II-67Short invited lectures – abstracts RELATIONSHIP OF THE REDUCED FOLATE CARRIER GENE POLYMORPHISM G80A TO METHOTREXATE TOXICITY AND PLASMA LEVELS IN CHILDHOOD ACUTE LYMPHOBLASTIC LEUKEMIA Barbara Faganel-Kotnik1, Janez Jazbec1, Vita Dolžan2 1 Division of Oncology and Hematology, University Children’s Hospital, Medical Centre Ljubljana, Ljubljana, Slovenia 2 Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia Background Methotrexate (MTX) is a key agent in the chemotherapeutic regiments used in the treat- ment of childhood acute lymphoblastic leukemia (ALL), the most frequent malignancy of the pediatric population. MTX inhibits RNA and DNA synthesis in the cell by blocking the turnover of folate. It is transported into the cell by the reduced folate carrier encoded by the gene RFC1. A common polymorphism at position 80 in exon 2 of the RFC1 gene has been identified. Recently higher MTX plasma levels were described with AA genotype. Aim To investigate whether common polymorphism G80A in the RFC gene is associated with a higher incidence of MTX toxicity and higher MTX plasma levels in children and adoles- cents with ALL. If this was the case, determination of RFC1 G80A polymorphism prior to the start of the chemotherapeutic regiment could be used to individualize the MTX dosage in ALL patients with the aim of reducing its toxicity. Methods Sixty-two individuals of Slovenian ethnicity (37 females and 25 males) were included in the study. Average age at the time of diagnose was 6.6 ± 5.0 years. During chemotherapeu- tic regiment subjects on 4 separate occasions received a high dose of MTX (5 g/m2). MTX toxicity was determined by collecting data on MTX and leucovorin administration, leuko- cyte and platelet counts, severity of mucositis, severity of neurotoxicity and survival status. Plasma MTX concentrations were measured 24, 36 and 42 hours after the MTX adminis- tration by the fluorescence polarization immunoassay following manufactures instruc- tions (TDX, Abbott). DNA was isolated from peripheral leukocytes obtained from blood draws using standard procedures. Genotypes of the individuals for G80A polymorphism were determined using the previously described PCR-RFLP test. Simple descriptive statis- tics, the Chi-square test, analysis of variance (ANOVA), Kruskal-Wallis test and T-test were used as appropriate. For statistical analysis statistical software SPSS version 10.0 (SPSS Inc., Chicago, II) was used. P < 0.05 was considered statistically significant, and all P- values were based upon two-tailed tests. Results There was no difference between three immunophenotype groups according to gender distribution, age at diagnosis, body weight and height. RFC1 polymorphism AA AG GG RFC1 frequency (%) 26.4 41.4 32.1 Delay* (No) 7 2 9 Mucositis (No) 6 14 11 Neurotoxic episodes (No) 5 3 8 Other complicatios (No) 7 6 13 Relaps (No) 4 0 3 Fatal outcome (No) 0 1 1 AUCMTX1 (mmol*h /L) 1486 ± 572 1629 ± 571 1352 ± 503 AUC MTX2 (mmol*h /L) 1414 ± 639 1605 ± 588 1378 ± 566 AUC MTX3 ± SD (mmol*h /L) 1358 ± 452 1470 ± 348 1420 ± 809 AUCMTX4 ± SD (mmol*h /L) 1354 ± 461 1415 ± 283 1309 ± 607 Legend: * delay of next MTX application; AUCMTX – average MTX concentration under the curve ± SD after first (1), second (2), third (3) and fourth (4) application respectively. The distribution of RFC genotypes in investigated ALL patients was similar to the distribu- tion in the general Slovene population. No correlation between any of the RFC1 genotypes II-68 Zdrav Vestn 2007; 76: SUPPL II and MTX toxicity on the bone marrow, need for delays of continuation of chemotherapy, oral mucositis, neurotoxicity, disease outcome or MTX concentration (area under the curve value) was detected after any of the MTX applications. Conclusions No correlation could be found between any of the RFC1 polymorphisms and any of the investigated MTX toxicities and MTX concentration. Determination of RFC1 G80A poly- morphism alone can not be used to individualize MTX dosage in ALL patients with the aim of reducing its toxicity.