Mechanisms of Chemoprevention by Isothiocyanates

异硫氰酸酯(ITCs)及其结合物在动物模型中是有效的抑制肺癌发生的药物。ITCs的化学预防活性主要归因于选择性抑制细胞色素P450和诱导II相酶。近年来，细胞培养研究显示了ITCs潜在的新的肿瘤抑制机制，包括通过激活信号转导通路诱导细胞凋亡和细胞周期停滞。这些研究表明，如果在启动后阶段给药，ITCs可能会抑制肿瘤的发生。事实上，我们已经证明，苯乙基和苄基ITCs的N-乙酰半胱氨酸偶联物在苯并[a]芘治疗后的饮食中给予显著抑制A/J小鼠肺部肿瘤的形成。此外，我们还首次展示了 在体内，在肿瘤生物检测条件下，这些药物通过激活MAP激酶、JNK、AP-1和P53磷酸化而诱导小鼠肺细胞凋亡，这是一系列与培养细胞中看到的相似的分子反应。在这个项目中，作为细胞培养和动物研究的延伸，我们的主要目标是研究ITCs在人肺细胞中的分子和细胞机制，将它们与动物中的ITCs进行比较，并探讨其活性的化学基础。我们假设ITCs通过与特定的靶蛋白结合来激活人肺细胞的信号转导通路和/或通过与谷胱甘肽结合来改变氧化还原电位来诱导细胞凋亡。在另一个目标中，我们将调查 谷胱甘肽转移酶基因多态性在人ITC代谢中的作用这一目标是基于最近的一项流行病学研究，该研究表明，摄入ITC对GSTM1和GSTT1基因缺失的个体具有高度保护作用。

Isothiocyanates (ITCs) and their conjugates are effective inhibitors against lung tumorigenesis in animal models. The chemopreventive activities of ITCs have been attributed mainly to selective inhibition of cytochrome-P450s and induction of phase II enzymes. In recent years, studies in cell culture showed a potentially important new mechanism of tumor inhibition by ITCs, involving induction of apoptosis and cell cycle arrest mediated through activation of signal transduction pathways. These studies suggested that ITCs may inhibit tumorigenesis when administered during post-initiation phases. Indeed, we have demonstrated that the N-acetylcysteine conjugates of phenethyl and benzyl ITCs given in the diet after benzo[a]pyrene treatment significantly inhibit lung tumor formation in A/J mice. Furthermore, we have shown for the first time in vivo, under the tumor bioassay conditions, that these agents induce apoptosis in mouse lung by activating MAP kinases, JNK, AP- 1 and p53 phosphorylation, a set of molecular responses similar to those seen in cultured cells. In this project, as an extension of cell culture and animal studies, our primary goals are to examine the molecular and cellular mechanisms of ITCs in human lung cells, comparing them to that in animals, and to investigate the chemical basis for their activities. We hypothesize that ITCs induce apoptosis by activating signal transduction pathways in human lung cells through binding to specific target proteins and/or altering redox potential by conjugating with glutathione. In a separate goal, we will investigate the role of glutathione transferase (GST) polymorphism in ITC metabolism by humans. This aim is based on a recent epidemiological study showing that ITC intake is highly protective in individuals with GSTM1 and GSTT1 null genotypes.