1 Cattedra di Ematologia, Divisione di Ematologia, Università Cattolica Sacro Cuore Roma; 2 Dipartimento di Biotecnologie Cellulari ed Ematologia, Università La Sapienza, Roma, Italy
Received 5 February 2002; revised 11 June 2002; accepted 18 June 2002
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Abstract |
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Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, a common mutation of the gene encoding the enzyme that catalyzes reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a carbon donor in the metabolism of folate, determines a striking reduction in the enzyme activity in carriers of mutation at homozygous status.
Patients and methods:
We retrospectively analyzed the incidence of MTHFR C677T and the influence of genotype on methotrexate (MTX) toxicity in patients with acute leukemia undergoing maintenance chemotherapy. Seventy-eight patients were analyzed and 61 were evaluable for toxicity. MTX toxicity was assessed on bone marrow, liver and mucosae.
Results:
The incidence of the C677T mutation was as expected in the general Italian population with 23.08% of patients being TT, 38.46% of patients CT and 38.46% of patients CC. The TT genotype was significantly associated with an increase of toxicity during MTX administration. No specific pattern of toxicity was detected, although in TT patients myelosuppression and liver toxicity were more pronounced.
Conclusions:
TT genotype may indicate a need to reduce the dose of MTX during prolonged administration. Considering the high prevalence of homozygous individuals in the Italian population, pretreatment screening may be worthwhile.
Key words: methotrexate, MTHFR, polymorphism
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Introduction |
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Patients and methods |
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MTHFR genotyping
Genomic DNA was used to determine MTHFR genotype using a PCR-based method that detects a single point mutation at nucleotide 677 [9]. Genotypes were in HardyWeinberg equilibrium.
Statistical analysis
Statistical analysis was performed using pair-wise comparison among the genotype groups and two-tailed Fishers exact test comparing CC and CT patients with TT patients with respect to residual enzyme activity in the heterozygous. Statistical significance was defined as P 0.05.
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Results |
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Toxicities are reported in Table 2. No major toxicities on mucosae were reported in the three different groups. Among these, MTX intolerance was encountered in seven of 21 CC patients (33.3%), in six out of 25 CT patients (24%) and in nine of 15 TT patients (60%) (P = 0.03, Fishers exact test). Twenty-three of 78 patients were also genotyped for thiopurine S-methyltransferase (TPMT) polymorphism (TPMT2, TPMT3B and TPMT3C): we found three patients to be heterozygous for TPMT3C, but none of these developed toxicity during maintenance therapy (preliminary data).
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Discussion |
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Recently, in a group of patients affected by breast cancer with a mutated MTHFR genotype, Toffoli et al. [11] described the occurrence of severe hematological toxicity after cyclophosphamide, MTX and fluorouracil treatment. More recently, reduced tolerance to maintenance chemotherapy with MTX and 6-MP has been attributed to TPMT deficiency [12]. Genetic polymorphism of TPMT causes a reduction of the enzyme activity and thus leads to accumulation of thioguanine in erythrocytes, which is proportional to the toxicity and efficacy of these drugs.
When MTHFR C677T was considered, further evidence of correlation between MTHFR genotype and MTX intolerance were demonstrated. Patients reported here were submitted to prolonged administration of MTX as part of their therapeutic program for at least 2 years. The vast majority of TT patients experienced MTX intolerance more frequently, requiring dose modification and temporary MTX withdrawal leading to overall poor compliance with maintenance. Time to completion of maintenance chemotherapy was also prolonged, although it was not significant (28.5 versus 26.5 months) in TT patients. Heterozygotes did not show any difference in terms of toxicity compared with wild-type patients. Combined toxicity on liver and bone marrow function was encountered more frequently in patients with the TT genotype (Table 2). After MTX dosage adjustments, patients who developed toxicity were subsequently treated with full doses of another chemotherapy.
Interpatient variability in drug response in terms of efficacy and toxicity is potentially regulated by several processes including drug transport and metabolism.
Currently, an empirical treatment approach is taken in most diseases, although at least nine enzymes metabolizing anticancer agents exhibit genetic polymorphisms [13]. It is probable that in the near future a panel of disease-specific genotypes will be utilized to identify subsets of patients who are genetically predisposed to develop toxicity from specific drugs. Recently, MTHFR polymorphism has been associated with higher risk of toxicity after very low doses of MTX given for GvHD prevention in patients submitted to allogeneic stem-cell transplantation [5]. The attribution of MTX toxicity to MTHFR genotype could be difficult in this setting [14], where toxicity is the result of conditioning regimen, GvHD occurrence and infections. In our study, maintenance chemotherapy that includes administration of small and continuous doses of chemotherapy allowed us to ascertain the role of MTHFR genotype in the development of toxicity during MTX administration. We conclude that the high prevalence of TT subjects in the Italian population suggests a benefit of genetic screening for this mutation in patients with acute leukemia undergoing prolonged administration of MTX.
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Acknowledgements |
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Footnotes |
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References |
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