Cell division cycle 7 kinase (CDC7; EC 2.7.11.1), is important for both the G1/S phase transition and S phase progression and critical for normal cell cycle progression. It has several structure/function relationships with the CDKs, making it an important target for pharmacological inhibition. Two important regulator proteins, Dbf4 and Drf1, bind to and modulate the kinase activity of human CDC7 which phosphorylates several sites on Mcm2 (minichromosome maintenance protein 2), one of the six subunits of the replicative DNA helicase needed for duplication of the genome. Through regulation of both DNA synthesis and DNA damage response, both key functions in the survival of tumour cells, CDC7 becomes an attractive target for pharmacological inhibition. XL 413 (Axon 2268) is such a potent, selective and orally bioavailable CDC7 inhibitor that induces tumor cell apoptosis and inhibition of tumor cell proliferation in CDC7-overexpressing tumor cells.