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Cell Biology International (2009) 33, 1065–1072 (Printed in Great Britain)

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Melanomas display increased cytoprotection to hypericin-mediated cytotoxicity through the induction of autophagy

Lester M. Davids^*, Britta Kleemann, Susan Cooper and Susan H. Kidson

Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, 7925 Cape Town, South Africa

Abstract

Photodynamic therapy (PDT) as a regime for melanoma is of limited success due to factors such as the efficacy of the photosensitizer used, penetration depth and the presence of pigment. We characterised a pigmented and an unpigmented melanoma cell line with respect to their phenotypes. Cell viability was assessed after exposure to hypericin, a UVA-activated photosensitizer. Exposure to 3μM activated hypericin induced a cytoprotective (autophagic) response from both cell lines. However, the pigmented cells accumulated a large amount of glycogen in their cytoplasm. We hypothesise that the treatment induces an initial cytoprotective response through autophagy, but with increased stress results in a different mode of cell death in pigmented melanoma cells from unpigmented cells. These results indicate that hypericin-PDT could be an adjuvant therapy for melanoma.

Key words: Hypericin, Photodynamic therapy, Melanoma, Autophagy, Apoptosis.

^*Corresponding author. Tel.: +27 21 406 6787; fax: +27 21 448 7226.

Received 5 December 2008/22 May 2009; accepted 27 June 2009