Photodynamic Therapy of a Murine Tumor Following Sensitisation With Chloro Aluminum Sulfonated Phthalocyanine

Syngeneic mice bearing a colorectal carcinoma (Colo 26) growing subcutaneously in the flank region received photodynamic therapy (PDT) when the tumor was 7‐12 mm diameter. Light (emission at 675 nm from an argon ion pumped dye laser, laser energy 100 J, power 50 mW) was delivered to the tumor 24‐28 h after the i.v. injection of a single dose of chloro aluminum sulfonated phthalocyanine (ClAlSPc) at 5 mg kg 1 body weight. Control tumor‐bearing animals received (1) phosphate buffered saline (PBS) but not PDT, (2) ClAlSPc but not PDT, or (3) PBS injection plus PDT. Five days later PDT tumors of the ClAlSPc + PDT group were markedly reduced in size (mean weight 0.075 ± 0.027 g) as compared with those from control groups 1 (0.408 ± 0.167 g), 2 (0.475 ± 0.143 g) or 3 (0.376 ± 0.153 g). Histological examination revealed that ClAlSPc + PDT induced severe necrosis and cytotoxicity of neoplastic cells with viable tumor limited to a small peripheral margin. Animals in the ClAlSPc + PDT group in a repeat experiment survived significantly longer than animals in the three control groups suggesting that ClAlSPc may be a useful photosensitiser for PDT of cancer.