靶向VEGFR2脂质微泡联合聚焦超声定向辐照治疗乏血供型原位胰腺移植瘤的研究

Microbubbles are gas-encapsulated lipid particles that have been used as ultrasound contrast agents in the context of diagnostic imaging for many diseases.Ultrasound-mediated microbubble destroy (UMMD) caused by acoustic cavitation has been demonstrated to be a potential therapeutic strategy for cancer. Under certain acoustic conditions, the intensity of ultrasonic cavitation is closely associated with the concentration of microbubbles accumulated in the tumor microvasculature. Previous studies have found that conventional microbubbles show limited ultrasonic cavitation efficacy due to their poor retention and accumulation properties at the target site especially in the tumor with poor vascularity. In addition, the ultrasonic radiation machine used in the previous studies for ultrasound cavitation could cause surrounding normal tissue damage and cannot localize deep or orthotopic transplanted tumor due to lack of focusing and ultrasonography features. In the present study we will develop a novel therapeutic strategy for microbubble-mediated ultrasonic catitatation by using tumor-targeted microbubble combined with our previously developed ultrasonic radiation machine with focusing and ultrasonography features. Microbubbles will be targeted to tumor by conjugating a VEGFR2-binding ligand to the surface of the microbubble. VEGFR2 is a molecular marker of angiogenesis, and its expression is correlated with growing tumors. VEGFR2 targeted microbubbles will exhibit increased retention and accumulation potential in tumor vascularity. Focused ultrasound in combination with ultrasonography will be utilized to generate optimal conditions for microbubble-mediated ultrasonic cavitation in an orthotopic pancreatic tumor model to destruct tumor vasculation with minimum normal tissue damage. We hypothesize that high concentrated anti-VEGFR2 conjugated microbubbles in tumor site will exert increased anti-angiogenesis efficacy by both competitive inhibition of tumor VEGFR / VEGF signaling pathways and simultaneously effective ultrasonic cavitation destruction on tumor vascularity.

超声介导微泡破坏即空化效应（UMMD）是一个很有前景的肿瘤治疗技术，在超声辐照参数一定的条件下，UMMD还与肿瘤血管内微泡聚集的数量有关。前期研究发现，裸脂质微泡因不具有靶向性而在肿瘤血管内聚集停留的性能较差，尤其对乏血供型肿瘤，UMMD所致的肿瘤血管破坏不明显；此外目前普遍使用的超声辐照设备无聚焦功能，超声辐照经路上产生的UMMD在一定程度上会造成正常组织的损伤，同时缺乏影像定位系统不能用于深部或原位移植瘤的治疗。本研究拟通过脂质微泡与抗VEGFR2抗体结合，制备靶向微泡，以提高微泡在裸鼠胰腺原位移植瘤内聚集黏附，通过VEGFR2抗体与VEGFR高亲和力结合，竞争抑制VEGFR/VEGF信号传导通路，使VEGF失去活性，抑制肿瘤血管形成；另一方面利用低频聚焦超声在常规超声影像定位下对瘤体血管内的微泡进行辐照，以增强对肿瘤血管的损伤和保存肿瘤周边正常组织，达到双重抗肿瘤血管的目的。

超声介导的微泡破坏即称为空化效应（UMMD），它是一个很有前景的肿瘤治疗技术，在超声辐照参数一定的条件下，UMMD与肿瘤血管内微泡聚集的数量有关。前期研究发现，裸脂质微泡因不具有靶向性而在肿瘤血管内聚集停留的性能较差，尤其对乏血供型肿瘤，UMMD不明显；此外，目前普遍使用的超声辐照设备无聚焦的功能，超声辐照经路上产生的空化效应会造成正常组织的损伤，同时缺乏影像定位系统不能用于深部或原位移植瘤的治疗。建立胰腺癌原位移植瘤模型，将24只原位移植胰腺癌的Balb/c裸鼠随机分为4组：A组（6只），空白对照组，不接受造影剂及超声辐照；B组（6只），生理盐水联合超声辐照；C组（6只），裸脂质微泡联合超声辐照；D组（6只），载VEGFR2脂质微泡联合超声辐照。治疗前后分别测量各组裸鼠质量和荧光摄片，测量肿瘤大小，计算肿瘤体积，绘制肿瘤体积生长曲线和裸鼠质量生长曲线。我们发现治疗前各组肿瘤体积和裸鼠质量无明显差异（P＞0.05），治疗后D组肿瘤体积生长缓慢，其余三组肿瘤体积逐渐增大，差异均有统计学意义（P＜0.05）。本研究通过脂质微泡与抗VEGFR2抗体结合，制备靶向脂质微泡，提高微泡在裸鼠原位胰腺癌内聚集黏附，通过VEGFR2抗体与VEGFR高亲和力结合，竞争抑制VEGFR/VEGF信号传导通路，使VEGF失去活性，抑制肿瘤血管形成；另一方面利用我们研制出的具有聚焦辐照和超声影像定位功能的治疗设备对高度聚集在瘤体血管内的微泡进行辐照，以增强对肿瘤血管的损伤和保存肿瘤周边正常组织，达到双重抗肿瘤血管的目的。