Quantification of Thiopurine Nucleotides in Erythrocytes and Clinical Application to Pediatric Acute Lymphoblastic Leukemia

Soo Young Moon, Ji Hyun Lim, Eun Hee Kim, Youngwon Nam, Kyung Sang Yu, Kyung Taek Hong, Jung Yoon Choi, Che Ry Hong, Hyery Kim, Hyoung Jin Kang, Hee Young Shin, Kyunghoon Lee, Junghan Song, Soo Youn Lee, Sang Hoon Song

Research output: Contribution to journalArticle

Abstract

Background:Concentrations of 6-thioguanine (6TG) nucleotides and 6-methylmercaptopurine (6MMP) nucleotides in RBCs were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This assay was validated for clinical use and was applied to blood samples from patients taking mercaptopurine (6MP).Methods:RBCs were hemolyzed and deproteinized using perchloric acid, followed by heating for the hydrolysis of nucleotides, and the resultant base was measured using LC-MS/MS. Precision, recovery, linearity, matrix effect, and limit of quantification was validated for clinical application. Our results were compared with another institution's established LC-MS/MS assay. We measured the concentrations of 6TG and 6MMP in RBCs of pediatric patients with acute lymphoblastic leukemia (ALL), and the clinical impact of those metabolites was investigated.Results:The imprecision coefficient of variations of 6TG and 6MMP were 5.7%-8.1%, and the bias was within 5%. Lower limits of quantification were set at 54 ng/mL for 6TG and 1036 ng/mL for 6MMP. Correlation coefficients for 6TG and 6MMP were 0.997 and 1.0 in a comparison study. For clinical proof-of-concept, 74 blood samples were collected from 37 pediatric ALL patients receiving maintenance therapy. Concentration of 6TG ranged from 16.1 to 880 pmol/8 × 108 RBCs and that of 6MMP from 55 to 20,937 pmol/8 × 108 RBCs. The 6MP metabolites were not correlated with WBC or absolute neutrophil count. On the other hand, the higher 6MMP level was associated with elevated alanine aminotransferase and aspartate aminotransferase.Conclusions:In this study, an assay for the quantification of 6TG and 6MMP in RBCs was established and applied to pediatric ALL patients. Interindividual variability in 6MP metabolite concentrations was considerable and associated with elevation of liver enzymes, which may be useful in the clinical monitoring of 6MP maintenance therapy in pediatric ALL patients.

Original languageEnglish
Pages (from-to)75-85
Number of pages11
JournalTherapeutic Drug Monitoring
Volume41
Issue number1
DOIs
StatePublished - 1 Feb 2019

Keywords

  • 6-methylmercaptopurine (6MMP)
  • 6-thioguanine (6TG)
  • LC-MS/MS
  • RBC
  • pediatric ALL

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