Biogenic Gas Nanostructures As Molecular Imaging Reporters For Ultrasound

描述(申请人提供)：超声是生物医学中应用最广泛的非侵入性成像手段之一，但由于缺乏合适的分子显像剂，在分子成像中的作用令人惊讶地小。尽管传统的微泡造影剂在某些心血管疾病和癌症的非侵入性诊断中得到了认可，但它们作为体外特定细胞和组织的标记作用有限。 血流，因为它们的微米大小通常将它们限制在血流中。因此，超声尚未充分发挥其在生物医学研究和潜在临床领域(包括癌症、免疫学、神经学和传染病)中实现方便、快速的分子成像的潜力。我们建议通过借鉴自然来满足这一需求。具体地说，我们将基于一种独特的被称为气泡(GV)的遗传编码气体纳米结构来开发分子成像试剂。GVS由水生微生物表示为一种控制浮力的手段，GVS是50-500纳米大小的中空蛋白质壳隔间，不包括水，但对气体具有渗透性。与人造微泡不同，GV不受压力，允许气体与周围介质自由交换。这导致了非常稳定的纳米级配置，从而实现了更广泛的潜在分子成像应用。在初步结果中，我们已经证明，来自多个物种的GV产生稳定的超声对比度，在体外、细胞内和体内都很容易检测到。这个 GV是基因编码的，这一事实为在基因水平上设计其特性提供了前所未有的机会，以优化其声学、生物分布和针对特定应用的目标。此外，有可能将GV作为报告基因--首次将超声波在体内进行深度成像的能力与遗传报告者直接观察基因表达等细胞事件的能力结合在一起。为了解决我们的假设，即GVS可以作为多功能的超声分子成像报告器，我们建议通过(1)通过物理特性和建模了解GVS的遗传编码的声学特性，(2)使用基因工程平台来优化GVS的声学、生物学和靶向特性，(3)展示这些纳米结构在体内靶向和成像血管外肿瘤细胞的能力，以及(4)在哺乳动物细胞中表达GV形成基因，从而开发这种新型的分子成像剂。该项目的成功完成将带来超声分子成像的革命性进展：一种稳定的、纳米尺寸的、基因可调的、分子可靶向的血管外成像试剂，与生物医学研究直接相关，并具有未来临床翻译的潜力。此外，这项工作将促进生物物理学、分子和细胞工程以及成像技术的进步，这些技术将对生物医学成像和生物工程研究做出更广泛的贡献。

DESCRIPTION (provided by applicant): Ultrasound is among the most widely used non-invasive imaging modalities in biomedicine, but plays a surprisingly small role in molecular imaging due to a lack of suitable molecular imaging agents. Although conventional microbubble contrast agents are gaining acceptance in non-invasive diagnosis of certain cardiovascular diseases and cancers, they have limited utility as labels of specific cells and tissues outside the bloodstream because their micron size typically confines them to the blood stream. As a result, ultrasound has yet to fulfill its full potential to enable convenient, rapid molecular imaging in biomedical research and potential clinical areas including cancer, immunology, neurology and infectious disease. We propose to address this need by borrowing from nature. Specifically, we will develop molecular imaging agents based on a unique class of genetically encoded gas nanostructures known as gas vesicles (GVs). Expressed by aquatic microorganisms as a means to control buoyancy, GVs are hollow protein-shelled compartments 50-500 nanometers in size that exclude water but are permeable to gas. Unlike artificial micro bubbles, GVs are not pressurized and allow gases to freely exchange with the surrounding medium. This results in a very stable nanoscale configuration enabling a broader range of potential molecular imaging applications. In preliminary results, we have demonstrated that GVs from multiple species produce stable ultrasound contrast that is readily detected in vitro, inside cells and in vivo. The fact that GVs are genetically en- coded provides an unprecedented opportunity of engineering their properties at the genetic level to optimize their acoustics, biodistribution and targeting fo specific applications. In addition, there is the potential of adapting GVs as reporter genes - for the first time combining the ability of ultrasound to image at depth in vivo with the ability of genetic reporters to directly visualize cellular events such as gene expression. To address our hypothesis that GVs can serve as versatile molecular imaging reporters for ultrasound, we propose to develop this new class of molecular imaging agents by (1) understanding GVs' genetically en- coded acoustic properties through physical characterization and modeling, (2) using a genetic engineering plat- form to optimize GVs' acoustic, biological and targeting properties, (3) demonstrating the ability of these nanostructures to target and image extravascular tumor cells in vivo and (4) expressing GV-forming genes in mammalian cells. Successful completion of this project will result in a transformative advance in molecular imaging with ultrasound: a fundamentally new class of stable, nanosized, genetically tunable, molecularly targetable extra- vascular imaging agents, with immediate relevance in biomedical research and the potential for future clinical translation. In addition, this work will stimulate advances in biophysics, molecular and cellular engineering and imaging technology that will contribute more generally to biomedical imaging and bioengineering research.