Belt J A
Mol Pharmacol. 1983 Nov;24(3):479-84.
The characteristics of nucleoside transport were examined in L1210 murine leukemia cells and five other cultured neoplastic cells. The initial rates of uridine, adenosine, and thymidine transport in L1210 cells were only partially inhibited by 1 microM nitrobenzylthioinosine (NBMPR), a potent inhibitor of nucleoside transport in other cells. The IC50 for NBMPR inhibition of uridine transport was 5 nM, but 20% of the activity remained insensitive to concentrations as high as 3 microM. Uridine uptake in the presence of 1 microM NBMPR was saturable and was inhibited by other nucleosides, suggesting the participation of an NBMPR-insensitive transport mechanism. There appeared to be little difference in the specificity of NBMPR-sensitive and -insensitive transport for the physiological nucleosides. Uridine, adenosine, and thymidine were all substrates for both mechanisms, and the Km values for total and NBMPR-insensitive uridine transport were the same (250 microM). Furthermore, little difference was found in the ability of several other nucleosides to inhibit total or NBMPR-insensitive uridine transport. In both cases, adenosine was the most effective inhibitor while cytidine and deoxycytidine were the least effective. The two transport processes did, however, differ from each other in their sensitivity to p-mercuribenzenesulfonate (pMBS). NBMPR-insensitive uridine transport was inhibited by pMBS with an IC50 less than 25 microM, while the IC50 for NBMPR-sensitive transport was greater than 400 microM. Cloning of the parent L1210 cell line indicated that both NBMPR-sensitive and -insensitive transport occurred in the same cell. Both types of uridine transport activity were also observed in three other cell lines (RPMI 6410, L5178Y, and P388), while two lines, S49 and Walker 256, exhibited only NBMPR-sensitive and -insensitive transport, respectively. The level of NBMPR-insensitive transport was an important determinant in the ability of NBMPR to inhibit uridine uptake over prolonged periods (10 min), with as little as 20% NBMPR-insensitive transport sufficient to render uptake over 10 min virtually insensitive to NBMPR. The existence of these two types of nucleoside transport activity in mammalian cells may have important implications in the chemotherapeutic use of transport inhibitors in combination with cytotoxic nucleosides or with inhibitors of pyrimidine and purine biosynthesis.
在L1210小鼠白血病细胞和其他五种培养的肿瘤细胞中研究了核苷转运的特性。L1210细胞中尿苷、腺苷和胸苷的初始转运速率仅被1 microM的硝基苄硫肌苷（NBMPR）部分抑制，NBMPR是其他细胞中核苷转运的有效抑制剂。NBMPR抑制尿苷转运的IC50为5 nM，但高达3 microM的浓度仍有20%的活性不受影响。在1 microM NBMPR存在下尿苷的摄取是可饱和的，并被其他核苷抑制，这表明存在一种对NBMPR不敏感的转运机制。对于生理性核苷，NBMPR敏感和不敏感转运的特异性似乎没有太大差异。尿苷、腺苷和胸苷都是这两种机制的底物，总尿苷转运和对NBMPR不敏感的尿苷转运的Km值相同（250 microM）。此外，在几种其他核苷抑制总尿苷转运或对NBMPR不敏感的尿苷转运的能力方面，未发现明显差异。在这两种情况下，腺苷都是最有效的抑制剂，而胞苷和脱氧胞苷是最无效的。然而，这两种转运过程对对氯汞苯磺酸盐（pMBS）的敏感性不同。对NBMPR不敏感的尿苷转运被pMBS抑制，IC50小于25 microM，而对NBMPR敏感转运的IC50大于400 microM。亲代L1210细胞系的克隆表明，对NBMPR敏感和不敏感的转运都发生在同一细胞中。在其他三种细胞系（RPMI 6410、L5178Y和P388）中也观察到了两种类型的尿苷转运活性，而S49和Walker 256这两种细胞系分别仅表现出对NBMPR敏感和不敏感的转运。对NBMPR不敏感的转运水平是NBMPR在较长时间（10分钟）内抑制尿苷摄取能力的重要决定因素，低至20%的对NBMPR不敏感的转运就足以使10分钟内的摄取对NBMPR几乎不敏感。哺乳动物细胞中这两种类型的核苷转运活性的存在可能对将转运抑制剂与细胞毒性核苷或嘧啶和嘌呤生物合成抑制剂联合用于化疗具有重要意义。
