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可以通过安全、非侵入性手段测量局部可溶血管内皮生长因子(VEGF)水平的造影剂。血管内皮生长因子有助于形成新的血管，为生长中的肿瘤提供营养，因此肿瘤环境中血管内皮生长因子水平的升高与乳腺癌和其他癌症的存活率呈负相关。癌症筛查结果呈阳性的患者通常会接受侵入性活组织检查，以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检，给患者带来了身体、经济和心理上的负担。因此，通过一种高度敏感和特定的非侵入性技术来测量特定环境中的生物标记物水平将是理想的--在特定环境中，特定的生物标记物可能被受体配体分泌、过度表达或招募。PIS计划通过利用他们的刺激响应型超声造影剂的设计和他们在使用超声进行对比剂增强癌症成像方面的经验来创造这样的技术。微泡是一种有效的超声造影剂，因为超声波会使气泡膨胀和收缩，产生可以以极高的特异性检测到的非线性回声。通过在气泡周围放置适体或与蛋白质有亲和力的DNA序列，将生物标记物敏感的活性赋予对血管内皮生长因子敏感的微泡，以形成一个链接网络，防止微泡的大小波动。血管内皮生长因子将导致适体链的去除，恢复壳的弹性，这是一种完全对比的活动。在之前的研究中，PI团队成功地使用了类似的策略来创建微泡，该微泡对凝血酶水平升高表现出敏感性，用于检测深静脉血栓 静脉血栓形成。此外，还将增加肿瘤特异性靶向配体，以保持肿瘤部位的微泡，确保有足够的信号。其次，将对微泡进行双重成像，以便对这些接收到的信号进行比较，从而提供更准确、更定量的血管内皮生长因子测量。拟议研究的完成将通过满足以下具体目标来完成：(1)对血管内皮生长因子敏感的微泡将 (2)将设计新的成像技术，通过建立信号-压力关系来基于微泡对VEGF水平进行定量，以及(3)将在体外和体外对乳腺癌细胞株和乳腺癌细胞株中的VEGF进行定量 体内乳腺癌异种移植模型。长期目标是将这项技术应用于其他类型的癌症，包括卵巢和胰腺癌，并推动这些工具在临床肿瘤学中的使用。

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.