Schirmer M, Stegmann A P, Geisen F, Konwalinka G
Department of Internal Medicine, University of Innsbruck, Austria.
Exp Hematol. 1998 Dec;26(13):1223-8.
Cross-resistance patterns between chemotherapeutic agents have implications for the treatment of hematologic and other diseases. Previous in vitro models have shown cross-resistance between the purine analog 2-chlorodeoxyadenosine (cladribine) and the pyrimidine analogs 2',2'-difluorodeoxycytidine (gemcitabine) and 1-beta-D-arabinofuranosylcytosine (cytosine arabinoside, cytarabine) with reduced deoxycytidine kinase (dCK) activity as the underlying determinant of resistance. In this study, we continuously exposed the human promyelocytic leukemia cell line HL60 to as much as 1024 nM cladribine. After limiting dilution, the cladribine concentrations that caused 50% growth inhibition (IC50) of the two clones R13 and R23 were 33.3- and 18.7-fold, respectively, higher than the IC50 of the parental HL60 cells (8.7+/-1.3 nM). These cladribine-resistant clones, however, showed no cross-resistance to gemcitabine and only 3.3- and 2.7-fold resistance to cytarabine, respectively. Characterization of both clones revealed stably elevated levels of purine-specific "high-Michaelis constant (Km)" 5'-nucleotidase (5'-NT) messenger RNA expression and specific activity, whereas pyrimidine-specific "low-Km" 5'-NT activity was undetectable, and dCK activity was only marginally decreased in R13. Thus, the ratio of dCK (specific for cladribine) to high-Km 5'-NT activity in R13 and R23 was reduced to 65.3% and 63.7%, respectively. These results show that changes of high-Km 5'-NT activity can induce cladribine resistance, without cross-resistance to gemcitabine.
化疗药物之间的交叉耐药模式对血液系统疾病和其他疾病的治疗具有重要意义。先前的体外模型已显示嘌呤类似物2-氯脱氧腺苷（克拉屈滨）与嘧啶类似物2'，2'-二氟脱氧胞苷（吉西他滨）和1-β-D-阿拉伯呋喃糖基胞嘧啶（阿糖胞苷）之间存在交叉耐药，脱氧胞苷激酶（dCK）活性降低是耐药的潜在决定因素。在本研究中，我们将人早幼粒细胞白血病细胞系HL60持续暴露于高达1024 nM的克拉屈滨中。通过有限稀释法，两个克隆R13和R23中导致50%生长抑制（IC50）的克拉屈滨浓度分别比亲代HL60细胞的IC50（8.7±1.3 nM）高33.3倍和18.7倍。然而，这些对克拉屈滨耐药的克隆对吉西他滨没有交叉耐药，对阿糖胞苷的耐药性分别仅为3.3倍和2.7倍。对两个克隆的特征分析显示，嘌呤特异性“高米氏常数（Km）”5'-核苷酸酶（5'-NT）的信使RNA表达水平和比活性稳定升高，而嘧啶特异性“低Km”5'-NT活性未检测到，并且R13中的dCK活性仅略有下降。因此，R13和R23中dCK（对克拉屈滨特异）与高Km 5'-NT活性的比率分别降至65.3%和63.7%。这些结果表明，高Km 5'-NT活性的变化可诱导对克拉屈滨的耐药性，而不会对吉西他滨产生交叉耐药。
