Drug Interactions at the Human Blood-Brain Barrier

描述（由申请人提供）：本申请涉及广泛的挑战领域（15）转化研究和多个特定的挑战主题：15-NS-101* 操纵血脑屏障以提供精神/神经系统疾病的CNS治疗; 06-GM-102* 化学家/生物学家合作促进工具开发; 05-AG-103* 影像和液体生物标志物用于包括神经退行性疾病在内的衰老相关疾病和病症的早期诊断和进展。血脑屏障（BBB）是将药物递送至中枢神经系统（CNS）和去除CNS内产生的潜在毒素（例如β-淀粉样蛋白）的重要屏障。与其他器官中的内皮细胞屏障相反，BBB具有防止显著的细胞旁扩散的紧密连接。虽然亲脂性药物能够容易地从血液扩散到脑中穿过BBB，但存在于该屏障处的几种外排转运蛋白可以显著减少这些药物进入CNS [1]。其中最突出的是P-糖蛋白（P-gp），一种由多药耐药1（MDR 1）基因编码的ABC外排转运蛋白[2]。由于P-gp在血脑屏障的高表达和广泛的底物选择性，P-gp被广泛认为是调节药物进入中枢神经系统的最重要的转运蛋白，转运超过30%的市场上的药物。在mdr 1a（-/-）小鼠的发育中证实了P-gp在BBB中的功能重要性。通过在BBB处消融P-gp，向mdr 1a（-/-）小鼠施用P-gp底物药物导致这些药物的脑分布显著增加。例如，与野生型小鼠相比，抗HIV蛋白酶抑制剂奈非那韦的脑：血浓度比增加了40倍。基于上述数据，已广泛预测啮齿动物中P-gp的诱导或化学/遗传敲除可预测可能在人BBB处观察到的P-gp活性的大小。如果这种被广泛接受的外推是正确的，克服人P-gp BBB将导致P-gp底物药物（例如抗HIV蛋白酶抑制剂）的CNS疗效显著增加。相反，在人BBB处诱导P-gp活性可显著增加潜在毒素从CNS（例如阿尔茨海默病中的β-淀粉样蛋白）的流出，或降低靶向CNS的药物用于治疗疼痛（例如阿片样物质）和其他CNS病症的功效。然而，一个关键问题仍然没有答案。人类血脑屏障中的P-gp活性在阻止药物进入大脑或从大脑中清除可溶性β-淀粉样蛋白方面是否与啮齿类动物一样重要？直到最近，这个重要的和临床相关的问题无法回答，因为测量P-gp活性或P-gp在人BBB的抑制/诱导的方法不可用。随着我们实验室开发出一种新颖、创新和非侵入性的正电子发射断层扫描（PET）成像方法来定量测量P-gp活性及其在人BBB的抑制/诱导，这一点发生了变化。因此，我们的具体目标旨在解决以下关键问题：（i）在从CNS中排除药物方面，人BBB中的P-gp与啮齿动物中的P-gp一样重要吗（目标1和2）？(ii)目前批准的FDA药物能否抑制人类BBB的P-gp活性？如果是，最大可能的抑制是否足以显著增加药物的递送，以治疗致死性CNS疾病（如脑肿瘤）或产生严重但无意的药物相互作用（目标1）？一个否定的答案也将是重要的，因为它将指导临床医生以及制药行业。目前，由于对基于P-gp的深刻药物相互作用的担忧，制药行业避免（可能不必要地）开发作为P-gp底物的CNS药物。因此，定义可能发生临床显著的基于P-gp的药物相互作用的边界将在药物开发过程和临床中非常有帮助。(iii)P-gp在人血脑屏障的活性能被诱导吗？如果是这样，FDA批准的药物利福平（一种P-gp的强效诱导剂）产生的最大诱导作用是多少（目标2）？如果P-gp在人血脑屏障的活性是可诱导的，这样的发现也将具有相当大的临床意义。首先，在人血脑屏障诱导P-gp，导致β-淀粉样蛋白从脑中的清除增强，可能是治疗阿尔茨海默病的潜在的新颖和创新的治疗策略。第二，这种方法可用于在药物滥用（例如美沙酮，P-gp底物）的情况下“收紧”BBB。第三，这将表明，当与靶向脑的P-gp底物药物联合给药时，必须避免使用强效P-gp诱导剂药物（例如圣约翰草、地塞米松、利福昔单抗）。完成后，我们的研究结果将对众多社区产生广泛的影响，包括阿尔茨海默病，脑肿瘤，艾滋病相关痴呆症和制药行业的整个CNS药物开发过程。 公共卫生相关性：本提案的目的是确定基于抑制性或诱导性P-糖蛋白的药物相互作用是否可在人血脑屏障发生。此外，我们的研究将测量这种相互作用的大小。我们的研究结果应该导致更好的药物治疗管理和药物开发过程的改进。

DESCRIPTION (provided by applicant): This application addresses broad Challenge Area (15) Translational Research and multiple specific Challenge Topics: 15-NS-101* Manipulating the blood-brain-barrier to deliver CNS therapies for Mental/Nervous System Disorders; 06-GM-102* Chemist/biologist collaborations facilitating tool development; 05-AG-103* Imaging and Fluid Biomarkers for Early Diagnosis and Progression of Aging-related Diseases and Conditions including Neurodegenerative Diseases. The blood brain barrier (BBB) is a significant barrier to delivery of drugs to the central nervous system (CNS) and in removal of potential toxins produced within the CNS (e.g. beta-amyloid). In contrast to the endothelial cell barrier in other organs, the BBB has tight junctions that prevent significant paracellular diffusion. Although lipophilic drugs are capable of readily diffusing from the blood to the brain across the BBB, several efflux transporters present at this barrier can significantly reduce the entry of these drugs into the CNS [1]. Prominent amongst these is P-glycoprotein (P-gp), an ABC efflux transporter encoded by the multi-drug resistance 1 (MDR1) gene [2]. Due to its high expression at the BBB and its wide substrate selectivity, P-gp is widely believed to be the most important transporter in modulating the entry of drugs into the CNS, transporting more than 30% of the drugs on the market. The functional importance of P-gp at the BBB was confirmed with the development of the mdr1a(-/-) mice. With ablation of P-gp at the BBB, administration of P-gp substrate drugs to mdr1a(-/-) mice results in a dramatic increase in the brain distribution of these drugs. For example, compared to the wild type mouse, the brain:blood concentration ratio of the anti-HIV protease inhibitor, nelfinavir, is increased 40-fold. Based on the above data, it has been widely predicted that induction or chemical/genetic knock-out of P-gp in rodents is predictive of the magnitude of P-gp activity likely to be observed at the human BBB. If this widely-accepted extrapolation is correct, overcoming the human P-gp BBB will result in significant increase in CNS efficacy of drugs that are P-gp substrates (e.g. anti-HIV protease inhibitors). Conversely, induction of P-gp activity at the human BBB could significantly increase the efflux of potential toxins from the CNS (e.g. beta-amyloid in Alzheimer's disease) or reduce the efficacy of drugs targeted to the CNS for the treatment of pain (e.g. opioids) and other CNS disorders. However, a key question remains unanswered. Is P-gp activity at the human BBB as important as in rodents in preventing delivery of drugs to the brain or in removal of soluble beta-amyloid from the brain? Until recently, this important and clinically relevant question could not be answered as methods to measure P-gp activity or P-gp inhibition/induction at the human BBB were not available. This changed with the development by our laboratory of a novel, innovative and non-invasive, Positron Emission Tomography (PET) imaging method to quantitatively measure P-gp activity and its inhibition/induction at the human BBB. Therefore, our specific aims are designed to address the following key questions: (i) Is P-gp at the human BBB as important as that in rodents in excluding drugs from the CNS (Aims 1 and 2)? (ii) Can P-gp activity at the human BBB be inhibited with currently approved FDA drugs? If so, is the maximum possible inhibition sufficient to significantly increase the delivery of drugs to treat lethal CNS disorders such as brain tumors or to produce profound, but inadvertent, drug interactions (Aim 1)? A negative answer will also be significant in that it will guide clinicians as well as the pharmaceutical industry. Currently, due to concerns of profound P-gp based drug interactions, the pharmaceutical industry avoids (perhaps unnecessarily) development of CNS drugs that are P-gp substrates. Thus, defining the boundaries within which clinically significant P-gp based drug interactions are likely to occur would be enormously helpful in the drug development process and in the clinic. (iii) Can P-gp activity at the human BBB be induced? If so, what is the maximum induction produced by a FDA-approved drug, rifampin, a potent inducer of P-gp (Aim 2)? If P-gp activity at the human BBB is inducible, such a finding would also have considerable clinical significance. First, induction of P-gp at the human BBB, resulting in enhanced clearance of beta-amyloid from the brain, could be a potential novel and innovative therapeutic strategy in the treatment of Alzheimer's disease. Second, such an approach could be used to "tighten" the BBB in the case of drug abuse (e.g. methadone, a P-gp substrate). Third, it would indicate that drugs that are potent P-gp inducers (e.g. St. John's Wort, dexamethasone, rifabutin) must be avoided when co-administered with P-gp substrate drugs targeted to the brain. On completion, the results of our study will have wide ranging implications on multitude of communities including people with Alzheimer's disease, brain tumors, HIV-associated dementia and the entire CNS drug development process in the pharmaceutical industry. PUBLIC HEALTH RELEVANCE: The aims of this proposal will determine if inhibitory or inductive P-glycoprotein based drug interactions can occur at the human blood-brain barrier. In addition, our studies will measure the magnitude of such interactions. The results of our study should lead to better management of drug therapy and improvement of the drug development process.