Construction Of Environment Responsive CEST MRI Contrast Agents And Its Feature’s Research

Magnetic resonance imaging (MRI) and magnetic resonance spectral (MRS) analysis are an excellent non-invasive diagnostic technology. According to magnetic resonance imaging’s advantages, it plays significance in various tissues’diagnosis at anatomic level in comparison to the traditional CT technology and nuclear medicine; because its features are high contrast and high penetrability at the soft tissue, non invasive and non radiation for human body, magnetic resonance has been widely used in the medical diagnosis and disease therapy. Nowadays, as the development of nuclear magnetic resonance imaging technologies and methods, the molecular imaging method makes MRI applied to the detection of molecular level. It can achieve the early detection of cancer and other latent disease. Because the tumor tissue has a special micro environment and specific markers can be detected by molecular imaging, it has very important clinical significance in the early detection of disease. However, due to the resolution is still limited by the sensitivity of magnetic resonance imaging, the in vivo diagnosis can only reach to the millimolar level. Therefore, the method to improve the sensitivity of magnetic resonance imaging are mainly depend on developing novel nuclear magnetic resonance imaging method, or designing new effective agent for MR contrast.Among these, the polymer micelle which considered as a nano material has excellent features in carrying and delivering the drugs and contrast agents. It is widely applied to the clinical diagnosis and treatment as it has been reported. In order to detect the tumor tissue’s complicated and changeable micro-environment, the amphiphilic polymers could be modified with several of sensitive monomer chains, and self-assembled into a sensitive micelle. This nanosystem can be response on the tissue’s microenvironment, such as the change of temperature, pH and concentration of some specific markers of metabolism. While its structure or morphology has changed, it could somewhat respond to the tissue’s features, and detect its specific environment at the molecular level. In this paper, we designed a series of novel environmental responsive polymeric micelles, and combined the novel magnetic resonance imaging method:the chemical exchange saturation transfer (CEST) imaging. Because the chemical exchange saturation transfer imaging is a good technique that could amplify and distinguish some weak signal. By virtues of those environment responsive polymeric micelles’characteristics, the tissue’s microenvironment or the concentrations of tissue’s specific substances could be detected; we hope to achieve early detection and diagnosis of cancer and other diseases by this novel method.First, according to the characteristics of tumor tissue’s temperature is slightly higher than normal tissues; we designed a kind of temperature sensitive polymer micelles named Eu-[PNIPAAm-b-MMA]-DO3AmcE. Our method was based on a nanomicelle modified with paramagnetic metal chelate Eu. The nanomicelle was designed as an amphiphilic polymer with hydrophilic temperature sensitive segments PNIPAAm. Meanwhile, the hydrophobic chain was modified with paramagnetic metal chelate Eu in polymers to obtain a paramagnetic chemical exchange saturation transfer (PARACEST) agent.In order to obtain the hybrid micelle embedded with the contrast agent, same polymer with different length of the chain segments was introduced into the hybrid. And this Eu-[PNIPAAm-b-MMA]-D03AmcE could self assembled as hybrid core-shell polymeric micelles under the synergy effect. In this kind of temperature sensitive polymer micelles, the temperature’s change at a range could make the morphology of the micelles changes in conditions, this progress could indirectly affect the environment of chemical exchange between Eu chelate’s bond water and bulk water. In order to obtain the micelle’s morphology change close to the human body temperature’s range, we modified the polymer micelles by mixing with different length chains. And the chemical exchange saturation transfer efficiency is largely enhanced with the increase of temperature around this temperature range. Both phenomenon in the spectrum analysis and magnetic resonance imaging have demonstrated that, the effect of the chemical exchange saturation transfer imaging have largely responsive on the physiological temperature range. Those experiments prove that this contrast agent might have significance in detection of physiological temperature.In addition, the tumor tissue is different from normal tissue, such as it could have some over-expression of glutathione GSH. Based on this mind, we design a kind of chemical exchange saturation transfer imaging contrast agent based on amino acid typed polymer micelles. The monomer polymers were synthesized by ring opening polymerization, and the polymers self-assemble as nanomicelle system. We obtained two types of polymer micelles linked with poly lysine chain segment by disulfide bond. When the hydrophobic core was formed with amino chains, the amino protons could not contact with bulk water to participate into chemical exchange. Due to the glutathione’s reduction interacting with disulfide bond, when the polymeric micelle was at high concentrations of glutathione, the micelle might gradually disassemble with the time. This progress increases the amount of amino proton’s exchange with bulk water. Because the glutathione molecules are involved in tumor cell reduction and is much higher over-expressed than the normal tissue, it is an important marker of tumor tissue distinguished with the normal tissue. The change of the exchange saturation transfer efficiency has important significance to identify the tumor tissue in the clinical detection. In order to further verify this characteristic, we also design a bimodal molecular polymer micelle probe with fluorescent dyes, and apply it to the detection of cell A549, and its simulation in tumor tissue of non-small cell lung cancer, variety of methods such as MRI and fluorescence imaging are used to detect and diagnose the tumor cells. To further demonstrate its sensitivity, we could obtain the CEST "off to on" imaging at high GSH level, and the CEST effect could achieve to 27.9%. Then we modified it with ligand c(RGD)ky to targeting the non small lung cancer cell A549. We demonstrate that this dual mode sensor can target to the A549 cancer cell and largely exist in the cytoplasm.