Pharmacological Ascorbate as a Radiosensitizer in Pancreatic Cancer

描述(申请人提供)：胰腺癌是美国癌症死亡的第四大原因，而且发病率正在上升。静脉注射抗坏血酸(即抗坏血酸、维生素C)，而不是口服抗坏血酸，会产生较高的血浆浓度，对肿瘤细胞具有细胞毒性。我们目前资助的为期两年的U01赠款CA166800“抗坏血酸诱导的胰腺癌放射增敏”的研究表明，在人类可以达到的剂量下，抗坏血酸通过过氧化氢介导的机制与电离辐射协同作用，降低所有被检查的胰腺癌细胞系的存活率和增殖。我们最近完成的第一阶段研究表明，药理抗坏血酸联合吉西他滨是安全和耐受性良好的，并可能导致对IV期胰腺癌患者的总体临床益处。该提案的重点是在胰腺癌的治疗中使用辅助方法(高剂量抗坏血酸)来提高标准抗癌疗法(电离辐射)的治疗比率。如果胰腺癌细胞(相对于正常细胞)更容易受到抗坏血酸诱导的细胞毒性的影响，这是由于抗坏血酸自氧化增加导致过氧化氢产生增加，那么抗坏血酸将有望成为患者对化疗辐射的有效和耐受性良好的佐剂。此外，提高抗坏血酸与氧化还原活性金属催化剂的自氧化速率以产生更多的H_2O_2应该选择性地增加抗坏血酸诱导的辐射增敏和氧化应激。最后，抗坏血酸诱导的放射增敏有望使肿瘤细胞对抑制过氧化氢清除的临床相关药理物质增敏。目前的提议将检验这样一种假设，即通过金属离子催化的抗坏血酸自氧化产生过氧化氢，介导了抗坏血酸诱导的细胞毒性和人胰腺癌的化疗放射增敏。我们将通过以下三个具体目标来检验我们的假设。1)在I期试验中确定在吉西他滨-放射治疗同时治疗不可切除的胰腺癌期间给予药理抗坏血酸的安全性；2)确定抗坏血酸诱导的放射增敏是否可以通过氧化还原活性金属催化剂选择性地增强；3)确定抗坏血酸诱导的放射增敏是否可以通过临床相关的葡萄糖和氢过氧化氢代谢的药理抑制剂来增强。I期试验将量化不良事件，并确定指示患者氧化应激的系统参数的变化。临床前研究将使用生物化学/分子 确定抗坏血酸诱导的放射增敏和氧化应激的生物学技术，并采用非侵入性体内细胞增殖指数。如果我们能够严格证明药物抗坏血酸介导的放射增敏在人胰腺癌细胞中诱导优先的氧化应激和随后的细胞毒性，那么这项研究计划的结果将为合理设计胰腺癌新的联合治疗方案提供基础。

DESCRIPTION (provided by applicant): Adenocarcinoma of the pancreas is the fourth leading cause of cancer death in the United States and is increasing in incidence. Intravenous ascorbate (i.e., ascorbic acid, vitamin C), but not oral ascorbate, produces high plasma concentrations, which are in the range that are cytotoxic to tumor cells. Studies from our currently funded 2 year U01 grant CA166800 "Ascorbate-induced radiosensitization in pancreatic cancer" have demonstrated that ascorbate, in doses achievable in humans, synergizes with ionizing radiation in decreasing viability and proliferation in all pancreatic cancr cell lines examined, via a H2O2-mediated mechanism. Our recently completed phase I study demonstrated that pharmacological ascorbate combined with gemcitabine is safe and well-tolerated and may lead to overall clinical benefit in patients with stage IV pancreatic cancer. Thi proposal focuses on improvement of the therapeutic ratio of a standard anti-cancer therapy (ionizing radiation) using a complementary approach (high dose ascorbate), in the treatment of pancreatic cancer. If pancreatic cancer cells (relative to normal cells) are more susceptible to ascorbate-induced cytotoxicity due to increased ascorbate auto-oxidation leading to increased H2O2 production, then ascorbate would be expected to be efficacious and well-tolerated adjuvant to chemo-radiation in patients. Furthermore, increasing the rate of auto- oxidation of ascorbate with redox active metal catalysts to generate more H2O2 should selectively increase ascorbate-induced radiosensitization and oxidative stress. Finally, ascorbate-induced radiosensitization would be expected to sensitize tumor cells to clinically relevant pharmacological agents that inhibit the removal of H2O2. The current proposal will test the hypothesis that production of H2O2 via the metal ion catalyzed auto- oxidation of ascorbate mediates ascorbate-induced cytotoxicity and chemo-radiosensitization in human pancreatic cancer. We will test our hypothesis with the following three Specific Aims. 1) Determine in a phase I trial the safety of administering pharmacological ascorbate during concurrent gemcitabine-radiation therapy for the treatment of non-resectable pancreatic cancer; 2) Determine if ascorbate-induced radiosensitization can be selectively enhanced by redox active metal catalysts; 3) Determine if the ascorbate-induced radiosensitization can be enhanced by clinically relevant pharmacological inhibitors of glucose and hydroperoxide metabolism. The phase I trial will quantify adverse events and determine changes in systemic parameters indicative of oxidative stress in patients. The preclinical studies will use biochemistry/molecular biology techniques to determine ascorbate-induced radiosensitization and oxidative stress and employ a non- invasive in vivo index of cell proliferation. If we can rigorously demonstrate that the radiosensitization mediated by pharmacological ascorbate induces preferential oxidative stress and subsequent cytotoxicity in human pancreatic cancer cells, then the results of this proposed research program will provide a foundation for the rational design of a novel combined modality cancer therapy for pancreatic cancer.