Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two cell lines, U-937 and MOLT-4, were used to investigate the toxicity, DNA incorporation, and effect on mitochondria of 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) and its putative metabolite 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-uracil (FAU). After 72-hr incubation, the IC50 values for FIAU were 6.4 microM for U-937 cells and 26 microM for MOLT-4 cells. IC50 values for FAU were 10-fold higher in both cell lines. Incubation for 24 hr with 10 microM [2-14C]FIAU led to 2.1% and 0.93% replacement of thymidine in DNA of U-937 and MOLT-4 cells, respectively. The predominant radioactive species measurable in DNA was FIAU. A similar incubation with [2-14C]FAU resulted in 4-fold lower DNA incorporation of a single radioactive species that coeluted with 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-methyluracil (FMAU). There was no evidence of a selective repair process after DNA incorporation of FIAU or FAU (FMAU). Increased intracellular concentrations of FIAU triphosphate and incorporation into DNA were associated with an increase in cellular toxicity. Continuous exposure to a clinically achievable concentration of FIAU, 0.44 microM, produced a constant DNA incorporation of 0.80% and 0.11% for U-937 and MOLT-4 cells, respectively. FIAU was not readily metabolized to FAU or iodouracil by human liver in vitro. Compared with 2',3'-dideoxycytidine as a positive control, after 12 days of continuous exposure of U-937 and MOLT-4 cells to FIAU there was no evidence of increased lactate production. These data negate several possible mechanisms (DNA chain termination, DNA polymerase inhibition, one form of selective mitochondrial poisoning, and FAU-mediated toxicity) and provide clues for possible mechanisms (FIAU triphosphate concentration and DNA incorporation). Further work is needed to develop a complete explanation for the delayed hepatic toxicity observed in the investigational clinical trials of FIAU.
 ...
PMID:Toxicity, metabolism, DNA incorporation with lack of repair, and lactate production for 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-iodouracil in U-937 and MOLT-4 cells. 780 43

The thymidine analog fialuridine deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) was toxic in trials for chronic hepatitis B infection. One mechanism postulated that defective mtDNA replication was mediated through inhibition of DNA polymerase-gamma (DNA pol-gamma), by FIAU triphosphate (FIALTP) or by triphosphates of FIAU metabolites. Inhibition kinetics and primer-extension analyses determined biochemical mechanisms of FIAU, 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) -5-methyluracil (FAU), 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil triphosphate (TP) inhibition of DNA pol-gamma. dTMP incorporation by DNA pol-gamma was inhibited competitively by FIAUTP, FMAUTP, and FAUTP (K1=0.015, 0.03, and 1.0 microM, respectively). By using oliginucleotide template-primers. DNA pol-gamma incorporated each analog into DNA opposite a single adenosine efficiently without effects on DNA chain elongation. Incorporation of multiple adjacent analogs at positions of consecutive adenosines dramatically impaired chain elongation by DNA pol-gamma. Effects of FIAU, FMAU, and FAU on HepG2 cell mmtDNA abundance and ultrastructure were determined. After 14 days, mtDNA decreased by 30% with 20 microM FIAU or 20 microM FMAU and decreased less than 10% with 100 microM FAU. FIAU and FMAU disrupted mitochondria and caused accumulation of intracytoplasmic lipid droplets. Biochemical and cell biological findings suggest that FIAU and its metabolites inhibit mtDNA replication, most likely at positions of adenosine tracts, leading to decreased mtDNA and mitochondrial ultrastructural defects.
 ...
PMID:Fialuridine and its metabolites inhibit DNA polymerase gamma at sites of multiple adjacent analog incorporation, decrease mtDNA abundance, and cause mitochondrial structural defects in cultured hepatoblasts. 862 80