Effect of photodynamic therapy (PDT) on the expression of pro‐apoptotic protein bak in nasopharyngeal carcinoma (NPC)

Background and Objective To investigate the effect of photodynamic therapy (PDT) on expression of the pro-apoptotic gene Bak in nasopharyngeal carcinoma (NPC). Study Design/Materials and Methods Apoptosis and expression of the pro-apoptotic gene Bak on the tumor tissues from both pre- and post-PDT were determined using the in situ end labeling (ISEL), standard immunohistochemistry technique and western blot, respectively, in 24 patients with either persistent or recurrent NPC after radiotherapy. Results Before PDT, apoptotic index (AI) in tumor tissue was 1.2 ± 0.6. At 6, 12, 24 and 48 hours after PDT, AI were 6.5 ± 3.1, 23.6 ± 8.3, 67.2 ± 14.2 and 89.3 ± 8.1, respectively. PDT caused apoptosis in a time-dependent fashion. Immunohistochemical assay indicated that 75% (18/24) of the patients had an upgrade expression of Bak protein in their tumor tissues after PDT. Increases in expression of Bak from PDT were also confirmed by western blot analysis. Conclusions PDT probably causes NPC cell apoptosis through an upregulation of the pro-apoptotic protein Bak expression. Lasers Surg. Med. 29:27–32, 2001. © 2001 Wiley-Liss, Inc.