| Glioma is the most common and aggressive type of primary intracranial neoplasm,accounting for more than 50% of all primary central nervous system tumors and 2% of adult malignancy.Chemotherapy is essential to surgical treatment because traditional surgical resectioncould not prevent the recurrence of glioma. However, traditional small molecule anticancer drugs often suffer from intrinsic limitations such as poorwater solubility, uncontrollable duration of circulation and improper biodistribution, and the possible ocurrence of severe side effects, which will considerably decrease the therapeutic efficacy. Therefore an effective drug delivery system for the treatment of glioma should be developed.With the development of nanotechnology,a new concept of theranostic agent, possessing integrated functions of targeted drug delivery, diagnosis, and real-time monitoring and evaluation of therapeutic progresses, has become a new research hotspot in tumor diagnosis and treatment in recent years.Aiming at fulfilling the above requirements, in Chapter One,we report on the design and fabrication of multifunctional polymeric micellesCD-P(CPTM-co-DEA)-b-P(OEGMA-co-Gd-co-ANG) as an integrated platform for glioma targeted drug delivery, magnetic resonance imaging contrast enhancement and controllable drug release under in vitro and in vivo conditions.The characteristics of polymeric micelleswere determined byusing TEM, FTIR spectroscopy, DL0 S and 1HMR spectrometry. It was found that the synthesized polymeric micelles were spherical in shape with an average size of 120 ± 13 nm, good dispersibility and nice agnetic relaxation performance.Meanwhile, the CPT and Gd3+content of the polymeric micelles were 19.2 wt% and 1.804 wt%, respectively. The micelles also demonstrated sustained release of CPT indifferent GSH solutions with the disulfide linkers in the micelles were cleaved rapidly. The result showed that ANPs/CPT retained not only significant responsive drug release activities but alsoT1 MR imaging capacity.In Chapter Two, Angiopep2 was modified on the surface of the polymeric micelles as brain-targeting molecule. The brain-targeting efficiency of Angiopep2 was evaluated both on brain capillary endothelial cells and in C6 cells. The findings demonstrated that Angiopep2 could increase the cellular uptake and promote the polymeric micelles accumulating in the brain. This chapter further explored the underlying mechanism of improved Angiopep2 modified polymeric micelles crossing the BBB. The results demonstrated that Angiopep2 maintained receptor-binding properties after modifying on the polymer micelles, and improved BBB-penetrability though LRP-mediated pathway. In addition, the distribution of ANPs in the tumor site 2 h after injection was more concentrative than that of NPs, which proved again Angiopep2 modification had the same dual targeting effect in vivo as in vitro.In Chapter Three,MRI measurement show that the tumor cells uptake of Angiopep2 modified drug-loading polymer micelles increased together with stronger signal, SNR and CNR than DOTA-Gd. In vivo MRI imaging confirmed ANPs/CPT showed excellent brain-targeting efficieney, which has higher CNR and T/N ratio compared with DOTA-Gd and NPs. During the experiment, due to covalent bonds with micelles, Gd3 + will not release from the micelle, so enhanced MR signal can prompt ANPs/CPT distribution. Further in vivo MR imaging experiments in rats demonstrated prominently positive brain targeting and extended blood circulation duration for the reported structurally stable micelles-based theranostic nanocarrier system.In Chapter Four, we tried to utilize the micelles to deliver the anti-tumor drug CPT for the glioma therapy. The anti-tumor efficacy was evaluated both in vitro and in vivo.In vitro, the cell apotosis was evaluated by cell level, tumor sphere and BBB model.With CPT concentration of 25μg/ml, more tumor cells were killed by means of the brain-targeting efficieney of Angiopep2.Tumor sphere experiment showed that ANPs/CPT has good penetrability to reach inside the sphere. In vivo, the glioma-bearing mice were treated with saline, CPT, ANPs/CPT, NPs/CPT. After treatment, the anti-tumor efficacy was evaluated through histopathology and the result further confirmed Angiopep2 modified nanomicelles has a good anti-glioma efficacy.In summary, Angiopep2 modified polymeric micelles were successfully synthesized as an integrated platform for glioma-targeted drug delivery and MR imaging contrast enhancement. In aqueous solution, the star blockcopolymers exist as structurally stable micelles possessing a hydrophobic core(DEA and CPTM) and a hydrophilic OEGMA outer corona covalently anchored with targeting moieties Angiopep2 and MRI contrastagents DOTA-Gd. The covalent binding of CPT within the hydrophobic core of the micelles and the controlledrelease of them were successfully achieved. CPT-loaded Angiopep-2 modified polymeric micelles exhibit considerably higher in vitro cytotoxicity compared to non-targeting ones presumably due to the LRP receptor-mediated endocytosis mechanism. In vitro MR imaging experiments revealed considerably enhanced T1 relativity for micelles to be used for the diagnosis of glioma, monitoring enrichment of drug in the tumor tissues, metabolism and biological distribution in different organs in real-time. |
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