Methods for inhibiting cell growth, inhibiting DNA polymerase activity, and inhibiting DNA replication and repair are provided. In a method of inhibiting cell growth, a cell, such as a cancer cell, is contacted with zelpolib or a derivative or pharmaceutically acceptable salt thereof. The cell growth can be inhibited in vivo, and in certain embodiments, the cell growth is inhibited in vitro. In a method for inhibiting DNA polymerase activity, a DNA polymerase is contacted with zelpolib or a derivative or pharmaceutically acceptable salt thereof. In certain embodiments, the DNA polymerase is Pol δ. In a method for inhibiting DNA replication and repair, a cell, such as a cancer cell, is contacted with zelpolib or a derivative or pharmaceutically acceptable salt thereof. The DNA replication and repair can be inhibited in vivo, and in certain embodiments, the DNA replication and repair is inhibited in vitro.