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MR Molecualr Imaging Of Tumor Angiogenesis And Biological Effects Of Iron Oxide Nanoparticles

Posted on:2011-01-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:X Y WuFull Text:PDF
GTID:1114360305458170Subject:Medical imaging and nuclear medicine
Abstract/Summary:PDF Full Text Request
Integrin is often significantly up-regulated in activated endothelial cells during tumor angiogenesis. The arginine-glycine-aspartic acid (RGD) peptide sequence is a specific recognition motif toαvβ3 integrin. Development of RGD peptide labeled, high specific MR probe for molecular imaging of tumor angiogenesis is capable to facilitate early dectection and may help monitor tumor vascular change during anti-angiogenesis therapy. In this study, a RGD labeled, Poly lactic acid (PLA) coated ultrasmall paramagnetic iron oxide (USPIO) (referred to as RGD-PLA-USPIO) were developed and the ability to detect tumor angiogenesis was investigated in vitro and in vivo. Pronounced signal decrease in T2*-weighted magnetic resonance image (MRI) and heterogeneous arrangement of neovasculature of tumor tissue were clearly identified in Vx-2 tumor model. The results demonstrate the efficiency of RGD-PLA-USPIO to visualizeαvβ3 integrin in activated tumor endothelial cells. In addition, the influence of dextran and citric acid coated IONPs on the behavior and function of human umbilical vein endothelial cells'(HUVECs) was discussed in concerned of viability, cytoskeleton, migration/invasion and differentiation. The thesis consists of four major sections.ⅠPLA-USPIO were prepared in situ by a modified co-precipitation method by sonification in Ethanol-Water solution. Spherical particle shape was determined by TEM and FTIR showed plenty of carboxyl groups on the surface of PLA-USPIO for better binding or conjugation with specific ligands. PLA-USPIO prolonged circulation time through decreased uptake by RES. Furthermore, PLA-USPIO generated significant signal reduction in T2WI and T2*WI and T2* relaxation time measurement was more sensitive to the magnetic field inhomogeneity induced by USPIO.II RGD-PLA-USPIO was prepared by crosslink reaction. The specific affinity of RGD-PLA-USPIO to integrin was identified by B16F10, SPC-Aland HUVECs binding tests and it was indicated that binding capacity was dependent with the level of integrin in cells. TEM confirmed the existence of RGD-PLA-USPIO in cytoplasm. MR scan of HUVECs incubated with RGD-PLA-USPIO exhibited a dose-dependent signal decrease in T2WI, which facilitated the utility of RGD-PLA-USPIO as a MR probe.III Vx-2 adenocarcinoma is highly malignant and is considered to be an ideal tumor model with significant integrin expressed in tumor endothelial cells. Compared with PLA-USPIO injection, Vx-2 tumor rabbits receiving RGD-PLA-USPIO revealed a marked decrease in T2*WI and T2WI, although not exclusively, asymmetrically located along the tumor periphery. The signal decease was typically seen in a patchy distribution adjacent to blood vessels and along the lateral tumor border as small spots. The T2 and T2* relaxation times of tumor accordingly decreased with the signal change in images and T2* relaxation time was more sensitive due to a susceptibility effect. Prussian blue stain of the Vx-2 tumor visualized blue granule in tumor endothelium and corroborated angiogenesis observed with MR images. Generally, RGD-PLA-USPIO hold promise to be uitilized as novel MR probe for in vivo detection of tumor angiogenesis.IV The biological effects of citrate and dextran coated IONP on HUVECs were investigated in terms of cell proliferation, cytoskeleton, migration/invasion and differentiation. Cell proliferation, migration and invasion were inhibited in a dose dependent manner and citrate-IONP had more toxic effects than dextran-IONP. The capacity of HUVECs to form vascular network on Matrigel diminished after exposure to IONPs. Cytoskeletal structures were greatly disrupted, as evidenced by diminished vinculin spots, and disorganized actin fiber and tubulin networks. Cell attachment is necessary to mediate the survival of anchorage-dependent cells and critical for efficient cell growth, migration, invasion and differentiation. The detachment after exposure to IONPs induced the dysfunction of HUVECs and the iron catalyzed free radical damage might attribute to it.In general, we have reported the development of RGD-PLA-USPIO as anαvβ3 integrin targeted MR probe and the results demonstrate RGD-PLA-USPIO can efficiently visiualize the expression ofαvβ3 integrin on tumor vascularature. Additionally, HUVECs proliferation, migration/invasion and differentiation is greatly inhibited after incubation with citrate and dextran-coated iron oxide nanoparticles.
Keywords/Search Tags:Molecular imaging, MRI, USPIO, Angiogenesis, Integrin, Cytotoxicity
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