pH响应/可降解硅基携氧纳米放疗增敏剂的构建及对脑胶质瘤放射治疗研究

In order to solve the clinical problem that glioma tumor is resistant to radiotherapy in hypoxia condition, an intracellular pH-responsive and degradable oxygen-carrying nanoradiosensitizer (PFH(O2)@GdHMSiO2(ACF)@Tf-RGD) has been constructed. The enhancing radiosensitive properties on radiotherapy have been studied at primary glioma cells and orthotopic glioma-bearing animal models. The nanoradiosensitizer has the following characteristics: (1) It utilizes the property of acidic microenvironment of the glioma tumor, which triggers the degradation and releasing radiosensitive O2 as well as ACF molecule, which shows "zero release" outside the tumor tissue that reduces damage to normal tissues during radiotherapy; It also presents the easy degradability and overcomes the problem that the conventional silica-based carrier is easy to accumulate together in tumor tissues. (2) The enhancement of the intratumoral MRI-T1 signal could be obtained by release of Gd3+ during the degradation of this nanoradiosensitizer. Thus radiotherapy could be efficiently guided in “visualization” by this change of MRI-T1 signal. (3) The enhancing chemical radiosensitivity of glioma on radiotherapy has been achieved by increasing the oxygen content in tumor tissue. At the same time the enhancement of biosensitization could also be obtained by inhibiting the synthesis of cellular hypoxia factor-1 that down-regulates the expression of radio-resistant genes. Furthermore, this dual-target nanoradiosensitizer has a synergistic radiosensitizing effect on radiotherapy. Once the project is successfully developed, it will provide a new opportunity for glioma treatment in clinical application.

针对临床上脑胶质瘤乏氧导致放射治疗耐受的问题，构建瘤内pH响应/可降解的携氧纳米放射治疗增敏剂（PFH(O2)@GdHMSiO2(ACF)@Tf-RGD），从细胞水平（原代细胞）和动物水平（原位脑胶质瘤模型）研究其对脑胶质瘤的放射增敏疗效。该纳米增敏剂具有以下特点：（1）利用肿瘤微环境呈现酸性降解/释放增敏物质（O2和ACF），实现肿瘤组织外“零释放”，减少对正常组织的损伤；GdHMSiO2具有可降解性，克服了传统硅基载体瘤组织内易蓄积“饱和”的问题。（2）降解过程中释放Gd3+增强瘤内MRI-T1信号，通过T1信号变化“可视化”引导放射治疗。（3）分别通过增加组织内O2含量，增加胶质瘤放疗敏感性（化学增敏）；抑制细胞乏氧因子-1（HIF-1）的合成，下调放疗抵抗性基因的表达（生物增敏），这种双靶点放射治疗增敏剂具有协同增敏效应。一旦该项目研制成功，将为临床放射治疗胶质瘤提供新的契机！

脑胶质瘤微环境乏氧导致放疗抵抗，这直接制约了放射治疗对于胶质瘤的治疗能力。针对脑胶质瘤肿瘤组织乏氧，通过瘤内pH可降解的硅基携氧纳米增敏剂PFH(O2)@GdHMSiO2(ACF)@Tf-RGD，实现了双靶点协同增敏放射治疗，提高脑胶质瘤的放射治疗效果。通过引入转铁蛋白和RGD肽修饰，实现高效跨血脑屏障（BBB）和精准靶向胶质瘤细胞，转铁蛋白修饰后跨BBB能力提高了5-8倍。RGD修饰后的增敏剂被胶质瘤细胞摄取含量增加了3-4倍，而且可以有效从溶酶体逃逸。通过Gd3+掺杂技术调控GdHMSiO2的pH敏感性，减小了在正常组织内蓄积导致的毒性作用。pH越低负载的氧气和ACF释放的越多，在pH=5.0时O2的释放可以达到加载量的80%，ACF的释放量最高可以达到加载量的95%，主要释放时间在6-12h以内。增敏剂中氧气含量的增加，纳米增敏剂的增敏效果随之增加，当氧气浓度达到3%时胶质瘤细胞几乎没有增殖。当接受放射治疗时，乏氧胶质瘤细胞的周期主要在G2/M期，处于放疗敏感时期，这说明了PFH(O2)@GdHMSiO2(ACF)@Tf-RGD是一种高效的放疗增敏剂，通过下调HIF-1蛋白增加细胞对X射线的敏感能力。降解过程中释放的Gd3+可以引起胶质瘤内MRI-T1信号变化，建立MRI-T1 Contrast变化量值与乏氧信号的关系并且绘制了MRI-T1 Contrast值与O2释放量的关系图，实现通过MRI-T1信号变化“可视化”O2释放。经过硅基携氧放疗增敏剂治疗后的脑部胶质瘤增殖能力明显受到抑制，中位生存期达到了55天。本项目的放疗增敏剂已经在动物上取得了初步的疗效，可以显著抑制胶质瘤的增殖，延长负荷胶质瘤小鼠的生存周期。经过进一步的工艺优化，具有很好的临床转化应用前景。特别是针对临床上乏氧型胶质瘤，这类肿瘤具有放疗抵抗性，采用硅基携氧纳米增敏剂可以克服肿瘤微环境乏氧，有效延长患者生存周期。