Anionic Phospholipid-Selective PET/SPECT Agent for Infection Imaging

描述（由申请人提供）：尽管快速和准确的诊断对于怀疑细菌感染的患者的管理至关重要，但目前可用的放射性药物无法区分无菌炎症和细菌感染。我们的目标是开发一种感染特异性PET/SPECT放射性药物，最终用于临床实践。在第一阶段，我们将评估两种独立的方法。在共价方法中，我们将结合用于PET/SPECT成像的放射性核素螯合剂与已知可选择性靶向带负电荷的细菌包膜的Zn-DPA靶向片段，以提供一种新型小分子核显像剂。在另一种非共价放射标记方法中，我们将使用链亲和素（SA）作为生物素化Zn-DPA靶向基序和生物素化螯合剂之间的连接剂，形成一种显像剂，这种显像剂可能比共价方法改善细菌病变积聚，因为：(i)由于尺寸增加而减慢药代动力学，（ii）它可能结合多达三个DPA基团以增强亲和力。我们的具体目标包括：1)合成并表征DOTA- DPA-(1 Zn)共价偶联方法，DOTA/SA/DPA-(1 Zn)非共价方法，并用PET同位素68Ga和SPECT同位素111In对含DOTA试剂进行放射性标记。2)共价[68Ga/111In-DOTA -DPA-(1zn)]和非共价[68Ga/111In-DOTA/SA/DPA-(1zn)]对化脓性链球菌的血清稳定性及体外评价。通过增加未标记的DOTA-DPA-Zn浓度来测量与细菌的结合，以评估与细菌的特异性结合。之后，标记的细菌将在37℃的血清环境中进行评估，以确定螯合物内两种放射性核素的稳定性以及两种试剂对细菌的稳定性。3)评估感染和炎症小鼠模型中共价和非共价方法的特异性积累证据。将SKH1无毛小鼠大腿注射活的化脓性链球菌提供细菌感染模型或脂多糖提供炎症模型。我们将分别使用小动物PET和SPECT/CT相机对小鼠模型中的68Ga和111In放射性标记剂进行评估。在所有病例中，将通过联合注射PSVue(R) 794（一种荧光细菌靶向探针）和在小型动物光学相机上成像来监测感染的位置和程度。将评估药物的药代动力学、在靶体内的积累、靶大腿/对侧正常大腿的积累、特异性感染成像证据和检测敏感性。在牺牲的情况下，将对每个放射性标签进行完整的生物分布，以补充成像结果。第一阶段的关键基准将是使用68Ga/111In- dota - DPA-Zn或68Ga/111In- dota /SA/DPA-Zn在10小时（68Ga）或24小时（111In）期间获得感染大腿/正常大腿的比率大于5，与炎症大腿相比，在感染大腿中获得统计学上更高的积累，并获得感染模型中检测下限的估计。

DESCRIPTION (provided by applicant): Although a rapid and accurate diagnosis is crucial to the management of patients suspected of bacterial infection, the currently available radiopharmaceuticals are not capable of distinguishing between sterile inflammation and bacterial infections. Our goal is to develop an infection-specific PET/SPECT radiopharmaceutical for eventual use in clinical practice. In Phase I, we will evaluate two independent approaches. In a covalent approach, we will conjugate a radionuclide chelator for PET/SPECT imaging with a Zn-DPA targeting moiety that is known to selectively target the negatively charged bacterial envelope, to provide a novel small molecule nuclear imaging agent. In an alternative, non-covalent radiolabeling approach, we will use streptavidin (SA) as a linker between the biotinylated Zn-DPA targeting motif and a biotinylated chelator to form an imaging agent which may have improved bacterial lesion accumulation over the covalent approach due to: (i) its slower pharmacokinetics because of increased size, and (ii) its potential to bind up to three DPA groups for affinity enhancement. Our Specific Aims include: 1) Synthesize and characterize DOTA- DPA-(1 Zn) for the covalent conjugation approach, DOTA/SA/DPA-(1 Zn) for the non-covalent approach and radiolabel the DOTA containing agents with the PET isotope 68Ga, as well as the SPECT isotope 111In. 2) Serum stability assays and in vitro evaluation of the covalent [68Ga /111In-DOTA-DPA-(1 Zn)] and non- covalent [68Ga/111In-DOTA/SA/DPA-(1 Zn)] agents to S. pyogenes. Specific binding to bacteria will be evaluated by measuring binding to bacteria with increasing concentrations of unlabeled DOTA-DPA-Zn. Thereafter, labeled bacteria will be evaluated in 37o C serum environments to determine the stability of both radionuclide within the chelate and the stability of both agents to the bacteria. 3) Evaluate the covalent and non-covalent approaches in infection and inflammation mouse models for evidence of specific accumulations. SKH1 hairless mice will be injected in the thigh with live S. pyogenes to provide the bacterial infection model or lipopolysaccharide to provide the inflammation model. We will evaluate the agents radiolabeled with 68Ga as well as 111In in the mouse models using small animal PET and SPECT/CT cameras respectively. In all cases, the location and extent of infection will be monitored by co-injecting PSVue(R) 794 (a fluorescent bacteria targeting probe) and imaging on a small animal optical camera. Agents will be evaluated for their pharmacokinetics, their accumulation in the target, their target thigh/contralateral normal thigh accumulation, evidence of specific infection imaging and sensitivity of detection. At sacrifice, full biodistributions of each radiolabel will be done to supplement the imaging results. Key benchmarks for Phase I will be to obtain using either 68Ga/ 111In-DOTA- DPA-Zn or 68Ga/111In-DOTA/SA/DPA-Zn an infected thigh/normal thigh ratio of greater than 5 within a 10 h (68Ga) or 24 h (111In) period, obtain a statistically higher accumulation in the infected thighs compared to the inflammation thighs, and obtain an estimate of the lower limits of detection in the infection model. PUBLIC HEALTH RELEVANCE: Bacterial infection is one of the major causes of morbidity and mortality not only in developing countries but globally. Early diagnosis of infection and an ability to distinguish between bacterial infection and sterile inflammation is critical to the effective management of these patients. However, despite the efforts of many international imaging groups, there is currently no validated bacterial imaging agent that can distinguish infection from sterile inflammation. Obviously, the development of such an agent would greatly advance our ability to detect, localize, and quantify infections, to prescribe the appropriate treatment and to follow the patient throughout the treatment. In this project we propose to evaluate two novel approaches aimed at developing a new radiopharmaceutical which would allow noninvasive imaging of bacterial infections with the sensitivity that nuclear imaging approaches promise and would also allow infectious and inflammatory abscesses to be distinguished.