title: CDA directs metabolism of epigenetic nucleosides revealing a therapeutic window in cancer.
abstract: Cells require nucleotides to support DNA replication and repair damaged DNA. In addition to de novo synthesis, cells recycle nucleotides from the DNA of dying cells or from cellular material ingested through the diet. Salvaged nucleosides come with the complication that they can contain epigenetic modifications. Because epigenetic inheritance of DNA methylation mainly relies on copying of the modification pattern from parental strands, random incorporation of pre-modified bases during replication could have profound implications for epigenome fidelity and yield adverse cellular phenotypes. Although the salvage mechanism of 5-methyl-2'deoxycytidine (5mdC) has been investigated before, it remains unknown how cells deal with the recently identified oxidized forms of 5mdC: 5-hydroxymethyl-2'deoxycytidine (5hmdC), 5-formy-2'deoxycytidine (5fdC) and 5-carboxyl-2'deoxycytidine (5cadC). Here we show that enzymes of the nucleotide salvage pathway display substrate selectivity, effectively protecting newly synthesized DNA from the incorporation of epigenetically modified forms of cytosine. Thus, cell lines and animals can tolerate high doses of these modified cytidines without any deleterious effects on physiology. Notably, by screening cancer cell lines for growth defects after exposure to 5hmdC, we unexpectedly identify a subset of cell lines in which 5hmdC or 5fdC administration leads to cell lethality. Using genomic approaches, we show that the susceptible cell lines overexpress cytidine deaminase (CDA). CDA converts 5hmdC and 5fdC into variants of uridine that are incorporated into DNA, resulting in accumulation of DNA damage, and ultimately, cell death. Our observations extend current knowledge of the nucleotide salvage pathway by revealing the metabolism of oxidized epigenetic bases, and suggest a new therapeutic option for cancers, such as pancreatic cancer, that have CDA overexpression and are resistant to treatment with other cytidine analogues.
authors.affiliation: Ludwig Cancer Research, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7DQ, UK.
authors.forename: Melania
authors.initials: M
authors.lastname: Zauri
authors.affiliation: Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7FZ, UK.
authors.forename: Georgina
authors.initials: G
authors.lastname: Berridge
authors.affiliation: Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7FZ, UK.
authors.forename: Marie-Laëtitia
authors.initials: ML
authors.lastname: Thézénas
authors.affiliation: 1] Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7FZ, UK [2] Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7DQ, UK.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Pugh
authors.affiliation: Centre for Pathology, Imperial College, London W2 1NY, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Goldin
authors.affiliation: Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7FZ, UK.
authors.forename: Benedikt M
authors.initials: BM
authors.lastname: Kessler
authors.affiliation: Ludwig Cancer Research, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7DQ, UK.
authors.forename: Skirmantas
authors.initials: S
authors.lastname: Kriaucionis
mesh_terms: D044503:5-Methylcytosine / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D003562:Cytidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism*; D003596:Cytosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry; D004249:DNA Damage / Q000187:drug effects; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D044127:Epigenesis, Genetic; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010084:Oxidation-Reduction; D010770:Phosphotransferases / Q000378:metabolism; D013379:Substrate Specificity; D015854:Up-Regulation; D014529:Uridine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism
chemical_list: C000600732:5-carboxyl-2'-deoxycytidine; C402104:5-formyl-2'-deoxycytidine; C540838:5-hydroxymethyl-2'-deoxycytidine; D009711:Nucleotides; D003841:Deoxycytidine; D003562:Cytidine; D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; C016569:5-methyldeoxycytidine; D010770:Phosphotransferases; C021892:nucleoside phosphotransferase; D004259:DNA-Directed DNA Polymerase; D003564:Cytidine Deaminase; D014529:Uridine