Efficient preparation of highly pure chlorin e(6) and its photodynamic anti-cancer activity in a rat tumor model

Abstract

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 e(6) (Ce-6) with high yield and purity, and to test antitumor activity of Ce-6-induced PDT (Ce-6-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 Ce-6 (10 mg/kg) and 24 h later, PDT was performed using a laser diode at a light dose of 100 J/cm(2). Ce-6- PDT generated reactive oxygen species and led to significant growth inhibition in RK3E-ras cell. In addition, Ce-6-PDT induced apoptosis through the activation of caspase-3 and its downstream target, PARP cleavage. The protein level of antiapoptotic bcl-2 was also reduced by Ce-6-PDT in RK3E-ras cells. In in vivo experiments, application of Ce-6-PDT led to a significant reduction of tumor size. PCNA immunostaining and TUNEL assay revealed that Ce-6-PDT inhibited tumor cell proliferation and increased apoptosis. These findings suggest that the newly purified Ce-6-PDT can effectively arrest tumor growth by inhibiting cell proliferation and inducing apoptosis.