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Molecules 2016, 21(11), 1460;

Red Light Activation of Ru(II) Polypyridyl Prodrugs via Triplet-Triplet Annihilation Upconversion: Feasibility in Air and through Meat

Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, Leiden 2333 CC, The Netherlands
Author to whom correspondence should be addressed.
Academic Editor: Derek J. McPhee
Received: 5 October 2016 / Revised: 24 October 2016 / Accepted: 26 October 2016 / Published: 1 November 2016
(This article belongs to the Special Issue Photoresponsive Drugs)
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Triplet-triplet annihilation upconversion (TTA-UC) is a promising photophysical tool to shift the activation wavelength of photopharmacological compounds to the red or near-infrared wavelength domain, in which light penetrates human tissue optimally. However, TTA-UC is sensitive to dioxygen, which quenches the triplet states needed for upconversion. Here, we demonstrate not only that the sensitivity of TTA-UC liposomes to dioxygen can be circumvented by adding antioxidants, but also that this strategy is compatible with the activation of ruthenium-based chemotherapeutic compounds. First, red-to-blue upconverting liposomes were functionalized with a blue-light sensitive, membrane-anchored ruthenium polypyridyl complex, and put in solution in presence of a cocktail of antioxidants composed of ascorbic acid and glutathione. Upon red light irradiation with a medical grade 630 nm PDT laser, enough blue light was produced by TTA-UC liposomes under air to efficiently trigger full activation of the Ru-based prodrug. Then, the blue light generated by TTA-UC liposomes under red light irradiation (630 nm, 0.57 W/cm2) through different thicknesses of pork or chicken meat was measured, showing that TTA-UC still occurred even beyond 10 mm of biological tissue. Overall, the rate of activation of the ruthenium compound in TTA-UC liposomes using either blue or red light (1.6 W/cm2) through 7 mm of pork fillet were found comparable, but the blue light caused significant tissue damage, whereas red light did not. Finally, full activation of the ruthenium prodrug in TTA-UC liposomes was obtained under red light irradiation through 7 mm of pork fillet, thereby underlining the in vivo applicability of the activation-by-upconversion strategy. View Full-Text
Keywords: photochemical upconversion; ruthenium prodrugs; phototherapy; liposomes; meat spectroscopy photochemical upconversion; ruthenium prodrugs; phototherapy; liposomes; meat spectroscopy

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Askes, S.H.C.; Meijer, M.S.; Bouwens, T.; Landman, I.; Bonnet, S. Red Light Activation of Ru(II) Polypyridyl Prodrugs via Triplet-Triplet Annihilation Upconversion: Feasibility in Air and through Meat. Molecules 2016, 21, 1460.

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