Department of Chemistry and Biochemistry and the Notre Dame Integrated Imaging Facility, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Bioconjug Chem. 2010 Jul 21;21(7):1297-304. doi: 10.1021/bc1000998.
Two structurally related fluorescent imaging probes allow optical imaging of bacterial leg infection models in living athymic and immunocompetent mice. Structurally, the probes are comprised of a deep-red fluorescent squaraine rotaxane scaffold with two appended bis(zinc(II)-dicolylamine) (bis(Zn-DPA)) targeting ligands. The bis(Zn-DPA) ligands have high affinity for the anionic phospholipids and related biomolecules that reside within the bacterial envelope, and they are known to selectively target bacterial cells over the nearly uncharged membrane surfaces of healthy mammalian cells. Planar, whole-animal optical imaging studies showed that intravenous dosing of either probe (10 nmol) allowed imaging of localized infections of Gram-positive Staphylococcus aureus and Gram-negative Salmonella enterica serovar typhimurium. High selectivity for the infected target leg (T) over the contralateral nontarget leg (NT) was reflected by T/NT ratios up to six. The infection imaging signal was independent of mouse humoral immune status, and there was essentially no targeting at a site of sterile inflammation induced by injection of lambda-carrageenan. Furthermore, the fluorescent probe imaging signal colocalized with the bioluminescence signal from a genetically engineered strain of S. enterica serovar typhimurium. Although not highly sensitive (the localized infection must contain at least approximately 10(6) colony forming units for fluorescence visualization), the probes are remarkably selective for bacterial cells considering their low molecular weight (<1.5 kDa) and simple structural design. The more hydrophilic of the two probes produced a higher T/NT ratio in the early stages of the imaging experiment and washed out more rapidly from the blood clearance organs (liver, kidney). Therefore, it is best suited for longitudinal studies that require repeated dosing and imaging of the same animal. The results indicate that fluorescent probes based on squaraine rotaxanes should be broadly useful for in vivo animal imaging studies, and they further validate the ability of imaging probes with bis(Zn-DPA) ligands to selectively target bacterial infections in living animals.
两种结构相关的荧光成像探针可用于在活体无胸腺和免疫功能正常的小鼠中对细菌性腿部感染模型进行光学成像。从结构上看，这些探针由一个深红色荧光方酸轮烷支架组成，该支架带有两个附加的双（锌（II）-二酰基苯胺）（双（Zn-DPA））靶向配体。双（Zn-DPA）配体与位于细菌包膜内的阴离子磷脂和相关生物分子具有高亲和力，并且已知它们选择性地靶向细菌细胞，而不是健康哺乳动物细胞几乎不带电荷的膜表面。平面，全动物光学成像研究表明，静脉内给予任一种探针（10 nmol）均可对革兰氏阳性金黄色葡萄球菌和革兰氏阴性鼠伤寒沙门氏菌的局部感染进行成像。感染的目标腿部（T）与对侧非目标腿部（NT）的 T/NT 比值高达 6，这表明对感染目标的选择性很高。感染成像信号与来自鼠伤寒沙门氏菌基因工程菌株的生物发光信号重合。尽管探针的灵敏度不高（荧光可视化时，局部感染必须至少包含大约 106 个菌落形成单位），但考虑到其低分子量（<1.5 kDa）和简单的结构设计，它们对细菌细胞的选择性非常高。两种探针中更亲水的一种在成像实验的早期产生更高的 T/NT 比值，并且从血液清除器官（肝脏，肾脏）中更快地冲洗掉。因此，它最适合需要对同一动物进行重复给药和成像的纵向研究。结果表明，基于方酸轮烷的荧光探针应该广泛用于体内动物成像研究，并且进一步验证了具有双（Zn-DPA）配体的成像探针选择性靶向活体动物细菌感染的能力。
