Abstract
A set of rhenium(V)-oxo meso-triarylcorroles bearing ester and carboxylic acid functionalities were synthesized with a view to determining their potential for photodynamic therapy. Toward this end, we measured their near-IR phosphorescence and their ability to sensitize singlet oxygen formation. The two esters studied, ReVO 5,10,15-tris(meta-carbomethoxyphenyl)corrole and ReVO 5,10,15-tris(para-carbomethoxyphenyl)corrole, were found to exhibit phosphorescence quantum yields of around 1% and fairly long phosphorescence lifetimes of about 60 μs in toluene. The corresponding carboxylic acids, which were examined in ethanolic/aqueous media, in contrast, showed much lower phosphorescence quantum yields on the order of 0.01% and somewhat shorter phosphorescent lifetimes. The quantum yields for singlet oxygen formation, on the other hand, turned out to be equally high (0.72 ± 0.02) for the esters and corresponding carboxylic acids. For the two carboxylic acids, we also carried out photocytotoxicity measurements on rat bladder cancer cells (AY27) and human colon carcinoma cells (WiDr). Cell viability measurements (MTT assays) indicated 50% cell death (LD50) for AY27 cells upon 5 min of blue light exposure with the meta carboxylic acid and upon 7 min of exposure with the para carboxylic acid; complete cell death resulted after 20 min for both compounds. The WiDr cells proved less sensitive, and LD50 values were reached after 8 and 12 min illumination with the meta and para carboxylic acids, respectively.
Highlights
Photodynamic therapy (PDT) relies on the combined action of a photosensitizer, light, and molecular oxygen to treat a variety of medical conditions, notably cancer and various skin conditions and increasingly bacterial, viral, and fungal infections.[1,2]
Λmax,em 783 777 773 766 φ (%) ∼0.03 ∼0.05 ∼0.01 ∼0.02 τ the phosphorescence quantum yields may be a result of deaggregation of the dyes upon deprotonation of the COOH groups
The phototoxic/cytotoxic effects of the ReVO corrole free acids, Re[mTCPC](O) and Re[pTCPC](O), were evaluated for rat bladder cancer cells (AY27)[26,27] and human colon carcinoma cells (WiDr),[29] indicating that these compounds trigger cell changes leading to cell death (Figure 3)
Summary
Photodynamic therapy (PDT) relies on the combined action of a photosensitizer, light, and molecular oxygen to treat a variety of medical conditions, notably cancer and various skin conditions and increasingly bacterial, viral, and fungal infections.[1,2] A common, but far from exclusive, mechanism involves photoexcitation of the sensitizer to a short-lived singlet excited state (S1), intersystem crossing to a longer lived triplet state (T1), and energy transfer to ground-state triplet oxygen (3Σg), leading to highly reactive singlet oxygen (1Δg) as the primary cytotoxic species. The phototoxic/cytotoxic effects of the ReVO corrole free acids, Re[mTCPC](O) and Re[pTCPC](O), were evaluated for rat bladder cancer cells (AY27)[26,27] and human colon carcinoma cells (WiDr),[29] indicating that these compounds trigger cell changes leading to cell death (Figure 3). The concentration of the compounds was chosen on the basis of earlier PDT studies on AY27 cells with the analogous gold complexes (Au[m/pTCPC]) on the AY27 cell line with the analogous gold complexes (Au[m/pTCPC]) and the same light source.[14] For both cell lines, the experiments described above showed a clear dependence of cell viability on the period of blue light exposure in the presence of the photosensitizer. Incubation with the photosensitizers in the absence of light resulted in modest cell death rates for the WiDr cell line, about 23 and 28% after incubation (24 h, 37 °C) with the meta and para isomers of the photosensitizer, respectively (Figure 3, green and pink violet points, respectively). Much weaker dark toxicity was observed for the AY27 cells, with death rates around 1 and 12% after incubation with the meta and para isomers, respectively
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