Increased cytotoxic effects of photodynamic therapy in IL-6 gene transfected cells via enhanced apoptosis.
PDT has been reported to induce cancer cell expression of cytokines, such as IL-6 and TNF-alpha, 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-alpha 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-alpha 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-alpha 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.
Usuda
J
J
Department of Surgery and Intractable Disease Research Center, Tokyo Medical University, Nishishinjuku, Tokyo, Japan. jusuda@xc4.s0-net.ne.jp
Okunaka
T
T
Furukawa
K
K
Tsuchida
T
T
Kuroiwa
Y
Y
Ohe
Y
Y
Saijo
N
N
Nishio
K
K
Konaka
C
C
Kato
H
H
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics / Q000276:immunology; D018827:Carcinoma, Lewis Lung / Q000235:genetics / Q000276:immunology / Q000473:pathology* / Q000628:therapy; D015870:Gene Expression / Q000187:drug effects; D015316:Genetic Therapy; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology; D008175:Lung Neoplasms / Q000235:genetics / Q000276:immunology / Q000473:pathology* / Q000628:therapy; D051379:Mice; D008810:Mice, Inbred C57BL; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D011166:Porphyrins / Q000493:pharmacokinetics / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
C494827:Bax protein, mouse; D015850:Interleukin-6; D017319:Photosensitizing Agents; D011166:Porphyrins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; C053434:Talaporfin