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）；最具侵袭性的原发性脑肿瘤，所有现有的治疗方法都束手无策。脑肿瘤的治疗首先是手术切除，然后是放疗或化疗。手术面临着切除周围组织的风险，这些组织可能承载着重要的大脑功能，而放疗和化疗也会在治疗过程中损害正常组织。由于姑息性反应和药物缺乏靶向性和选择性，化疗的应用一直非常有限。本文提出了一种以磁性氧化铁纳米颗粒（MION）为载体的新型给药系统（DDS），以实现脑肿瘤的MRI和药物同步治疗。它在单一DDS中包含所有理想的特征，包括：[1]MRI，[2]磁靶向，[3]前药和[4]细胞药物摄取，克服脑药物输送障碍，实现MRI可视化，高效肿瘤治疗，药物诱导毒性最小。原则上，具有无与伦比的胶质瘤特异性和效能的大分子药物（例如ATF5-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，而具有超顺磁性行为和优越磁泳流动性的MION将被生物相容的肝素-葡聚糖聚合物包裹。LMWP修饰的药物（LMWP- drug）和肝素包被的MION （Hep- MION）会通过阳离子LMWP和阴离子肝素之间的静电结合自动组合成复合物。组装后，由于肝素结合抑制LMWP的跨细胞活性，LMWP- drug /Hep-MION在肿瘤靶向过程中表现出独特的前药特征。为了克服第一次器官清除从而最大化肿瘤中MION的积累，这些复合物将通过动脉内途径注射。然后，优化磁场地形，以阻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。在通过被动EPR和主动磁靶向对MION进行肿瘤定位后，通过MRI验证，鼻给药鱼精蛋白（一种临床肝素解毒剂，与肝素的结合比LMWP强）将触发Hep-MION释放LMWP-药物。一旦通过LMWP介导的内化进入肿瘤细胞，药物将通过提高胞质还原酶活性降解S-S键与LMWP分离，启动肿瘤凋亡。由于大剂量药物是不渗透细胞的，因此细胞溶胶递送的药物不会受到耐多药的影响。初步发现非常有希望，因为他们迄今为止首次真正成功地将大量465-KDa-半乳糖苷酶选择性地输送到脑肿瘤中，而不是同侧或对侧正常大脑区域。在这个新的R01应用中，我们计划使用成熟的大鼠胶质瘤模型来证实这种DDS在体内的效用。

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.