Effect of novel benzoylphenylurea derivatives on DNA polymerase α activity using the synthesome-based in vitro model system

Six benzoylphenylurea (BPU) derivatives have been synthesized in Japan and extensively evaluated by the U.S. National Cancer Institute. They demonstrated potent antitumor activity in vitro against several cancer cell lines as well as in vivo against several tumor models. One of these agents, NSC639829, has now entered clinical trials. Studies have shown that these compounds are effective inhibitors of in vitro tubulin polymerization. The parent compound, NSC624548 (HO-221), has been shown to inhibit calf thymus DNA polymerase α activity. In this study we examined the effects of four BPU derivatives (NSC624548, NSC639828, NSC639829, and NSC654259) on the activity of the synthesome- associated DNA polymerase α, Escherichia coli DNA polymerase I, and calf thymus DNA polymerase α. Among the compounds tested, only NSC624548 and NSC639828 inhibited the activities of E. coli DNA polymerase I and calf thymus DNA polymerase α. Excess DNA polymerase I or DNA polymerase α dramatically reduced the inhibition produced by these compounds. NSC624548 and NSC639828 also showed inhibitory effects of the synthesome-associated DNA polymerase α similar to that produced upon using the purified E. coli and calf thymus enzymes. All of the four compounds did not show inhibitory effect on DNA polymerase 6. The similar pattern of inhibition these compounds exert on both the purified calf thymus and the synthesome-associated DNA polymerase α offers further support for the validity of the DNA synthesome as a novel in vitro model system for studying anticancer drug action.