Carter G L, Cory J G
Department of Internal Medicine, University of South Florida College of Medicine, H. Lee Moffitt Cancer Center, Tampa.
Cancer Res. 1988 Oct 15;48(20):5796-9.
Hydroxyurea is an inhibitor of ribonucleotide reductase and is specifically directed at the non-heme iron subunit (which contains the free radical) of this enzyme. Leukemia L1210 cells, grown in the presence of increasing concentrations of hydroxyurea, developed resistance to hydroxyurea. For hydroxyurea, the wild-type L1210 cells required a drug concentration of 85 microM to inhibit cell growth by 50%, and the hydroxyurea-resistant (HU-7-S7) cells required a concentration of approximately 2000 microM. The resistant L1210 cells were cross-resistant to 2,3-dihydro-1H-pyrazolo[2,3-a]imidazole/Desferal. However, these HU-7-S7 cells remained sensitive to 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone and 1-isoquinolylmethylene-N-hydroxy-N'-amino-guanidine tosylate (inhibitors directed at the same subunit as hydroxyurea). The HU-7-S7 cells retained their sensitivity to deoxyadenosine/erythro-9-(2-hydroxy-3-nonyl)adenine and deoxyguanosine/8-amino-guanosine (inhibitors directed at the effector-binding subunit of ribonucleotide reductase). The L1210 cells developed for resistance to hydroxyurea were sensitive to the non-ribonucleotide reductase inhibitors, methotrexate and 1-beta-D-arabinofuranosylcytosine. Ribonucleotide reductase activity was elevated in the HU-7-S7 cells (CDP reductase, 5.5-fold increase; ADP reductase, 13.2-fold increase). The addition of exogenous effector-binding subunit caused much greater stimulation of reductase activities in the extracts from the resistant cells than from the wild-type cells. The reductase activity in cell-free extracts from the resistant cells was inhibited by hydroxyurea, 2,3-dihydro-1H-pyrazolo[2,3-a]imidazole and dATP to the same extent as the activity from the wild-type L1210 cells. These data indicate that resistance to hydroxyurea in these L1210 cells is to some extent related to increased reductase activity. However, the specificity of resistance of these L1210 cells to inhibitors of ribonucleotide reductase depends on the nature of the inhibitor and the subunit at which the inhibitor is directed.
羟基脲是核糖核苷酸还原酶的抑制剂，它特异性作用于该酶的非血红素铁亚基（其中含有自由基）。在浓度不断增加的羟基脲存在下培养的白血病L1210细胞，对羟基脲产生了抗性。对于羟基脲，野生型L1210细胞抑制细胞生长50%需要85微摩尔的药物浓度，而耐羟基脲的（HU-7-S7）细胞则需要约2000微摩尔的浓度。耐药的L1210细胞对2,3-二氢-1H-吡唑并[2,3-a]咪唑/去铁胺具有交叉抗性。然而，这些HU-7-S7细胞对4-甲基-5-氨基-1-甲酰基异喹啉硫代半卡巴腙和1-异喹啉基亚甲基-N-羟基-N'-氨基胍甲苯磺酸盐（与羟基脲作用于同一亚基的抑制剂）仍敏感。HU-7-S7细胞对脱氧腺苷/赤藓红-9-(2-羟基-3-壬基)腺嘌呤和脱氧鸟苷/8-氨基鸟苷（作用于核糖核苷酸还原酶效应物结合亚基的抑制剂）保持敏感。为抵抗羟基脲而培养的L1210细胞对非核糖核苷酸还原酶抑制剂甲氨蝶呤和1-β-D-阿拉伯呋喃糖基胞嘧啶敏感。HU-7-S7细胞中的核糖核苷酸还原酶活性升高（CDP还原酶增加5.5倍；ADP还原酶增加13.2倍）。添加外源性效应物结合亚基对耐药细胞提取物中还原酶活性的刺激比对野生型细胞提取物的刺激大得多。耐药细胞无细胞提取物中的还原酶活性被羟基脲、2,3-二氢-1H-吡唑并[2,3-a]咪唑和dATP抑制的程度与野生型L1210细胞的活性相同。这些数据表明，这些L1210细胞对羟基脲的抗性在一定程度上与还原酶活性增加有关。然而，这些L1210细胞对核糖核苷酸还原酶抑制剂抗性的特异性取决于抑制剂的性质以及抑制剂作用的亚基。
