pH敏感变构聚合物载体FRET模型构建及其肿瘤诊疗一体化研究

As a research focuse on developing functional material, obtaining tumor-specific imaging with low background interference and the enrichment of therapeutic molecules in diseased region are important issues for the development of tumor theranosis. Fluorescence resonance energy transfer (FRET), which could regulate optical imaging by controlling the distance between its donator and receptor, has outstanding advantages in the analysis of molecular conformation and molecular interactions dynamically. In a block copolymer, the polymer block composition and nanostructure conformation are alterable, and thus the FRET could be implemented. Combined with block polymer self-assembly principle in this study, we attempt to build a pH-sensitive polymer poly(ε-caprolactone)-poly(ethylene glycol)-poly(L-histidine)(PCL-PEG-PLH). After introduced a thiocyanate and the fluorescent probe molecules at both ends of the molecular, a coated gole nanoparticle and probe could construct a FRET-based tumor theranosis model. Poly(L-histidine) is a pH sensitive polymer and its hydrophobicity is changed in acidic microenvironment within the tumor model. The changes of distance between the fluorescent probe and the gold nanoparticle control the FRET, then complete a tumor-specific near-infrared imaging and tumor tumor photothermal therapy. After preliminary experiment, next we attempt to test and optimize the model composition. Additionally, we will explore the practical effect of the FRET-based model and clarify the relationship between the structural composition and FRET. The project could provied a ideal method for tumor theranosis.

肿瘤诊疗一体化作为功能材料设计与研究的热点，完成低背景干扰的肿瘤特异成像并富集治疗性分子于病变部位是发展肿瘤诊疗的重要课题。荧光共振能量转移(FRET)借助供、受体距离调控光学成像，在动态研究分子构象及分子相互作用方面具有突出优势。聚合物中可由改变嵌段组成和纳米结构构象来调控供、受体距离，实现对FRET调控。结合嵌段聚合物自组装原理，设计构建pH敏感聚合物PCL-PEG-PLH，经分子两端分别引入巯基和荧光探针分子，构建包覆金颗粒的FRET模型。模型中聚组氨酸对肿瘤内酸性微环境的pH响应能改变其空间构象，引起荧光探针与金距离的改变，使模型中FRET消失并恢复探针荧光，完成更少背景干扰且肿瘤特异的近红外成像并由富集的金颗粒实现肿瘤光热治疗。经过合成预实验，下一步，我们将检测并优化该FRET模型，阐明组成结构与FRET构效关系并探索模型实际效果，为构建肿瘤成像与治疗双功能体系提供新的思路。

肿瘤诊断与治疗是纳米医药技术研究的重要内容之一。创新药物载体设计中，结合肿瘤微环境，功能化的嵌段聚合物能够完成药物的靶向递送并实现肿瘤的多模态成像。本研究中，利用FRET（荧光共振能量转移）原理，结合肿瘤部位酸性的微环境，通过调节自组装复合体系中供体-受体间的距离，以期实现荧光的开关调节，从而完成肿瘤部位的低背景特异性成像。自组装体系由Cy7标记的PLH-PEG-PCL（聚组氨酸-聚乙二醇-聚己内酯）与金纳米棒（Au NRs）通过巯基特异性结合而成。在PLH-PEG-PCL自组装中，PLH由咪唑基团构成，碱性条件下，PLH疏水作用引导Cy7靠近复合体系中心的金纳米棒，通过FRET淬灭荧光；反之，酸性条件下，Cy7由于PLH亲水而疏远金纳米棒，实现荧光的恢复。围绕这一设计思路，我们合成了多种组分的Cy7-PLH-PEG-PCL-LA嵌段聚合物。使用DMSO溶解并透析过程中，聚合物均能在水相自组装为纳米颗粒，纳米粒子粒度与形貌的结果验证了该聚合物pH敏感变构的可行性；，随后加入金纳米棒，制备FRET复合物模型：石英晶体微天平检测证实聚合物具有pH敏感变构的特点，荧光光谱检测也证实部分荧光信号发生FRET；荷瘤小鼠肿瘤成像未能很好的实现设计思路，结果提示探针分子在肿瘤部位的聚集还不是很明显，还需更多组成和合成细节的调整，以期更好的肿瘤成像效果。经过课题的具体实施，课题组熟练掌握了一种NCA开环聚合引入聚组氨酸链段的方法，验证了该FRET模型中聚合物的pH响应性，该响应可以用于智能递送肿瘤化疗药物；如果FRET效应进一步证实，可以有效利用该模型完成多种潜在的诊疗一体化应用。