Photodynamic therapy and the role of heat shock protein 70

Photodynamic therapy (PDT) is an effective treatment for superficial epithelial skin cancers and is also being utilised for skin rejuvenation. PDT with porphyrin-derived photosensitisers may be capable of inducing rapid cytochrome c release initiating apoptotic cascade via an activation of different caspases. Hsp70 has been demonstrated to directly bind to the caspase recruitment domain (CARD) of apoptotic-protease activating factor 1 (Apaf-1), thereby preventing the recruitment of oligomerisation of Apaf-1 and association of Apaf-1 with procaspase 9. Further, cytoplasmic Hsp70 rapidly translocates to the cell surface where it stabilises damaged membranes and preserves their integrity depending on the PDT dose. The induced cell surface expression and release of Hsp70 and its relevance for tumor response or skin rejuvenation is not fully understood, but seems to be of interest for monitoring, predicting or optimising treatment regimens. This review aims to summarise the current knowledge on PDT mediated cell signalling.