Methotrexate binds to recombinant thiopurine S-methyltransferase and inhibits enzyme activity after high-dose infusions in childhood leukaemia

Abstract

METHODSFifty-three children with ALL treated according to the NOPHO-ALL 2000 protocol were included. TPMT enzyme activity was measured at six different times starting from diagnosis until after the end of maintenance treatment. TPMT and 6-MP metabolites were measured before and 66 hours after start of high-dose MTX infusions. The interaction between MTX and TPMT was investigated in vitro using recombinant TPMT protein and a leukemic cell line. RESULTSForty percent of TPMT wild-type individuals had deceptively low TPMT enzyme activity compared to genotype at the time of diagnosis. TPMT decreased significantly 66 hours after the start of high-dose MTX infusions (-9.2 per cent, p=0.013). MTX bound to recombinant TPMT protein and inhibited the TPMT enzyme to a remaining activity of 16 percent. CONCLUSIONSThis study shows that TPMT genotyping should be preferred in children with ALL, since 40per cent of TPMT wild-type children are at risk of initial under-dosing of 6-MP in cases where 3 only TPMT enzyme activity is determined. MTX inhibits the TPMT enzyme activity after high-dose MTX infusions due to protein binding.

Tpmt Gene Expression is Increased During Maintenance Therapy in Childhood Acute Lymphoblastic Leukemia Patients in a TPMT Gene Promoter Variable Number of Tandem Repeat-Dependent Manner

“…So far, it has been reported that the TPMT enzyme activity in erythrocytes was approximately 30% higher in childhood ALL patients during maintenance therapy than in healthy individuals or patients not receiving the therapy [13,[21][22][23][24][25]. Our previous pharmacogenetic study revealed that childhood ALL patients, heterozygous carriers of TPMT genetic variants in the coding region, after initially reduced doses, could reach and tolerate full 6-MP protocol doses without developing any toxicity, pointing out that during maintenance therapy TPMT enzyme activity increases [26].…”

Thiopurine S-methyltransferase testing for averting drug toxicity: a meta-analysis of diagnostic test accuracy

“…This resulted in two strata for the test of deficient TPMT enzyme activity/homozygous TPMT mutation versus the rest of the population: (1) studies where the genotype test only considered TPMT*2 and *3, [33][34][35][36][37][38][39][40][41][42] and (2) studies where the genotype test considered TPMT*2, TPMT*3 and additional polymorphisms. [43][44][45] There were three strata for the test of low or intermediate TPMT enzyme activity/ homozygous or heterozygous TPMT mutation versus the rest of the population: (1) studies where the genotype test only considered TPMT*3, 46,47 (2) studies where the genotype test considered TPMT*2 and TPMT*3, 6,[33][34][35][36][37][38][39][40][41][42][48][49][50][51][52][53][54][55][56] and (3) studies where the genotype test considered TPMT*2, TPMT*3 and additional polymorphisms. [42][43][44][45]57,58 The meta-analysis used a Bayesian model.…”

Update on the Pathomechanism, Diagnosis, and Treatment Options for Rheumatoid Arthritis

“…Additionally, methotrexate was reported to inhibit the binding of IL-1ß to the IL-1ßR, preventing IL-1ß-induced inflammatory responses [182]. Moreover, methotrexate was suggested to have effects on many other enzymes such as for example methyltransferases (which are important in both B-and T cell function) [183].…”