Glutathione reductase and tumor sensitivity to radiation

描述（由申请人提供）：癌症对辐射的抗性通常是放射治疗失败的原因;细胞内谷胱甘肽（GSH）被认为是抗性的主要原因之一。GSH通过终止辐射产生的自由基和活性氧（ROS）来破坏癌细胞，从而增加癌症对辐射的抵抗力。已经做出了广泛的努力来通过减少细胞内GSH来增加癌症对辐射的敏感性。减少细胞内GSH的最广泛研究的方法是使用丁硫酰亚胺亚砜（BSO），一种GSH合成的抑制剂。BSO已被证明可以有效降低GSH水平，增加癌症对辐射的敏感性。在该应用中，我们提出通过抑制谷胱甘肽还原酶（GR）来增加癌症对辐射的敏感性。这一假设，即抑制GR可能提供一种替代的和可能更有效的方式来增加癌症对辐射的反应，是基于这样的事实，即在终止自由基或ROS时，GSH被氧化成其氧化形式GSSG。GR是负责将GSSG还原为GSH的酶。GR的抑制将阻碍细胞将GSSG转化回GSH以维持细胞内GSH水平的能力。因此，GR的抑制不仅会降低细胞内GSH水平，而且会导致GSSG的积累。本实验室用OVCAR-3细胞（一种对化疗和放疗具有抗性的人卵巢癌细胞系）进行的初步实验表明，GR的抑制确实减少了细胞内GSH，并且GSH的减少导致OVCAR-3对化疗剂美法仑的敏感性增加。在这项应用中，我们计划扩展这项工作，以确定GR的抑制是否也可以增加OVCAR-3对辐射的敏感性。此外，我们还计划研究GR抑制对细胞氧化还原状态和负责终止自由基和ROS的酶系统的影响，因为这些酶系统会影响癌症对辐射的敏感性。这项研究将提供GR抑制对癌症对辐射的敏感性，细胞氧化还原状态（通过硫醇/二硫化物的比例），以及参与终止自由基和ROS的酶系统的影响的信息。长期目标是开发一种新的方法来增加癌症对辐射的敏感性。

DESCRIPTION (provided by applicant): Cancer resistance to radiation is often the cause of failure in radiotherapy; intracellular glutathione (GSH) has been implicated as one of the major causes of the resistance. GSH increases cancer resistance to radiation by terminating free radicals and reactive oxygen species (ROS) that are generated by radiation to destroy cancer cells. Extensive efforts have been made to increase cancer sensitivity to radiation through decreasing intracellular GSH. The most extensively investigated approach in reducing intracellular GSH has been the use of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis. BSO has been demonstrated to effectively reduce GSH levels and increase cancer sensitivity to radiation. In this application, we propose to increase cancer sensitivity to radiation through inhibition of glutathione reductase (GR). This proposed hypothesis, that is inhibition of GR may provide an alternative and possibly more effective way to increase cancer response to radiation, is based on the fact that in terminating free radicals or ROS, GSH is oxidized to its oxidized form GSSG. GR is the enzyme responsible for the reduction of GSSG to GSH. Inhibition of GR will hamper the cell's ability to convert GSSG back to GSH to maintain intracellular GSH levels. As a result, inhibition of GR will not only reduce intracellular GSH levels but also cause accumulation of GSSG. Therefore, inhibition of GR may have more impact on cancer sensitivity to radiation than inhibition of GSH synthesis.Preliminary experiments conducted in this laboratory with OVCAR-3 ceils, a human ovarian cancer cell line with resistance to chemotherapy and radiotherapy, have shown that inhibition of GR did reduce intracellular GSH and the reduction of GSH led to an increase in the sensitivity of OVCAR-3 to melphalan, a chemotherapeutic agent. In this application, we are planning to extend the work to determine if inhibition of GR can also increase the sensitivity of OVCAR-3 to radiation. In addition, we are also planning to investigate the effect of GR inhibition on the cellular redox state and the enzyme systems responsible for terminating free radicals and ROS, since these enzyme systems will affect cancer sensitivity to radiation. This investigation will provide information on the effect of GR inhibition on cancer sensitivity to radiation, cellular redox state (via the ratio of thiol/disulfide), and enzyme systems involved in terminating radicals and ROS. The long-term objective is to develop a novel approach to increase cancer sensitivity to radiation.