title: The impact of 5-formyltetrahydrofolate on the anti-tumor activity of pralatrexate, as compared to methotrexate, in HeLa cells in vitro.
abstract: OBJECTIVE
  To investigate the impact of 5-formyltetrahydrofolate on the activities of pralatrexate, as compared to methotrexate (MTX), in vitro.
  
  
  METHODS
  Cells were exposed to (6S)5-formyltetrahydrofolate (5-formylTHF) for 24 h, before or after a 6-h exposure to antifolates following which the cellular accumulation and activities of the drugs were evaluated in HeLa cells.
  
  
  RESULTS
  A 24-h delay between a 6-h exposure to antifolates and a subsequent 24-h exposure to 4 μM 5-formylTHF sustained the full activities of both antifolates. A 72-h interval was required between a single exposure of up to 4 μM 5-formylTHF and subsequent exposure to drugs to sustain activities of the antifolates. When cells were incubated with 4 μM 5-formylTHF for 24 h weekly, for 4 weeks, there was no significant increase in the IC50 for pralatrexate, but the MTX IC50 increased 2.5-fold as compared to cells growing continuously in 25 nM 5-formylTHF. This cyclical exposure to 5-formylTHF increased the cell folate pool by 16 %, had no significant effect on the intracellular pralatrexate level, but decreased intracellular MTX by 15 %. An extracellular concentration of MTX 50-fold higher than that of pralatrexate was required to achieve an intracellular level, and growth inhibition, comparable to that of pralatrexate.
  
  
  CONCLUSIONS
  Cyclical exposures to 5-formylTHF at levels in excess of what is achieved in most clinical "rescue" regimens do not affect pralatrexate accumulation nor antitumor activity in HeLa cells, in contrast to MTX. An important element in preserving pralatrexate activity is achieving a sufficient interval between exposure to 5-formylTHF and the next dose of antifolate.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein Cancer Center, Albert Einstein College of Medicine, Chanin 2, 1300 Morris Park Avenue, Bronx, NY, USA.
authors.forename: Michele
authors.initials: M
authors.lastname: Visentin
authors.forename: Ersin Selcuk
authors.initials: ES
authors.lastname: Unal
authors.forename: I David
authors.initials: ID
authors.lastname: Goldman
mesh_terms: D000630:Aminopterin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D019731:Carbon-Nitrogen Ligases / Q000378:metabolism*; D005493:Folic Acid Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D008727:Methotrexate / Q000008:administration & dosage / Q000494:pharmacology*; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: C418863:10-propargyl-10-deazaaminopterin; D005493:Folic Acid Antagonists; D019731:Carbon-Nitrogen Ligases; C021557:5,10-methenyltetrahydrofolate synthetase; D000630:Aminopterin; D008727:Methotrexate