Zidovudine phosphorylation after short-term and long-term therapy with zidovudine in patients infected with the human immunodeficiency virus.
BACKGROUND
Resistance of human immunodeficiency virus (HIV) to zidovudine (AZT) has been associated with mutations in the viral reverse transcriptase gene. However, recent studies suggest that host cellular factors such as a decreased thymidine kinase activity or an increased cellular P-glycoprotein expression may be important. This study compared concentrations of zidovudine monophosphate, zidovudine diphosphate, and zidovudine triphosphate with P-glycoprotein expression in peripheral blood mononuclear cells from patients receiving long-term (> 18 months) and short-term (< 2 months) zidovudine treatment.


METHODS
Ten subjects in the short-term group and 11 subjects in the long-term group with CD4 counts between 300 and 500 received a single oral dose of zidovudine (200 mg) after a 24-hour washout period. Blood samples were collected at 0, 1, 2, 4, and 6 hours. Intracellular nucleotide concentrations were measured by a combined HPLC-radioimmunoassay method, and P-glycoprotein expression was determined by fluorescence activated cell sorting (FACS) analysis with use of the monoclonal mouse antibody MRK-16.


RESULTS
Zidovudine monophosphate was the predominant compound, accounting for 73.4% +/- 7.1% (SD) of the total phosphates in the long-term treatment group and 74.2% +/- 15.0% (SD) in the short-term group. Zidovudine diphosphate accounted for 13.3% +/- 3.3% (SD) in the long-term group and 12.5% +/- 6.6% (SD) in the short-term group. Zidovudine triphosphate accounted for 13.4% +/- 4.1% (SD) in the long-term group and 13.5% +/- 8.3% (SD) in the short-term group. Mean peak concentrations for the active zidovudine triphosphate were 0.04 +/- 0.02 (SD) pmol/10(6) cells in both groups. Comparison of the individual zidovudine phosphate concentrations and P-glycoprotein expression revealed no significant difference in the two patient populations.


CONCLUSIONS
These data suggest that intracellular phosphorylation does not change over time and that zidovudine does not select for P-glycoprotein expressing cells.
Peter
K
K
Department of Clinical Pharmacy, University of California, San Francisco 94143-0622, USA.
Gambertoglio
J G
JG
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000097:blood; D000284:Administration, Oral; D019380:Anti-HIV Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D002469:Cell Separation; D002851:Chromatography, High Pressure Liquid; D005434:Flow Cytometry; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D015658:HIV Infections / Q000097:blood* / Q000188:drug therapy*; D006801:Humans; D007963:Leukocytes, Mononuclear; D009711:Nucleotides / Q000097:blood; D010710:Phosphates / Q000097:blood; D010766:Phosphorylation; D011863:Radioimmunoassay; D013997:Time Factors; D015215:Zidovudine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D019380:Anti-HIV Agents; D009711:Nucleotides; D010710:Phosphates; D015215:Zidovudine