MION for Synchronized MRI and Drug Therapy of Brain Tumor

每年约有40，000名美国人被诊断患有脑肿瘤，其中15 - 35%为多形性胶质母细胞瘤（GBM）;这是最具侵袭性的原发性脑肿瘤，无法接受所有现有的治疗方式。治疗脑肿瘤首先是手术切除，然后是放疗或化疗。手术面临着切除可能携带重要脑功能的周围组织的风险，而放疗和化疗也会损害治疗途径上的正常组织沿着。由于药物的姑息性反应以及缺乏靶向和选择性，化疗的应用非常有限。本文提出了一种新型的药物递送系统（DDS），其将利用MION（磁性氧化铁纳米颗粒）作为载体来实现脑肿瘤的同步MRI和药物治疗。它在单个DDS中包含所有期望的特征，包括：[1] MRI、[2]磁靶向、[3]前药和[4]细胞药物摄取，以克服脑药物递送中的障碍并实现MRI可视化的高效肿瘤治疗，具有最少的药物诱导的毒性作用。原则上，具有不匹配的神经胶质瘤特异性和效力的大分子药物（例如ATF 5-siRNA）将通过细胞溶胶可降解的S-S键与无毒的细胞穿透LMWP连接，而携带超顺磁性行为和上级磁泳迁移率的MION将被生物相容性肝素-葡聚糖聚合物涂覆。LMWP修饰的药物（LMWP-Drug）和肝素包被的MION（Hep-MION）将通过阳离子LMWP和阴离子肝素之间的静电结合自动形成复合物。组装后，由于肝素结合抑制LMWP的跨细胞活性，LMWP-Drug/Hep-MION在肿瘤靶向期间将显示独特的前药特征。为了战胜首过器官清除，从而使肿瘤处的MION积聚最大化，将通过动脉内途径注射复合物。然后将遵循优化的磁场地形图，以中止动脉血管系统的可能栓塞并最大化肿瘤靶向选择性。在通过MRI验证通过被动EPR和主动磁靶向的MION肿瘤定位后，将随后鼻内给予鱼精蛋白（一种比LMWP更强地结合肝素的临床肝素解毒剂）以触发LMWP药物从Hep-MION释放。一旦通过LMWP介导的内化进入肿瘤细胞内，药物将通过升高的胞质还原酶活性降解S-S键而从LMWP脱离，从而引发肿瘤细胞凋亡。由于大的药物是细胞不可渗透的，因此细胞溶胶递送的药物不会受到MDR的影响。初步发现是非常有希望的，因为它们证明了迄今为止第一次真正成功地将大量的465-KDa β-半乳糖苷酶选择性地递送到脑肿瘤中，而不是同侧或对侧正常脑区域。在这个新的R01应用中，我们计划使用完善的大鼠胶质瘤模型来确认这种DDS在体内的实用性。

Approximately 40,000 Americans are diagnosed with brain tumors each year, with15-35% being glioblastoma multiforme (GBM); the most aggressive primary brain tumor that has defied all existing treatment modalities. Treating brain tumors begins with surgical resection then follows with radiation or chemotherapy. Surgery faces the risks of removing surrounding tissues that may carry vital brain functions, while both radiation and chemotherapy can also harm normal tissues along the treatment pathway. Chemotherapy has been offering very limited applications, due to the palliative response and lack of targeting and selectivity of the drugs. Proposed herein is a novel drug delivery system (DDS) that will utilize MION (magnetic iron oxide nanoparticles) as the carrier to achieve synchronized MRI and drug therapy of brain tumors. It contains all desirable features within a single DDS including: [1] MRI, [2] magnetic targeting, [3] prodrug, and [4] cellular drug uptake, in overriding obstacles in brain drug delivery and achieving MRI-visualized, highly effective tumor therapy with least drug- induced toxic effects. In principle, macromolecular drug (e.g. ATF5-siRNA) with unmatched glioma specificity and potency will be linked to the non-toxic cell-penetrating LMWP via cytosol-degradable S-S bond, whereas MION carrying superparamagnetic behavior and superior magnetophoretic mobility will be coated with a bio- compatible heparin-dextran polymer. The LMWP-modified drug (LMWP-Drug) and heparin-coated MION (Hep- MION) will automatically group into a complex via electrostatic binding between the cationic LMWP and anionic heparin. After assembly, LMWP-Drug/Hep-MION shall display a unique prodrug feature during tumor targeting, due to inhibition of LMWP’s trans-cell activity by heparin binding. To prevail over first-pass organ clearance thus maximizing MION accumulation at the tumor, the complexes will be injected via intra-arterial route. Optimized magnetic field topography will then follow to abort possible embolism of arterial vasculature and maximize tumor targeting selectivity. After tumor localization of MION via passive EPR- and active magnetic-targeting is verified by MRI, nasal administration of protamine, a clinical heparin antidote that binds heparin stronger than LMWP, will be followed to trigger release of LMWP-Drug from Hep-MION. Once inside tumor cells by LMWP-mediated internalization, the drug will be detached from LMWP by degradation of the S-S bond via elevated cytosolic reductase activity, initiating tumor apoptosis. Since large drugs are cell-impermeable, the cytosol-delivered drugs will not be affected by MDR. Preliminary findings were extremely promising, as they demonstrated by far the first true success of delivering a significant amount of the 465-KDa -galactosidase selectively into the brain tumor but not ipsilateral or contralateral normal brain regions. In this new R01 application, we plan to confirm the utility of this DDS in vivo using well-established rat glioma models.