Targeted Microbubbles for Noninvasive Measurement of Tumor VEGF Levels

描述（由申请人提供）：拟议研究的目的是设计造影剂，可以通过安全、无创的方式测量局部可溶性血管内皮生长因子（VEGF）水平。VEGF有助于形成新的血管，为生长中的肿瘤提供养分，因此，肿瘤环境中VEGF水平的升高与乳腺癌和其他癌症的存活呈负相关。癌症筛查结果呈阳性的患者通常会接受侵入性活检来测量这些生物标志物的水平。然而，筛查中的高假阳性率导致了不必要的活组织检查，给患者带来了身体、经济和心理上的负担。因此，通过高度敏感和特异性的非侵入性技术，在特定环境中测量生物标志物水平将是理想的——在特定环境中，特定生物标志物可能被分泌、过度表达或被受体配体募集。pi计划利用他们设计的刺激反应超声造影剂和他们使用超声进行对比增强癌症成像的经验来创造这种技术。微泡是一种有效的超声造影剂，因为超声可以使微泡膨胀和收缩，产生非线性回声，可以以极好的特异性检测到。通过在微泡周围放置适体或具有蛋白质亲和力的DNA序列，生物标志物敏感活性将被赋予vegf敏感微泡，以形成防止微泡大小波动的连接网络。VEGF会导致适配体链的移除，恢复外壳的柔韧性和充分的对比活性。在之前的研究中，PI团队成功地采用了类似的策略来制造微泡，这些微泡对凝血酶水平的升高表现出敏感性，用于检测深度

DESCRIPTION (provided by applicant): The aim of the proposed research is to design contrast agents that can measure local levels of soluble Vascular Endothelial Growth Factor (VEGF) via safe, noninvasive means. VEGF helps to form new blood vessels that feed a growing tumor, and thus elevated VEGF levels in the tumor environment correlates negatively with survival in breast and other cancers. Patients who have received a positive result from a cancer screening usually undergo an invasive biopsy to measure the levels of such biomarkers. However, high false positive rates in screening have led to unnecessary biopsies that burden a patient with physical, financial, and psychological costs. Thus it would be ideal to measure biomarker levels in a specific environment - where a specific biomarker may be secreted, overexpressed, or recruited by receptor ligands - through a highly sensitive and specific noninvasive technique. The PIs plan to create such a technique by leveraging their design of stimulus-responsive ultrasound contrasts agents with their experience in using ultrasound for contrast-enhanced cancer imaging. Microbubbles are potent ultrasound contrast agents because ultrasound causes the bubble to expand and contract, generating a nonlinear echo that can be detected with excellent specificity. Biomarker-sensitive activity will be imparted to the VEGF-sensitive microbubbles through placement of aptamers, or DNA sequences with affinity for proteins, around the bubble to form a network of links that prevent the microbubbles from fluctuating in size. VEGF will cause removal of the aptamer strands, restoring shell flexibility an full contrast activity. In previous research, the PI team successfully employed a similar strategy to create microbubbles that exhibited sensitivity to elevated thrombin levels for detection of deep venous thrombosis. In addition, tumor-specific targeting ligands will be added to hold microbubbles at the tumor site, ensuring sufficient signal. Second, the microbubbles will be dually imaged such that comparison of these received signals will provide a more accurate, quantitative measurement of VEGF. Completion of the proposed research will be accomplished through satisfaction of the following specific aims: (1) microbubbles with sensitivity to VEGF will be designed and validated in nonbiological phantoms, (2) new imaging techniques will be designed for microbubble-based quantification of VEGF levels through establishment of signal-pressure relationships, and (3) VEGF will be quantified in breast cancer cell lines in vitro and an in vivo breast cancer xenograft model. The long-term goal is to apply this technology to other types of cancers, including ovarian and pancreatic, and advance these tools for use in clinical oncology.