STUDIES OF MULTIDRUG RESISTANCE IN MAMMALIAN CELLS

观察到对化疗药物的耐药性的发展 临床，并在组织培养细胞中得到了广泛的研究。一 不寻常的表型是多药耐药，在这种情况下， 用任何一种细胞毒药物挑战都会产生抗药性 不仅对选择剂，而且对其他的交叉抗性， 看似不相关的化合物。这种多药耐药(MDR)表型 与膜糖蛋白的过度生产有关，包括 P-糖蛋白，并在某些情况下胞浆产生过剩 蛋白质也是。因此，表型是复杂的，而遗传 阻力和交叉阻力的基础被以下事实所掩盖 多个基因的差异扩增(我们称之为MDRA基因) 调节糖蛋白的过度生产，而其他共扩增的 基因调节至少一种胞浆蛋白的表达，并可能 其他蛋白质也是如此。虽然多药耐药的最终原因 是降低了细胞内药物浓度，任何一种 耐药或交叉耐药机制中的扩增基因产物 在模型组织培养系统中和在人类肿瘤中 化疗，仍然是个谜。利用重组DNA技术， DNA转染技术和核径流转录分析，我们 建议确定MDRA基因产物在建立中的作用 MDR表型，并确定其产物也可能 参与到它的表达中。此外，当放大时， MDRA基因的表达可能远远超过其基因拷贝数，这表明 这种过度表达并不是单靠扩增来调节的。我们会的， 因此，确定这种增强表达的分子基础 它可能表明了一种在没有 放大。最后，我们建议衡量基因的表达水平 大量人类肿瘤细胞系和正常细胞中的MDRA基因 线条，肿瘤和正常组织，努力确定范围 这些基因在人类细胞中的表达，以及它们的 可以证明过度表达与许多抗药性有关 患者对各种各样的化疗药物都有反应。

The development of resistance to chemotherapeutic agents is observed in the clinic, and has been studied extensively in tissue culture cells. One unusual phenotype is that of multidrug resistance, in which cells that are challenged with any one of a variety of cytotoxic drugs develop resistance not only to the selective agent but also cross-resistance to other, seemingly unrelated, compounds. This multidrug-resistant (mdr) phenotype is associated with the overproduction of membrane glycoproteins, including p-glycoprotein, and in some cases with the overproduction of cytosolic proteins as well. The phenotype is complex, therefore, and the genetic basis for resistance and cross-resistance is obscured by the fact that the differential amplification of multiple genes (which we call MDRA genes) mediates the overproduction of the glycoproteins, whereas other coamplified genes mediate the expression of at least one cytosolic protein and probably other proteins as well. While the ultimate cause of multidrug resistance is the lowered intracellular concentration of drug, the role of any of the amplified gene products in the mechanism of resistance or cross-resistance in model tissue culture systems and in human tumors refractory to chemotherapy, remains obscure. With the use of recombinant DNA technology, DNA transfection techniques, and nuclear runoff transcription assays, we propose to define the role of the MDRA gene products in the establishment of the mdr phenotype, and to identify other genes whose products may also be involved in its expression. Additionally, when amplified, the expression of MDRA genes can far exceed their gene copy number, suggesting that overexpression is not mediated by amplification alone. We will, therefore, determine the molecular basis for this enhanced expression for it may indicate a mechanism for overexpression in the absence of amplification. Finally, we propose to measure the levels of expression of MDRA genes in a large number of human tumor cell lines and normal cell lines, and tumors and normal tissues in an effort to determine the extent to which these genes are expressed in human cells and whether their overexpression can be shown to be associated with the resistance that many patients display to a wide variety of chemotherapeutic agents.