INDUCTION OF APOPTOTIC CELL-DEATH BY PHOTODYNAMIC THERAPY IN HUMAN KERATINOCYTES

The use of photodynamic therapy (PDT) for the treatment of skin and or al cancer has been the subject of several clinical studies but there h as been little scientific evaluation of its mechanism of action. Evide nce to date suggests that whilst epithelial cell death may be secondar y to vascular damage, direct cell killing may occur and may involve an apoptosis-like mechanism. To investigate the mechanism of epithelial cell death following PDT, two cell lines, human epidermal keratinocyte s (UP) and oral squamous cell carcinoma-derived cells (H376) were subj ected to PDT with aluminium disulphonated phthalocyanine (AlS2Pc) as t he photosensitizer and red laser light at 675 nm. Control groups recei ved red laser light, photosensitizer or neither. The effects of PDT we re assessed using an MTS cell-proliferation assay, which showed a sign ificant reduction in viability (p < 0.01) for PDT-treated cells compar ed to controls. For morphological analysis, cells were stained with ha emotoxylin and eosin and the numbers showing typical apoptotic feature s counted. The treated cultures showed significantly increased numbers of apoptotic cells. Moreover, the H376 control cultures showed a base line level of apoptosis of approx. 15%. Apoptosis was confirmed by ult rastructural analysis and by in situ end-labelling of DNA fragments. T he results show that PDT using AlS2Pc as a photosensitizer promotes ap optotic cell death in UP and H376 cells in vitro and suggest that dire ct killing of epithelial cells may contribute to tumour necrosis in vi va. (C) 1998 Elsevier Science Ltd. All rights reserved.