title: Concentrations of the DNA methyltransferase inhibitor 5-fluoro-2'-deoxycytidine (FdCyd) and its cytotoxic metabolites in plasma of patients treated with FdCyd and tetrahydrouridine (THU).
abstract: OBJECTIVE
  Although the DNA methyltransferase inhibitor 5-fluoro-2'-deoxycytidine (FdCyd), is being evaluated clinically, it must be combined with the cytidine deaminase inhibitor tetrahydrouridine (THU) to prevent rapid metabolism of FdCyd to the pharmacologically active, yet unwanted, metabolites 5-fluoro-2'-deoxyuridine (FdUrd), 5-fluorouracil (FU), and 5-fluorouridine (FUrd). We assessed plasma concentrations of FdCyd and metabolites in patients receiving FdCyd and THU.
  
  
  METHODS
  We validated an LC-MS/MS assay, developed for a preclinical study, to quantitate FdCyd and metabolites in human plasma. Patients were treated with five daily, 3-h infusions of FdCyd at doses of 5-80 mg/m(2) with 350 mg/m(2) THU. Plasma was obtained during, and before the end of infusions on days 1 and 5.
  
  
  RESULTS
  The lower limits of quantitation for FU, FdUrd, FUrd, FC and FdCyd were 1, 1.5, 10, 3, and 10 ng/ml, respectively. Plasma FdCyd increased with dose, from 19-96 ng/ml at 5 mg/m(2) to 1,600-1,728 ng/ml at 80 mg/m(2). FdUrd was undetectable in patients treated with FdCyd doses <20 mg/m(2), and increased from 2.3 ng/ml at 20 mg/m(2) to 3.5-5.7 ng/ml at 80 mg/m(2). FU increased from 1.2-5.5 ng/ml at 5 mg/m(2) to 6.0-12 ng/ml at 80 mg/m(2).
  
  
  CONCLUSIONS
  By co-administering FdCyd with THU, FdCyd plasma concentrations were achieved that are known to inhibit DNA methylation in vitro. The accompanying plasma FU and FdUrd concentrations are <10% those observed after therapeutic infusions of FU or FdUrd, while FdCyd levels are well above those required to inhibit methylation in vitro. Therefore, inhibition of DNA methylation with FdCyd and THU appears feasible.
authors: Molecular Therapeutics/Drug Discovery Program, University of Pittsburgh Cancer Institute, Pittsburgh, PA, 15213, USA. beumerjh@upmc.edu
authors: Jan H
authors: JH
authors: Beumer
authors: Robert A
authors: RA
authors: Parise
authors: Edward M
authors: EM
authors: Newman
authors: James H
authors: JH
authors: Doroshow
authors: Timothy W
authors: TW
authors: Synold
authors: Heinz-Josef
authors: HJ
authors: Lenz
authors: Merrill J
authors: MJ
authors: Egorin
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors*; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005467:Floxuridine / Q000097:blood; D005472:Fluorouracil / Q000097:blood; D006801:Humans; D007262:Infusions, Intravenous; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry; D013767:Tetrahydrouridine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D014529:Uridine / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D000970:Antineoplastic Agents; D005467:Floxuridine; D003841:Deoxycytidine; D013767:Tetrahydrouridine; C001943:5-fluorouridine; D015254:DNA Modification Methylases; C007746:5-fluoro-2'-deoxycytidine; D005472:Fluorouracil; D014529:Uridine