NADPH Oxidase 1: A Novel Target for Colon Cancer Therapy

上皮性NADPH氧化酶是一种黄素蛋白，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阴离子。目前的证据表明，NADPH依赖的活性氧物种在生长因子介导的信号转导中起着关键作用，NADPH氧化酶1亚型在人类结肠癌中大量表达。由于一系列以碘为基础的黄素蛋白抑制剂在相同浓度范围内能够抑制人结肠癌细胞系构成氧化剂的产生和细胞生长，以及诱导细胞凋亡和阻断G1/S转变和诱导p27的表达，因此Doroshow博士的研究表明，碘NADPH氧化酶抑制剂的治疗潜力可能与修改结直肠癌细胞生长所必需的氧化还原相关信号转导通路有关。在两个人结肠癌异种移植模型中也发现了碘的衍生物活性。在未来的研究中，Doroshow博士计划开发更多的新型碘药物，作为潜在的治疗剂。Doroshow博士还利用他的实验室开发的稳定的shRNA结构(能够将NADPH氧化酶1的表达降低80%)来专门研究这种蛋白质在结直肠癌细胞增殖中的作用。这些最近的研究表明，NADPH Oxidase 1的下调导致了HT-29细胞中活性氧产生的显著减少，细胞周期阻滞于G1期，大量的抗血管生成基因下调，并通过几种受体蛋白激酶抑制了活性氧介导的信号转导。此外，我们还发现，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都会增加。在体内，NADPH氧化酶1的下调显著减少了HT-29异种移植瘤的生长，部分原因是血管生成减少。这些研究有力地表明NADPH氧化酶1是治疗结肠癌的一个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.