Anionic Phospholipid-Selective PET/SPECT Agent for Infection Imaging

描述(申请人提供)：尽管快速和准确的诊断对疑似细菌感染的患者的治疗至关重要，但目前可用的放射性药物不能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的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。在一种共价方法中，我们将用于PET/SPECT成像的放射性核素螯合剂与已知的选择性靶向负电荷细菌膜的部分锌-DPA偶联，以提供一种新型的小分子核显像剂。在另一种非共价放射性标记方法中，我们将使用链霉亲和素(SA)作为生物素化的锌-DPA靶向基序和生物素化的螯合剂之间的连接物，以形成一种可能比共价方法更好地改善细菌损伤积累的显像剂，这是因为：(I)由于尺寸增大而药代动力学变慢，以及(Ii)其结合多达三个DPA基团以提高亲和力的潜力。我们的具体目标包括：1)合成和表征用于共价连接的DOTA-DPA-(1)锌，用于非共价连接的DOTA/SA/DPA-(1)锌，以及用PET同位素68Ga和SPECT同位素111In标记DOTA的试剂。2)共价[68Ga/111In-DOTA-DPA-(1 Zn)]和非共价[68Ga/111In-DOTA/SA/DPA-(1 Zn)]试剂对化脓性链球菌的血清稳定性测定和体外评价。随着未标记DOTA-DPA-锌浓度的增加，将通过测量与细菌的结合来评估对细菌的特异性结合。此后，将在37oC的血清环境中对标记的细菌进行评估，以确定螯合物中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的共价和非共价方法，以寻找特定蓄积的证据。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内毒素提供炎症模型。我们将分别使用小动物PET和SPECT/CT相机在小鼠模型中评估标记68Ga和111In的试剂。在所有情况下，感染的位置和程度都将通过共同注射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。将评估药物的药代动力学、在靶区的蓄积、靶侧/对侧正常大腿的蓄积、特定感染成像的证据和检测的敏感性。在牺牲时，将对每个放射性标记进行完全的生物分布，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)内获得大于5的感染大腿/正常大腿比率，获得与炎症大腿相比在统计上更高的大腿蓄积，并获得感染模型中检测下限的估计。 与公共卫生的相关性：细菌感染不仅在发展中国家，而且在全球都是发病率和死亡率的主要原因之一。感染的早期诊断和区分细菌感染和无菌炎症的能力对这些患者的有效治疗至关重要。然而，尽管许多国际成像组织做出了努力，目前还没有经过验证的细菌显像剂可以区分感染和无菌炎症。显然，这种试剂的开发将极大地提高我们检测、定位和量化感染、开出适当的治疗方法以及在整个治疗过程中跟踪患者的能力。在这个项目中，我们建议评估两种新的方法，旨在开发一种新的放射性药物，它将允许以核成像方法承诺的灵敏度对细菌感染进行非侵入性成像，并将允许区分感染性和炎症性脓肿。

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.