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Cancer Lett. 2004 Apr 30;207(2):175-81.

Photoactivation of hypericin down-regulates glutathione S-transferase activity in nasopharyngeal cancer cells.

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  • 1Department of Anatomy, Faculty of Medicine, National University of Singapore, 4 Medical Drive, MD 10, Singapore, Singapore S117 597.


Photodynamic therapy (PDT) is a new modality of treatment for cancer. Hypericin is a photosensitizer, which is known to generate reactive oxygen species upon activation with light. We observed that photoactivated hypericin induces the generation of reactive oxygen intermediates in nasopharyngeal cancer (NPC) cells in vitro. There was also significant reduction of Glutathione S-transferase (GST) activity in HK1 and CNE-2 NPC cells and in tumor tissues from the NPC/HK1 murine tumor model by hypericin-mediated PDT. As antioxidants protect cells against phototoxicity, down-regulation of GST activity would potentiate the efficacy of hypericin-PDT treatment.

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