GENETIC ANALYSIS OF THE MULTIDRUG RESISTANCE PHENOTYPE IN TUMOR CELLS

对多种药物的耐药性是成功治疗的主要障碍 人类癌症的化疗。多药耐药的一种机制是 170，000道尔顿能量依赖性药物外排泵的表达 （P-糖蛋白或多药转运蛋白，人MDR 1的产物） 基因），其赋予对秋水仙碱，阿霉素，长春新碱， 长春碱、嘌呤霉素和放线菌素D。几条调查线 关于多药转运蛋白的研究一直在进行：1） P-糖蛋白在囊泡和跨囊泡中的ATP依赖性转运活性 已经获得了上皮单层; 2）新的表达载体， 利用全长MDR 1 cDNA作为显性选择标记， 在培养细胞中引入和扩增非选择性基因和MDR 1 逆转录病毒载体已经被开发出来; 3）许多人类肿瘤表达MDR 1 这种表达可以预测某些癌症的耐药性， 与其他药物耐药性的发展相关; 4）转基因 已经构建了小鼠，其中人MDR 1 mRNA表达在小鼠的 骨髓中的水平与人类肿瘤中发现的水平相当。这个水平 的MDR 1表达足以赋予对诱导的白细胞减少症的抗性 5）MDR 1 RNA的表达增加已被证明是由MDR药物引起的。 再生大鼠肝脏，在培养的啮齿动物细胞暴露后， 化疗剂，以及在热休克后的肾癌细胞中; 6） 人MDR 1基因的内含子-外显子结构已经确定， 支持两半独立进化的模型， 多药转运蛋白类似地，对MDR 1 cDNA进行缺失分析。 这与氨基和氨基都贡献的重要功能一致， 一项研究表明， 通过疏水性的光亲和标记P-糖蛋白的两半 药物3 H-叠氮平;和7）P-糖蛋白通过泵送而起作用的证据 疏水药物的脂质双层已经获得。

Resistance to multiple drugs is major impediment to the successful chemotherapy of human cancers. One mechanism of multidrug-resistance is the expression of a 170,000 dalton energy-dependent drug efflux pump (P-glycoprotein or the multidrug transporter, the product of the human MDR1 gene) which confers resistance to colchicine, adriamycin, vincristine, vinblastine, puromycin, and actinomycin D. Several lines of investigation concerning the multidrug transporter have been pursued: 1) Evidence for ATP-dependent transport activity of P-glycoprotein in vesicles and across epithelial monolayers has been obtained; 2) Novel expression vectors which utilize a full-length MDR1 cDNA as a dominant selectable marker are used to introduce and amplify non-selectable genes in cultured cells and MDR1 retroviral vectors have been developed; 3) Many human tumors express MDR1 RNA, and this expression may predict drug-resistance in some cancers, and correlate with the development of drug-resistance in others; 4) Transgenic mice have been constructed in which the human MDR1 mRNA is expressed in the bone marrow at levels comparable to those found in human tumors. This level of MDR1 expression is sufficient to confer resistance to leukopenia induced by MDR drugs; 5) Increased expression of MDR1 RNA has been demonstrated in regenerating rat liver, in cultured rodent cells after exposure to chemotherapeutic agents, and in kidney cancer cells after heat shock; 6) The intron-exon structure of the human MDR1 gene has been determined and supports a model of independent evolution of the two halves of the multidrug transporter. Similarly, a deletion analysis of the MDR1 cDNA is consistent with important functions being contributed by both the amino and carboxy-terminal halves of the molecule as is a study demonstrating photoaffinity labeling of both halves of P-glycoprotein by the hydrophobic drug 3H-azidopine; and 7) Evidence that P-glycoprotein acts by pumping hydrophobic drugs out of the lipid bilayer has been obtained.