Precise coordination of the S and M phases of the eukaryotic cell cycle is critical not only for normal cell division, but also for effective growth arrest under conditions of stress. When damaged, a cell must communicate signals to both the mitotic and DNA synthesis machineries so that a mitotic block is not followed by an extra S phase, or vice versa. The biochemical mechanisms regulating this coordination, termed checkpoints, have been identified in lower eukaryotes, but are largely unknown in mammalian cells.sup.1-3.
DNA-damaging agents are used in the clinic to preferentially kill cancer cells. However, there is a need in the art to discover additional therapeutic agents which are selectively toxic to cancer cells.