Abstract: Li Jingjing, Lyu Ting, Wang Hongwei, Wang Peiru, Wang Xiuli *. *Shanghai Skin Disease Hospital, Shanghai 200050, China Corresponding author: Wang Xiuli, Email: xlwang2001@aliyun.com 【Abstract】 Objective To investigate the mechanisms underlying the effect of 5-aminolevulinic acid photodynamic therapy （ALA-PDT） on cutaneous squamous cell carcinoma（SCC） in mice. Methods A model of cutaneous SCC was established in 21 SKH-1 hairless mice, which were treated with topical ALA 8% cream followed by single irradiation with He-Ne laser at a total dose of 30 J/cm2 （ALA-PDT）. Three mice were sacrificed before and at 1, 3, 6, 12, 24 hours and 7 days after the irradiation, separately, and SCC tissue was taken from the mice. Transmission electron microscopy （TEM） and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling （TUNEL） were performed to determine the pattern of tumor cell death（necrosis, apoptosis and autophagy） during 1 － 24 hours after ALA-PDT, and immunohistochemical techniques were used to estimate the expressions of LC3B and CD34 on SCC cells, as well as the quantity of CD1a+ cells, CD4+ T and CD8+ T lymphocytes in SCC tissue 7 days after the irradiation. Statistical analysis was done by two-sample t test using SPSS 17.0 software. Results TEM showed gradual necrosis and apoptosis （especially necrosis） of tumor cells and formation of autophagosomes in macrophages within 24 hours after ALA-PDT. The number of apoptotic cells per high power field （× 400） in SCC tissue significantly increased at 24 hours compared with that before ALA-PDT （7.30 ± 2.18 vs. 2.00 ± 0.69, P < 0.05）. As immunohistochemistry revealed, there was a significant decrease in the number of CD34+ cells （1.33 ± 0.58 vs. 19.00 ± 2.66, P < 0.01）, but a marked increase in that of CD1a+ cells （23.01 ± 2.04 vs. 10.33 ± 1.88, P < 0.05）, CD4+ T cells（28.67 ± 1.76 vs. 12.40 ± 2.27, P < 0.05）, CD8+ T cells （25.79 ± 2.37 vs. 11.67 ± 1.45, P < 0.05） and LC3B+ interstitial cells （30.6 ± 3.21 vs. 21.44 ± 4.3, P < 0.05） per high power field （× 400） in SCC tissue on day 7 compared with that before ALA-PDT. Conclusions ALA-PDT may directly kill SCC cells by inducing cell necrosis and apoptosis rather than autophagy. Additionally, ALA-PDT can injure microvascular endothelial cells and cause the aggregation of dendritic cells, CD4+ T cells and CD8+ T cells in SCC tissue.

Key words: Carcinoma, squamous cell, Phototherapy, Cell death, Microvascular injury, Immunological effects