Molecular basis of the antineoplastic activity of 3'-amino-3'-deoxythymidine

3'-Amino-3'-deoxythymidine decreased the incorporation of [2-14C]thymidine into DNA of L1210 cells in vitro, and produced an accumulation of [2-14C]thymidine di- and triphosphate. The extent of these effects varied with the amount of recovery time after removal of 3'-amino-3'-deoxythymidine prior to addition of labeled thymidine. The distribution of radioactivity in the acid-soluble fraction derived from [3H]3'-amino-3'-deoxythymidine was as follows: 50% as 3'-amino-3'-deoxythymidine, 20% as the monophosphate, 10% as the diphosphate, and 20% as the triphosphate derivatives. No incorporation of [3H]3'-amino-3'-deoxythymidine into L1210 DNA could be detected. 3'-Amino-3'-deoxythymidine-5'-triphosphate is a competitive inhibitor against dTTP with a Ki of 3.3 microM, whereas the Km for dTTP was 8 microM using activated calf thymus DNA as the template and DNA polymerase-alpha. These data indicate that a major site of inhibition by 3'-amino-3'-deoxythymidine is inhibition of the DNA polymerase reaction.