       Document 0602
 DOCN  M9630602
 TI    2',3'-Dideoxycytidine metabolism in a new drug-resistant cell line.
 DT    9603
 AU    Magnani M; Brandi G; Casabianca A; Fraternale A; Schiavano GF; Rossi L;
       Chiarantini L; Istituto di Chimica Biologica G. Fornaini, Universita
       degli; Studi di Urbino, Italy.
 SO    Biochem J. 1995 Nov 15;312 ( Pt 1):115-23. Unique Identifier : AIDSLINE
       MED/96077134
 AB    2',3'-Dideoxycytidine (ddC) is a nucleoside analogue that inhibits human
       immunodeficiency virus type 1 (HIV-1) replication in vitro and is
       currently used in the therapy of acquired immune deficiency syndrome
       (AIDS). This compound exerts a delayed cytotoxicity due to inhibition of
       mitochondrial DNA (mDNA) synthesis. Long-term exposure of U937 human
       monoblastoid cells to ddC resulted in a time- and
       concentration-dependent decrease in mDNA content and Rhodamine 123
       fluorescence. However, after 2 months on 0.1 microM ddC, a
       drug-resistant cell line (U937-R) with 66% of the normal amount of mDNA
       was isolated. ddC transport in U937 and U937-R cell lines was similar.
       In contrast, U937-R accumulated ddC phosphorylated derivatives at a much
       lower rate and to a reduced concentration into acid-soluble material.
       The rate of 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) formation in
       U937-R cells was almost one-third of that measured in normal cells,
       although the rate of ddCTP catabolism was similar in both cell lines.
       Dideoxyliponucleotide (ddCDP-choline and ddCDP-ethanolamine) formation
       was also much slower (between one-half and one-third as fast) in U937-R
       than in control cells, although catabolism occurred at similar rates.
       ddC was phosphorylated by a cytoplasmic deoxycytidine kinase in both
       cell lines. This enzyme showed Km values for ddC of 80 +/- 7 and 140 +/-
       9 microM in U937 and U937-R cells respectively. Furthermore, Vmax was 12
       +/- 1.1 and 7.8 +/- 0.5 pmol/min per mg of protein in U937 and U937-R.
       Thus resistance to ddC toxicity may be due to cells' decreased ability
       to accumulate intracellular ddC anabolites, which may depend on
       cytoplasmic deoxycytidine kinase.
 DE    Biological Transport  Cell Division/DRUG EFFECTS  Chromatography, High
       Pressure Liquid  Deoxycytidine Kinase/METABOLISM  Drug Resistance  DNA,
       Mitochondrial/DRUG EFFECTS/METABOLISM  Electrophoresis, Agar Gel  Flow
       Cytometry  Human  Kinetics  Leukemia, Monocytic, Acute/METABOLISM
       Monocytes/CYTOLOGY/DRUG EFFECTS/*METABOLISM  Phosphorylation  Reverse
       Transcriptase Inhibitors/*METABOLISM/PHARMACOLOGY  Support, Non-U.S.
       Gov't  Tumor Cells, Cultured  Zalcitabine/*METABOLISM/PHARMACOLOGY
       JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

