Targeting TGFbeta/PDK4 to Overcome Drug Resistance in Colorectal Cancer

摘要 结直肠癌(CRC)是美国癌症死亡的第二大原因。 治疗的失败是由于对化疗的耐药性，这是治疗的最大障碍之一 有效的癌症治疗。因此，迫切需要确定分子或途径。 这可以作为克服耐药性和改善癌症治疗的靶向。 转化生长因子β具有多种功能，包括诱导耐药。然而， 转化生长因子β介导化疗耐药的机制尚不清楚。PDK4是 丙酮酸脱氢酶(PDK)的异构体，使丙酮酸磷酸化 脱氢酶(PDH)和调节葡萄糖代谢。我们发现了一种新的功能 介导结肠癌细胞对5-FU治疗反应的PDK4。我们证明了 PDK4，而不是PDK1-3，在结肠癌细胞中差异表达，其表达 5-FU耐药与化疗耐药呈正相关。PDK4基因敲除使结肠增敏 5-FU或奥沙利铂诱导癌细胞凋亡。小鼠肿瘤移植瘤的实验研究 模型表明，PDK4的敲除增加了5-FU介导的药物的有效性 抑制体内肿瘤生长。此外，我们第一次建立了一部小说 转化生长因子β信号与PDK4信号的相互作用：转化生长因子β促进PDK4的表达 增强转化生长因子β信号，形成正反馈循环。PDK4表达升高 有助于转化生长因子β介导的结肠癌细胞耐药。对患者样本的研究 提示PDK4和转化生长因子β信号的表达呈正相关。 结直肠癌的化疗耐药。因此，我们的研究揭示了一个重要的功能 转化生长因子β/PDK4在结直肠癌耐药中的作用 在这个提案中，我们将确定潜在的串扰机制(S) 转化生长因子β信号转导与PDK4，阐明PDK4介导耐药的机制(S) 鉴定PDK4的新底物。我们将确定PDK4在结肠癌中的功能作用 PDK4及其与转化生长因子β的串扰在结直肠癌耐药中的作用及转移 使用原位小鼠模型。我们还将在患者身上展示其临床相关性。 样本。这些研究的完成将确定转化生长因子β/PDK4是一种新的 大肠癌的化疗耐药，极大地促进了我们对分子机制的理解 并提供了5-FU与5-FU联合应用的概念验证 PDK4或转化生长因子β的抑制剂可能是潜在的有效治疗方法 结直肠癌治疗的化疗耐药。

Abstract Colorectal cancer (CRC) is the second leading cause of cancer mortality in the USA. The failure of treatment is due to resistance to chemotherapy, one of the biggest obstacles for effective cancer therapy. Therefore, there is an urgent need to identify molecules or pathways that can be targeted to overcome drug resistance and improve cancer treatment. TGFβ plays multiple functions including conferring drug resistance. However, the mechanisms underlying TGFβ-mediated chemoresistance are not clear. PDK4 is one of the isoforms of pyruvate dehydrogenase kinase (PDK), which phosphorylate pyruvate dehydrogenase (PDH) and regulate glucose metabolism. We have discovered a novel function of PDK4 that mediates the response of colon cancer cells to 5-FU treatment. We show that PDK4, but not PDK 1-3, is differentially expressed in colon cancer cells, and that its expression positively correlates with the resistance to 5-FU treatment. Knockdown of PDK4 sensitizes colon cancer cells to 5-FU- or oxaliplatin-induced apoptosis. Experiments in tumor xenograft mouse models demonstrate that knockdown of PDK4 increases the effectiveness of 5-FU-mediated inhibition of tumor growth in vivo. Furthermore, for the first time, we have established a novel crosstalk between TGFβ signaling and PDK4: TGFβ increases PDK4 expression while PDK4 enhances TGFβ signaling, which forms a positive feedback loop. Elevated PDK4 expression contributes to TGFβ-mediated drug resistance in colon cancer cells. Studies of patient samples indicate that expression of PDK4 and TGFβ signaling positively correlate with each other and with chemoresistance in CRC. Therefore, our studies unveil an important function of TGFβ/PDK4 in mediating drug resistance in CRC. In this proposal, we will determine the mechanism(s) underlying the crosstalk between TGFβ signaling and PDK4, elucidate the mechanism(s) of PDK4-mediated drug resistance and identify novel substrates of PDK4. We will determine the functional role of PDK4 in colon cancer metastasis and the contribution of PDK4 and its crosstalk with TGFβ in CRC drug resistance using an orthotopic mouse model. We will also demonstrate the clinical relevance in patient samples. The completion of these studies will identify TGFβ/PDK4 as a novel regulator of chemoresistance in CRC, substantially advance our understanding of molecular mechanisms underlying drug resistance and provide proof-of-concept that combinations of 5-FU with inhibitors of PDK4 or TGFβ could be potentially effective therapies to overcome chemoresistance for CRC treatment.