Polymorphisms in genes of folate metabolism and effects of high-dose methotrexate in patients with primary central nervous system lymphoma

Abstract

7558 Background: The antifolate methotrexate (MTX) is the single most effective agent in primary central nervous system lymphoma (PCNSL) when given intravenously in high doses. MTX inhibits 5,10-methylentetrahydrofolate reductase (MTHFR) as well as thymidylate synthase (TYMS) in target cells what eventually results in decreased DNA synthesis. Intracellular uptake of folates is mediated by the reduced folate carrier (RFC). Two common MTHFR single nucleotide polymorphisms (SNPs) affect enzyme activity: 677 C→T and 1298A→C. A 28 base pair (bp) tandemly repeated sequence in the TYMS enhancer region (5’-UTR) containing either 2 or 3 repeats alters enzyme activity as does a 6 bp deletion (del) polymorphism in the 3’-UTR of TYMS. An RFC SNP (80G→A) is known to influence folate and MTX transport. We hypothesized that these polymorphisms may be directly linked to toxicity in PCNSL patients receiving high-dose MTX. Methods: Genomic DNA was prospectively collected from patients (pts) who received high-dose (HD) MTX 4 g/m2 every 2 weeks after enrolment onto the German multicenter G-PCNSL-SG1 trial. Genotyping of the two MTHFR and the RFC SNPs was performed by melting point analysis using the Light Cycler technology. Genotyping of the TYMS 28bp polymorphism was performed by conventional PCR followed by agarose gel electrophoresis. The TYMS 6bp del polymorphism was analyzed by PCR, restriction enzyme digest and agarose gel electrophoresis. Response, hematologic (Hb, WBC, ANC, platelets) as well as cumulative incidence of non-hematologic toxicity (renal, pulmonary, mucositis) were assessed prospectively. Results: 123 pts are evaluvable for clinical parameters. Relative risk of any °III/IV toxicity was 26-fold higher for pts with 677TT when compared to CT or CC genotype (p = 0.009). °III/IV non-hematologic toxicity for TT was 10-fold higher than with CT or CC (p = 0.02). Significant differences for hematologic values were restricted to WBC and ANC and found to be associated with RFC 80 GG vs. AG/AA (p = 0.047). Conclusions: Pharmacogenetic studies may identify PCNSL pts who are at risk for severe hematologic and non-hematologic toxicity when treated with HD-MTX. No significant financial relationships to disclose.