NOVEL PET AGENT FOR MYOCARDIAL PERFUSION IMAGING

描述(申请人提供)：基于机制的PET血流示踪器的开发摘要：心血管疾病是美国主要的死亡原因之一。心肌灌注成像(Mpi)是临床诊断的通用工具，在临床诊断中发挥着重要作用。 在冠状动脉疾病(CAD)的无创性评估中。目前，常用的单光子发射计算机断层扫描(SPECT)MPI试剂包括201Tl或中度疏水和阳离子的99mTc-络合物，如99mTC-Sestamibi和99mTc-Tetrofosmin，用于测定患者的心肌血流量(MBF)。然而，SPECT显像剂有其固有的局限性，包括99mMo/99mTc-发生器严重短缺的持续威胁。此外，目前的SPECT示踪剂还存在药代动力学、心肌提取、放射性示踪剂随时间重新分布到非靶向组织以及血流升高时摄取的非线性(“滚落”现象)等方面的不足。相比之下，正电子发射断层扫描(PET)提供了技术优势，包括更高的空间分辨率，改进的衰减校正，以及在应力峰值进行定量测量的能力。常用的PET MPI示踪剂有：82RbCl、13NH3和H215O。然而，由于这些试剂的物理半衰期很短(&lt；10分钟)，其实用性受到限制，因此很难容易地接触到这些试剂。其他有希望的18F标记药物，如线粒体膜电位探针18F-BnTP和线粒体复合体I抑制剂18F-BMS-747158、18F-10、18F-RP1004和18F-MCI27，都有不同的优点和缺点，但也依赖于基于18F的分布模式，这可能不容易被美国或其他发展中国家服务不足的地区获得。因此，PET示踪剂表现出较高的心肌首次通过提取、快速从肝脏清除、在心肌内滞留以实现延迟成像，以及基于可能在现场由发电机产生(而不是回旋加速器产生)的同位素，将有助于广泛获得PET MPI。为了解决这一未实现的目标，我们已经确定了一种基于发电机产生的镓-68的铅阳离子中等疏水性放射性药物1A，该药物显示出对正常小鼠和大鼠心肌的高提取，包括由多药耐药P-糖蛋白(PGP)转运体驱动的血池和肝脏的有效清除。试剂1A随着时间的推移保留在心肌中，并保持非代谢状态，允许稳定的分布和高计数统计，从而转化为高质量的心肌图像。重要的是，microPET/CT(68Ga)和NanSPECT/CT(67Ga)均显示在大鼠静脉注射后60min，1A在心脏中高度蓄积，随后从肝脏中容易清除。最后，在静脉注射67Ga-1A后，纳米SPECT/CT成像清楚地显示了左室壁的非灌注区，表明我们的先导剂有可能对大鼠模型的心肌灌注缺陷进行无创成像。因此，有了这些试验数据，R01提案的具体目标是：1)进行一项有针对性的SAR研究，以进一步优化我们的领先68Ga放射性药物作为潜在的MPI制剂的生化靶向和药代动力学。2)对我们在心肌细胞、HepG2细胞、表达Pgp的KB细胞、转导Pgp的MCF-7细胞中的新型68Ga放射性药物进行基于机理的评估和验证，并将这些数据与99mTC-Sestamibi相关联，99mTc-Sestamibi是一种在类似条件下得到充分验证的SPECT探针。3)通过在大鼠体内的药代动力学分析，测定放射性药物进入心肌的萃取率，以及在类似条件下与99mTC-Sestamibi和其他潜在的18F MPI药物的心/肝比率的比较分析，评价有希望的先导。4)通过在应激/静息条件下评估大鼠心肌梗死范围、首次通过提取和血流提取相关性，以及随后使用microPET成像对兔的导联进行评估，来表征和验证在SAR研究中出现的铅68Ga-放射性药物1A或其他潜在的导联作为无创MPI试剂。5)鉴定我们的先导剂或第二代68Ga放射性药物在犬模型中作为MPI剂的潜力；进行安全药理学概况研究、剂量分析，并准备eind备案材料。上述目标的成功实现将为MPI和CAD的管理提供一种分子靶向的68Ga-PET试剂。

DESCRIPTION (provided by applicant): Development of Mechanism-Based PET Flow Tracer Abstract: Cardiovascular disease is among the leading causes of death in the United States. Myocardial perfusion imaging (MPI), a versatile tool in clinical diagnosis, plays an important role in the noninvasive assessment of coronary artery disease (CAD). Currently, common single-photon emission computed tomography (SPECT) MPI agents comprise 201Tl or moderately hydrophobic and cationic 99mTc-complexes, such as 99mTc-sestamibi and 99mTc-tetrofosmin, for determining myocardial blood flow (MBF) in patients. However, SPECT imaging agents have inherent limitations, including the continuing threat of serious shortages of 99mMo/99mTc-generators. Additionally, current SPECT tracers also suffer from shortcomings in pharmacokinetics, myocardial extraction, redistribution of the radiotracer to non-targeted tissues over time, and non-linearity of uptake at elevated blood flow (the "roll-off" phenomenon). By comparison, positron emission tomography (PET) provides technical advantages, including higher spatial resolution, improved attenuation correction, and the capability to perform quantitative measurements at the peak of stress. Commonly employed PET MPI tracers are: 82RbCl, 13NH3, and H215O. However, the utility of these agents is limited due to their short physical half-life (<10 min), thus posing difficulties for easy access to these agents. Other promising 18F-labeled agents such as18F- BnTP, a mitochondrial membrane potential probe, and 18F-BMS-747158, 18F-10, 18F-RP1004, and 18F-MCI27, mitochondrial complex I inhibitors, have various strengths and weaknesses, but also depend on a 18F-based distribution model, which may not be readily accessible to underserved regions of the U.S. or other developing countries. Thus, PET tracers demonstrating high myocardial first pass extraction, rapid clearance from the liver, retention within the myocardium to enable delayed imaging, and based on isotopes that could potentially be generator-produced on site (rather than cyclotron produced) would facilitate wide access to PET MPI. To address this unmet goal, we have identified a lead cationic and moderately hydrophobic radiopharmaceutical 1A based on generator-produced gallium-68 that demonstrates high extraction into the myocardium of normal mice and rats, including efficient clearance from the blood pool and liver driven by the multidrug resistance P- glycoprotein (Pgp) transporter. The agent 1A is retained in myocardium over time and remains nonmetabolized, allowing stable distribution and high count statistics that translate into high quality myocardial images. Importantly, both microPET/CT (68Ga) and nanoSPECT/CT (67Ga) reveal high accumulation of 1A in heart followed by facile clearance from liver 60 min post intravenous injection in rats. Finally, following intravenous injection of 67Ga-1A, nanoSPECT/CT imaging clearly visualized the non-perfused region of the left ventricle wall indicating the potential of our lead agent to noninvasively image the myocardial perfusion defect in rat models. Thus, armed with these pilot data, specific objectives of this R01 proposal are: 1) Perform a focused SAR study to further optimize biochemical targeting and pharmacokinetics of our lead 68Ga- radiopharmaceutical as a potential MPI agent. 2) Perform mechanism-based assessment and validation of novel 68Ga-radiopharmaceuticals derived from our focused SAR studies in cardiomyocytes, HEPG2 cells, Pgp- expressing KB cells, Pgp-transfected MCF-7 cells, and correlate these data with 99mTc-Sestamibi, a well- validated and FDA approved SPECT probe under similar conditions. 3) Evaluate promising leads via pharmacokinetic analysis in rats, determining extraction fractions of radiopharmaceuticals into myocardium and comparative analysis of heart/liver ratios under similar conditions with 99mTc-Sestamibi and other potential 18F MPI agents. 4) Characterize and validate the lead 68Ga-radiopharmaceutical 1A or other potential leads emerging through SAR studies as a noninvasive MPI agent by assessment of myocardial infarct size, first pass extraction, and flow-extraction correlation under stress/rest conditions in rats, followed by assessment of leads in rabbits, using microPET imaging. 5) Characterize the potential of our lead agent or a second-generation 68Ga- radiopharmaceutical as a MPI agent in canine models; perform safety pharmacological profile studies, dosimetry analysis, and prepare eIND filing materials. Successful execution of the outlined objectives should provide a molecular-targeted 68Ga-PET agent for MPI and management of CAD.