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

描述（由申请人提供）：阿尔茨海默病（AD）病理生理学中的新兴模型表明AB（β-淀粉样蛋白）快速且动态地穿过血脑屏障（BBB）交换，血脑屏障将AB加工的CNS和外周来源分开。最近的研究表明，位于毛细血管内皮细胞管腔表面的MDR 1 P-糖蛋白（Pgp）介导了AB从脑中排出的最后一步，表明Pgp在AD进展中的潜在作用。此外，影响这种转运活性的Pgp多态性在人群中很常见。因此，能够询问Pgp介导的运输在BBB的成像方法可以提供一个有价值的诊断生物标志物，用于确定一个新的风险因素在AD。使用过表达人淀粉样前体蛋白（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99 mTc-Sestamibi，一种FDA批准的显像剂和MDR 1 P-糖蛋白的有效转运底物，在年龄匹配的APP-Pgp-null小鼠的脑中的摄取比APP-Pgp WT小鼠高至少3倍。我们建议对99 mTc-Sestamibi进行先进的临床前验证：a）通过在存在有效和特异性Pgp抑制剂的情况下在APP-Pgp WT小鼠中进行药代动力学研究，评估99 mTc-Sestamibi作为AD中Pgp介导的b-淀粉样蛋白流出的诊断标志物的潜力，并将结果与不存在抑制剂的APP-Pgp-null小鼠进行比较; B）在不存在或存在Pgp抑制剂的情况下，分别在年龄匹配的APP-Pgp缺失小鼠和APP-PgpWT小鼠中，通过nanoSPECT和microPET成像，评估99 m/94 mTc-Sestamibi用作BB B处Pgp转运的非侵入性探针的潜力; c）表征大鼠脑内皮细胞中与99 mTc-Sestamibi转运相关的临床相关Pgp点突变;以及d）对参与者进行试点人类研究（先前通过11 C-PIB PET扫描表征为痴呆或正常受试者）来分析99 mTc-Sestamibi成像提供BBB处Pgp介导的转运的功能评估的潜力。这一策略的成功实施可以提供一种分子靶向诊断剂，用于评估AD中的新风险因素，帮助患者分层，并监测疾病管理中的治疗效果。公共卫生相关性：阿尔茨海默病（AD）病理生理学中的新兴模型表明，位于毛细血管内皮细胞腔表面的MDR 1 P-糖蛋白（Pgp）可介导Ab（b-淀粉样蛋白）从脑中排出。因此，能够探测血脑屏障（BBB）处Pgp介导的功能性转运的成像剂可以作为新的诊断生物标志物，用于确定AD中的这种新的风险因素。拟议的项目涉及开发单光子发射计算机断层扫描（SPECT）或正电子发射断层扫描（PET）成像剂，能够在BBB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这一风险因素在人群中易患AD。该策略的成功实施可以提供一种分子靶向诊断剂，用于评估AD中的新风险因素，并可以帮助受试者分层，指导治疗选择，以使患者在未来的疾病管理中受益。

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.