EFFECTS OF PHOTODYNAMIC THERAPY ON LEUKOCYTE-ENDOTHELIUM INTERACTION - DIFFERENCES BETWEEN NORMAL AND TUMOR-TISSUE

An inflammatory reaction is regularly noticed in irradiated tissues fo llowing photodynamic therapy (PDT). This observation is potentially as sociated with leucocyte-mediated tissue damage, which might further co ntribute to the tumoricidal effect of this therapy. The objective of o ur study was to investigate the effects of PDT on leucocyte-endotheliu m interaction in the microvasculature of tumours and normal tissue. Ex periments were performed in the dorsal skinfold chamber preparation of Syrian golden hamsters bearing amelanotic melanoma A-Mel-3. The photo sensitiser Photofrin (5 mg kg(-1) i.v.) was injected 24 h before laser irradiation (630 nm, 100 mW cm(-2), 10 J cm(-2) or 100 J cm(-2)). Pos t-capillary confluent venules (diameter 15-40 mu m) of subcutaneous (s .c.) tissue or the amelanotic melanoma A-Mel-3 were observed by intrav ital microscopy before, 5, 30, 60 and 180 min after laser irradiation and recorded for off-line analysis. Before treatment, the number of ad herent leucocytes in tumour vessels was only 22% of the number observe d in vessels of s.c. tissue (P < 0.01). The maximum increase in adheri ng leucocytes was observed in post-capillary venules of s.c. tissue 1 h after PDT (P < 0.01). In contrast, enhanced leucocyte-endothelium in teraction was missing in tumour vessels and in control groups. These r esults indicate that the tumour destruction observed after PDT is not mediated by leucocyte-endothelium interaction in the tumour. Induction of leucocyte adhesion in the PDT-treated normal tissue suggests a con tribution to the peritumoral inflammatory response. Different maturati onal status or biochemical properties of tumour microvascular endothel ium may explain the lack of leucocyte adherence upon PDT.