SEP enhanced the antitumor activity of 5-fluorouracil by up-regulating NKG2D/MICA and reversed immune suppression via inhibiting ROS and caspase-3 in mice

// Mengyun Ke 1, 3, * , Hui Wang 1, * , Yiran Zhou 2, * , Jingwen Li 1 , Yang Liu 1 , Min Zhang 1 , Jie Dou 1 , Tao Xi 1 , Baiyong Shen 2 , Changlin Zhou 1 1 State Key Laboratory of Natural Medicines, School of Life Science and Technology, China Pharmaceutical University, Nanjing, Jiangsu, 210009, PR China 2 Department of General Surgery, Rui Jin Hospital, Research Institute of Pancreatic Diseases, School of Medicine, Shanghai JiaoTong University, Shanghai, 200025, PR China 3 Research Institute of Advanced Surgical Techniques and Engineering of Xi’an Jiaotong University, Regenerative Medicine and Surgery Engineering Research Center of Shaanxi Province, First Affiliated Hospital, Xi’an Jiaotong University, Shaanxi, Xi’an, 710061, PR China * These authors contributed equally to this work Correspondence to: Baiyong Shen, email: shenby@shsmu.edu.cn Changlin Zhou, email: cl_zhou@cpu.edu.cn Keywords: SEP, 5-fluorouracil, antitumor activity, immunotherapy, apoptosis Received: October 07, 2015      Accepted: June 16, 2016      Published: July 01, 2016 ABSTRACT Chemotherapy and immunotherapy are the main remedies used in cancer treatment. Because immunotherapy can not only reduce the toxicity of chemotherapeutics but also enhance antitumor effects in vivo , combining these two therapies is a trend that continues to gain more attention in clinic. SEP, a polysaccharide isolated from Strongylocentrotus nudus egg, has been reported to display antitumor activity by stimulating immune cells, including NK and T cells, via TLR2 and TLR4. In the present study, the synergistic effect between SEP and 5-fluorouracil (5-FU), a traditional cytotoxic drug, in vitro and in vivo was investigated. The results obtained indicated that SEP alone stimulated NK-92 cytotoxicity and coordinated with 5-FU to augment the cytotoxicity of NK-92 cells against HepG-2 or A549 cells in vitro . SEP promoted NK-92 activity by stimulating NKG2D and its downstream DAP10/PI3K/Erk signaling pathway. Additionally, 5-FU could increase MICA expression on HepG-2 or A549 cells and prevent membrane MICA from shedding as soluble MICA, which were abrogated in the tumor cells transfected with ADAM 10 overexpression plasmid. Moreover, in H22- or Lewis lung cancer (LLC)-bearing mouse models, SEP reversed 5-FU-induced atrophy and apoptosis in both the spleen and bone marrow in vivo by suppressing ROS generation and caspase-3 activation. All of these results highlight the potential for the combination of SEP and 5-FU in cancer therapy in the future.