6 and [Ir(sec)(ppy)(terpy)]PF6.
• Photochemical studies to elucidate distinct bond cleavage pathways upon visible light activation.
• Assessment of singlet oxygen production quantum yields and photodynamic therapy (PDT) mechanism.
• Evaluation of dark toxicity and photocytotoxicity in A549 cancer cells at different wavelengths.

Main Results:

• Both complexes are stable in the dark but release active species upon light exposure.
• Distinct photochemical pathways were observed: sulfur complex involves sulfinato intermediate, while selenium complex forms an unprecedented selenite intermediate.
• High singlet oxygen production quantum yields (40%-48%) indicate efficient PDT potential.
• Minimal dark toxicity (EC50 > 150 µM) but potent photocytotoxicity was observed under blue and green light.

Conclusions:

• Chalcogen coordination significantly influences the photoreactivity and therapeutic efficacy of iridium(III) complexes.
• These photocaged iridium(III) pro-sensitizers show promise for combined photochemotherapy and photodynamic therapy (PDT) applications.
• The developed complexes offer a new strategy for targeted cancer treatment with enhanced spatial and temporal control.