RT Journal Article SR Electronic T1 2′-C-Cyano-2′-deoxy-1-β-d-arabino-pentofuranosylcytosine: A Novel Anticancer Nucleoside Analog that Causes Both DNA Strand Breaks and G2 Arrest JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 725 OP 731 DO 10.1124/mol.59.4.725 VO 59 IS 4 A1 Atsushi Azuma A1 Peng Huang A1 Akira Matsuda A1 William Plunkett YR 2001 UL http://molpharm.aspetjournals.org/content/59/4/725.abstract AB The mechanism of 2′-C-cyano-2′-deoxy-1-β-d-arabino-pentofuranosylcytosine (CNDAC) action was investigated in human lymphoblastoid CEM cells and myeloblastic leukemia ML-1 cells. CNDAC was metabolized to its 5′-triphosphate and incorporated into DNA, which was associated with inhibition of DNA synthesis. After incubation of cells with [3H]CNDAC, metabolites were detected in 3′→5′ phosphodiester linkage and at the 3′ terminus of cellular DNA. Specific enzymatic hydrolysis of DNA demonstrated that the parent nucleoside and its 2′-epimer 2′-C-cyano-2′-deoxy-2-ribo-pentofuranosylcytosine accounted for approximately 65% of the total analogs incorporated into DNA and essentially all of the drug in the 3′→5′ phosphodiester linkage. In contrast, all detectable radioactivity at 3′ termini was associated with 2′-C-cyano-2′,3′-didehydro-2′,3′-dideoxycytidine. This de facto DNA chain-terminating nucleotide arises from an electronic characteristic and cleavage of the 3′-phosphodiester bond subsequent to the addition of a nucleotide to the incorporated CNDAC moiety by β-elimination, a process that generates a single strand break in DNA. Investigation of the biological consequences of these actions indicated that, after incubation with cytostatic concentrations of CNDAC, cell cycle progression was delayed during S phase, but that cells arrested predominantly in the G2 phase. This differed from the S phase-arresting actions of ara-C and gemcitabine, other deoxycytidine analogs that inhibit DNA replication but do not cause strand breaks. Thus, once incorporated into DNA, the CNDAC molecule appears to act by a dual mechanism that 1) delays the progress of further DNA replication, but 2) upon addition of a deoxynucleotide results in the conversion of the incorporated analog to a de facto DNA chain terminator at the 3′ terminus of a single strand break. It is likely that DNA strand breaks trigger cell cycle arrest in G2.