Background The entire Hypericum japonicum selleck chem MG132 herb, named Tianji huang, is widely used for the treatment of infectious hepatitis, acute and chronic hepatitis, and tumour in China. An 85% ethanol treated water extract is docu mented in the Chinese Pharmacopoeia as an injection for the treatment of viral hepatitis. Moreover, H. japonicum is used as an animal feed in China because of its widespread growth. These records demonstrate the clinical safety of H. japonicum. However, the molecular mechanisms of its effects are unclear. To better understand the mechanisms of H. japonicum, its chemical composition was systematically isolated and analysed in our previous study. In this study, we identified jacarelhyperol A, a characteristic constituent of H.

japonicum, as a potent in hibitor of Bcl 2 proteins via high throughput screening of an in house natural product library. The Bcl 2 family of proteins play an important role in apoptosis through the balance of antiapoptotic proteins and proapoptotic proteins. The ability of antiapoptotic pro teins to form heterodimers with a number of proapoptotic proteins is believed to play a crucial role in their antiapop totic function. Antiapoptotic Bcl 2 proteins are overex pressed in a variety of tumours, which can protect cancer cells from apoptosis. Owing to their important func tions in regulating cell death, the pharmacological inhib ition of Bcl 2 proteins is a promising strategy for apoptosis induction or sensitisation to chemotherapy. Protein se quence analysis and structure function studies revealed that the BH3 domain of proapoptotic proteins is the fundamen tal motif for the dimerisation with antiapoptotic proteins.

The three dimensional structure of a complex of Bcl xL and the Bak BH3 domain peptide showed that the Bak pep tide is an amphipathic helix that binds to a hydrophobic groove on the surface of Bcl xL. Based on these studies, screening new ligands that bind to the same pocket became an anti cancer drug discovery strategy to search for antia poptotic protein inhibitors. To screen for Bcl 2 protein inhibitors, we used fluorescence polarisation, whose basic principle is that a fluorescent peptide tracer and a nonfluorescent small molecule inhibitor com pete for binding to the Bid BH3 domain of Bcl 2 proteins. Jac A was chosen as the candidate compound for further research because of its high affinity with Bcl 2 proteins and favorable binding mode with Bcl xL.

Then, we tested its anti cancer activity in vitro and in vivo. Jac A possesses a broad antitumour effect for all tested cancer cells and re markably inhibited the proliferation of leukaemia cells. Moreover, Jac A not only induced K562 cell apoptosis in vitro, but also inhibited human K562 cell growth in a mouse xenograph Anacetrapib tumour model, which provided evidence for using H. japonicum as an anti cancer herbal medicine.