Pharmacogenetics of methotrexate in pediatric hematological neoplasm treatment: does it need a personalized regimen based on MTHFR polymorphisms?

Keywords::

• hematological malignancy
• MTHFR polymorphisms
• methotrexate
• pharmacogenomic

Nowadays in cancer therapy it is important to consider future patients’ quality life, especially in pediatric age; for this reason, pharmacogenomic and personalized therapy plays a key role. Much evidence has shown that polymorphisms in the methotrexate (MTX) pathway genes influence response and efficacy of high-dose MTX. In the literature, there exists conflicting data on the association of methylenetetrahydrofolate polymorphisms with increased risk of MTX toxicity and relapse in acute lymphoblastic leukemia and non-Hodgkin lymphoma. The identification of genetic polymorphisms that predict for drug response is the first step toward the translation of pharmacogenetic studies into clinical practice, especially in patients who are long-term survivors. Hence, using the polymorphisms of folate metabolizing enzymes to manage MTX treatment could be favourable as a pharmacogenetic determinant into future protocols.

The outcome for pediatric cancer patients has improved dramatically over the past 6 decades, with 5-year survival rates currently at 75 versus 20% in the 1950s. Accordingly, the cure rates of acute lymphoblastic leukemia (ALL), which is the most common childhood cancer, are higher than 80% due to optimized chemotherapy protocols. Most protocols consist of methotrexate (MTX) as a key chemotherapeutic agent with high therapeutic efficiency [1]. Nevertheless, MTX causes severe dose-limiting adverse events and organ toxicities. The great inter-individual variability in drug effects and efficacy is one of the major issues in the clinical management of pediatric ALL patients. The severe toxicity is often the treatment’s major limitation as the relapse of disease is the most common reason of pediatric hematological neoplasm treatment failure.

MTX acts as an antifolate agent blocking the conversion of dihydrofolates to tetrahydrofolates. Polymorphisms in the MTX pathway genes (SLCO1B1, ABCC2, SLC19A1, methylenetetrahydrofolate [MTHFR], TYMS) substantially influence the kinetics response and efficacy of high-dose MTX.

Its toxicity is one of the main reasons for the interruption or discontinuation of chemotherapy, which may in turn increase the relapse rate for the disease. Germline polymorphisms in MTHFR reductase are significantly associated with kinetics, toxicity and outcome.

Many studies have reported that the two common functional polymorphisms of MTHFR, C677T and A1298C, are associated with MTX-related toxicity and survival both in adults and in children with ALL, while others showed controversial results [1–3].

Based on the strength of evidence of previously published association studies, in 2013, Radtke et al. confirmed positive associations in 499 ALL pediatric patients (aged >1–18 years) enrolled in the ALL-Berlin–Frankfurt–Munster (BFM) 2000 trial and treated with courses of MTX at 5 g/sq among minimal residual disease (MRD) and MTHFR A1298C single nucleotide polymorphism. MRD stratification, evaluated after induction (day 33) and consolidation therapy (day 78), required at least two PCR-MRD targets with a sensitivity of at least 10^–4 cells with residual disease. The authors demonstrated a significant association with EFS rates (the adjusted hazard ratios were 7.3–95% CI: 2.5–21.3; p = 3.2 × 10^–4) between MRD-slow early responder versus MRD standard risk [4] patients and (the hazard ratios were 3.1–95% CI: 1.2–7.7; p = 0.015) between homozygous carriers of the MTHFR A1298 C allele versus patients with the AA reference genotype [1]. As mentioned in this study, whether polymorphisms in a specific gene affect EFS rates may depend on the specific treatment protocol. Remission rates, relapse or secondary leukemia depend on the respective protocol applied in a study. Thus, the association between MTHFR A1298C and outcome may be specific for the ALL-BFM 2000 protocol and must not apply to other protocols for treatment of pediatric ALL.

Moreover, in 2011, D’Angelo et al. studied in a homogeneous monocentric study the roles of the MTHFR C677T and A1298C genetic polymorphisms in modulating the clinical toxicity and efficacy of high doses MTX in 178 pediatric ALL patients treated with Associazione Italiana Ematologia Oncologia Pediatrica (AIEOP) ALL ‘95-’00. Patients treated with MTX 2 g/sq and 677TT genotype had a 12-fold higher risk of developing toxicity and in a subset of patients a 13-fold greater risk of non-hematological toxicity. Moreover, 677TT genotype conferred a higher risk of relapse compared with other genotypes with a lower probability of disease-free survival and overall survival [5].

An alteration in reduced folate pools, derived from inherited changes in MTHFR activity, may have a significant effect on the response of malignant and non-malignant cells to MTX, whose activity depends by cellular composition of folate. MTX-associated toxicity could alter the response to therapy and thus lead to a higher number of relapses [5]. Yang et al. analyzed a total of 104 studies in the literature, selecting 14 eligible studies to assess the possible associations between MTHFR polymorphisms and MTX-induced toxicities in patients with ALL. In summary, this meta-analysis provided evidence for the association between MTHFR C677T polymorphism and increased risk of MTX-induced toxicities [2]. Hagleitner et al. studied in a Dutch cohort of 98 pediatric patients treated with high doses of MTX, the influence of MTHFR 677C> T on hepatotoxicity using a generalized estimating equation (GEE) analysis that showed an increased risk of developing hepatotoxicity for T allele versus C allele in patients with osteosarcoma (odds ratio: 1.8; 95% CI: 1.0–3.2; p = 0.04). However, this finding was not supported by a meta-analysis performing on seven studies and 1044 patients [6]. Also, in 2013, D’Angelo et al. investigated in 95 pediatric patients affected by non-Hodgkin lymphoma (NHL) and treated with AIEOP LNH 97 and EURO LB-02 protocols, the role of C677T and A1298C MTHFR genetic polymorphisms in the risk of MTX-induced toxicities. In this study, it was demonstrated that patients with histopathological B-cell NHL and 677T genotype had an approximately sixfold greater risk of developing hematological toxicity than wild-type patients. In particular, patients with 677T carriers and B-cell NHL showed more hematological toxicity in the treatment group receiving course A (1 g/sq MTX). Moreover, the authors showed in these patients a higher risk of relapse compared with wild-type patients (67 vs 100%). These findings suggest that genotyping of MTHFR could enable us to predict the need for additional leucovorin rescue, although further clinical studies are necessary [7]. It is noteworthy to underline the importance of these results in the new AIEOP-BFM ALL 2009 study where planned high doses of MTX (5 g/sq) in all patients enrolled therefore could increase the occurrence of patients showing toxicity to MTX.

These considerations suggest that the MTHFR C677T polymorphism, alone or with other MTX pathway polymorphisms, could be a useful factor to manage the antifolate doses in children and adolescents with ALL treated with high doses of MTX in order to reduce the associated toxicity with possible effects on the prognosis [8,9].

However, we must consider that several studies did not find a significant association between the MTHFR 677T low-functional allele and MTX toxicity [10,11]. A possible explanation for these discrepancies are differences in treatment protocols among studies, small or non-homogeneous populations, ethnic differences and the use of different criteria defining toxicity.

Certainly, MTHFR A1298C polymorphism seems to be more likely a protective factor against various types of MTX toxicity. In a recently published meta-analysis, the authors only observed a slight protective effect of the 1298CC genotype for leucopenia [3].

More extensive studies regarding the pharmacogenetics can be conducted closely pondering several crucial factors that can influence the interpretation of data such as the age of patients and ethnic differences.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.