Protein kinases constitute a large group of enzymes in eukaryotes and have an important role in many cellular processes. Several of these proteins are active kinases, such as haploid germ cell-specific nuclear protein kinase (Haspin), an atypical eukaryotic protein kinase that lacks sequence similarity with other
eukaryotic protein kinases. Haspin is a serine/threonine kinase that associates with chromosome and phosphorylates threonine 3 of histone 3 during mitosis. Haspin overexpression or deletion results in defective mitosis. It has been shown that Haspin inhibitors have potent anti-tumoral effects. Given that the only Haspin substrate is threonine 3 of histone 3, inhibition of Haspin might have fewer adverse
effects compared with other anticancer agents. Here, we highlight the chemical structures and actions of currently known Haspin inhibitors.