Pharmacological Ascorbate as a Radiosensitizer in Pancreatic Cancer

描述（由申请人提供）：胰腺腺癌是美国癌症死亡的第四大原因，并且发病率正在增加。静脉注射抗坏血酸（即抗坏血酸、维生素 C）（而非口服抗坏血酸）会产生高血浆浓度，该浓度处于对肿瘤细胞具有细胞毒性的范围内。我们目前资助的 2 年 U01 资助 CA166800“抗坏血酸诱导的胰腺癌放射增敏”研究表明，在人类可达到的剂量下，抗坏血酸与电离辐射协同作用，通过 H2O2 介导的机制降低所有检查的胰腺癌细胞系的活力和增殖。我们最近完成的一期研究表明，药理学抗坏血酸与吉西他滨联合使用是安全且耐受性良好的，可能会给 IV 期胰腺癌患者带来总体临床获益。该提案的重点是使用补充方法（高剂量抗坏血酸）提高标准抗癌疗法（电离辐射）在胰腺癌治疗中的治疗率。如果胰腺癌细胞（相对于正常细胞）由于抗坏血酸自氧化增加导致 H2O2 产生增加而更容易受到抗坏血酸诱导的细胞毒性的影响，那么抗坏血酸将有望成为患者放化疗的有效且耐受性良好的佐剂。此外，用氧化还原活性金属催化剂提高抗坏血酸的自动氧化速率以产生更多的H2O2，应该选择性地增加抗坏血酸诱导的放射增敏和氧化应激。最后，抗坏血酸诱导的放射增敏作用有望使肿瘤细胞对抑制 H2O2 去除的临床相关药物变得敏感。目前的提案将检验以下假设：通过金属离子催化抗坏血酸自氧化产生 H2O2 介导抗坏血酸诱导的细胞毒性和人类胰腺癌的化学放射增敏作用。我们将通过以下三个具体目标来检验我们的假设。 1) 在 I 期试验中确定在同步吉西他滨放射治疗治疗不可切除的胰腺癌期间施用药理学抗坏血酸的安全性； 2）确定氧化还原活性金属催化剂是否可以选择性增强抗坏血酸诱导的放射增敏作用； 3) 确定抗坏血酸诱导的放射增敏作用是否可以通过临床相关的葡萄糖和氢过氧化物代谢的药理学抑制剂来增强。 I 期试验将量化不良事件并确定表明患者氧化应激的全身参数变化。临床前研究将使用生物化学/分子 生物学技术来确定抗坏血酸诱导的放射增敏和氧化应激，并采用细胞增殖的非侵入性体内指数。如果我们能够严格证明药理学抗坏血酸介导的放射增敏作用会在人胰腺癌细胞中诱导优先氧化应激和随后的细胞毒性，那么本研究计划的结果将为合理设计新型胰腺癌联合疗法奠定基础。

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.