title: Paracetamol inhibits replicative DNA synthesis and induces sister chromatid exchange and chromosomal aberrations by inhibition of ribonucleotide reductase.
abstract: Effects of paracetamol have been studied in a hydroxyurea (HU)-resistant mouse mammary tumour cell line TA3H2, shown to overproduce the small subunit of ribonucleotide reductase. These TA3H2 cells were much more resistant than the TA3H (wild-type) cells towards the inhibitory effect of paracetamol on cell growth, IC50 0.55 mM paracetamol for the wild-type compared to 2.7 mM for the HU-resistant cells. The reduced cell growth was due to an inhibition of replicative DNA synthesis, judged from an increased percentage of cells in S-phase measured by flow cytometry. Furthermore, in the wild-type cells, the increase in the number of cells in S phase was already observed at 0.1 mM while in the HU-resistant cell line this effect was first seen at 3.0 mM paracetamol. HU inhibits ribonucleotide reductase by destroying a tyrosyl free radical located on the small subunit of the enzyme. By electron paramagnetic resonance we demonstrate that paracetamol added to crude cell extracts of HU-resistant cells also immediately destroys this radical. These results show that paracetamol reduces DNA synthesis by a specific inhibition of ribonucleotide reductase. A concentration-dependent induction of sister chromatid exchanges was found both with paracetamol (1.0-10 mM) and HU (0.3-3 mM) in wild-type cells whereas no such increase was observed in HU-resistant cells. Paracetamol (1 mM for 2 h) also increased the number of chromosomal aberrations CAs in wild-type cells (i.e. chromatid breaks and chromatid exchanges). The frequency of CAs was not increased in HU-resistant cells at paracetamol concentrations up to 10 mM.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Toxicology, National Institute of Public Health, Oslo, Norway.
authors.forename: J K
authors.initials: JK
authors.lastname: Hongslo
authors.forename: C
authors.initials: C
authors.lastname: Bjørge
authors.forename: P E
authors.initials: PE
authors.lastname: Schwarze
authors.forename: A
authors.initials: A
authors.lastname: Brøgger
authors.forename: G
authors.initials: G
authors.lastname: Mann
authors.forename: L
authors.initials: L
authors.lastname: Thelander
authors.forename: J A
authors.initials: JA
authors.lastname: Holme
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002869:Chromosome Aberrations; D004261:DNA Replication / Q000187:drug effects*; D004351:Drug Resistance; D004578:Electron Spin Resonance Spectroscopy; D005434:Flow Cytometry; D005609:Free Radicals; D008325:Mammary Neoplasms, Experimental; D051379:Mice; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors*; D012854:Sister Chromatid Exchange; D014407:Tumor Cells, Cultured
chemical_list: D005609:Free Radicals; D000082:Acetaminophen; D012264:Ribonucleotide Reductases