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Panchromatic Osmium Complexes for Photodynamic Therapy: Solutions to Existing Problems and New Questions.

ABSTRACT: This article is a highlight of the paper by Lazic et al. in this issue of Photochemistry and Photobiology, https://doi.org/10.1111/php.12767. It describes the validation of osmium coordination complexes as photosensitizers for photodynamic therapy, with very promising in vivo results that demonstrate radical improvements in survival following irradiation with visible (635 nm) or near-IR (NIR; 808 nm) light. An unusual feature in the study is that the different complexes exhibit disparate photophysical and photobiological characteristics, despite sharing common structural motifs. These findings raise hopes for the development of novel photosensitizers that overcome the limitations of current commercially available systems for PDT, but also raise questions regarding the most efficacious biological mechanisms of action for this treatment modality.

SUBMITTER: Glazer EC

PROVIDER: S-EPMC5603404 | biostudies-other | 2017 Oct

REPOSITORIES: biostudies-other

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Panchromatic Osmium Complexes for Photodynamic Therapy: Solutions to Existing Problems and New Questions.

Glazer Edith C EC

Photochemistry and photobiology 20170807 5

This article is a highlight of the paper by Lazic et al. in this issue of Photochemistry and Photobiology, https://doi.org/10.1111/php.12767. It describes the validation of osmium coordination complexes as photosensitizers for photodynamic therapy, with very promising in vivo results that demonstrate radical improvements in survival following irradiation with visible (635 nm) or near-IR (NIR; 808 nm) light. An unusual feature in the study is that the different complexes exhibit disparate photoph ...[more]

PMID: 28543667

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Project description:Six homo- or heteroleptic tricationic Ir(R1-tpy)(R2-tpy)3+ complexes (Ir1-Ir6, R1/R2 = Ph, 4'-N(CH3)2Ph, pyren-1-yl, or 4'-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}Ph, tpy = 2,2';6',2"-terpyridine) were synthesized and tested for photodynamic therapy (PDT) effects. The ground- and excited-state characteristics of these complexes were studied systematically via spectroscopic methods and quantum chemistry calculations. All complexes possessed intraligand charge transfer (1ILCT) / metal-to-ligand charge transfer (1MLCT) dominated transition(s) in their low-energy absorption bands, which red-shifted with the increased electron-releasing strength of the R1/R2 substituent. Five of the complexes exhibited ligand-centered 3 π,π*/3ILCT/3MLCT emission. With a stronger electron-releasing R1/R2 substituent, the degree of charge transfer contribution increased, leading to a decrease of the emission quantum yield. When the 4'-N(CH3)2Ph substituent was introduced on both tpy ligands, the emission of Ir3 was completely quenched. Our study on the transient absorption of these complexes demonstrated that they all possessed broadband triplet excited-state absorption in the 400-800 nm region. Pyrenyl substitution of one or more tpy ligands, as in Ir4 and Ir5, increased the lifetimes of the lowest triplet excited state and the singlet oxygen (1O2) production efficiencies. Ir1-Ir5 were nontoxic toward SK-MEL-28 cells, with photocytotoxicities that varied from 0.18 to 153 µM. Among them, Ir4 had the highest 1O2 quantum yield (0.81) in cell-free conditions, showing the largest photocytotoxicity against SK-MEL-28 cells for Ir(III) PSs to date, and was the most efficient generator of reactive oxygen species (ROS) in vitro. Ir4 possessed a very large phototherapeutic index (PI = dark EC50 / light EC50) of >1657, the largest reported for an Ir(III) complex photosensitizer upon broadband visible light (400-700 nm) activation. Ir4 also exhibited a very strong PDT effect toward MCF-7 breast cancer cells and its xenograft tumor model. Upon 450-nm light activation, Ir4 dramatically inhibited the xenograft tumor growth and exhibited negligible side effects upon PDT treatment.

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Panchromatic Osmium Complexes for Photodynamic Therapy: Solutions to Existing Problems and New Questions.

Publications

Panchromatic Osmium Complexes for Photodynamic Therapy: Solutions to Existing Problems and New Questions.

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