IMAGING FUNCTIONAL P-GLYCOPROTEIN TRANSPORT AT THE BBB IN ALZHEIMER'S DISEASE

描述(申请人提供)：阿尔茨海默病(AD)病理生理学的新兴模型表明，AB(β-淀粉样蛋白)正在快速和动态地穿过分隔中枢神经系统和AB处理的外周来源的血脑屏障(BBB)进行交换。最近的研究表明，位于毛细血管内皮细胞管腔表面的MDR1P-糖蛋白(Pgp)介导了AB从脑内排出的最后一步，提示Pgp在AD的进展中具有潜在的作用。此外，影响这种转运活性的PGP多态在人群中很常见。因此，一种能够询问PGP介导的血脑屏障转运的成像方法可以为确定AD的新的危险因素提供一个有价值的诊断生物标志物。利用过表达人类淀粉样前体蛋白(APP)的转基因小鼠与Pgp基因敲除或WT小鼠杂交，我们还证明了FDA批准的显像剂和mdr1 P-糖蛋白的有效转运底物99mTC-Sestamibi在年龄匹配的APP-Pgp缺失小鼠脑组织中的摄取量至少是APP-PgpWT小鼠的3倍。我们建议进行99mTC-Sestamibi的高级临床前验证：a)通过在APP-PgpWT小鼠中进行药代动力学研究，评估99mTC-Sestamibi作为Pgp介导的b-淀粉样蛋白外流在AD中的诊断标记物的潜力，并与APP-Pgp缺失小鼠在没有抑制剂的情况下进行比较；b)在年龄匹配的APP-Pgp缺失型和APP-PgpWT小鼠中，分别通过SPECT和显微PET成像，评估99m/94mTC-Sestamibi作为Pgp在BBB处转运的无创性探针的可能性；C)确定与99mTc-Sestamibi转运相关的临床相关PGP点突变在大鼠脑内皮细胞中的特征；以及d)对参与者(先前通过11C-PIB PET扫描确定为痴呆或正常受试者)进行一项试验性人体研究，以分析99mTc-Sestamibi显像的潜力，以提供PGP介导的血脑屏障转运的功能评估。这一策略的成功实施可以为评估AD的新危险因素提供分子靶向的诊断试剂，帮助患者分层，并在疾病管理中监测治疗效果。公共卫生相关性：阿尔茨海默病(AD)病理生理学的新模型表明，位于毛细血管内皮细胞管腔表面的MDR1P-糖蛋白(PGP)可以介导抗体(b-淀粉样蛋白)从脑中排出。因此，能够探测PGP介导的血脑屏障(BBB)功能转运的显像剂可以作为新的诊断生物标志物来确定这一新的AD危险因素。拟议的项目包括开发一种单光子发射计算机断层扫描(SPECT)或正电子发射断层扫描(PET)显像剂，能够在血脑屏障询问这一关键的生化过程，并可能提供一种创新的方法来评估易患AD的人群中的这一危险因素。这一策略的成功实施可以为评估AD的一个新的危险因素提供一个分子靶向的诊断试剂，并可以帮助受试者分层指导治疗选择，从而有利于未来患者的疾病管理。

DESCRIPTION (provided by applicant): Emerging models in Alzheimer's Disease (AD) pathophysiology indicate that AB (beta-Amyloid) is rapidly and dynamically exchanging across the blood-brain barrier (BBB) separating CNS and peripheral sources of AB processing. Recently, it has been shown that MDR1 P-glycoprotein (Pgp), located on the luminal surface of capillary endothelial cells, mediates the final step of AB extrusion from the brain, indicating a potential role for Pgp in progression of AD. Additionally, Pgp polymorphisms impacting this transport activity are common in the population. Thus, an imaging method capable of interrogating Pgp-mediated transport at the BBB could provide a valuable diagnostic biomarker for determining a novel risk factor in AD. Using transgenic mice that overexpress human amyloid precursor protein (APP) cross bred to Pgp gene knockout or WT mice, we have also demonstrated that 99mTc-Sestamibi, a FDA approved imaging agent and an efficient transport substrate of MDR1 P-glycoprotein, shows at least 3-fold higher uptake in brains of age-matched APP-Pgp-null mice compared with their APP-PgpWT counterparts. We propose to perform advanced preclinical validation of 99mTc-Sestamibi: a) evaluate the potential of 99mTc-Sestamibi to serve as a diagnostic marker for Pgp-mediated efflux of b-amyloid in AD via pharmacokinetic studies in APP-PgpWT mice in the presence of potent and specific Pgp inhibitors and compare results with APP-Pgp-null mice in the absence of inhibitors; b) evaluate the potential of 99m/94mTc-Sestamibi to serve as a noninvasive probe of Pgp transport at the BBB via nanoSPECT and microPET imaging, respectively, in age-matched APP-Pgp-null mice and APP-PgpWT mice, in the absence or presence of Pgp inhibitors; c) characterize clinically-relevant Pgp point mutations in relation to 99mTc-Sestamibi transport in rat brain endothelial cells; and d) perform a pilot human study of participants (previously characterized via 11C-PIB PET scans as demented or normal subjects) to analyze the potential of 99mTc-Sestamibi imaging to provide a functional assessment of Pgp-mediated transport at the BBB. Successful execution of this strategy could provide a molecular-targeted diagnostic agent for assessment of a novel risk factor in AD, assist patient stratification, and monitor therapeutic efficacy in disease management. PUBLIC HEALTH RELEVANCE: Emerging models in Alzheimer's Disease (AD) pathophysiology indicate that MDR1 P-glycoprotein (Pgp) located on the luminal surface of capillary endothelial cells could mediate Ab (b-Amyloid) extrusion from the brain. Therefore, imaging agents capable of probing Pgp-mediated functional transport at the blood-brain barrier (BBB) could serve as novel diagnostic biomarkers for determining this novel risk factor in AD. The proposed project involves development of a single photon emission computed tomography (SPECT) or positron-emission tomography (PET)-imaging agent, capable of interrogating this critical biochemical process at the BBB, and potentially offering an innovative approach to assess this risk factor in the segment of population susceptible to AD. Successful execution of this strategy could provide a molecular-targeted diagnostic agent for assessment of a novel risk factor in AD and could assist subject stratification in guiding therapeutic choices to benefit disease management of patients in future.