title: Methotrexate in pediatric osteosarcoma: response and toxicity in relation to genetic polymorphisms and dihydrofolate reductase and reduced folate carrier 1 expression.
abstract: OBJECTIVE
  To determine the influence of the genotype and the level of expression of different enzymes involved in folate metabolism on the response to and toxicity of high-dose methotrexate treatment in pediatric osteosarcomas.
  
  
  METHODS
  DHFR and Reduced folate carrier 1 (RFC1) semiquantitative expression was analyzed in 34 primary and metastatic osteosarcoma tissues by real-time polymerase chain reaction. The following polymorphisms were also analyzed in peripheral blood from 96 children with osteosarcoma and 110 control subjects: C677T, A1298C (MTHFR), G80A (RFC1), A2756G (MTR), C1420T (SHMT), the 28bp-repeat polymorphism, and 1494del6 of the TYMS gene. Treatment toxicity was scored after each cycle according to criteria from the World Health Organization.
  
  
  RESULTS
  DHFR and RFC1 expression was lower in initial osteosarcoma biopsy specimens than in metastases (P = .024 and P = .041, respectively). RFC1 expression was moderately decreased in samples with poor histologic response to preoperative treatment (P = .053). Patients with osteosarcoma with G3/G4 hematologic toxicity were more frequently TT than CT/CC for C677T/MTHFR (P = .023) and GG for A2756G/MTR (P = .048 and P = .057 for gastrointestinal and hematologic toxicity, respectively).
  
  
  CONCLUSIONS
  The role of C677T/MTHFR and A2756G/MTR on chemotherapy-induced toxicity should be further investigated in pediatric osteosarcomas receiving high-dose methotrexate. Altered expression of DHFR and RFC1 is a feasible mechanism by which osteosarcoma cells become resistant to methotrexate.
authors.affiliation: Laboratory of Pediatrics, University of Navarra/University Clinic, Pamplona, Spain. apatigar@unav.es
authors.forename: Ana
authors.initials: A
authors.lastname: Patiño-García
authors.forename: Marta
authors.initials: M
authors.lastname: Zalacaín
authors.forename: Lucía
authors.initials: L
authors.lastname: Marrodán
authors.forename: Mikel
authors.initials: M
authors.lastname: San-Julián
authors.forename: Luis
authors.initials: L
authors.lastname: Sierrasesúmaga
mesh_terms: D000293:Adolescent; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000009:adverse effects*; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000401:mortality; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D016022:Case-Control Studies; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000235:genetics / Q000378:metabolism; D005767:Gastrointestinal Diseases / Q000139:chemically induced; D005838:Genotype; D006402:Hematologic Diseases / Q000139:chemically induced; D006801:Humans; D007674:Kidney Diseases / Q000139:chemically induced; D008297:Male; D008727:Methotrexate / Q000008:administration & dosage / Q000009:adverse effects*; D012516:Osteosarcoma / Q000188:drug therapy* / Q000235:genetics / Q000401:mortality; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate