Decrease in S-adenosylmethionine synthesis by 6-mercaptopurine and methylmercaptopurine ribonucleoside in Molt F4 human malignant lymphoblasts

Abstract

6-Mercaptopurine (6-MP) and methylmercaptopurine ribonucleoside (Me-MPR) are purine anti-metabolites which are both metabolized to methylthio-IMP (Me-tIMP), a strong inhibitor of purine synthesis de novo. Me-MPR is converted directly into Me-tIMP by adenosine kinase. 6-MP is converted into tIMP, and thereafter it is methylated to Me-tIMP by thiopurine methyltransferase, an S-adenosylmethionine (S-Ado-Met)-dependent conversion. S-Ado-Met is formed from methionine and ATP by methionine adenosyltransferase, and is a universal methyl donor, involved in methylation of several macromolecules, e.g. DNA and RNA. Therefore, depletion of S-Ado-Met could result in an altered methylation state of these macromolecules, thereby affecting their functionality, leading to dysregulation of cellular processes and cytotoxicity. In this study the effects of 6-MP and Me-MPR on S-Ado-Met, S-adenosylhomocysteine (S-Ado-Hcy), homocysteine and methionine concentrations are determined. Both drugs cause a decrease in intracellular S-Ado-Met concentrations and an increase in S-Ado-Hcy and methionine concentrations in Molt F4 human malignant lymphoblasts. The effects of both 6-MP and Me-MPR can be ascribed to a decreased conversion of methionine into S-Ado-Met, due to the ATP depletion induced by the inhibition of purine synthesis de novo by Me-tIMP. Both 6-MP and Me-MPR thus affect the methylation state of the cells, and this may result in dysregulation of cellular processes and may be an additional mechanism of cytotoxicity for 6-MP and Me-MPR.

The accumulation of mercaptopurine metabolites in age fractionated red blood cells.

“…The ability of the TPMT reaction (i.e. MeMP formation) to deplete intracellular concentrations of the universal methyl donor S-adenosylmethionine may influence cellular mechanisms on many different levels [21].…”

Effects on transmethylation by high-dose 6-mercaptopurine and methotrexate infusions during consolidation treatment of acute lymphoblastic leukemia

“…Next to its role in protein synthesis, the essential aminoacid methionine can be activated as methyldonor by formation of AdoMet, using ATP as co substrate [11]. Recently, we reported the effect of 6MP on the principal transmethylation metabolites it vitro [12]. Incubation of Molt-F4 human malignant ALL lymphoblasts with 6MP resulted in a decrease in AdoMet and the AdoMet/AdoHcy ratio, in an increase in AdoHcy and methionine in these cells, and a decreased release of homocysteine into the cul ture medium [12].…”

Novel evidence for an ecto-phospholipid methyltransferase in isolated rat hepatocytes

“…The acidinsoluble pellet obtained by centrifugation (10 000 g for 30 s) was used to determine the radioactivity incorporated into phospholipids, as described previously [6]. The supernatant was used for the measurement of methylated acid-soluble metabolites by HPLC [10]. [Methyl-"%C]phosphocholine was identified by TLC as described previously [11].…”