Efficient preparation of highly pure chlorin e6 and its photodynamic anti-cancer activity in a rat tumor model.

Photodynamic therapy (PDT) is currently being used as an alternative therapeutic modality for a variety of malignant tumors. This study was performed to show an efficient preparation of second generation of photosensitizer chlorin e6 (Ce6) with high yield and purity, and to test antitumor activity of Ce6-induced PDT (Ce6-PDT) both in vitro and in vivo using a rat tumor model. Three-week-old male Sprague-Dawley (SD) rats were inoculated s.c. on the right flank with 5x10(6) RK3E-ras cells. The animals were administered i.v. with Ce6 (10 mg/kg) and 24 h later, PDT was performed using a laser diode at a light dose of 100 J/cm2. Ce6-PDT generated reactive oxygen species and led to significant growth inhibition in RK3E-ras cell. In addition, Ce6-PDT induced apoptosis through the activation of caspase-3 and its downstream target, PARP cleavage. The protein level of anti-apoptotic bcl-2 was also reduced by Ce6-PDT in RK3E-ras cells. In in vivo experiments, application of Ce6-PDT led to a significant reduction of tumor size. PCNA immunostaining and TUNEL assay revealed that Ce6-PDT inhibited tumor cell proliferation and increased apoptosis. These findings suggest that the newly purified Ce6-PDT can effectively arrest tumor growth by inhibiting cell proliferation and inducing apoptosis.