生物合成超声造影剂及其在肿瘤上皮-间质转化中的分子影像评价研究

Tumor metastasis is the most important biological feature for malignant tumors, and is also the main cause of mortality in patients with cancer. Evidences demonstrated epithelial-mesenchymal transition (EMT) plays a key role in cancer metastasis. During this process, E-cadherin (E-cad) trends to decrease and N-cadherin (N-cad) does to increase, which called E- to N-cadherin transition. Some floated microorganisms can produce nanoscale bubbles that have been proved to be able to function as ultrasound contrast agents, and nano-bubbles with different sound pressure tolerances can be obtained through bio-synthetic approach. In this project, we propose a novel approach to monitor epithelial-mesenchymal transition process of tumor through ultrasound molecular complex imaging. In brief, we will synthesize nano-bubbles with different sound pressure tolerances via microorganisms and construct the E-cadherin and N-cadherin targeted bubbles (NBE-cad and NBN-cad). Their ultrasound molecular imaging signals will obtained during epithelial-mesenchymal transition process of tumor through destructing the targeted bubbles in sequence. By analyzing the correlations between the signal dynamics and tumor metastasis, the epithelial-mesenchymal transition process will be monitored in a noninvasive manner. Our previous study have developed the bio-synthetic system to produce the bio-nanobubbles. Also, we have proved these bio-nanobubbles have excellent ultrasound imaging capability and found bio-nanobubbles from different microorganisms can be destructed by different ultrasound pressures. This project will further investigate the targeting modification of these bio-nanobubbles, their capability for ultrasound molecular complex imaging and the feasibility of monitoring epithelial-mesenchymal transition process of tumors in a noninvasive manner. Our study will provide a novel idea to monitor the epithelial-mesenchymal transition process of tumors.

肿瘤转移是恶性肿瘤最重要的生物学特征。研究表明，肿瘤转移能力的获得与肿瘤发生上皮-间质转化(EMT)密切相关，在肿瘤EMT发生过程中，E-钙黏蛋白(E-cad)逐渐下降，而N-钙黏蛋白(N-cad)逐渐上升，表现出钙黏蛋白转换现象。某些微生物产生的纳泡可用于超声成像，且可获得不同声压耐受的纳泡。因此，本研究提出一种基于生物合成纳泡用于超声分子复合成像监测肿瘤EMT发生发展进程的方法，拟利用微生物合成不同声压耐受的纳泡，构建针对E-cad和N-cad的靶向纳泡，在肿瘤转移模型鼠中同时注射两种纳泡并依次爆破获取相应的超声分子影像信号，从而实现肿瘤EMT过程的无创在体监测。我们前期实验已经建立了生物合成纳泡的方法和体系，初步证实不同生物来源的纳泡能耐受不同的声压。本项目将进一步研究生物纳泡的靶向修饰、超声分子复合成像及其监测肿瘤EMT进程的可行性，以期为肿瘤EMT进程的影像 监测提供新的手段。

制备成像性能佳、靶向性能好、肿瘤血管渗透性强的超声造影剂是实现肿瘤上皮-间质转化（EMT）超声分子影像学评价的关键，在本项目中，我们利用生物合成的纳米气囊，制备获得了靶向肿瘤EMT标志物E-钙黏蛋白（E-cad）和N-钙黏蛋白（N-cad）的超声分子成像探针，成功实现了肿瘤转移过程中EMT转变的超声分子成像检测。我们的结果表明：1）生物气囊具有优良的超声造影成像性能和良好的肿瘤血管渗透能力，在肿瘤缺血区的成像信号是磷脂微泡的15.5倍；2）借助细胞靶向性实验确认了两种靶向造影剂均能与肿瘤细胞E-cad或N-cad结合；3）成功在动物模型内实现了肿瘤EMT进展的超声分子成像，成像结果与组织学结果具有良好的相关性（R2=0.83），并进一步验证了超声成像结果与肿瘤转移的一致性。综合上述结果，本研究制备了靶向生物合成超声造影剂，实现了肿瘤EMT演变进程的在体无创超声分子影像监测，为探讨通过EMT的超声分子成像评估肿瘤转移潜力奠定了坚实的基础。