Background: Monitoring 6-thiopurine S-methyltransferase
(TPMT; EC 2.1.1.67) activity is especially important when patients are treated with
6-thiopurine drugs, since severe bone marrow toxicity may be induced if patients have
deficient TPMT activity.
Methods: We have developed a method based on high-performance liquid
chromatography (HPLC) for the measurement of TPMT activity in various cell types:
erythrocytes (RBC), human peripheral blood mononuclear cells (pMNC) and human
malignant lymphoblasts (Molt-F4). The enzymatic activity is measured by the amount of
6-methylmercaptopurine formed, using 6-mercaptopurine (6MP) as substrate and
S-adenosylmethionine as co-substrate.
Results: The K
m values calculated for 6MP were 0·54 (RBC), 0·85 (pMNC) and 0·65 (Molt-F4
cells) mmol/L. The K
m values for S-adenosylmethionine were 11·9 (RBC), 16·4
(pMNC) and 6·65 (Molt-F4 cells) µmol/L. The assay variation was
8·2-17%. TPMT activity was determined in a control group of 103 children and young
adults (44 female, 59 male). The values observed were (mean ± standard deviation):
female children and young adults, 15·1 ± 4·8 pmol/107 cells per h
(n = 44); male children and young adults, 15·8 ± 6·4
pmol/107 cells per h (n = 59). No gender or age
differences were found.
Conclusion: The HPLC-based method enables the rapid screening of TPMT
activities in large groups of patients treated with 6-thiopurines.
