title: 2',3'-Dideoxycytidine metabolism in a new drug-resistant cell line.
abstract: 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.
mesh_terms: D001692:Biological Transport; D002455:Cell Division / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004272:DNA, Mitochondrial / Q000187:drug effects / Q000378:metabolism; D003842:Deoxycytidine Kinase / Q000378:metabolism; D004351:Drug Resistance; D004587:Electrophoresis, Agar Gel; D005434:Flow Cytometry; D006801:Humans; D007700:Kinetics; D007948:Leukemia, Monocytic, Acute / Q000378:metabolism; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D018894:Reverse Transcriptase Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D016047:Zalcitabine / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D004272:DNA, Mitochondrial; D018894:Reverse Transcriptase Inhibitors; D016047:Zalcitabine; D003842:Deoxycytidine Kinase