MION for Synchronized MRI and Drug Therapy of Brain Tumor

每年约有40,000名美国人被诊断出患有脑瘤，其中15%-35%是多形性胶质母细胞瘤(GBM)，这是一种最具侵袭性的原发脑瘤，已挑战所有现有的治疗方式。治疗脑瘤首先是手术切除，然后是放射或化疗。手术面临着移除可能承载重要大脑功能的周围组织的风险，而放射和化疗也可能损害治疗过程中的正常组织。由于药物的姑息性反应以及缺乏靶向性和选择性，化疗的应用一直非常有限。本文提出了一种新型的药物传递系统(DDS)，该系统将利用Mion(磁性氧化铁纳米颗粒)作为载体来实现脑肿瘤的MRI和药物治疗的同步。它包含了单个DDS中的所有理想功能，包括：[1]MRI、[2]磁靶向、[3]前药和[4]细胞药物摄取，克服了脑内药物输送的障碍，实现了MRI可视化、高效的肿瘤治疗，药物引起的毒性作用最小。原则上，具有无与伦比的胶质瘤特异性和有效性的大分子药物(例如，ATF5-siRNA)将通过胞浆可降解的S-S键连接到无毒的穿透细胞的低分子聚合物上，而携带超顺磁性和优越磁致迁移率的Mion将被生物兼容的肝素-葡聚糖聚合物包裹。LMWP修饰的药物(LMWP-Drug)和肝素包裹的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体。组装后，由于肝素结合抑制了LMWP的跨细胞活性，LMWP-Drug/Hep-Mion在肿瘤靶向过程中将显示出独特的前药特性。为了克服首次通过的器官清除，从而最大限度地增加Mion在肿瘤中的积聚，将通过动脉内途径注射复合体。优化的磁场拓扑图随后将终止可能的动脉血管栓塞，并最大限度地提高肿瘤靶向选择性。在MRI证实通过被动EPR和主动磁靶向对Mion进行肿瘤定位后，鼻腔给药鱼精蛋白将触发Hep-Mion释放LMWP-药物。鱼精蛋白是一种临床肝素解毒剂，它与肝素的结合比LMWP更强。一旦药物进入肿瘤细胞内，通过LMWP介导的内化，药物将通过胞浆还原酶活性升高而降解S-S键，启动肿瘤细胞凋亡。由于大的药物是细胞不渗透的，胞质递送的药物不会受到MDR的影响。初步发现非常有希望，因为它们证明了到目前为止第一次真正成功地将相当数量的465kDa-半乳糖苷酶选择性地输送到脑瘤中，而不是同侧或对侧正常脑区。在这一新的R01应用中，我们计划使用成熟的大鼠胶质瘤模型在体内证实这种DDS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.