Enhanced cell death in NR-S1 tumor by photodynamic therapy: Possible involvement of Fas and Fas ligand system

Back ground and Objectives: To investigate the effect of photodynamic thera py (PDT) on cell death in malignant tumor tissue, the frequency of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-posit ive cells and the possible involvement of Fas and Fas ligand system were ev aluated. Study Design/Materials and Methods: NR-S1 tumor-bearing C3H/HeNCrj mice wer e treated by PDT with Photofrin(R) (12 mg/kg body weight) and Nd:YAG dye la ser (630 nm, 10 Hz, 150 J/cm(2)). Paraffin-embedded tissue sections from th e excised tumor tissues at 6, 12, 24, 48 hours after PDT were analyzed by T UNEL for the occurrence of apoptosis and by immunohistochemistry for Fas an d Fas ligand (Fast) expression. TUNEL-positive cells as well as Fas- or Fas t-positive cells were counted and expressed as a percentage of positive cel ls per total cells. Results: Based on the percent area of tumor necrotic foci, the most effecti ve conditions for PDT were first determined. Under these conditions, PDT in creased the number of TUNEL-positive tumor cells at 12 hours after irradiat ion. In parallel with the increase in TUNEL-positive cells, Fas-positive tu mor cells were also found in the same area where many TUNEL-positive tumor cells were found. The expression of Fas ligand was found in the tumor cells surrounding TUNEL-positive cells on serial sections. A significant increas e in Fast-positive lymphocytes was observed at 12 hours, whereas the infilt ration of such lymphocytes into the area where TUNEL-positive tumor cells w ere observed was rare. Conclusion: The possible role of Fas/FasL system in the cell death induced by PDT with Photofrin(R) and Nd:YAG dye laser was suggested. Moreover, the role of infiltrated lymphocytes seemed not to be so much in this model. (C) 2000 Wiley-Liss, Inc.