MTHFR variant is associated with high-dose methotrexate-induced toxicity in the Chinese osteosarcoma patients

Background: The role of Methylene tetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms in the efficacy and toxicity of MTX-based therapy remains uncertain. Our purpose was to clarify whether these two polymorphisms are associated with the outcome of chemotherapy in a cohort of Chinese osteosarcoma (OS) patients treated by high-dose MTX. Methods: 109 OS patients who had sequentially received high-dose MTX therapy were included in this study. Plasma MTX level was measured routinely at 0, 24, 48 and 72 h after the administration of MTX. Two variants of MTHFR were genotyped using TaqMan SNP Genotyping Assay, including rs1801133 (C667T) and rs1801131 (A1298C). The extent of toxicity induced by MTX, including hematological toxicity, hepatic toxicity, renal toxicity and mucositis, was scored from grade 1 to 4. Severe toxicity was defined as a grade score of ≥3. Patients were dichotomized as follows: grade 0.2 µmol/L for plasma MTX level at 72 h. The frequencies of genotypes and allele were compared between the dichotomized groups with the Chi-square test. Results: 24.8% (27/109) of the patients were found to have significantly high plasma MTX level at the 72 h. Patients with high MTX level at 72 h were found to have significantly higher frequency of genotype TT of rs1801133 (p = 0.002). As for rs1801131, no significant association was found with plasma MTX level. Patients with severe hepatic toxicity or mucositis were found to have remarkably higher incidence of genotype TT of rs1801133 than those with mild toxicity (33.3% vs. 14.8%, p = 0.04 for hepatic toxicity; 34.8% vs. 19.8%, p = 0.05 for mucositis). Conclusions: Variant rs1801133 was confirmed to have remarkable influence on the MTX-induced toxicity. We recommend identification of the genotype of MTHFR variant prior to the application of high-dose MTX to OS patients, which could be an important predictor to screen severe toxicities and thus improve treatment outcomes. Keywords: Osteosarcoma, MTX, Variants, MTHFR, Toxicity