Photodynamic Mechanisms induced by a Combination of Hypericin and a Chlorin Based‐Photosensitizer in Head and Neck Squamous Cell Carcinoma Cells

Abstract

The aim of this study was to elucidate photodynamic therapy (PDT) effects mediated by hypericin and a liposomal meso-tetrahydroxyphenyl chlorin (mTHPC) derivative, with focus on their 1:1 mixture, on head and neck squamous cell carcinoma cell lines. Absorption, excitation and photobleaching were monitored using fluorescence spectrometry, showing the same spectral patterns for the mixture as measured for single photosensitizers. In the mixture mTHPC showed a prolonged photo-stability. Singlet oxygen yield for light-activated mTHPC was Φ(Δ) = 0.66, for hypericin Φ(Δ) = 0.25 and for the mixture Φ(Δ) = ~0.4. A linear increase of singlet oxygen yield for mTHPC and the mixture was found, whereas hypericin achieved saturation after 35 min. Reactive oxygen species fluorescence was only visible after hypericin and mixture-induced PDT. Cell viability was also more affected with these two treatment options under the selected conditions. Examination of death pathways showed that hypericin-mediated cell death was apoptotic, with mTHPC necrotic and the 1:1 mixture showed features of both. Changes in gene expression after PDT indicated strong up-regulation of selected heat-shock proteins. The application of photosensitizer mixtures with the features of reduced dark toxicity and combined apoptotic and necrotic cell death may be beneficial in clinical PDT. This will be the focus of our future investigations.

Anti- and Pro-apoptotic Bcl2 Proteins Distribution and Metabolic Profile in Human Coronary Aorta Endothelial Cells Before and After HypPDT

“…Thus, our findings are in good agreement with the results in BAECs [40]. The mechanisms underlying Hyp dark toxicity are not well understood [5,41,42], but one possibility may be that Hyp accumulated in mitochondria interacts with members of the Bcl2 family and that in turn results in an increase of apoptotic cells.…”

“…This was an unexpected finding, because Hyp itself has been reported to display low-dark toxicity in many cell lines [4,12]. However, recently evidence emerged that showed similar dark cytotoxicity in malignant cells [5], and there are contradictory results regarding Hyp dark toxicity also in endothelial cells.…”

“…In addition, in most PDT treatments, PS is administered systemically and can result in high light independent exposure of endothelial cells to PS [5]. This may be clinically relevant if PS molecules affect the pro-apoptotic cascade without illumination.…”

“…In most PDT treatments, PS is administered systemically and usually shows a preferential accumulation in malignant cells. Nevertheless, PS uptake into healthy nonmalignant cells remains potentially high especially in the vasculature, resulting in high exposure of ECs to PS [5]. PS accumulation in nonmalignant ECs may be clinically relevant if PS molecules affect the pro-apoptotic cascade without illumination.…”

Photoinduced effects of m-tetrahydroxyphenylchlorin loaded lipid nanoemulsions on multicellular tumor spheroids

“…In a previous study we have shown that this is perfectly feasible and may be advantageous to detect (subtle) differences between effects of treatment regimes [24]. With the aim to preserve some morphology and avoid complete RNA degradation [25, 26] for our microscopic and RNA studies, we furthermore had to reduce the illumination time from 20 to 1 min.…”