Altered Arachidonic Acid Balance and Colon Cancer

描述（由申请人提供）：花生四烯酸（AA）代谢和下游类花生酸信号传导途径是结肠癌化学预防剂的公认靶点。肿瘤细胞中通过磷脂酶的作用产生AA。一种特别感兴趣的磷脂酶是细胞质磷脂酶A2（cPLA 2）。该酶通过考克斯-2催化的AA转化促进促癌的前列腺素（PG）的产生。此外，cPLA 2对细胞内AA水平的调节影响凋亡信号传导，因为不被考克斯-2消耗的AA控制鞘磷脂转化为神经酰胺，神经酰胺是一种关键的死亡效应物。使用缺乏cPLA 2的BALB/c小鼠，我们获得的证据表明，cPLA 2在结肠中通过凋亡调节的生长抑制作用可能优于其通过前列腺素合成作为肿瘤促进剂的作用。我们提出了一系列的小鼠体内研究和结肠癌细胞体外研究，以评估cPLA 2在结直肠癌（CRC）发病机制中的作用。目的1将验证cPLA 2通过其对AA代谢和鞘磷脂酶（Smase）-神经酰胺凋亡途径的作用来抑制结肠癌发生的假设。我们将评估cPLA 2在AOM和ApcMin引发的肿瘤中的作用。这些研究将提供cPLA 2状态如何影响肠道肿瘤发生的全面观点。目的2探讨cPLA 2调控肿瘤细胞生长的机制。我们将从cPLA 2缺失小鼠中收获肿瘤细胞，并使用同基因小鼠在体外和原位模型中测试其生长。将使用条件Tet-off cPLA 2表达系统进行机制研究，以评价一组凋亡效应物。目的3将测试cPLA 2对考克斯抑制剂舒林酸的化学预防的影响。将在cPLA 2水平正常或降低的小鼠中评价疗效。由于考克斯抑制剂仅对一部分病变有效，我们将使用一种新的染色镜成像方法来预测和跟踪化学预防对具有不同cPLA 2遗传背景的个体AOM诱导的腺瘤的生物学命运的影响。将开发反应性和非反应性腺瘤的遗传特征，其可用于将化学预防策略靶向于具有最大CRC风险的反应性个体。通过腺瘤的分子谱预测药物反应将成为癌症预防的重要考虑因素。我们的目标将是提高最有可能对影响AA代谢途径的化学预防剂产生反应的个体的靶向。

DESCRIPTION (provided by applicant): Arachidonic acid (AA) metabolism and downstream eicosanoid signaling pathways are well-established targets for colon cancer chemopreventive agents. AA is generated in tumor cells by the actions of phospholipases. One phospholipase of particular interest is cytoplasmic phospholipase A2 (cPLA2). This enzyme contributes to the production of cancer-promoting prostaglandins (PGs) via the Cox-2-catalyzed conversion of AA. Additionally, cPLA2 regulation of intracellular AA levels affects apoptotic signaling, as AA not consumed by Cox-2 controls sphingomyelin conversion to ceramide, a key death effector. Using BALB/c mice that are deficient in cPLA2, we obtained evidence that the growth inhibitory role of cPLA2 in colon via apoptosis regulation may predominate over its role as a tumor promoter through prostaglandin synthesis. We propose a series of in vivo studies in mice and in vitro studies in colon cancer cells to evaluate the role of cPLA2 in the pathogenesis of colorectal cancer (CRC). Aim 1 will test the hypothesis that cPLA2 suppresses colon carcinogenesis through its actions on AA metabolism and the sphingomyelinase (Smase) - ceramide apoptotic pathway. We will evaluate the cPLA2 effect in AOM- and ApcMin-initiated tumors. These studies will provide a comprehensive view of how cPLA2 status impacts intestinal tumorigenesis. Aim 2 will explore mechanisms by which cPLA2 controls tumor cell growth. We will harvest tumor cells from cPLA2-null mice and test their growth in vitro and in an orthotopic model using syngeneic mice. Mechanistic studies will be performed using a conditional Tet-off cPLA2 expression system to evaluate a panel of apoptotic effectors. Aim 3 will test the influence of cPLA2 on chemoprevention by the Cox inhibitor, sulindac. Efficacy will be evaluated in mice with normal or reduced levels of cPLA2. Since Cox inhibitors are only effective on a subset of lesions, we will use a novel chromendoscopic imaging approach to predict and track the effects of chemoprevention on the biological fate of individual AOM-induced adenomas with different cPLA2 genetic backgrounds. Genetic signatures of responsive and non-responsive adenomas will be developed that may be used to target chemoprevention strategies to responsive individuals at the greatest risk for CRC. Predicting drug response through molecular profiling of adenomas will become an important consideration in cancer prevention. Our goal would be to improve targeting of individuals most likely to respond to chemopreventive agents that impact the AA metabolic pathway.