MOLECULAR CHANGES IN THE NKFB PATHWAY IN RESPONSE TO CHEMORADIATION THERAPY IN RE

虽然结直肠癌的早期诊断有了很大的提高，但局部晚期结直肠癌的发生仍然是一个主要的医学问题，因为这些患者的预后非常差。显然，治疗结直肠癌的新方法是必要的。与标准的放化疗方案相比，存在的两个主要障碍是：(I)结直肠肿瘤对治疗的抵抗力；(Ii)由于正常肠道组织的纤维化而导致的治疗剂量限制。放射耐药和化疗耐药的特点是既有耐药，基于某些蛋白的结构性表达，如mdr1或抗凋亡蛋白，如bcl2，以及失去促凋亡因子，如p53，或者是诱导性耐药。可诱导耐药是一种相对较少描述的现象，在这种现象中，肿瘤在暴露于治疗后瞬时诱导耐药。在一些研究中，肿瘤反应与诱导细胞凋亡相关。因此，肿瘤化疗/放射耐药的一个主要成分可能是抑制细胞凋亡。我们已经报道，转录因子NF-KB通过转录调控编码抑制细胞凋亡的蛋白的基因，提供了强大的抗凋亡机制。重要的是，在大肠肿瘤组织中基本检测到核因子-KB的激活(尽管表达可能主要局限于肿瘤相关的巨噬细胞)，并且在放疗或化疗暴露后的肿瘤细胞中被强烈激活。基于这些发现，我们有 结果表明，通过基因传递途径抑制核因子-kB可通过诱导细胞凋亡来增强化疗诱导的实验性结直肠肿瘤细胞毒作用。此外，我们使用了FDA批准的一种药物(PS-341，一种蛋白酶体抑制剂)，该药物可以强烈阻断核因子-KB的激活，以增强结直肠肿瘤对放射和基于CPT-11的化疗的异种移植反应。我们假设辐射诱导的核因子-KB激活和相关的下游转录反应将发生在结直肠肿瘤中，这将通过提供抗凋亡信号而与降低的治疗反应相关。为了验证我们的假设，我们建议：(I)确定在术前放化疗中是否存在辐射诱导的核因子-kB及其相关诱导基因的激活，并确定这种反应是否与临床反应相关，(Ii)确定PS-341调节核因子-kB依赖反应的能力，并测量术前放化疗中PS-341的毒性。此外，这些研究将测量放化疗后正常肠道组织中核因子-KB的激活和转录因子依赖的转录反应的诱导，作为癌症治疗诱导的肠道纤维化的潜在分子相关性。我们还假设，通过使用更具体的药物，辅助放化疗反应将会得到改善，总体毒性将会降低。 核因子-KB途径的抑制物。因此，我们将评估核因子-KB抑制剂作为放射治疗或最新联合化疗方案对包括肝转移在内的不同实验肿瘤的疗效。这些I期临床研究和基础转译实验有可能显著改进晚期结直肠癌的治疗方法。

Although early diagnosis for colorectal cancer has been significantly improved, the occurrence of locally advanced colorectal cancer is still a major medical problem since these patients have extremely poor prognosis. Clearly, new approaches for treatment of colorectal cancer are needed. Two major obstacles which exist relative to standard radiation and chemotherapy protocols are: (i) resistance of colorectal tumors to treatment and (ii) dose limitations of treatment due to fibrosis of normal intestinal tissue. Radio- and chemoresistance are characterized either as pre-existing resistance, based on constitutive expression of certain proteins such as MDR1 or anti-apoptotic proteins such as Bcl-2 and on loss of pro-apoptotic factors such as p53, or as inducible resistance. Inducible resistance is a relatively poorly characterized phenomenon in which tumors transiently induce resistance following exposure to treatment. In several studies, tumor response correlates with induction of apoptosis. Thus, it is likely that one major component of tumor chemo/radioresistance is suppression of apoptosis. We have reported that the transcription factor NF-KB provides a powerful anti-apoptotic mechanism through its ability to transcriptionally regulate genes encoding proteins which suppress apoptosis. Importantly, NF-KB activation is basally detected in colorectal tumor tissue (although expression may predominantly be localized in tumor-associated macrophages) and is strongly activated in tumor cells following radiation or chemotherapy exposure. Based on these findings, we have shown that inhibition of NF-KB through a gene delivery approach strongly potentiates chemotherapy-induced experimental colorectal tumor cytotoxicity through the induction of apoptosis. Furthermore, we have used an FDA-approved drug (PS-341, a proteasome inhibitor) which strongly blocks NF-KB activation to enhance colorectal tumor xenograft responses to both radiation and to CPT-11 based chemotherapy. We hypothesize that radiation-induced NF-KB activation and associated downstream transcriptional responses will occur in colorectal tumors and that this will correlate with a decreased therapeutic response by providing an anti-apoptotic signal. To test our hypothesis, we propose to: (i) determine whether radiation-induced activation of NF-KB and associated induced genes occurs in pre-operative radiochemotherapy and determine whether this responses correlates with clinical response and (ii) determine the ability of PS-341 to modulate NF-KB-dependent responses and to measure the toxicity of PS-341 delivered with pre-operative radiochemotherapy. Additionally, these studies will measure NF-KB activation and induction of transcription factor-dependent transcription responses in normal intestinal tissue following radiochemotherapy as a potential molecular correlate for cancer therapy-induced intestinal fibrosis. We also hypothesize that adjuvant radiochemotherapy responses will be improved and overall toxicity reduced through the use of more specific inhibitors of the NF-KB pathway. Thus, we will measure the efficacy of NF-KB inhibitors as an adjuvant approach with radiation or with the newest combination of chemotherapy regimens on different experimental tumors including liver metastases. These phase I clinical studies and basic translational experiments have the potential to significantly improve therapeutic approaches for advanced colorectal cancer.