St John's Wort (Hypericum perforatum L.) Photomedicine: Hypericin-Photodynamic Therapy Induces Metastatic Melanoma Cell Death

Abstract

Hypericin, an extract from St John's Wort (Hypericum perforatum L.), is a promising photosensitizer in the context of clinical photodynamic therapy due to its excellent photosensitizing properties and tumoritropic characteristics. Hypericin-PDT induced cytotoxicity elicits tumor cell death by various mechanisms including apoptosis, necrosis and autophagy-related cell death. However, limited reports on the efficacy of this photomedicine for the treatment of melanoma have been published. Melanoma is a highly aggressive tumor due to its metastasizing potential and resistance to conventional cancer therapies. The aim of this study was to investigate the response mechanisms of melanoma cells to hypericin-PDT in an in vitro tissue culture model. Hypericin was taken up by all melanoma cells and partially co-localized to the endoplasmic reticulum, mitochondria, lysosomes and melanosomes, but not the nucleus. Light activation of hypericin induced a rapid, extensive modification of the tubular mitochondrial network into a beaded appearance, loss of structural details of the endoplasmic reticulum and concomitant loss of hypericin co-localization. Surprisingly the opposite was found for lysosomal-related organelles, suggesting that the melanoma cells may be using these intracellular organelles for hypericin-PDT resistance. In line with this speculation we found an increase in cellular granularity, suggesting an increase in pigmentation levels in response to hypericin-PDT. Pigmentation in melanoma is related to a melanocyte-specific organelle, the melanosome, which has recently been implicated in drug trapping, chemotherapy and hypericin-PDT resistance. However, hypericin-PDT was effective in killing both unpigmented (A375 and 501mel) and pigmented (UCT Mel-1) melanoma cells by specific mechanisms involving the externalization of phosphatidylserines, cell shrinkage and loss of cell membrane integrity. In addition, this treatment resulted in extrinsic (A375) and intrinsic (UCT Mel-1) caspase-dependent apoptotic modes of cell death, as well as a caspase-independent apoptotic mode that did not involve apoptosis-inducing factor (501 mel). Further research is needed to shed more light on these mechanisms.

Differential susceptibility of primary cultured human skin cells to hypericin PDT in an in vitro model

“…Previously, we have shown that 3 lM activated HYP used during HYP-PDT induces cytotoxic effects in human melanoma cancer cells [17,18]. Therefore, a 4 h incubation time for HYP implemented in this study, was adjusted to correlate with optimal accumulation times of HYP in melanoma cells.…”

“…Therefore, in the case of Mc, we postulate that both functions may be at play. Initially the melanin could function as an antioxidant and reduce the ROS by directing/sinking the HYP in melanosomes, as we have previously shown that HYP localizes to melanosomal membranes [17]. However, with increased oxidative stress an overwhelming oxidative burden may affect the integrity of the melanosomes and hence causes leakage of the toxic melanin intermediates, thereby leading to cell death.…”

“…Currently, porfimer sodium (Photofrin Ò ), 5-aminolevulinic acid (5-ALA) (Levulan Ò ) and its methyl ester (MAL) (Metvix Ò ), Visudyne Ò and Foscan Ò are the most commonly used FDA-approved photosensitizers (PS) however, other promising types of PS include chlorins, phthalocyanines and naphthodianthrones [4,[10][11][12]. We have recently reported on the increased efficacy of the napthodianthrone compound, hypericin, in killing both non-melanoma and melanoma cells in vitro [13][14][15][16][17][18]. Due to its hydrophobic nature, hypericin passively enters all cells via their cell membranes and therefore, in addition to it being a potentially effective photosensitizer of tumor tissue, peri-tumoral cells are also prone to photodamage [19,20].…”

Investigating the effect of poly-l-lactic acid nanoparticles carrying hypericin on the flow-biased diffusive motion of HeLa cell organelles

“…Hypericin, a constituent from Hypericum perforatum L., is a potent photosensitizer for clinical PDT due to its excellent photosensitizing properties, high‐quantum yield of fluorescence and singlet oxygen generation upon photoexcitation, good photostability and a relatively low dark toxicity . Cytotoxicity induced by photoexcited hypericin elicits tumour cell death by various mechanisms including apoptosis, necrosis and autophagy‐related cell death . Hypericin‐based PDT destroys the cancer cells with significantly less side‐effects compared to the current treatments like radiation and chemotherapy.…”

“…[3,4] Cytotoxicity induced by photoexcited hypericin elicits tumour cell death by various mechanisms including apoptosis, necrosis and autophagy-related cell death. [2,5] Hypericin-based PDT destroys the cancer cells with significantly less side-effects compared to the current treatments like radiation and chemotherapy. However, systemic administration and bioavailability of this photosensitizer are limited by its hydrophobic nature.…”