The chemical biology of pharmacological ascorbate in cancer treatment

描述(由申请人提供)：本研究计划将调查药理抗坏血酸(大剂量，静脉注射)的使用。维生素C)在癌症治疗中的应用。药理抗坏血酸(Asch-)利用Asch的基本化学性质将其用作药物；事实上，由于其作为还原剂的特性，药理Asch-是将细胞外过氧化氢输送到肿瘤细胞的前体药物。在使用Asch-时，必须静脉给药；达到20-30 mM的血浆水平；健康人的血浆抗坏血酸水平约为50μM(0.05 mM)。使用药理Asch-目标是实现血浆中抗坏血酸的瞬时水平，大约是典型健康“营养”水平的300-500倍。在这些高水平的血浆中，Asch-in的半衰期为H2.3小时。因此，在治疗后的12-24小时内，Asch-in的血浆水平大大超过健康的“营养”水平。我们建议研究药理Asch的作用机制，以了解：(1)什么生化特性使癌细胞对药理Asch敏感；(2)为什么它对正常组织无毒。我们的目标是揭开基本的生化机制，以便这种疗法可以应用于广泛的适当选择的癌症。我们假设，细胞对药物Asch-的敏感性差异是将其细胞内氧化还原缓冲液(GSSG，2H+/2GSH)维持在与生命相容的半细胞还原电位(EHC)的能力。这一假说的基本原理是：(1)Asch-容易自氧化产生(在细胞培养液和体内)的H_2O_2通量；(2)高水平的细胞外 Asch-由静脉注射实现。输送(H300-500X“营养”水平)产生高通量的过氧化氢；(3)细胞去除这种高通量的过氧化氢导致对细胞内还原的巨大需求 同等物，即谷胱甘肽(GSH)和NADPH；(4)这会导致细胞内氧化还原缓冲，导致静止或细胞死亡，具体取决于氧化程度。保持适当减少的细胞内氧化还原缓冲的细胞将不太容易受到药物Asch-的影响；不能维持细胞内氧化还原缓冲的细胞将死亡。由于氧化还原缓冲液的状态是由磷酸戊糖途径(PPP)维持的，我们进一步提出，氧化挑战的氧化还原缓冲液将与也与PPP连接的试剂协同作用，例如吉西他滨、5-氟尿嘧啶，特别是电离辐射。这项研究计划通过解决为什么药理抗坏血酸对生物体无毒，即对人无毒，但癌细胞可能非常敏感这一根本问题来支持翻译工作。这项研究的结果将指导翻译工作，为治疗和可能从这种治疗方法中受益的癌症(患者)选择适当的佐剂。

DESCRIPTION (provided by applicant): This research program will the investigate use of pharmacologic ascorbate (high-dose, i.v. delivery of vitamin C) in the treatment of cancer. Pharmacological ascorbate (AscH-) takes advantage of the basic chemical properties of AscH- to use it as a drug; in fact because of its properties as a reducing agent, pharmacologic AscH- is a pro-drug for the delivery of extracellular H2O2 to tumor cells. In this use of AscH-, it must be given intravenously; plasma levels of 20 - 30 mM are achieved; healthy individuals have plasma ascorbate levels on the order of 50 μM (0.05 mM). With pharmacological AscH- the goal is to achieve a transient level of ascorbate in plasma on the order of 300-500 times that of typical healthy "nutritional" levels. The half-life of AscH- in plasma at these high levels is H2.3 h. Thus for 12 - 24 h after treatment, levels of AscH- in plasma greatly exceed healthy "nutritional" levels. We propose to investigate the mechanism of action of pharmacological AscH- to learn: (1) what biochemical properties make cancer cells susceptible to pharmacological AscH-; and (2) why it is not toxic to normal tissue. Our goal is to unravel basic biochemical mechanisms so this therapy can be employed in a broad range of appropriately selected cancers. We hypothesize that the difference in susceptibility of cells to pharmacological AscH- is the ability o maintain their intracellular redox buffer (GSSG,2H+/2GSH) at a half-cell reduction potential (Ehc) compatible with life. The rationale for this hypothesis is that: (1) AscH- readily autoxidize producing a flux of H2O2 (in cell culture media and in vivo); (2) the high levels of extra cellular AscH- achieved by i.v. delivery (H300-500X "nutritional" levels) produce a high flux of H2O2; (3) the removal of this high flux of H2O2 by cells results in a great demand for intracellular reducing equivalents, i.e. glutathione (GSH) and NADPH; (4) this results in oxidation of the intracellular redox buffer, leading to quiescence or cell death, depending on the extent of oxidation. Cells that maintain an appropriately reduced intracellular redox buffer will be less susceptible to exposure to pharmacological AscH-; cells that cannot maintain their intracellular redox buffer will die. Because the status of the redox buffer is maintained by the pentose phosphate pathway (PPP), we further propose that an oxidatively challenged redox buffer will be synergistic with agents that also connect to the PPP, e.g. gemcitabine, 5-fluorouricil, and especially ionizing radiation. This research program supports translational efforts by addressing the fundamental question of why pharmacological ascorbate is non-toxic to organisms, i.e. people, yet cancer cells can be very susceptible. The results of this study will guide translational efforts in selectng appropriate adjuvants for therapy and cancers (patients) that may benefit from this approach to treatment.