Photodynamic Therapy for Experimental Tumors Using ATX‐S10(Na), a Hydrophilic Chlorin Photosensitizer, and Diode Laser

ATX‐S10(Na), a hydrophilic chlorin photosensitizer having an absorption maximum at 670 nm, is a candidate second‐generation photosensitizer for use in photodynamic therapy (PDT) for cancer treatment. The effectiveness of PDT using ATX‐S10(Na) and a diode laser for experimental tumors was evaluated in vitro and in vivo. In‐vitro PDT using ATX‐S10(Na) and the diode laser showed drug concentration‐, laser dose‐ and drug exposure time‐dependent cytotoxicity to various human and mouse tumor cell lines. In Meth‐A sarcoma‐implanted mice, optimal PDT conditions were found where tumors were completely eliminated without any toxicity. Against human tumor xenografts in nude mice, the combined use of 5 mg/kg ATX‐S10(Na) and 200 J/cm2 laser irradiation 3 h after ATX‐S10(Na) administration showed excellent anti‐tumor activity, and its efficacy was almost the same as that of PDT using 20 mg/kg porfimer sodium and a 100 J/cm2 excimer dye laser 48 h after porfimer sodium injection. Microscopic observation of tumor tissues revealed that PDT using ATX‐S10(Na) and the diode laser induced congestion, thrombus and degeneration of endothelial cells in tumor vessels, indicating that a vascular shutdown effect plays an important role in the anti‐tumor activity of PDT using ATX‐S10(Na) and the diode laser.