Role of 5′-nucleotidase in thiopurine metabolism: Enzyme kinetic profile and association with thio-GMP levels in patients with acute lymphoblastic leukemia during 6-mercaptopurine treatment

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• 作者：Connie Brouwer ; Trude M. Vogels-Mentink ; Jenneke J. Keizer-Garritsen ; Frans J.M. Trijbels ; Jos P.M. B6 ; kkerink ; Peter M. Hoogerbrugge ; Elisabeth R. van Wering ; Anjo J.P. Veerman and Ronney A. De A
• 关键词：5′ ; -Nucleotidase ; 6-Thiopurines ; Acute lymphoblastic leukemia ; Substrate specificity
• 刊名：Clinica Chimica Acta
• 出版年：2005
• 期刊代码：54_00098981
• 类别：med
• 出版时间：2005
• 卷：361
• 期：1-2
• 页码：95-103
• 文件大小：132 K

摘要

Thiopurines are used for treatment of several diseases. Cytotoxicity is caused by the derived compounds 6-thioguanine nucleotides (TGNs) and methyl-6-thioinosine monophosphate (methylthio-IMP). The 6-thiopurine mononucleotides 6-thio-IMP (thio-IMP), 6-thio-GMP (thio-GMP) and methylthio-IMP can be catabolized by purine 5′-nucleotidase. It has been shown that the various 5′-nucleotidases are key enzymes for (6-thio)-purine metabolism. We aimed to investigate whether the overall 5′-nucleotidase (5′NT) activity is correlated with the efficacy and toxicity of 6-thiopurine nucleotides.

Substrate affinity of 5′NT for IMP, GMP, AMP, thio-IMP, thio-GMP and methylthio-IMP was studied in human lymphocytes. For each of the substrates, the pH for optimal overall enzyme activity has been determined at a pH range between 6 and 10. At the optimal pH, assays were performed to establish K_m and V_max values.

Optimal pH values for the various substrates were between 7 and 8.5. K_m values ranged from 33 to 109 μM, V_max ranged from 3.99 to 19.5 nmol/10⁶ peripheral mononuclear cells (pMNC) h, and V_max/K_m ratios ranged from 105 to 250.

The results did not show a distinct preference of 5′NT activity for any of the tested thiopurine nucleotides. The enzyme kinetic studies furthermore revealed substrate inhibition by thio-IMP and thio-GMP as a substrate. Inhibition by thio-GMP also seems to occur in patients treated with 6-mercaptopurine (6 MP); subsequently, this may lead to toxicity in these patients.