Targeting TGFbeta/PDK4 to Overcome Drug Resistance in Colorectal Cancer

摘要 结直肠癌（CRC）是美国癌症死亡率的第二大原因。 治疗的失败是由于对化疗的抵抗，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 可以靶向克服耐药性和改善癌症治疗。 TGFβ发挥多种功能，包括赋予耐药性。但 TGFβ介导的化学抗性的潜在机制尚不清楚。PDK 4是一种 磷酸化丙酮酸的丙酮酸脱氢酶激酶（PDK）的亚型 脱氢酶（PDH）和调节葡萄糖代谢。我们发现了一个新的功能 PDK 4介导结肠癌细胞对5-FU治疗的反应。我们证明了 PDK 4，而不是PDK 1-3，在结肠癌细胞中差异表达，并且其表达 与对5-FU治疗的耐药性呈正相关。PDK 4的敲低使结肠敏感 癌细胞对5-FU或奥沙利铂诱导的凋亡的敏感性。肿瘤异种移植小鼠实验 模型表明，PDK 4的敲低增加了5-FU介导的 抑制体内肿瘤生长。此外，我们第一次建立了一部小说， TGFβ信号传导和PDK 4之间的串扰：TGFβ增加PDK 4表达，而PDK 4 增强TGFβ信号传导，形成正反馈回路。PDK 4表达升高 导致结肠癌细胞中TGFβ介导的耐药性。患者样本研究 表明PDK 4和TGFβ信号传导表达彼此正相关， 化疗耐药的癌症。因此，我们的研究揭示了 TGFβ/PDK 4介导结直肠癌耐药 在本提案中，我们将确定 TGFβ信号传导和PDK 4，阐明PDK 4介导的耐药性的机制， 鉴定PDK 4新底物。我们将确定PDK 4在结肠癌中的功能作用， PDK 4及其与TGFβ的相互作用在结直肠癌耐药中的作用 使用原位小鼠模型。我们还将证明患者的临床相关性 样品这些研究的完成将确定TGFβ/PDK 4作为一种新的调节剂， 化疗耐药性的CRC，实质上推进我们的分子机制的理解 潜在的耐药性，并提供5-FU与 PDK 4或TGFβ的抑制剂可能是潜在的有效疗法， CRC治疗的化学抗性。

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.