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

 描述（由申请人提供）：结肠癌作为美国第三大流行癌症和第二大癌症死亡原因，仍然是一个重大的健康问题。研究表明，由于环氧合酶 (COX) 催化的过氧化反应会形成有害代谢物，因此 ω-6 脂肪酸与癌症有关。相比之下，基于ω-3脂肪酸的饮食护理已与多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-6s影响人类健康的分子机制仍不清楚。我们的初步数据首次表明，通过COX催化的过氧化反应，DGLA产生抑制结肠癌细胞生长的独特自由基，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内过氧化物衍生自由基。我们假设：(1) COX 催化的花生四烯酸与 DGLA 过氧化反应形成的不同自由基副产物解释了它们相反的生物活性，(2) 下调 γ5-去饱和酶可以抑制结肠癌细胞生长，并通过限制 DGLA 转化为花生四烯酸、激活 DGLA 介导的促凋亡和抗增殖途径来抑制结肠癌细胞生长并增强癌症治疗。我们将追求两个具体目标： (AIM-1) 确定 COX 催化过氧化形成的不同花生四烯酸和 DGLA 自由基副产物在结肠癌细胞生长中的作用。我们将检验以下假设：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）具有生长刺激和抑制作用。将研究这些副产物对参与细胞周期和细胞凋亡反应的关键蛋白表达的单独和组合影响； (AIM-2) 确定 5-去饱和酶的下调是否会增强 COX 催化的过氧化过程中 DGLA 自由基副产物的形成，从而抑制结肠癌生长并增强体内外对化疗和/或靶向治疗药物的反应。我们将使用体外（三种结肠癌细胞系及其 5-去饱和酶敲低对应物）和体内（用 5-去饱和酶 shRNA 操作的异种移植肿瘤）策略来检验以下假设：下调 5-去饱和酶将增强 COX-2（在癌症中高且易于诱导）催化的 DGLA 过氧化，增强生长抑制并提高化疗效果。和/或靶向治疗。我们的长期目标是开发一种策略来修改细胞 ω-6 转化和 COX 催化的自由基过氧化作用，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.