2'-C-CYANO-2'-DEOXY-1-BETA-D-ARABINOFURANOSYL-CYTOSINE (CNDAC) - A MECHANISM-BASED DNA STRAND-BREAKING ANTITUMOR NUCLEOSIDE

The antitumor mechanism of action of 2'-C-cyano-2'-deoxy-1-beta-D-arabinofuranosylcytosine (CNDAC) has been examined. CNDAC was designed as a potentially DNA-self-strand-breaking nucleoside. It had potent antitumor effects against various solid tumors in vitro as well as in vivo. Using a chain-extension method with Vent (exo(-)) DNA polymerase and a short primer/template system, we found that 5'-triphosphate of CNDAC (CNDACTP) was incorporated into the primer at a site opposite a guanine residue in the template. After further chain-extension reaction of the primer containing CNDAC at the 3'-terminus, chain elongation was not observed. Therefore, CNDACTP appeared to act as a chain-terminator. Analyses of the structure of the 3'-terminus in the primer revealed 2'-C-cyano-2'-3'-didehydro-2',3'-dideoxycytidine (ddCNC) together with CNDAC and 2'C-cyano-2'-deoxy-1-beta-D-ribofuranosylcytosine (CNDC). The existence of ddCNC in the 3'-end of the primer would be due to the self-strand-break by the nucleotide incorporated next to CNDAC. We also found that CNDAC was epimerized to CNDC in near-neutral to alkaline media. Therefore, CNDC found in the primer was epimerized after incorporation of CNDACTP into the primer. We also described the metabolism of CNDAC.