Altered Arachidonic Acid Balance and Colon Cancer

描述(申请人提供)：花生四烯酸(AA)代谢和下游二十烷类信号通路是结肠癌化学预防药物公认的靶点。AA是通过磷脂酶的作用在肿瘤细胞中产生的。一种特别感兴趣的磷脂酶是细胞质磷脂酶A2(CPLA2)。这种酶有助于通过环氧合酶-2催化的AA转化产生促癌前列腺素(PGs)。此外，cPLA2调节细胞内AA水平影响凋亡信号，因为AA不被COX-2消耗控制着神经鞘磷脂向神经酰胺的转化，神经酰胺是一个关键的死亡效应因子。利用缺乏cPLA2的BALB/c小鼠，我们获得的证据表明，cPLA2通过调节细胞凋亡而抑制结肠的生长，而不是通过合成前列腺素来促进肿瘤的作用。我们提出了一系列在小鼠体内和在结肠癌细胞中的体外研究，以评估cPLA2在结直肠癌(CRC)发病机制中的作用。目的1验证cPLA2通过作用于AA代谢和神经鞘氨酸酶-神经酰胺凋亡途径抑制结肠癌发生的假说。我们将评估cPLA2在AOM和ApcMin启动的肿瘤中的作用。这些研究将为cPLA2状态如何影响肠道肿瘤的发生提供一个全面的视角。目的2将探索cPLA2控制肿瘤细胞生长的机制。我们将从cPLA2基因缺失的小鼠中获取肿瘤细胞，并在体外和使用同基因小鼠的原位模型中测试它们的生长。机制研究将使用条件Tet-off cPLA2表达系统来评估一组凋亡效应因子。目的3将测试cPLA2对环氧合酶抑制剂舒林酸化学预防的影响。疗效将在cPLA2水平正常或降低的小鼠身上进行评估。由于COX抑制剂只对一小部分病变有效，我们将使用一种新的染色内窥镜成像方法来预测和跟踪化学预防对具有不同cPLA2遗传背景的AOM诱导的腺瘤的生物学命运的影响。反应性和非反应性腺瘤的遗传特征将被开发出来，可用于针对具有最大结直肠癌风险的反应性个体的化学预防策略。通过腺瘤的分子图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对最有可能对影响AA代谢途径的化学预防药物有反应的个体的靶向性。

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.