Aurora kinases are clearly implicated in tumorgenesis and have emerged as promising targets for cancer therapy in recent years.In a virtual screening attempt,22 compounds were identified from nearly 15,000 microbial natural products as potential small-molecule inhib- itors of human Aurora-B kinase.When tested in yeast models,2 compounds(one is Jado- mycin B)showed preferential inhibition of ipl1-321(yeast Aurora kinase temperature sen- sitive mutant)than wild type yeast cell,suggesting these compounds are true Aurora kinase inhibitors.Further in vitro biochemical assay using purified recombinant Aurora-B kinase showed Jadomycin B inhibits Aurora-B activity in a dose-dependent fashion while two Jadomycin congeners,Jadomycin S and T,showed no activity.The marked differences in activities of Jadomycins were explained by docking analyses.Our results also showed that Jadomycin B competes with ATP for the kinase active center,which is consistent with our docking prediction.Like other Aurora kinase inhibitors,Jadomycin B also reduced the phos- phorylation of histone H3 on Ser10 in vivo.Cell culture based tests of Jadomycin B activity confirmed previous results that Jadomycin B could induce apoptosis of tumor cells without blocking cell cycle.Above results indicate that Jadomyicn B is a new Aurora B kinase inhibi- tor worthy of further investigation.The SAR(structure and activity relationship)analysis in- dicated that groups attached to the oxazolone ring of Jadomycin were important for its ability to enter the catalytic cleft and occupy the active site to inhibit Aurora-B kinase.Jadomycin offers an ideal scaffold to generate novel derivatives with a hydrophobic side chain on their oxazolone rings,from which we may find Aurora-B inhibitors with improved activity. Aurora kinases are clearly implicated in tumorgenesis and have emerged as promising targets for cancer therapy in recent years. In a virtual screening attempt, 22 compounds were identified from nearly 15,000 microbial natural products as potential small-molecule inhib- itors of human Aurora-B kinase .When tested in yeast models, 2 compounds (one is Jado-mycin B) showed preferential inhibition of ipl1-321 (yeast Aurora kinase temperature sen-sitive mutant) than wild type yeast cell, suggesting these compounds are true Aurora kinase inhibitors. in vitro biochemical assay using purified recombinant Aurora-B kinase showed Jadomycin B inhibits Aurora-B activity in a dose-dependent fashion while two Jadomycin congeners, Jadomycin S and T, showed no activity. The marked differences in activities of Jadomycins were explained by docking analyses.Our results also showed that Jadomycin B competes with ATP for the kinase active center, which is consistent with our docking prediction. Like other Aurora kinase inhibitors, Jadomycin B also reduced the phos- phorylation of histone H3 on Ser10 in vivo. Cell culture based tests of Jadomycin B activity confirmed previous results that Jadomycin B could induce apoptosis of tumor cells without blocking cell cycle. Abbove results indicate that Jadomyicn B is a new Aurora B kinase inhibi- tor worthy of further investigation. SAR (structure and activity relationship) analysis in- dicated that groups attached to the oxazolone ring of Jadomycin were important for its ability to enter the catalytic cleft and occupy the active site to inhibit Aurora-B kinase. Jomyomycin offers an ideal scaffold to generate novel derivatives with a hydrophobic side chain on their oxazolone rings, from which we may find Aurora-B inhibitors with improved activity.