The chemical biology of pharmacological ascorbate in cancer treatment

描述（由申请人提供）：本研究计划将研究药物抗坏血酸盐（高剂量，静脉注射维生素C）在癌症治疗中的应用。药理学抗坏血酸盐（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性质，药理学AscH-是将细胞外H2 O2递送到肿瘤细胞的前药。在AscH-的这种用途中，它必须静脉内给予;血浆水平达到20 - 30 mM;健康个体的血浆抗坏血酸水平约为50 μM（0.05 mM）。与药理学AscH-的目标是实现一个短暂的水平抗坏血酸在血浆中的顺序上的300-500倍的典型的健康“营养”水平。在这些高水平下，血浆中AscH-的半衰期为H2.3 h。因此，治疗后12 - 24小时，血浆中的AscH-水平大大超过健康的“营养”水平。我们建议研究药理学AscH-的作用机制，以了解：（1）什么生化特性使癌细胞对药理学AscH-敏感;（2）为什么它对正常组织无毒。我们的目标是解开基本的生化机制，使这种疗法可以在广泛的适当选择的癌症。 我们假设细胞对药理学AscH-敏感性的差异是维持其细胞内氧化还原缓冲液（GSSG，2 H +/2GSH）在与生命相容的半细胞还原电位（Ehc）的能力。这一假设的基本原理是：（1）AscH-容易自氧化产生H2 O2通量（在细胞培养基和体内）;（2）高水平的细胞外分泌物， AscH-通过静脉内递送（H300- 500 X“营养”水平）实现，产生高通量的H2 O2;（3）通过细胞去除这种高通量的H2 O2导致对细胞内还原的巨大需求。 （4）这导致细胞内氧化还原缓冲液的氧化，导致静止或细胞死亡，这取决于氧化的程度。维持适当降低的细胞内氧化还原缓冲液的细胞将不太容易暴露于药理学AscH-;不能维持其细胞内氧化还原缓冲液的细胞将死亡。 由于氧化还原缓冲液的状态由磷酸戊糖途径（PPP）维持，我们进一步提出，氧化挑战的氧化还原缓冲液将与也连接到PPP的试剂（例如吉西他滨、5-氟尿嘧啶，尤其是电离辐射）协同作用。 该研究计划通过解决为什么药理学抗坏血酸对生物体（即人）无毒的基本问题来支持翻译工作，但癌细胞可能非常敏感。这项研究的结果将指导翻译工作，选择适当的佐剂用于治疗和癌症（患者），可能受益于这种治疗方法。

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.