New Paradigm of Targeting COX-Catalyzed Free Radical Peroxidation in Colon Cancer

 描述(申请人提供)：结肠癌仍然是一个重大的健康问题，在美国，结肠癌是第三大最常见的癌症，是癌症死亡的第二大原因。研究表明，ω-6脂肪酸与癌症有关，原因是环氧合酶(COX)催化的过氧化反应形成了有害的代谢物。相比之下，基于ω-3脂肪酸的饮食护理已与各种治疗方法一起应用于结肠癌的治疗。越来越多的证据表明，二高--亚麻酸(DGLA)可能是一种特殊的ω-6，具有与ω-3类似的有益生物活性。然而，ω-6影响人类健康的分子机制仍不清楚。我们的初步数据首次显示，通过COX催化的过氧化，DGLA产生专有的自由基，抑制结肠癌细胞生长，而其下游产物花生四烯酸(由5-去饱和酶介导的转化)产生可能刺激癌细胞生长的过氧化内源自由基。我们假设(1)COX催化的花生四烯酸与DGLA的过氧化反应产生的不同的自由基副产物解释了它们相反的生物活性；(2)下调5-去饱和酶可以限制DGLA向花生四烯酸的转化，激活DGLA介导的促凋亡和抗增殖途径，从而抑制结肠癌细胞的生长，增强癌症治疗。将追求两个特定的目标：(AIM-1)确定由COX催化的过氧化反应形成的独特的花生四烯酸和DGLA自由基副产物在结肠癌细胞生长中的作用。我们将验证这样的假设，即花生四烯酸和DGLA的不同自由基副产物分别对结肠癌细胞(HCA-7、HT-29和HCT-116，具有3种不同的COX-2和P53状态)具有生长促进和抑制作用。这些副产物将被研究它们对细胞周期中关键蛋白的表达和凋亡反应的单独和联合影响；以及(目的-2)确定在COX催化的过氧化过程中下调DGLA 5-去饱和酶是否增强自由基副产物的形成，从而在体外和体内抑制结肠癌的生长并增强对化疗和/或靶向治疗药物的反应。我们将使用体外(三个结肠癌细胞系及其5-去饱和酶基因敲除的对应物)和体内(使用5-去饱和酶shRNA操纵的异种移植瘤)策略来验证这一假设，即下调5-去饱和酶将加剧由COX-2(在癌症中高水平且容易诱导)催化的DGLA过氧化，增强对生长的抑制，并提高化疗和/或靶向治疗的有效性。我们的长期目标是开发一种策略，修改细胞ω-6转化和COX催化的自由基过氧化，用于饮食方案，以优化结肠癌治疗中的癌症治疗。

 DESCRIPTION (provided by applicant): Colon cancer remains a significant health concern as the third most prevalent cancer and the second leading cause of cancer deaths in the United States. Research suggests that ω-6 fatty acids are implicated in cancer due to the formation of deleterious metabolites from cyclooxygenase (COX)- catalyzed peroxidation. In contrast, ω-3 fatty acid-based dietary care has been applied in colon cancer treatment along with a variety of therapeutic approaches. Increasing evidence indicates that dihomo-- linolenic acid (DGLA) may represent an exceptional ω-6 that possesses beneficial bioactivities similar to ω-3s. However, the molecular mechanisms by which ω-6s can influence human health are still unclear. Our preliminary data has shown for the first time that, via COX-catalyzed peroxidation, DGLA produces exclusive free radicals that inhibit colon cancer cell growth, while its downstream product arachidonic acid (the conversion mediated by 5-desaturase) produces endoperoxide-derived free radicals that may stimulate cancer cell growth. We hypothesize that (1) the distinct free radical byproducts formed from COX-catalyzed peroxidation of arachidonic acid vs. DGLA account for their opposing bioactivities, and (2) down-regulation of 5-desaturase can inhibit colon cancer cell growth and enhance cancer therapy by limiting the conversion of DGLA to arachidonic acid, activating DGLA mediated pro-apoptotic and anti-proliferative pathways. Two specific aims will be pursued: (AIM-1) determine the role in colon cancer cell growth of the distinct arachidonic acid and DGLA free radical byproducts formed from COX-catalyzed peroxidation. We will test the hypothesis that the distinct free radical byproducts of arachidonic acid and DGLA are growth stimulatory and inhibitory, respectively, to colon cancer cells (HCA-7, HT-29, and HCT-116, with 3 different COX-2 and p53 statuses). These byproducts will be studied for their individual and combined effects on the expression of key proteins involved in the cell cycle and the apoptotic response; and (AIM-2) determine whether down-regulation of 5-desaturase enhances the formation of DGLA free radical byproducts during COX-catalyzed peroxidation, leading to inhibition of colon cancer growth and enhanced responses to chemo- and/or targeted therapeutic drugs in vitro and in vivo. We will use in vitro (three colon cancer cell lines and their 5-desaturase knockdown counterparts) and in vivo (xenograft tumors manipulated with 5- desaturase shRNA) strategies to test the hypothesis that down-regulation of 5-desaturase will intensify DGLA peroxidation catalyzed by COX-2 (high and readily inducible in cancer), enhance the inhibition of growth, and improve the efficacy of chemo- and/or targeted therapy. Our long term objective is to develop a strategy to modify cellular ω-6 conversion and COX-catalyzed free radical peroxidation for use in dietary regimens to optimize cancer therapies in colon cancer treatment.