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

Abstract

']a r is e n R o n n e y A. De Ahreu,*f HenkJ. Blom* Jos P.M. Bokkerinkf andj. M. Frans Trijbels* ♦ L a b o r a t o r y o f P e d i a t r i c s , a n d t C e n t e r f o r P e d ia t r ic : O n c o l o g y S.E. N e t h e r l a n d s , U n i v e r s i t y H o s p i t a l S t . R a d b o u d , P.O. Box 9101» 6500 HB N ijm e g e n , T h e N e t h e r l a n d s A BSTRA CT. 6 -mercaptopurine (6MP) cytotoxicity is caused by thioguanine and methylthioinosine nucleo tides. Thiopurine méthylation occurs to a large extent in vivo and in vitro. In this reaction, S-adenosyl-Lmethionine (AdoMet), produced from methionine and ATP, is converted into S-adenusy l-L-htunocysreine (AdoHcy) which, in turn, is hydrolyzed into homocysteine. Remethylation of homocysteine into methionine is inhibited by methotrexate (MTX). In cultured lymphoblasts, AdoMenAdoHcy ratio and DNA méthylation decrease after incubation with 6MP. The aim of the present study was to investigate the influence of high-do.se 6MP on the méthylation capacity in children with acute lymphoblastic leukemia. Five patients received 4 courses with high-dose intravenous MTX (5 g • m in 24 hr) immediately followed by high-dose 6MP (1300 mg • m~2 in 24 hr). Five control patients received high-dose MTX and oral 6MP (25 mg • m~2 daily for 8 weeks). Leucovorin rescue was started at .36 hr in both groups.In the intravenous 6MP group, 6-methylmercaptopurine, its riboside, and 6-methylmercapto-8-hydroxypurine were detectable in plasma in concentrations of 0.3-2.6 |jlM (6MP steady state levels: 11.6 (xM). In red blood cells, mean methylthioinosine nucleotide levels were one third of those of ATP (13,1 nmol/10"). AdoHcy levels (10 pmol/108) remained constant in both groups and AdoMet was not detectable (<20 pmol/10,s). In both groups, plasma homocysteine increased and methionine decreased following administration of MTX. The delay in the recovery of methionine in the intravenous 6MP group after MTX infusion is probably the result-of an increased demand on methyl groups during 6MP infusion. BIOCHKM PHARMACOL 51;9:1165-1171, KEY W ORDS. 6 -mercaptopurine; methotrexate; acute lymphoblastic leukemia; méthylation § is used in the treatment of ALL. It has no intrinsic cytotoxic activity, but is converted into active metabolites intracellularly (Scheme 1). 6MP tlMP which, itself, can be conve MetlMP. Both pathways ferase (EC 2.1.1.67) (TPMT). The TPMT activity is con trolled by a genetic polymorphism and the activity in RBC correlates with that in lymphoblasts, lymphocytes, plate lets, liver, and ki •' V ** % oi in cytotoxicity in vitro, ei ther by incorporation of thioguanine nucleotides into DNA and RNA [1,2] or by inhibition of purine de novo synthesis by MetlMP [2,3]. 6MP is methylated into MeMP and 6MP-riboside into MeMPR (Scheme 1). The thiopurine meththe frequency distribution is trimodal with subjects displaying high activity, 11.1% intermediate activ ity, and 1 out of 300 subjects having undeteetahle TPMT . Thiopurine méthylation requires AdoMet as onor [9]. AdoMet is the universa...

In Vitro Study of 6-mercaptopurine Oxidation Catalysed by Aldehyde Oxidase and Xanthine Oxidase

“…34) Although these reactions could be oxidized by either XO or AO, the diŠerence in metabolite proˆle between oral and intravenus administration indicates that AO may be the major enzyme in 8-hydroxylation. 16) In addition, the results obtained in the present study and a higher capability of AO to produce 8-hydroxy metabolites from guanine and purine analogs compared with XO, 10,23) provide more support for the involvment of AO in the matabolism of thioxanthine to thiouric acid as the major enzyme. This may be account for the results obtained by Keuzenkamp-Jansen et al 32) These authors indicated that co-administration of allopurinol and high dose 6-MP infusion to patients with non-Hodgkin lymphoma resulted in a relatively higher plasma levels of 6-MP, 6thioxanthine and methylpurine and a lower thiouric acid plasma level compared to those who did not receive allopurinol.…”

“…According to some reports, 6-MP is converted to 6thiouric acid through 6-thioxanthine, 6,32) whereas, other authors have suggested that the oxidation intermediate is 8-hydroxy-6-mercaptopurine. 1,9,10,17) The reason for this contraversy could be due in part to the diŠerence in metabolite proˆle between oral and intravenous administration of the drug. 16,33) It is more likely that following oral administration, 6-MP is predominantely oxidized to 6-thiouric acid via 6-thioxanthine.…”

“…1,9) However, Zimm et al have identiˆed 6-thioxanthine in the urine samples of some patients who received 6-MP by intravenous infusion which may indicate that 6-MP is converted to 6-thiouric acid via 6-thioxanthine. 6) 6-Methylmercapto-8-hydoxypurine has been identiˆed by others 10) as a major metabolite of 6-MP in plasma during intravenous administration. The oxidative inactivation of 6-MP has been attributed to xanthine oxidase (XO) activity in intestinal mucosa and liver.…”

“…17) To our knowledge, there is not a direct and comparative study of the involvement of molybdenum hydroxylases in this oxidative reactions. Furthermore, 8-hydroxy-6mercaptopurine 1,9,10,17) and 6-thioxanthine 6,10) have been suggested to be the intermediate in the conversion of 6-MP to 6-thiouric acid. Therefore, in the present study, the oxidation of 6-MP by BMXO and partially puriˆed guinea pig liver molybdenum hydroxylases have been investigated.…”

Voltammetric determination of 6-mercaptopurine using [Co(phen)3]3+/MWNT modified graphite electrode

“…It is found that the 6-MP plasma concentrations are unexpectedly low and highly variable with marked individual differences. By using standardized treatment regimens for some patients, the drug is difficult to keep in an optimal plasma level [5][6][7]. As a result, the use of a universal ''target dose" based on weight is not optimal and the determination of 6-MP over time becomes very important.…”