Chemosensitization of Pancreatic Tumors via Inhibition of a DNA BER Enzyme, Ape1

描述(申请人提供)：胰腺癌是一种致命的疾病，几乎永远无法治愈，因此我们的长期目标是为胰腺癌患者开发治疗方案，使这些耐药肿瘤对治疗敏感，并实现长期的患者反应。这项建议将研究在多大程度上削弱胰腺癌细胞对治疗后DNA损伤的反应能力，将导致对DNA损伤剂治疗的反应增加。为了提高胰腺癌细胞的化疗效果，我们计划抑制DNA碱基切除修复(BER)途径中的一种关键蛋白。BER通路包括脱嘌呤/脱嘧啶核酸内切酶/氧化还原因子(APE1/Ref-1或APE1)，在化疗药物所致损伤的修复中起重要作用。除了DNA修复活性外，APE1还与许多转录因子(HIF1-a、P53、AP1、NF？B等)相互作用，促进它们的DNA结合。吉西他滨是一种DNA链终止剂，是目前用于治疗胰腺癌的最主要的化疗药物。研究表明APE1的3‘到5’外切酶活性在从DNA中去除脱氧核糖核苷类似物中的作用，为APE1DNA修复抑制剂与吉西他滨的联合治疗提供了理论基础。此外，APE1蛋白水平的降低使胰腺癌细胞对吉西他滨敏感。此外，已知核因子？B受APE1氧化还原控制，核因子？B活性是胰腺癌细胞对吉西他滨反应的决定因素。我们有能力通过阻断APE1的S功能的小分子来独立检测APE1的内切酶和氧化还原功能。因此，我们的短期目标是建立APE1作为使胰腺肿瘤对化疗敏感的靶点。胰腺癌的不良反应率需要更好的和新的治疗方法，因此我们建议联合使用替莫唑胺(TMZ)和APE1氧化还原/DNA修复抑制剂。TMZ是一种烷化剂，它产生DNA损伤，通过BER途径修复。我们的初步数据显示，在胰腺癌细胞系中，TMZ与小分子APE1抑制剂甲氧胺(MX)联合使用，显著增强了TMZ诱导的细胞毒性。因此，TMZ是胰腺癌联合治疗的极佳候选药物，除吉西他滨外，还使用APE1抑制剂。这项拟议工作的总体假设是，吉西他滨和TMZ可以通过阻断APE1的活性和DNA损伤的修复来改善胰腺癌的治疗。除了在APE1DNA修复或氧化还原抑制剂存在的情况下提高对化疗(吉西他滨或TMZ)敏感性的临床应用外，我们还将更深入地了解胰腺细胞对吉西他滨或TMZ的反应机制以及APE1在这一反应中所起的作用。胰腺癌是一种致命的疾病，几乎无法治愈，而且已知对大多数化疗方案都有耐药性。我们希望通过抑制一种参与DNA修复和氧化还原信号的蛋白质APE1来使这些耐药肿瘤对治疗敏感，并实现更长的患者反应。这项提案将研究在多大程度上削弱胰腺癌细胞对化疗后DNA损伤的反应能力，将导致对DNA损伤剂吉西他滨和替莫唑胺治疗的反应增加。

DESCRIPTION (provided by applicant): Pancreatic cancer is a deadly disease that is virtually never cured, therefore our long-term goal is to develop therapeutic regimens for pancreatic cancer patients that sensitize these chemo-resistant tumors to therapy and achieve prolonged patient response. This proposal will investigate to what extent impairing the ability of the pancreatic cancer cells to respond to DNA damage following therapy will result in an increase in response to treatment with DNA damaging agents. To increase the efficacy of chemotherapy in pancreatic cancer cells, we plan to inhibit a key protein in the DNA base excision repair (BER) pathway. The BER pathway including apurinic/apyrimidinic endonuclease/redox factor (Ape1/Ref-1 or Ape1) plays a major role in the repair of damage caused by chemotherapeutic agents. In addition to DNA repair activity, Ape1 also interacts with a number of transcription factors (Hif1-a, p53, AP1, NF?B, etc) to facilitate their DNA binding. Gemcitabine, a DNA chain terminator, is the foremost chemotherapeutic agent currently used to treat pancreatic cancer. Studies demonstrating a role for the 3' to 5' exonuclease activity of Ape1 in the excision of deoxyribonucleoside analogs from DNA provide rationale for combining Ape1 DNA repair inhibitors with gemcitabine treatment. In addition, a reduced level of Ape1 protein sensitized pancreatic cancer cells to gemcitabine. Furthermore, NF?B is known to be under redox control by Ape1, and Nf?B activity is a determinant of pancreatic cancer cells' response to gemcitabine. We have the ability to examine the endonuclease and the redox functions of Ape1 independently by using small molecules that block both of Ape1's functions. Therefore, our short term goal is to establish Ape1 as a target to sensitize pancreatic tumors to chemotherapy. Dismal response rates in pancreatic cancer necessitate better and novel therapies, therefore we propose the use of temozolomide (TMZ) in combination with Ape1 redox/DNA repair inhibitors. TMZ is an alkylating agent which creates DNA lesions that are repaired by the BER pathway. We have preliminary data demonstrating a dramatic enhancement of TMZ-induced cytotoxicity in combination with small molecule Ape1 inhibitor, methoxyamine (MX) in pancreatic cancer cell lines. TMZ is, therefore, an excellent candidate for combination therapy in pancreatic cancer involving Ape1 inhibitors in addition to gemcitabine. The overall hypothesis of the proposed work is that treatment of pancreatic cancer with gemcitabine and TMZ can be improved by blocking the activity of Ape1 and the repair of DNA lesions. In addition to the clinical application of enhanced sensitivity to chemotherapy (gemcitabine or TMZ) in the presence of Ape1 DNA repair or redox inhibitors, we will also gain a more thorough understanding of the mechanism of pancreatic cells' response to gemcitabine or TMZ and the role that Ape1 plays in that response. Pancreatic cancer is a deadly disease that is virtually never cured and known to be resistant to most chemotherapy regimens. We want to sensitize these chemo-resistant tumors to therapy and achieve prolonged patient response by inhibiting a protein involved in DNA repair and redox signaling, Ape1. This proposal will investigate to what extent impairing the ability of the pancreatic cancer cells to respond to DNA damage following chemotherapy will result in an increase in response to treatment with DNA damaging agents, gemcitabine and temozolomide.