Multidrug resistance Mediated by P-glycoprotein

P-糖蛋白介导的多药耐药性

• 批准号: 7331398
• 负责人: Antonio Fojo
• 金额: --
• 依托单位: DIVISION OF CLINICAL SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7331398
• 关键词: Multidrug; resistance; Mediated; glycoprotein

Background: In the field of multidrug resistance mediated by the multidrug transporter, P glycoprotein, which is encoded by the MDR-1 gene, our efforts continue to have a major focus on translational research, while trying to pursue basic investigations that have the potential for future clinical correlations.Since its original description nearly 20 years ago, increased expression of P-glycoprotein (Pgp) has been frequently observed in cell culture models of multidrug resistance and in clinical samples obtained from refractory patients. But while progress has been made, the regulation of Pgp expression is not fully understood. Is MDR-1/Pgp expression in drug selected cells and refractory tumors under similar regulatory control as that in normal tissues, or drug sensitive cells? Our results suggest the answer is no. In all drug resistant cell lines derived from parental cells that do not normally express MDR-1 or express MDR-1 at low levels, the mechanisms regulating MDR-1 expression are acquired and abnormal. Expression from an unrelated, active promoter, proceeding in a normal or an aberrant direction, can control transcription. This occurs principally as a result of a gene rearrangement that leads to capture of MDR-1 by an unrelated promoter. Alternately, aberrant transcription can begin in a region 112 kb 5 prime of MDR-1. Following drug selection this region functions as a promoter. Evidence suggests that an HERV LTR is involved in this aberrant transcription and that acetylation of a nearby sequence may be an important epigenetic event in the activation of this aberrant promoter. Our research goals are to (1) understand the molecular basis of acquired MDR-1 expression; (2) comprehend how/why these changes occur; (3) search for them in clinical samples and (4) devise strategies to reduce or prevent their occurrence. In the clinic, in collaborative studies with Susan Bates, M.D. we continue to conduct trials examining the use of Pgp antagonists as modulators of drug sensitivity.Project Description and Plans: We have identified gene rearrangements as the mechanism responsible for the activation of MDR-1 in a large number of cell lines, and in patient samples. These rearrangements occur randomly and are characterized by the juxtaposition of a transcriptionally active gene 5 prime to MDR-1, thus avoiding disruption of MDR-1 structure. These gene rearrangements leading to activation of MDR-1 represent a mechanism of resistance with the following characteristics: (i) the rearrangement is an acquired phenotype, not detected in parental cells, and (ii) the rearrangement provides a mechanism for activation of MDR-1 in cells that do not express MDR-1 or express MDR-1 at very low levels; this is not a mechanism for over-expression of MDR-1 in a cell that expresses MDR-1 endogenously at significant levels. Additional characteristics include the following: (1) The majority of MDR-1 transcripts in these cells are hybrid mRNAs. (2) Activation occurs by juxtaposing an active promoter 5 prime to MDR-1, and initiating transcription at this promoter. Expression of the non-MDR-1 gene can be readily detected in a variety of cells suggesting the non-MDR-1 gene is constitutively active and has widespread expression. Furthermore, where information has been available for the non-MDR-1 sequences, the residues fused to MDR-1 have been from the 5 prime UTR of the respective genes (3) The rearrangements appear to occur randomly and involve genes found in chromosome 7 and in chromosomes other than 7. The sequences within 7 are found either centromeric or telomeric of MDR-1 (i.e. inversions occur). The breakpoints have been characterized in eight drug resistant cell lines. Rearrangements occurred as a result of either homologous recombination or non-homologous end joining.

Background: In the field of multidrug resistance mediated by the multidrug transporter, P glycoprotein, which is encoded by the MDR-1 gene, our efforts continue to have a major focus on translational research, while trying to pursue basic investigations that have the potential for future clinical correlations.Since its original description nearly 20 years ago, increased expression of P-glycoprotein (Pgp) has been frequently observed in cell culture models of multidrug抵抗和从难治性患者获得的临床样本中。但是，尽管取得了进展，但PGP表达的调节尚未完全理解。 MDR-1/PGP在选定的细胞中的表达和在正常组织或药物敏感细胞类似的调节性对照下的难治性肿瘤中是否表达？我们的结果表明答案是否定的。在所有通常不表达MDR-1或表达MDR-1的耐药细胞系中，在低水平上，调节MDR-1表达的机制均获得和异常。从正常或异常方向进行的无关，主动启动子的表达可以控制转录。这主要是由于基因重排导致无关启动子捕获MDR-1的结果。或者，异常转录可以从MDR-1的112 kb 5素数开始。在药物选择之后，该区域起启动子的作用。有证据表明，HERV LTR参与了这种异常转录，而附近序列的乙酰化可能是激活该异常启动子的重要表观遗传事件。我们的研究目标是（1）了解获得的MDR-1表达的分子基础； （2）理解这些变化是如何/为什么发生的； （3）在临床样本中搜索它们，（4）制定策略以减少或防止其发生。在诊所中，在与苏珊·贝茨（Susan Bates）的合作研究中，我们继续进行研究，以研究PGP拮抗剂作为药物敏感性的调节剂的使用。项目描述和计划：我们已经将基因重排作为负责在大量细胞系中以及在患者样品中激活MDR-1的机制。这些重排随机发生，其特征是转录活性基因5素与MDR-1并置，从而避免了MDR-1结构的破坏。这些基因重排导致MDR-1的激活代表具有以下特征的抗性机制：（i）重排是一种获得的表型，未在亲本细胞中检测到，并且（ii）重排提供了一种在不表达MDR-1或表达MDR-1非常低水平的细胞中MDR-1激活的机制；这不是在显着水平内源表达MDR-1的细胞中MDR-1过表达的机制。其他特征包括以下内容：（1）这些细胞中的大多数MDR-1转录本是杂化mRNA。 （2）激活是通过将Active启动子5 Prime与MDR-1并置并在该启动子处启动转录而发生。在各种细胞中可以很容易地检测到非MDR-1基因的表达，这表明非MDR-1基因具有组成性活性，并且具有广泛的表达。此外，如果已适合非MDR-1序列的信息，则融合到MDR-1的残基是来自相应基因的5个主要UTR（3）重排似乎是随机发生的，涉及在染色体7和7中发现7的染色体中发现的基因。在7中发现了7。这些断点已在八种耐药细胞系中表征。重排是由于同源重组或非同源末端连接而发生的。