Combination of Chemotherapy and Photodynamic Therapy of Human Gastrointestinal Tumor Xenografts in Nude Mice

Gastrointestinal tumours have a poor prognosis. Therefore, new treatment modalities, compe-rativly efficient but less aggressive must be found to treat superficial cancers of the gastrointestinal tract. Photodynamic therapy (PDT), which presently is under investigation in experimental and clinical practice, might well give new answers and solutions to this problem. PDT is based on the principle of phototoxicity [1], induced by the intravenous injection of a non-toxic dye which after some time is retained in a higher concentration in the tumour than in the surrounding normal tissue. Irradiation with light, which is harmless in the absence of the dye, leads to the activation of the photosensitizer and is followed by the local destruction of the tumour. Two main mechanisms are involved in this destruction [2]: PDT kills malignant cells by impairing mitochondrial functions and altering cytoplasmatic or mitchondrial membranes. On the other hand PDT destroys the tissue blood circulation, probably by disruption of the endothelium of the tumour capillaries.