Mechanism of action and therapeutic utility of immunosuppressive oligonucleotide

表达重复TTAGGG基序的合成寡核苷酸（ODN）在哺乳动物端粒中以高频率存在的六聚体序列之后图案化，下调由广泛的TLR配体引起的炎性免疫应答和由多克隆活化剂和抗原诱导的适应性免疫细胞应答。这些抑制性ODN可用于治疗以过度旺盛的免疫应答为特征的疾病，包括败血性休克和自身免疫。我的研究小组的结果表明，系统性给予Sup ODN改变了宿主的免疫环境，并可用于降低对炎症诱导的癌症的易感性。本研究的最初重点是检查Sup ODN在皮肤癌发生的DMBA/TPA模型中的作用。我们发现，Sup ODN显着减少了发展DMBA/TPA依赖性乳头状瘤的小鼠的数量和乳头状瘤/动物的数量，在这个炎症相关的肿瘤发生的小鼠模型。为了证实这一发现，我们在一个完全不同的炎症促进肿瘤发生的模型系统中开始了研究。首先，我们证明Sup ODN可有效预防/治疗由矽肺（一种影响美国和国外许多矿工的疾病）引起的危及生命的肺部炎症。对这些矿工的流行病学研究表明，二氧化硅颗粒（以及石棉和煤尘）引起的炎症增加了他们对吸烟引起的肺癌的易感性。这促使我们开发了一种新的模型来研究暴露于二氧化硅粉尘加上NNK（香烟烟雾中存在的主要致癌物质）是否会增加小鼠患肺癌的风险。我们的研究结果证明了这一点（提供了第一个二氧化硅诱导肺癌敏感性的小鼠模型）。更重要的是，我们发现用Sup ODN治疗硅肺炎症不仅可以减少肺部炎症，还可以使癌症易感性恢复到背景水平。为了阐明Sup ODN抑制肿瘤发展的机制，检查了炎症的各种测量。在研究的两种模型中，白细胞浸润和促炎细胞因子和趋化因子的产生显著减少，而对照ODN没有显著影响。我们正在扩展这些研究，以包括其他引起肺部炎症和疾病的药物。我们也在使用微阵列技术来鉴定由抑制性ODN触发的基因和调控网络。这些微阵列研究表明，在施用抑制性ODN后，非常大量的基因被迅速下调。Sup ODN广泛降低基因表达的两种机制是正在进行的评估的焦点：i）Sup ODN靶向关键基因（如MAPK）调控区中存在的TTAGGG和/或CCCTAA基序，ii）Sup ODN抑制bZIP蛋白（共享碱性亮氨酸拉链结构域的调控DNA结合蛋白）的活性。在MAPK调控的背景下，编码MAPK 1、MAPK 3和MAPK 14（分别刺激ERK-2、ERK-3和p38依赖性途径）的mRNA以及它们调控的转录因子（ATF 2、CREB 1、NFKB 1）在其调控区域中含有TTAGGG和/或CCCTAA基序，其可通过反义机制被Sup ODN靶向。由于MAPK对编码多种炎性基因的mRNA发挥稳定作用，因此下调其表达可能对先天免疫应答产生广泛影响。bZIP蛋白是广泛影响基因表达的转录因子。转录结合位点分析表明，许多被Sup ODN下调的基因含有bZIP蛋白识别的调控结构域（如CREB 1、CEBPA和FOS）。事实上，79%的TLR 9信号通路中由bZIP蛋白调节的组分被Sup ODN显著下调（p 0.0001）。我们研究了Sup ODN是否抑制bZIP蛋白与其靶DNA序列的结合，发现Sup ODN选择性地抑制三种不同类型的bZIP蛋白（CREB，C/EBPa和MAFg）与其靶DNA的结合。关于抑制性ODN作用的靶点和机制的信息将支持旨在探索其治疗效用的研究。

Synthetic oligonucleotides (ODN) expressing repetitive TTAGGG motifs patterned after hexameric sequences present at high frequency in mammalian teleomeres down-regulate the inflammatory immune responses elicited by a broad range of TLR ligands and the adaptive immune cell responses induced by polyclonal activators and antigens. These suppressive ODN are useful in the treatment of diseases characterized by over-exuberant immune responses, including septic shock and autoimmunity. Results from my group show that systemically administered Sup ODN alter the host immune milieu and can be harnessed to reduce susceptibility to inflammation-induced cancer. The initial focus of this research examined the effect of Sup ODN in the DMBA/TPA model of skin carcinogenesis. We found that Sup ODN significantly reduce both the number of mice that develop DMBA/TPA dependent papillomas and the number of papillomas/animal in this murine model of inflammation-associated tumorigenesis. To confirm this finding, we initiated studies in a completely different model system of inflammation-promoted tumorigenesis. First, we demonstrated that Sup ODN were effective in preventing/treating the life-threatening pulmonary inflammation caused by silicosis (a disease that affects many miners in the US and abroad). Epidemiologic studies of such miners suggest that the inflammation induced by silica particles (as well as asbestos and coal dust) increases their susceptibility to lung cancer induced by exposure to cigarette smoke. This led us to develop a novel model to examine whether exposure to silica dust plus NNK (the major carcinogen present in cigarette smoke) increase the risk of lung cancer in mice. Our findings demonstrate this to be the case (providing the first murine model of silica-induced sensitivity to lung cancer). More importantly, we show that treating silicotic inflammation with Sup ODN not only reduces pulmonary inflammation but returns cancer susceptibility to background. To clarify the mechanism by which Sup ODN inhibit tumor development, various measures of inflammation were examined. In both models studied, leukocyte infiltration and the production of pro-inflammatory cytokines and chemokines were significantly reduced whereas control ODN had no significant effect. We are extending these studies to include other agents that cause pulmonary inflammation and disease. We are also using microarray technology to identify the genes and regulatory networks triggered by suppressive ODN. These microarray studies indicate that very large numbers of genes are rapidly down-regulated following the administration of suppressive ODN. Two mechanisms by which Sup ODN broadly reduce gene expression are the focus of ongoing evaluation: i) that Sup ODN target TTAGGG and/or CCCTAA motifs present in the regulatory regions of critical genes (such as MAPKs) and ii) that Sup ODN inhibit the activity of bZIP proteins (regulatory DNA binding proteins that share a basic leucine zipper domain). In the context of MAPK regulation, mRNA encoding MAPK1, MAPK3 and MAPK14 (which stimulate the ERK-2, ERK-3 and p38 dependent pathways, respectively), as well as the transcription factors they regulate (ATF2, CREB1, NFKB1), contain TTAGGG and/or CCCTAA motifs in their regulatory regions that could be targeted by Sup ODN via an anti-sense mechanism . Since MAPKs exert a stabilizing effect on mRNAs encoding multiple inflammatory genes, down-regulating their expression could have a broad effect on the innate immune response. bZIP proteins are transcription factors that broadly influence gene expression. Transcription binding site analysis shows that many genes down-regulated by Sup ODN contain regulatory domains recognized by bZIP proteins (e.g. CREB1, CEBPA, and FOS). Indeed, 79% of the components in the TLR9 signaling pathway regulated by bZIP proteins are significantly down-regulated by Sup ODN (p < .0001). We examined whether Sup ODN inhibited the binding of bZIP proteins to their target DNA sequences and found that Sup ODN selectively inhibited the binding of three different classes of bZIP protein (CREB, C/EBPa and MAFg) to their target DNAs. Information gathered on the targets and mechanism(s) of action of suppressive ODN will support studies designed to explore their therapeutic utility.