PDT has been reported to induce cancer cell expression of cytokines, such as IL-6 and TNF-␣, but it has been unclear whether cytokine expression by cancer cells is directly related to the antitumor effect of PDT. We treated Lewis lung carcinoma (LLC) cells with a new photosensitizer, mono-Laspartyl chlorin e6 (NPe6) and light from a diode laser and found that expression of the mRNA of IL-2, IL-6, and TNF-␣ was increased by NPe6-mediated-PDT 6 hr later. To elucidate the mechanism of the direct anti-tumor effect of cytokine expression, we examined the photosensitivity of cytokine- To enhance the potential of PDT and to extend its clinical applications, a second generation of photosensitizers is now being assessed, and it is important to elucidate their mechanism of action in PDT. Mono-L-aspartyl chlorin e6 (NPe6) is a water-soluble substance, and NPe6-mediated-PDT has been shown to have an antitumor effect in several experimental models and is currently undergoing clinical evaluation in Japan.Granville et al. 3 reported that PDT induces apoptosis in various tumor cell lines. PDT also induces nonspecific and specific immune responses against tumors in vitro and in vivo. Krosl et al. 4 reported that the antitumor efficacy of PDT is improved by the administration of macrophage activating factors such as granulocyte-macrophage colony activating factor (GM-CSF), whereas Gollnick et al. 5 demonstrated that PDT alters expression of IL-6 and IL-10 in vivo. The immune mechanisms of PDT have never been clarified, however, and it is unknown whether cytokine expression is involved in the antitumor effects of PDT. To elucidate the immune response and the mechanisms of action involved in NPe6-mediated PDT, we examined the effects of cytokine overexpression on PDT by using cytokine gene transfected cells and we have characterized the apoptotic mechanism.
MATERIAL AND METHODS
Laser light delivery systemA new high-power red laser diode system (Matsushita Industrial Equipment Co., Osaka, Japan), with potential for use in photodynamic therapy (PDT) with NPe6, was employed. This system has a power output of 10 -500 mW/cm 2 at the fiber tip. The irradiation mode is continuous wave (CW), and the delivered energy can be adjusted from 1-1,000 J/cm.2 . 2 Although it runs on 100 V current, the system is 49 ϫ 20 ϫ 40 cm in size, weighs 20 kg, and is easy to take into a sickroom. The power of the laser is easily adjusted, the wavelength of the light is stable (within 0.2 nm), and it is delivered through a quartz fiber. The full width at half maximum is less than 2 nm, which enables uniform, high-density photoradiation, and the power density distribution of the laser, analyzed by a charge-coupled device (CCD) camera, is uniform throughout the photoradiated field. In our study, the diode laser wavelength was adjusted to 664 nm to match the absorption bands of NPe6.
PHOTOSENSITIZERCompound NPe6 is an effective photosensitizer that possesses properties such as chemical purity and a major absorption band at 664 nm, features that are potentiall...
