Biogenic Gas Nanostructures As Molecular Imaging Reporters For Ultrasound

描述（由申请人提供）：超声是生物医学中使用最广泛的非侵入性成像方式之一，但由于缺乏合适的分子成像剂，其在分子成像中发挥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无创诊断中越来越被接受，但它们作为体外特定细胞和组织的标记的用途有限。 血液中，因为它们的微米尺寸通常将它们限制在血流中。因此，超声波尚未充分发挥其在生物医学研究和癌症、免疫学、神经病学和传染病等潜在临床领域中实现方便、快速分子成像的潜力。我们建议通过借鉴自然来满足这一需求。具体来说，我们将开发基于一类独特的基因编码气体纳米结构（称为气体囊泡（GV））的分子成像剂。 GV 被水生微生物表达为控制浮力的一种手段，是一种尺寸为 50-500 纳米的中空蛋白质外壳隔室，可排除水但可渗透气体。与人造微泡不同，GV 不加压，允许气体与周围介质自由交换。这产生了非常稳定的纳米级结构，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 可以产生稳定的超声对比度，可以在体外、细胞内和体内轻松检测到。的 事实上，GV 是经过基因编码的，这为在基因水平上改造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，还有可能采用 GV 作为报告基因——首次将超声波体内深度成像的能力与基因报告基因直接可视化细胞事件（例如基因表达）的能力结合起来。为了解决我们的假设，即GV可以作为超声的多功能分子成像记者，我们建议通过以下方式开发这种新型分子成像剂：（1）通过物理表征和建模了解GV的基因编码声学特性，（2）使用基因工程平台优化GV的声学、生物和靶向特性，（3）证明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。该项目的成功完成将带来超声分子成像的革命性进展：一类全新的稳定、纳米级、基因可调、分子靶向血管外成像剂，与生物医学研究具有直接相关性，并具有未来临床转化的潜力。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，从而为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.