Biogenic Gas Nanostructures As Molecular Imaging Reporters For Ultrasound

描述（申请人提供）：超声是生物医学中最广泛使用的非侵入性成像方式之一，但由于缺乏合适的分子成像剂，在分子成像中发挥的作用令人惊讶地小。尽管常规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获得认可，但是它们作为微泡外的特定细胞和组织的标记物的效用有限。 因为它们的微米尺寸通常将它们限制在血流中。因此，超声尚未充分发挥其潜力，使生物医学研究和潜在的临床领域，包括癌症，免疫学，神经学和传染病方便，快速的分子成像。我们建议通过向大自然借鉴来满足这一需求。具体来说，我们将开发基于一类独特的遗传编码气体纳米结构的分子成像剂，称为气体囊泡（GV）。GV由水生微生物表达为控制浮力的一种手段，是尺寸为50-500纳米的中空蛋白质壳隔室，不含水但可渗透气体。与人造微气泡不同，GV不加压，允许气体与周围介质自由交换。这导致非常稳定的纳米级配置，从而能够实现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，细胞内和体内很容易检测到。的 GV被基因编码的事实提供了在基因水平上工程化其特性以优化其声学、生物分布和针对特定应用的靶向的前所未有的机会。此外，还有可能将GV作为报告基因-首次将超声在体内深度成像的能力与遗传报告基因直接可视化细胞事件（如基因表达）的能力相结合。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报告者，我们提出通过以下方式开发这类新的分子成像剂：（1）通过物理表征和建模来理解GV的遗传编码的声学特性，（2）使用基因工程平台来优化GV的声学、生物学和靶向特性，（3）证明这些纳米结构在体内靶向血管外肿瘤细胞并使其成像的能力和（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导致超声分子成像的变革性进展：一种全新的稳定，纳米尺寸，遗传可调，分子靶向血管外成像剂，与生物医学研究直接相关，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，从而更普遍地促进生物医学成像和生物工程研究。

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.