Shin Vivian Y, Wu William K K, Ye Yi-Ni, So Wallace H L, Koo Marcel W L, Liu Edgar S L, Luo Jiing-Chyuan, Cho Chi-Hin
Department of Pharmacology, Faculty of Medicine, The University of Hong Kong, Hong Kong, HKSAR, China.
Carcinogenesis. 2004 Dec;25(12):2487-95. doi: 10.1093/carcin/bgh266. Epub 2004 Aug 19.
Early studies revealed that cigarette smoke promotes gastric cancer growth through the induction of cyclooxygenase-2 (COX-2). Nicotine, one of the active ingredients in cigarette smoke, has detrimental effects in the stomach. To date, there is no direct evidence to validate the effect of nicotine on gastric tumor growth and its carcinogenic mechanism(s). We therefore investigated whether nicotine could promote tumor growth and neovascularization in vivo, and the biological mechanism(s) in connection with the signaling cascade involving COX-2 and extracellular signal-regulated protein kinase (ERK). Athymic nude mice, with gastric cancer cells (AGS) orthotopically implanted into the gastric wall, treated with nicotine (50 or 200 microg/ml) in their drinking water for 3 months developed larger tumor areas than mice in the control group. Nicotine further increased proliferating cellular nuclear antigen (PCNA) staining and microvessel density by 70 and 30%, respectively, with concomitant activation of ERK phosphorylation, COX-2 and vascular endothelial growth factor (VEGF) expression in the tumors. Intraperitoneal administration of a selective COX-2 inhibitor (SC-236, 2 mg/kg) prevented the nicotine-induced tumor growth and neovascularization dose-dependently. Consistent with our animal model, an in vitro study also demonstrated that incubation with nicotine (50-200 microg/ml) for 5 h stimulated cell proliferation dose-dependently and increased COX-2 expression, prostaglandin E(2) (PGE(2)) and VEGF release, as well as activation of ERK phosphorylation. Pre-treatment with specific mitogen-activated protein kinase kinase (MEK) inhibitors (U0126 or PD98059) attenuated COX-2 expression and subsequent PGE(2) release by nicotine. Furthermore, the stimulatory action of nicotine on cancer cell growth and angiogenic factor VEGF production was suppressed by inhibitors of MEK (U0126) and COX-2 (SC-236). These findings reveal a direct promoting action of nicotine on the growth of gastric tumor and neovascularization through sequential activation of the ERK/COX-2/VEGF signaling pathway, which can be targeted for chemoprevention of gastric cancer, particularly in cigarette smokers.
早期研究表明，香烟烟雾通过诱导环氧化酶-2（COX-2）促进胃癌生长。尼古丁是香烟烟雾中的活性成分之一，对胃部有有害影响。迄今为止，尚无直接证据证实尼古丁对胃肿瘤生长的影响及其致癌机制。因此，我们研究了尼古丁是否能在体内促进肿瘤生长和新血管形成，以及与涉及COX-2和细胞外信号调节蛋白激酶（ERK）的信号级联相关的生物学机制。将胃癌细胞（AGS）原位植入胃壁的无胸腺裸鼠，饮用含尼古丁（50或200微克/毫升）的水3个月后，其肿瘤面积比对照组小鼠更大。尼古丁使增殖细胞核抗原（PCNA）染色和微血管密度分别进一步增加70%和30%，同时肿瘤中ERK磷酸化、COX-2和血管内皮生长因子（VEGF）表达激活。腹腔注射选择性COX-2抑制剂（SC-236，2毫克/千克）可剂量依赖性地阻止尼古丁诱导的肿瘤生长和新血管形成。与我们的动物模型一致，一项体外研究也表明，用尼古丁（50 - 200微克/毫升）孵育5小时可剂量依赖性地刺激细胞增殖，并增加COX-2表达、前列腺素E2（PGE2）和VEGF释放，以及ERK磷酸化激活。用特异性丝裂原活化蛋白激酶激酶（MEK）抑制剂（U0126或PD98059）预处理可减弱尼古丁诱导的COX-2表达及随后的PGE2释放。此外，MEK抑制剂（U0126）和COX-2抑制剂（SC-236）可抑制尼古丁对癌细胞生长和血管生成因子VEGF产生的刺激作用。这些发现揭示了尼古丁通过依次激活ERK/COX-2/VEGF信号通路对胃肿瘤生长和新血管形成具有直接促进作用，这可为胃癌的化学预防提供靶点，尤其是在吸烟者中。
