NADPH Oxidase 1: A Novel Target for Colon Cancer Therapy

上皮NADPH氧化酶是一种黄蛋白，在与受体酪氨酸激酶（包括EGF、PDGF、VEGF）的配体结合后，催化NADPH依赖的氧还原为超氧化物。目前的证据表明，NADPH依赖的活性氧在生长因子介导的信号转导中起着关键作用，NADPH氧化酶1异构体在人类结肠癌中大量表达。由于一系列基于碘的黄蛋白抑制剂在相同浓度范围内可以抑制人结肠癌细胞系的组成性氧化剂产生和细胞生长，诱导细胞凋亡，阻断G1/S转变和诱导p27，Doroshows博士的研究表明，碘NADPH氧化酶抑制剂的治疗潜力可能与结直肠癌细胞生长所必需的氧化还原相关信号转导途径的修饰有关。碘衍生物也被发现在两种人类结肠癌异种移植模型中有活性。在未来的研究中，Doroshow博士计划开发更多的碘类药物的新成员作为潜在的治疗药物。Doroshow博士还利用其实验室开发的稳定shRNA构建体（能够下调NADPH氧化酶1表达80%）专门研究该蛋白在结直肠癌细胞增殖中的作用。这些最近的研究表明，下调NADPH氧化酶1导致HT-29细胞活性氧产生显著减少，G1细胞周期阻滞，大量抗血管生成基因下调，以及通过几种受体蛋白激酶抑制活性氧介导的信号传导。此外，我们发现当NADPH氧化酶被敲除时，几种丝氨酸、苏氨酸和酪氨酸磷酸酶的活性增加。在体内，NADPH氧化酶1的下调会显著降低HT-29异种移植物的生长，部分原因是血管生成减少。这些研究强烈提示NADPH氧化酶1是结肠癌重要的潜在药物靶点。

Epithelial NADPH oxidases are flavoproteins that catalyze the NADPH-dependent reduction of oxygen to superoxide following binding of ligands for receptor tyrosine kinases (including EGF, PDGF, VEGF). Current evidence suggests that NADPH-dependent reactive oxygen species play a critical role in growth factor-mediated signal transduction, and that the NADPH oxidase 1 isoform is abundantly expressed in human colon cancers. Because inhibition of constitutive oxidant production and cell growth of human colon cancer cell lines, as well as induction of apoptosis and blockade of the G1/S transition and induction of p27, occurred over the same concentration range for a series of iodonium-based flavoprotein inhibitors, Dr. Doroshows studies suggest that the therapeutic potential of iodonium NADPH oxidase inhibitors may be related to modification of redox-related signal transduction pathways essential for colorectal cancer cell growth. Iodonium derivatives have also been found to be active in two human colon cancer xenograft models. In future studies, Dr. Doroshow plans to develop additional, novel members of the iodonium drug class as potential therapeutic agents. Dr. Doroshow has also employed stable shRNA constructs developed in his laboratory (that are capable of downregulating NADPH oxidase 1 expression by >80%) to specifically investigate the role of this protein in colorectal cancer cell proliferation. These recent studies demonstrate that downregulation of NADPH Oxidase 1 leads to a significant decrease in reactive oxygen production in HT-29 cells, a G1 cell cycle block, down regulation of a large number of antiangiogenic genes, and inhibition of reactive oxygen-mediated signaling through several receptor protein kinases. In addition, we have found that the activity of several serine threonine and tyrosine phosphatases are increased when NADPH oxidase is knocked out. In vivo, downregulation of NADPH oxidase 1 dramatically decreases the growth of HT-29 xenografts, in part due to diminished angiogenesis. These studies strongly suggest that NADPH oxidase 1 is an important potential drug target in colon cancer.