Wright J E, Rosowsky A, Cucchi C A, Flatow J, Frei E
Dana-Farber Cancer Institute, Boston, MA 02115.
Biochem Pharmacol. 1993 Sep 1;46(5):871-6. doi: 10.1016/0006-2952(93)90496-j.
In a continuing investigation of determinants of their 200-fold methotrexate resistance and their collateral sensitivity to gamma-tert-butyl methotrexate, the ability of CEM/MTX cells to transport the two drugs was analyzed and compared with that of CEM cells. The Km and Vmax values for the influx of methotrexate into CEM cells did not differ significantly from those of CEM/MTX cells, and this was the case for gamma-tert-butyl methotrexate as well. Surface binding and influx rates were proportional to cell surface area, but differences in efflux rates and methotrexate uptake were too large to be explained on this basis. Neither methotrexate nor trimetrexate competed with gamma-tert-butyl methotrexate influx in CEM cells. However, both drugs perturbed the gamma-tert-butyl methotrexate steady state in CEM cells, resulting in slightly less uptake than with gamma-tert-butyl methotrexate alone. However, the major difference between the two cell types was in the methotrexate uptake plateau, which was much greater in the case of the parental cell line. A related observation was the more rapid efflux of methotrexate from CEM/MTX cells than from CEM cells. The poor uptake, the associated meager capacity to polyglutamylate methotrexate and the enhanced methotrexate efflux appear to be responsible for its decreased activity against CEM/MTX cells. Half-lives for gamma-tert-butyl methotrexate efflux were the same in both cell lines, allowing the drug to accumulate to cytotoxic levels despite its inability to form polyglutamates.
在一项对其200倍甲氨蝶呤耐药性及其对γ-叔丁基甲氨蝶呤的协同敏感性决定因素的持续研究中，分析了CEM/MTX细胞转运这两种药物的能力，并与CEM细胞进行了比较。甲氨蝶呤流入CEM细胞的Km和Vmax值与CEM/MTX细胞的这些值没有显著差异，γ-叔丁基甲氨蝶呤也是如此。表面结合和流入速率与细胞表面积成正比，但流出速率和甲氨蝶呤摄取的差异太大，无法以此为基础进行解释。在CEM细胞中，甲氨蝶呤和三甲曲沙均不与γ-叔丁基甲氨蝶呤的流入竞争。然而，这两种药物都扰乱了CEM细胞中γ-叔丁基甲氨蝶呤的稳态，导致摄取量略低于单独使用γ-叔丁基甲氨蝶呤时。然而，两种细胞类型之间的主要差异在于甲氨蝶呤摄取平台期，在亲代细胞系中该平台期要大得多。一个相关的观察结果是，甲氨蝶呤从CEM/MTX细胞中的流出比从CEM细胞中更快。摄取不良、相关的甲氨蝶呤聚谷氨酸化能力不足以及甲氨蝶呤流出增强似乎是其对CEM/MTX细胞活性降低的原因。γ-叔丁基甲氨蝶呤在两种细胞系中的流出半衰期相同，尽管其无法形成聚谷氨酸盐，但仍能使其积累到细胞毒性水平。
