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Increased cytotoxic effects of photodynamic therapy in IL‐6 gene transfected cells via enhanced apoptosis
Author(s) -
Usuda Jitsuo,
Okunaka Tetsuya,
Furukawa Kinya,
Tsuchida Takaaki,
Kuroiwa Yukari,
Ohe Yuichiro,
Saijo Nagahiro,
Nishio Kazuto,
Konaka Chimori,
Kato Harubumi
Publication year - 2001
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.1374
Subject(s) - transfection , apoptosis , cytotoxic t cell , microbiology and biotechnology , cytokine , dna fragmentation , biology , tumor necrosis factor alpha , photodynamic therapy , cancer research , cancer cell , mtt assay , gene expression , cell culture , chemistry , programmed cell death , immunology , in vitro , gene , cancer , biochemistry , genetics , organic chemistry
PDT has been reported to induce cancer cell expression of cytokines, such as IL‐6 and TNF‐α, 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‐ L ‐aspartyl chlorin e6 (NPe6) and light from a diode laser and found that expression of the mRNA of IL‐2, IL‐6, and TNF‐α 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‐gene‐transfected cells, namely LLC‐IL‐2, LLC‐IL‐6, and LLC‐TNF‐α cells, by MTT assay. The IL‐6 gene transfected, LLC‐IL‐6 cells were significantly more sensitive to cytotoxic effects than the parent LLC cells and other cytokine gene‐transfected cells. This finding indicates that IL‐6 expression modulates cellular sensitivity to PDT and that IL‐2 and TNF‐α expressions does not. In addition, the apoptosis of LLC‐IL‐6 cells induced by NPe6‐PDT was greater than in the other cells as determined by DNA fragmentation and staining of apoptotic nuclei. Because IL‐6 has been reported to induce apoptosis by downregulating expression of Bcl‐2, we analyzed the expression of apoptosis‐related Bcl‐2, Bax, and cytochrome C by Western blot analysis. Decreased expression of Bcl‐2 and cytochrome C was observed in both LLC cells and LLC‐IL‐6 cells. Bax protein increased in a time‐dependent manner, and the ratio of Bax to Bcl‐2 rose markedly after PDT in LLC‐IL‐6 cells. These results suggest that the increased sensitivity of LLC‐IL‐6 cells to PDT‐induced cytotoxicity results from the high ratio of Bax to Bcl‐2 in the IL‐6‐dependent apoptotic pathway. In conclusion, IL‐6 expression plays a role in cellular sensitivity to PDT, and combination of IL‐6 and PDT may provide a new strategy for cancer treatment. © 2001 Wiley‐Liss, Inc. © 2001 Wiley‐Liss, Inc.