Design, Synthesis And Performance Evaluation Of Peptide-based Tumor-targeting Magnetic Resonance Imaging Contrast Agents

Magnetic Resonance Imaging (MRI) is recognized as an advanced and powerful medical imaging diagnostic techniques due to its lots of advantages such as noninvasiveness, non-ionizing radiation, high spatial and temporal resolution, etc.. This technique plays an important role in the diagnosis and positioning of tumor and other diseases. MRI contrast agents is an important part of this technology. At present, small molecular contrast agents, they commonly are used Clinical, have a lot of disadvantages, shch as short time of blood circulation, non-specificity, low relaxivity, high biological toxicity and so on. In order to enhance the signal intensity of imaging and ensure the accuracy of clinical diagnosis, the high performance contrast agent must be development, a major development direction of MRI contrast agents is to design and synthesis new contrast agents with high relaxivity, tissue-targeted or organ-targeted, low toxicity, and low preparation cost.The study on MRI contrast agents are mainly concentrated to modification the ligand skeleton of small contrast agents by chemical method. The property of molecule, such as molecular volume, hydrophobicity, osmotic pressure, the selectivity of tissues or organs etc., can be changed by introducing all kinds of chemical groups. Predecessor’ research result shows that it will obtain higher relaxivity and targeting effect if the small molecular contrast agents are modified with targeting macromolecular. Based on this, we modified a small contrast agent (DOTA-Gd) with tumor-targeted polypeptide in order to improve its relaxivity and give its good tumor-targeted effect. In order to realize the above general objective, the author designed and synthesized a peptide-based tumor-targeted binary targeting vector (PI). The vector contain Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) motifs. The Arg-Gly-Asp (RGD) can bind specificity to integrin αvβ3and the Asn-Gly-Arg (NGR) can recognize specificity aminopeptidase N (CD13). Integrin αvβ3and CD13are the two biomarker of tumor. So the peptide containing RGD and NGR can bind specificity to tumors. a small contrast agent (DOTA-Gd) was modified with P1to become macromolecule contrast agents. The structure of all products were characterized by high resolution mass spectrometry. Using Magnevist as a controlled experiment, the relaxivity and imaging property of designing contrast agents were investigated. Using Human lung adenocarcinoma epithelial cells (A549), Human breast cancer cells(MDA-MB-231), Human prostate cancer cells(PC-3) as the experimental materials, the targeting-tumor performance and cells imaging performance of the designed contrast agents were investigated. And the specificity of P1combining with integrin αvβ3and CD13was confirmed by competition binding oexperiments. The WST-1method was used to investigate the cells inhibition toxicity of the designed contrast agents. Finally, the combination pattern of integrin αvβ3and CD13with was tentative studied by the computer simulation.The experimental results show that the relaxivity of the designing contrasted agents is much higher than that of magnevist, the relaxivity of desiged three contrast agents is higher77.6%,92.8%and51.58%than that of magnevist respectively. Imaging effect of aqueous solution is much better than that of magnevist. The designed contrast agents can bind specificity to integrin αvβ3and CD13. The combination is completed through integrin αvβ3specific recognizing RGD motif, and CD13specific recognizing NGR motif.This research conclusion is presentation as follow, it can improve targeting tumor effect if the two tumor-targeted segments of RGD and NGR were put together to become binary targeting contrast agents. And the contrast agents can aggregate more on the tumor cell surface than that single targeting contrast agents, so it have better imaging effect. The designed contrast agents can realized the purpose that a contrast agent detect a wide variety of tumors. So the design strategy is effective and feasible. The results reach basically the primary goals of this design. The designing target molecules have the potential as MRI contrast agent to using in cancer diagnosis.