Monks A, Marquez V E, Mao D T, Cysyk R L
Cancer Lett. 1985 Aug;28(1):1-8. doi: 10.1016/0304-3835(85)90085-0.
Tiazofurin (TR), a new antitumor agent, enters human erythrocytes by utilizing their facilitated nucleoside transport system. TR competes with endogenous nucleosides for this transport mechanism, thereby reducing nucleoside uptake into the cells. Pre-incubation of erythrocytes for 10 min at 22 degrees C with 100 microM and 500 microM TR reduced the transport of 14C-uridine into the cells by 27% and 74%, respectively. Simultaneous exposure of cells to TR and [14C]uridine did not alter the inhibitory effect of TR. Furthermore, the transport inhibitory effect of TR was lost when cells were washed twice with Hanks basal salt solution following a 10-min pre-incubation with TR. The Km and Vmax (+/- S.E.) for radiolabeled TR transport into erythrocytes are 170 +/- 26 microM and 55 +/- 13 nmol/h per 10(6) cells, respectively, which is similar to the kinetic constants measured for uridine transport into erythrocytes (Km = 168 +/- 37 microM and Vmax = 61 +/- 16 nmol/h per 10(6) cells). The Ki (+/- S.E.) of TR for uridine transport is 178 +/- 11 microM and for thymidine transport is 102 +/- 59 microM. Three analogues of TR (its selenium isostere (SR), and Ara (Ara-TR) and Xylo (Xylo-TR) derivatives) were compared with TR for their ability to compete with and inhibit uridine transport, as these analogues were not available in a radiolabeled form for direct measurement of their transport into the cell. SR had similar kinetic characteristics of inhibition of uridine transport to TR (Ki = 145 +/- 15 microM) but Ara-TR had a Ki = 1.04 +/- 0.13 mM while Xylo-TR inhibited uridine transport with a Ki = 1.57 +/- 0.67 mM. Thus, TR is transported into erythrocytes with the same velocity and affinity for the carrier as uridine and competitively inhibits nucleoside transport into the cell. Of 3 other C-nucleoside derivatives examined, SR is of similar potency to TR but Ara-TR and Xylo-TR are much less effective at competing with uridine for the nucleoside transporter.
硫唑嘌呤（TR）是一种新型抗肿瘤药物，它通过利用人类红细胞的易化核苷转运系统进入红细胞。TR与内源性核苷竞争这种转运机制，从而减少核苷进入细胞。将红细胞在22℃下用100微摩尔/升和500微摩尔/升的TR预孵育10分钟，分别使14C-尿苷进入细胞的转运减少了27%和74%。细胞同时暴露于TR和[14C]尿苷中并没有改变TR的抑制作用。此外，在与TR预孵育10分钟后，用汉克斯基础盐溶液洗涤细胞两次，TR的转运抑制作用就会消失。放射性标记的TR转运进入红细胞的米氏常数（Km）和最大反应速度（Vmax，±标准误）分别为170±26微摩尔/升和每10^6个细胞55±13纳摩尔/小时，这与测量的尿苷转运进入红细胞的动力学常数相似（Km = 168±37微摩尔/升，Vmax = 61±16纳摩尔/小时每10^6个细胞）。TR对尿苷转运的抑制常数（Ki，±标准误）为178±11微摩尔/升，对胸苷转运的抑制常数为102±59微摩尔/升。比较了TR的三种类似物（其硒代类似物（SR）、阿糖（Ara-TR）和木糖（Xylo-TR）衍生物）与TR竞争和抑制尿苷转运的能力，因为这些类似物没有放射性标记形式可用于直接测量它们进入细胞的转运。SR对尿苷转运的抑制动力学特征与TR相似（Ki = 145±15微摩尔/升），但Ara-TR的Ki = 1.04±0.13毫摩尔/升，而Xylo-TR抑制尿苷转运的Ki = 1.57±0.67毫摩尔/升。因此，TR以与尿苷相同的速度和对载体的亲和力转运进入红细胞，并竞争性抑制核苷转运进入细胞。在所研究的其他三种碳核苷衍生物中，SR的效力与TR相似，但Ara-TR和Xylo-TR在与尿苷竞争核苷转运体方面的效果要差得多。
