title: Time-dependent changes in HIV nucleoside analogue phosphorylation and the effect of hydroxyurea.
abstract: BACKGROUND
  Nucleoside analogues are activated to their triphosphates, which compete with endogenous deoxynucleoside triphosphate (dNTP) pools to inhibit HIV reverse transcriptase. Hydroxyurea has been administered with nucleoside analogues to modulate intracellular dNTP pools and thus the ratio of drug triphosphate:endogenous triphosphate.
  
  
  OBJECTIVE
  To examine changes in drug activation over time and investigate the effects of hydroxyurea on intracellular phosphorylation of antiretroviral nucleoside analogues.
  
  
  METHODS
  A total of 229 HIV-infected individuals receiving abacavir, lamivudine and zidovudine were randomly assigned to receive or not nevirapine and hydroxyurea. Twenty-four patients were recruited to an observational substudy measuring intracellular drug triphosphate and dNTP concentrations at 0, 2, 6, 12, 24 and 48 weeks.
  
  
  METHODS
  Drugs were extracted from isolated peripheral blood mononuclear cells before analysis of endogenous dNTP and drug triphosphates by primer extension assays.
  
  
  RESULTS
  Twenty-two out of 24 patients were followed to completion of the substudy. Hydroxyurea had no demonstrable effect on endogenous dNTP or drug triphosphate levels at any timepoint. However, the ratio of zidovudine triphosphate to endogenous deoxythymidine triphosphate was significantly increased with hydroxyurea. A significant decrease in lamivudine triphosphate (3TCTP) and the 3TCTP:endogenous deoxycytidine triphosphate ratio was seen over 48 weeks. In five patients who failed therapy in the first 24 weeks, significantly reduced 3TCTP was seen.
  
  
  CONCLUSIONS
  Hydroxyurea does not affect measurable pools of endogenous nucleosides in vivo. Decreased lamivudine phosphorylation over time may provide a novel pharmacological explanation for the mechanism of resistance to this drug.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Liverpool, Ashton Street, Liverpool L69 3GE, UK. patrick@liverpool.ac.uk
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hoggard
authors.forename: Stephen
authors.initials: S
authors.lastname: Kewn
authors.forename: Anlie
authors.initials: A
authors.lastname: Maherbe
authors.forename: Robin
authors.initials: R
authors.lastname: Wood
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Almond
authors.forename: Sean D
authors.initials: SD
authors.lastname: Sales
authors.forename: Jayne
authors.initials: J
authors.lastname: Gould
authors.forename: Yu
authors.initials: Y
authors.lastname: Lou
authors.forename: Corry
authors.initials: C
authors.lastname: De Vries
authors.forename: David J
authors.initials: DJ
authors.lastname: Back
authors.forename: Saye H
authors.initials: SH
authors.lastname: Khoo
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000493:pharmacokinetics / Q000627:therapeutic use*; D023241:Antiretroviral Therapy, Highly Active; D015224:Dideoxynucleosides / Q000493:pharmacokinetics / Q000627:therapeutic use; D004347:Drug Interactions; D024882:Drug Resistance, Viral; D005260:Female; D015658:HIV Infections / Q000188:drug therapy*; D006801:Humans; D006918:Hydroxyurea / Q000627:therapeutic use*; D019259:Lamivudine / Q000493:pharmacokinetics / Q000627:therapeutic use; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019829:Nevirapine / Q000627:therapeutic use*; D009705:Nucleosides / Q000378:metabolism*; D010766:Phosphorylation; D018894:Reverse Transcriptase Inhibitors / Q000627:therapeutic use*; D015215:Zidovudine / Q000493:pharmacokinetics / Q000627:therapeutic use; D000099227:Abacavir
chemical_list: D019380:Anti-HIV Agents; D015224:Dideoxynucleosides; D006918:Hydroxyurea; D019259:Lamivudine; D019829:Nevirapine; D009705:Nucleosides; D018894:Reverse Transcriptase Inhibitors; D015215:Zidovudine; D000099227:Abacavir