title: 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.
authors: Redox Laboratory and Confocal and Light Microscope Imaging Facility, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.
authors: Britta
authors: B
authors: Kleemann
authors: Department of Physiological Sciences, Stellenbosch University, Stellenbosch, South Africa.
authors: Benjamin
authors: B
authors: Loos
authors: South African TB Vaccine Initiative, Institute of Infectious Disease and Molecular Medicine and School of Child and Adolescent Health, University of Cape Town, Cape Town, South Africa.
authors: Thomas J
authors: TJ
authors: Scriba
authors: Redox Laboratory and Confocal and Light Microscope Imaging Facility, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.
authors: Dirk
authors: D
authors: Lang
authors: Redox Laboratory and Confocal and Light Microscope Imaging Facility, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.
authors: Lester M
authors: LM
authors: Davids
mesh_terms: D000873:Anthracenes; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D048429:Cell Size / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000473:pathology; D005260:Female; D006801:Humans; D020902:Hypericum / Q000737:chemistry; D008545:Melanoma / Q000188:drug therapy* / Q000473:pathology; D008875:Middle Aged; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000378:metabolism / Q000494:pharmacology*; D010858:Pigmentation / Q000187:drug effects; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000473:pathology; D015533:Transcriptional Activation
chemical_list: D000873:Anthracenes; D051017:Apoptosis Regulatory Proteins; D017319:Photosensitizing Agents; D010569:Perylene; C004965:hypericin