Bacteria-Based MR Molecular Imaging of Tumor Oxygenation

描述（申请人提供）：肿瘤氧合在肿瘤生长、侵袭和治疗中起着至关重要的作用。肿瘤组织通常会产生内皮生长因子（如VEGF），刺激血管新生，以满足快速生长的肿瘤细胞对营养的高需求。肿瘤细胞因其与血管的距离不同而具有不同的特征，并可通过其氧合程度来进行分类：最具活力的细胞灌注和氧合良好，缺氧细胞氧合不良，坏死中心含有因缺氧而死亡的细胞。这些肿瘤细胞具有不同的遗传和分子特征，可能对各种治疗干预措施（包括放疗和化疗）有不同的反应。目前，有创微电极方法被用作测量肿瘤氧合的金标准。这种方法的关键是采样位置的选择，因为当需要在同一组织位置周围进行多个电极测量时，可能会产生伪影。我们提出了一种新的分子成像方法来绘制肿瘤氧合在体内基于鼠伤寒沙门菌的减毒菌株，选择性地积累和增殖在肿瘤组织。肌红蛋白将通过基因工程植入沙门氏菌中，作为氧气传感器。由于沙门氏菌可以渗透到肿瘤的缺氧区域，该方法将给出肿瘤氧合的完整图谱。在这个R21提案中，我们将开发一种新的分子成像方法，利用过表达氧传感蛋白肌红蛋白的减毒鼠伤寒沙门菌菌株来绘制小鼠肿瘤模型中的肿瘤氧张力。脱氧肌红蛋白可以直接在体内测量，在质子光谱中使用-80 ppm的特征峰进行氧张力计算，或间接在高分辨率肿瘤组织水成像中测量，而脱氧肌红蛋白则用作松弛对比剂。这种新的肿瘤氧张力测量方法将用于观察原发性和转移性肿瘤。这些方法将在考虑特定肿瘤微环境的生理参数的抗癌药物的临床前开发中有许多应用。由于鼠伤寒沙门氏菌目前处于I期临床试验阶段，该项目可能对未来原发性肿瘤和远处转移的诊断，以及癌症临床结果的治疗计划和监测产生重大影响。

DESCRIPTION (provided by applicant): Tumor oxygenation plays a critical important role in tumor growth, invasion, and therapy. Tumor tissues usually produce endothelial growth factors (such as VEGF) that stimulate new growth of blood vessels to meet the high nutrient demands of the fast growing tumor cells. Tumor cells have different characteristics as a function of their distance from the blood vessels and can be typified by their degree of oxygenation: the most viable cells are well perfused and oxygenated, the hypoxic cells are poorly oxygenated, and the necrotic center contain dead cells as a result of oxygen deprivation. These tumor cells have different genetic and molecular characteristics and possibly different response to various therapeutic interventions including radiation and chemotherapy. Currently, invasive microelectrode approach is used as a gold standard measurement of tumor oxygenation. Crucial is the selection of the sampling locations with this method since artifacts may be generated when multiple electrode measurements are required around the same tissue location. We propose a novel molecular imaging approach to map tumor oxygenation in vivo based on an attenuated strain of Salmonella typhimurium that selectively accumulates and proliferate in tumor tissues. Myoglobin will be genetically engineered into the Salmonella bacteria as an oxygen sensor. Since Salmonella can penetrate into the hypoxic areas in the tumor, the method will give a full mapping of tumor oxygenation. In this R21 proposal, we will develop a novel molecular imaging methods to map tumor oxygen tension in murine tumor models using the attenuated Salmonella typhimurium strain that over-expresses the oxygen sensing protein myoglobin. Deoxymyoglobin can be measured directly in vivo using a signature peak at -80 ppm in the proton spectroscopy for oxygen tension calculations, or indirectly in high-resolution tumor tissue water imaging whereas deoxymyoglobin functions as a relaxation contrast reagent. This novel measurement of tumor oxygen tension will be applied to observe the primary and metastasized tumors. The methods will have numerous applications in preclinical development of anticancer drugs considering physiological parameters in a particular tumor microenvironment. Since Salmonella typhimurium is currently in phase I clinical trials, the project may have a major impact in the future diagnosis of both primary tumors and distant metastasis, as well as therapeutic planning and monitoring of the cancer clinical outcomes.