The Role of a Novel Vitamin E Metabolite in Colon Cancer Prevention and Therapy

描述(申请人提供)：环氧合酶(COX：COX-1/-2)和5-脂氧合酶(5-LOX)催化的反应在结肠癌进展中起重要作用。包括布洛芬在内的COX抑制剂被称为非类固醇抗炎药(NSAIDs)，已被证明是有效的结肠癌抗癌剂。然而，使用这些酶的特定抑制剂的一个关键障碍是与COX抑制剂相关的副作用，包括胃毒性和心血管疾病风险增加。因此，我们需要寻找新的预防和治疗策略，既有强大的抗癌作用，又有可能降低毒性。我们最近证实维生素E的形式包括3-生育酚(3T)、4-生育酚(4T)和3-生育三烯酚(3TE)在人体细胞和大鼠体内被代谢成长链羧基色满醇及其硫酸盐化产物。重要的是，含有13个碳长的羧化侧链的E代谢物13‘-羧基色甘醇(13’-COOH)是COX-1/-2的强有力的竞争性抑制剂，其效力与布洛芬相似，而3T、4T和3TE或较短侧链的羧基色甘醇是弱得多的COX抑制剂。我们的初步数据表明，13‘-COOH对5-LOX催化的白三烯B4(LTB4)也有抑制作用。COXS和5-LOX的双重抑制不仅可能产生更强的抗炎和抗癌作用(通过抑制多个促炎途径)，而且还可能减少花生四烯酸代谢分流到任何一个途径所引起的潜在不良反应。因此，我们推测13‘-COOHs可能是很好的抗癌药物。为了验证这一假说，将通过追求细胞培养和动物研究的下列特定目标来验证这一假说：1)研究4-13‘-COOH(一种从4-生育酚衍生的13’-COOH)对结肠上皮细胞的抗炎和抗癌活性，并阐明通过酶动力学抑制5-LOX的机制；2)在以偶氮甲烷(AOM)诱导结肠癌并经葡聚糖硫酸钠(DSS)诱导结肠炎的小鼠模型上，研究4-13‘-COOH的体内抗癌活性。4-13‘-COOH的疗效将与其未代谢的前体4T和常用的非甾体抗炎药布洛芬进行比较。4-13‘-COOH在长期补充期间的生物利用度和潜在的不良反应也将被调查。这些研究可能会发现一类新的有效的抗癌药物，即长链羧基铬醇，它可能比非甾体抗炎药和维生素E形式更有效，而且由于其独特的性质而几乎没有不良反应。这些研究将扩展并将基于机制的发现转化为临床相关的癌症模型，并为人类临床研究获得重要的临床前数据。 公共卫生相关性：环氧合酶和5-脂氧合酶催化的反应对结肠癌的发生有重要作用。我们最近已经证明，长链羧基色甘醇是一种新型的维生素E代谢物，能有效地抑制环氧合酶和5-脂氧合酶介导的反应。本应用旨在研究一种长链羧基铬醇在结肠癌细胞和小鼠结肠癌模型中的抗癌活性。这些研究可能会发现一类潜在低毒的新型有效抗癌药物，将基于机制的发现扩展并转化为临床相关的动物模型，并将收集对人类临床研究重要的必要的临床前数据。

DESCRIPTION (provided by applicant): Cyclooxygenases (COXs: COX-1/-2) and 5-lipoxygenase (5-LOX) catalyzed reactions play significant roles in colon cancer progression. COX inhibitors including ibuprofen, known as non-steroid anti- inflammatory drugs (NSAIDs), have been shown to be effective anticancer agents against colon cancer. However, a critical barrier to utilize the specific inhibitors of these enzymes is associated adverse effects including gastrotoxicity and increased risk of cardiovascular diseases for COX inhibitors. Therefore, we need to search for new prevention and therapeutic strategies that have strong anti-cancer effects with potentially reduced toxicity. We have recently demonstrated that vitamin E forms including 3-tocopherol (3T), 4-tocopherol (4T) and 3-tocotrienol (3TE) are metabolized to long-chain carboxychromanols and their sulfated counterparts in human cells and in rats. Importantly, 13'-carboxychromanol (13'-COOH), the E metabolite containing 13-carbon-length carboxylated side chain, is a potent competitive inhibitor of COX-1/-2 with the potency similar to ibuprofen, while 3T, 4T and 3TE or shorter-side chain carboxychromanols are much weaker COX inhibitors. Our preliminary data indicate that 13'-COOH also inhibited 5-LOX catalyzed leukotriene B4 (LTB4). The dual inhibition of COXs and 5-LOX may not only result in more potent anti-inflammatory and anti-cancer effect (by inhibiting multiple proinflammatory pathways), but may also reduce potential adverse effect caused by a shunt in arachidonate metabolism to either pathway. Therefore, we hypothesize that 13'-COOHs may be excellent anticancer agents. This hypothesis will be tested by pursuit of the following Specific Aims in cell culture and animal studies:1) investigate anti-inflammatory and anticancer activity of 4-13'-COOH (a 13'-COOH derived from 4-tocopherol) in colon epithelial cells and elucidate the mechanism underlying the inhibition of 5-LOX by enzyme kinetics, and 2) investigate in vivo anti-cancer activity of 4-13'-COOH in a mouse model, in which colon carcinogenesis is induced by azoxymethane (AOM) and is accelerated by dextran sulfate sodium (DSS)-caused colon inflammation. The efficacy of 4-13'-COOH will be compared with its unmetabolized precursor 4T and a commonly used NSAID, ibuprofen. The bioavailability and potential adverse effects of 4-13'-COOH during long-term supplementation will also be investigated. The proposed studies may discover a new class of effective anticancer agents, i.e., long-chain carboxychromanols, which may be more effective than NSAIDs and vitamin E forms, and exhibit few adverse effects due to their unique properties. These studies will extend and translate mechanism- based findings to a clinically relevant cancer model and obtain important preclinical data for human clinical studies. PUBLIC HEALTH RELEVANCE: Cyclooxygenases and 5-lipoxygenase catalyzed reactions contribute significantly to the development of colon cancer. We have recently demonstrated that long-chain carboxychromanols, which are novel vitamin E metabolites, potently inhibit cyclooxygenases- and 5-lipoxygenase-mediated reactions. This application is to investigate the anticancer activities of a long-chain carboxychromanol in colon cancer cells and in a colon cancer model in mice. These studies may discover a new class of effective anticancer agents with potentially low toxicity, will extend and translate mechanism-based findings to a clinically relevant animal model, and will gather necessary preclinical data important to human clinical studies.