CNS specific Knock-out and Multidrug Transport

描述(申请人提供)：在所有组织中都存在mdr1基因缺失(零突变)的转基因动物的发展，使人们对mdr1产物、P-糖蛋白或Pgp在调节多种药物的疗效和毒性方面的生物和运输功能的了解有限。然而，零突变的小鼠不能准确地阐明转运蛋白在决定药物对中枢神经系统的可获得性中的作用。此外，在癌症患者中使用Pgp抑制剂(如PSC833)的临床研究表明，由于Pgp在药物吸收和药物消除的主要器官中表达，Pgp功能的全局抑制也增强了外周的剂量限制性毒性。为了阐明组织特定的转运机制，而不混淆并经常抵消同一药物在肝、肾和肠道等其他组织中遇到的转运和消除作用，需要一个更精确的动物模型系统。因此，该建议的目标是建立一个动物模型系统，允许选择性地关闭中枢神经系统中已被描述的药物转运体mdr1，以直接阐明和量化药物转运体在中枢神经系统药物输送和处置中的功能作用。R21探索性拨款提案的中心假设如下：在不影响其他组织的情况下，特定组织地取消血-脑脊液和血-脑屏障以及中枢神经系统中mdr1的表达，将提高药物在大脑中的可获得性。我们将通过以下目标验证这一假设：目标1：建立一种仅在中枢神经系统组织中缺失MDR1产物Pgp的转基因小鼠模型。这将通过(A)确定适合于开发脑特异性组织敲除系统的CNS特异性启动子，以及(B)选择优化的启动子，将开发和验证组织特异性mdr1基因敲除系统；目标2：比较CNS特异性mdr1基因敲除系统和整个动物mdr1基因敲除系统中探针底物的运输和处置。通过拟议的研究，我们将开发一种针对中枢神经系统的基因敲除小鼠模型，该模型将允许对mdr1产物Pgp在整个治疗光谱中的药物传递和处置进行定量和明确的估计。这种实验模型的可获得性将为研究中枢神经系统特有的其他生物和神经过程提供工具。这一工具可能成为研究在全身多个组织中表达的中枢神经系统蛋白不可或缺的工具。对整个生物医学研究的潜在好处超过了与这项探索性研究相关的计算风险。

DESCRIPTION (provided by applicant): Development of transgenic animals with MDR1 gene deletions (null mutation) in all tissues, has provided limited understanding of biologic and transport functions of MDR1 product, P-glycoprotein or Pgp in modulating efficacy and toxicity of a broad range of drugs. However, mice with null mutations are not able to precisely clarify the role of transporters in dictating drug availability to the CNS*. Also, clinical studies with Pgp inhibitors such as PSC833 in cancer patients suggest that global inhibition of Pgp function also enhances dose-limiting toxicity in periphery, due to expression of Pgp in the major organs of drug absorption and drug elimination. To elucidate tissue-specific transport mechanisms without the confounding and often counteracting transport and elimination actions encountered by the same drug in other tissues, such as liver, kidney and gut, a more precise animal model system is required. Therefore, the goal of this proposal is to develop an animal model system that allows selective shut-down of a well-described drug transporter, MDR1 in CNS to directly elucidate and quantify the functional role of drug transporters in delivery and disposition of drug in the CNS. The central hypothesis of this R21 exploratory grant proposal is as follows: Tissue-specific abrogation of MDR1 expression at the blood-cerebral spinal fluid and blood-brain barrier, and in the CNS, without compromising other tissues, will enhance drug availability in the brain. We will test this hypothesis using the following aims: Aim 1: To develop a transgenic mouse model depleted of the MDR1 product, Pgp, only in CNS tissues. This will be accomplished by (a) identifying a CNS-specific promoter suitable for use in developing a brain-specific tissue knockout system, and (b) with the optimized promoter selected, the tissue-specific MDR1 knockout system will be developed and validated; Aim 2: To compare transport and disposition of probe substrates in CNS-specific vs. whole animal MDR1 knockout systems. With the proposed studies, we will develop a CNS-specific knockout mouse model that would allow quantitative and definitive estimates of the MDR1 product, Pgp, in delivery and disposition of drugs across the therapeutic spectrum. Availability of such an experimental model will provide a tool for studies of other biological and neurological processes specific to CNS. This tool could become an indispensable one to study CNS proteins that express in multiple tissues throughout the body. The potential benefits to overall biomedical research outweigh the calculated risks associated with this exploratory research.