Folate pathway gene expression differs in subtypes of acute lymphoblastic leukemia and influences methotrexate pharmacodynamics

Abstract

The ability of leukemia cells to accumulate methotrexate polyglutamate (MTXPG) is an important determinant of the antileukemic effects of methotrexate (MTX). We measured in vivo MTXPG accumulation in leukemia cells from 101 children with acute lymphoblastic leukemia (ALL) and established that B-lineage ALL with either TEL-AML1 or E2A-PBX1 gene fusion, or T-lineage ALL, accumulates significantly lower MTXPG compared with B-lineage ALL without these genetic abnormalities or compared with hyperdiploid (fewer than 50 chromosomes) ALL. To elucidate mechanisms underlying these differences in MTXPG accumulation, we used oligonucleotide microarrays to analyze expression of 32 folate pathway genes in diagnostic leukemia cells from 197 children. This revealed ALL subtype-specific patterns of folate pathway gene expression that were significantly related to MTXPG accumulation. We found significantly lower expression of the reduced folate carrier (SLC19A1, an MTX uptake transporter) in E2A-PBX1 ALL, significantly higher expression of breast cancer resistance protein (ABCG2, an MTX efflux transporter) in TEL-AML1 ALL, and lower expression of FPGS (which catalyzes formation of MTXPG) in T-lineage ALL, consistent with lower MTXPG accumulation in these ALL subtypes. These findings reveal distinct mechanisms of subtype-specific differences in MTXPG accumulation and point to new strategies to overcome these potential causes of treatment failure in childhood ALL. IntroductionDuring the past 2 decades, antileukemic agents for the treatment of childhood acute lymphoblastic leukemia (ALL) have remained essentially unchanged; hence the significant increase in event-free survival is attributed largely to optimization of existing medications. Current strategies are aimed at further enhancing efficacy and reducing toxicity of ALL therapy, based on a better understanding of cellular mechanisms of antileukemic effects, and insights into the biological basis of ALL subtype differences in treatment response. Subtypes with a relatively unfavorable prognosis on many treatment protocols include T-lineage ALL (T-ALL) and ALL with rearranged MLL genes or with BCR-ABL gene fusion, whereas ALL with either TEL-AML1 or E2A-PBX1 gene fusions, or hyperdiploid karyotypes (fewer than 50 chromosomes), have a relatively good prognosis with most treatment protocols (1).

Clinical features, early treatment responses, and outcomes of pediatric acute lymphoblastic leukemia in china with or without specific fusion transcripts: A single institutional study of 1,004 patients

“…Thus, to improve further the outcome of pediatric ALL, it is necessary to apply fusion gene or subtype‐specific treatment protocols, or combine the current chemotherapy regimens with new target drugs. Two reports from St. Jude Children's Research Hospital indicated that TEL‐AML1 + patients should be treated with intensive asparaginase and high‐dose methotrexate [45, 46]. Imatinib has been reported to enhance the 3‐year EFS rate of BCR‐ABL + ALL to 80% [47] significantly, which is twice the rate achieved before imatinib was used.…”

Delayed neurotoxicity associated with therapy for children with acute lymphoblastic leukemia

“…Clinical characteristics (age, phenotype, presenting WBC count, and cytogenetics) may soon give way to molecular diagnostics related to differences in relative gene expression or presence of single nucleotide polymorphisms. Among patients with ALL [Kager et al, 2005;Pui and Evans, 2006] or rheumatoid arthritis [Dervieux et al, 2004[Dervieux et al, , 2005 treated with MTX, for example, patterns of gene expression or of polymorphisms within genes relevant to (anti)folate metabolism have been used to distinguish subsets of patients with dissimilar risks of treatment response or toxicity. It is reasonable to expect that this approach will identify patient subsets at higher than average risk of delayed neurotoxicity.…”

Mathematical modeling of folate metabolism

“…For example, Zaza et al 41 showed that several genes involved in purine metabolism were differentially expressed (lower) in the TEL-AML1 ALL subtype and this subtype had lower DNPS activity. In addition, this subtype had lower MTXPG accumulation ( Figure 3) and Kager et al 31 described how genes involved in folate transport, metabolism, and polyglutamylation were differentially expressed in different ALL subtypes, including TEL-AML1 (Figure 2). Data from these results can help validate folate pathway model simulations and help develop and test hypotheses on why TEL-AML1 ALL has a favorable prognosis.…”

“…The use of this approach has the potential to yield a more robust and complete understanding of how sensitive the system is to biologically plausible perturbations such as those resulting from polymorphisms in folate pathway genes. 7,30 An example of the correlation structure of folate-related gene expression is described by Kager et al 31 They showed that the expression levels of DHFR, TYMS, MTHFD1, MTHFD2, ATIC, GART, and RUVBL2 are strongly correlated with each other. This suggests an appropriate approach to investigating the sensitivity of the model is to vary this group of enzymes (parameters) in the same correlated manner.…”

“…Several studies investigated differences in the reduced folate carrier (RFC) in pediatric ALL blasts. 31,37 These have shown that RFC (SLC19A1) expression is significantly higher in B-lineage hyperdiploid (BHD) ALL cells and lower in E2A-PBX1 ALL cells compared with other subtypes of ALL. In a similar manner, the expression of the efflux transporters MRP1 (ABCC1) and BCRP (ABCG2) are higher in T-lineage ALL and TEL-AML1 ALL cells respectively ( Figure 2).…”