Microenvironment and Arsenic Lung Tumorigenesis

摘要 长期接触环境中的砷会导致皮肤癌、膀胱癌、肝癌和肺癌。然而， 砷肺癌的发病机制尚不清楚。来自动物模型和研究的证据 癌症患者表示，免疫系统监控宿主识别和反应 新出现的转化/肿瘤细胞以阻止/控制肿瘤的形成。免疫者之间的遭遇 系统和转化/肿瘤细胞启动一种称为“免疫编辑”的过程，该过程可以带来大约三个 结果：转化/肿瘤细胞从免疫控制中消除、平衡或逃脱。宿主免疫力 抑制肿瘤发展，而肿瘤的形成意味着转化/肿瘤的成功逃脱 来自免疫系统监控的细胞。效应性T细胞，特别是细胞毒性T(TC)细胞 是细胞介导的抗肿瘤免疫的主要组成部分。调节T细胞抗肿瘤的机制之一 效应器功能涉及T细胞膜上的激活/抑制受体。T细胞抗肿瘤的抑制作用 通过激活免疫检查点通路(例如PD-1/PD-L1通路)的功能已被证明 促进肿瘤细胞免疫逃逸和肿瘤形成。此外，之前的报告表明，异常 STAT3在许多人类肿瘤中被激活，STAT3介导的PD-L1上调阻碍T细胞 具有抗肿瘤作用。我们先前的体外研究表明，IL-6/STAT3轴在砷中毒中起着关键作用。 诱导人支气管上皮细胞转化。使用肺肿瘤小鼠模型，我们新的 初步数据显示，长期接触砷会增加肺癌的发病率和多发性 A/J小鼠。此外，砷暴露剂量依赖地激活STAT3，增加了STAT3与 PD-L1基因启动子与小鼠肺中PD-L1的上调。流式细胞仪数据进一步表明 注射砷可使肺组织中PD-1+T细胞数量增加，CD8+/CD4+T细胞比例降低 PD-1或PD-L1抗体可逆转CD8+/CD4+比值的下降。由于PD-1/PD-L1上调可能 抑制T细胞抗肿瘤功能，促进转化细胞逃避宿主免疫监视和 最终导致肿瘤形成，我们假设砷通过 STAT3/PD-1/PD-L1介导的T细胞抗肿瘤功能抑制提出了三个具体目标： 目的1：探讨慢性砷暴露是否抑制T细胞的抗肿瘤功能及细胞类型。 砷可上调A/J小鼠肺组织中PD-1或PD-L1的表达。 目的2：确定抑制PD-1/PD-L1通路是否能改善砷诱导的T细胞功能障碍 并在A/J小鼠肺部形成肿瘤。 目的3：确定信号转导通路3的激活是否是砷增强PD-L1上调的机制。 调节、T细胞功能障碍与A/J小鼠肺部肿瘤的形成。

Abstract Chronic exposure of environmental arsenic promotes skin, bladder, liver and lung cancers. However, the mechanism underlying arsenic lung carcinogenesis is unclear. Evidence from animal models and studies in cancer patients indicate that the immune system monitors the host body recognizing and reacting against newly arising transformed/tumor cells to stop/control tumor formation. The encounter between the immune system and transformed/tumor cells initiates a process termed “immunoediting” that can bring about three outcomes: elimination, equilibrium or escape of transformed/tumor cells from immune control. Host immunity suppresses tumor development, whereas tumor formation implies the successful escape of transformed/tumor cells from the surveillance of the immune system. Effector T cells, particularly cytotoxic T (Tc) cells, represent a major component of cell-mediated anti-tumor immunity. One of the mechanisms modulating T cell antitumor effector function involves the activation/inhibition receptors on a T cell membrane. Inhibition of T cell antitumor function through the activation of immune checkpoint pathways (e.g. PD-1/PD-L1 pathway) has been shown to promote tumor cell immune escape and tumor formation. In addition, previous reports indicate that the aberrant activation of STAT3 occurs in many human tumors and STAT3-mediated PD-L1 up-regulation impedes T cell antitumor function. Our previous in vitro study showed that the IL-6/STAT3 axis plays a critical role in arsenic- induced transformation in human bronchial epithelial cells. Using a lung tumor mouse model, our new preliminary data show that long-term arsenic exposure increased lung tumor incidence rate and multiplicity of A/J mice. In addition, arsenic exposure dose-dependently activated STAT3, increased the binding of STAT3 to the promoter of the PD-L1 gene and up-regulated PD-L1 in mouse lungs. Flow cytometry data further indicated that arsenic increased PD-1+ T cell numbers and decreased CD8+/CD4+ T cell ratio in the lungs, while injection of PD-1 or PD-L1 antibodies reversed the decreased CD8+/CD4+ ratio. Since PD-1/PD-L1 up-regulation may inhibit T cell antitumor function and promote escape of transformed cells from host immunosurveillance and eventually lead to tumor formation, we hypothesize that arsenic promotes lung tumor formation through STAT3/PD-1/PD-L1-mediated inhibition of T cell antitumor function. Three specific aims are proposed: Aim 1: To determine if chronic arsenic exposure inhibits T cell antitumor function and the types of cells in which PD-1 or PD-L1 is up-regulated by arsenic in the lungs of A/J mice. Aim 2: To determine if inhibition of the PD-1/PD-L1 pathway ameliorates arsenic-promoted T cell dysfunction and tumor formation in the lungs of A/J mice. Aim 3: To determine if activation of STAT3 is the mechanism underlying arsenic-enhanced PD-L1 up- regulation, T cell dysfunction and tumor formation in the lungs of A/J mice.