LINOLEIC ACID METABOLISM AND COLON CARCINOGENESIS

候选人寻求在癌症化学预防领域发展他的职业生涯，他现在的工作环境非常有利于这种研究。该提案为候选人计划开发化学预防研究的多学科转化方法提供了框架。需要更好的干预措施来预防结肠癌的高死亡率。亚油酸（LA）是一种常见的膳食多不饱和脂肪酸，可转化为花生四烯酸（AA），而花生四烯酸又可形成有丝分裂代谢物[如前列腺素、E2 （PGE2）和白三烯B4 (LTB4)]。LA也是15-脂氧合酶-1 （15-lox-1）形成13- s -羟基十八烯二烯（13-S-HODE）的底物。我们发现15- lox-1和13-S-HODE在人类结肠癌中减少，13-S-HODE诱导转化的结肠细胞凋亡。在正常细胞中，δ 6-去饱和酶（d-6-d）形成γ -亚麻酸（GLA），开始将LA转化为AA。许多肿瘤细胞缺乏d-6-d活性，并死于GLA暴露。一些证据表明，肿瘤细胞通过另一种途径将LA转化为AA，这种途径需要δ 5-去饱和酶（d-5-d）。假设亚油酸代谢从产生促凋亡产物[13-S-HODE和（GLA）]转变为形成花生四烯酸的有丝分裂代谢物（如PGE2和LTB4），显著促进了结肠癌的发生。具体目的是1)确定与体外结肠细胞转化和分化状态相关的替代转化途径的活性；2)通过临床观察性研究模型（通过测量3组患者（正常、息肉和结肠癌）结肠组织中LA替代途径的活性以及LA和AA的相关酶和代谢物[如13-S-HODE、PGE2、LTB4、d-6-d和15-lox-1]的水平），评估LA代谢变化与人类结肠癌发生进展步骤之间的关系；3)评价异位d-6-d表达对体外转化结肠细胞凋亡、分化和LA代谢的影响；4)评价选择性d-5-d抑制对体外转化结肠细胞LA代谢和存活的影响；5)在已建立的短期实验中确定选择性d-5-d抑制对大鼠结肠癌发生的影响。这项工作将为未来LA替代途径调节作为结肠癌化学预防手段的动物和临床研究奠定基础。

The candidate seeks to develop his career as a translational researcher in the field of cancer chemoprevention and he is now working in an environment highly conducive to such research. This proposal provides the framework for the candidate's plans to develop a multidisciplinary translational approach to chemoprevention research. Better interventions are needed to prevent the high mortality of colon cancer. Linoleic acid (LA), a common dietary polyunsaturated fatty acid, can be convertted to arachidonic acid (AA) that can in turn form mitogenic metabolites [e.g. prostaglandin, E2 (PGE2) and leukotriene B4 (LTB4)]. LA is also the substrate for 15-lipoxygenase-1 (15-lox-1) in forming 13-S-hydroxyoctadecadienoic (13-S-HODE). We have found that 15- lox-1 and 13-S-HODE are reduced in human colon cancers and that 13-S-HODE induces apoptosis in transformed colonic cells. In normal cells, the enzyme delta 6-desaturase (d-6-d) forms gamma- linolenic acid (GLA) to start the conversion of LA to AA. Many tumor cells lack d-6-d activity and die by GLA exposure. Some evidence suggests tumor cells convert LA to AA by an alternative pathway that requires delta 5-desaturase (d-5-d). The hypothesis is that a shift in linoleic metabolism from producing pro- apoptosis products [13-S-HODE and (GLA)] to the formation of mitogenic metabolites of arachidonic acid (e.g. PGE2 and LTB4) significantly contributes to colonic carcinogenesis. The specific aims are 1) to determine the activity of the alternative conversion pathway in relation to the transformation and differentiation states of colonic cells in vitro; 2) to evaluate the association between the shift in LA metabolism and the progressive steps of human colonic carcinogenesis using a clinical observational study model(by measuring the activity of LA alternative pathway and levels of related enzymes and metabolites of LA and AA [e.g. 13-S-HODE, PGE2, LTB4, d-6-d, and 15-lox-1] in colonic tissues from 3 patient groups [normal, polyp, and colon cancers]); 3) to evaluate the effects of ectopic d-6-d expression on apoptosis, differentiation, and LA metabolism in transformed colonic cells in vitro; 4) to evaluate the impact of selective d-5-d inhibition on LA metabolism and the survival of transformed colonic cells in-vitro; and 5) to determine the effects of selective d-5-d inhibition on colon carcinogenesis in an established short-term assay in rats. This work will set the stage for future animals and clinical studies of LA alternative pathway modulation as means of colon cancer chemoprevention.