Ginkgetin inhibits the growth of DU-145 prostate cancer cells through inhibition of signal transducer and activator of transcription 3 activity.

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in human cancers. Therefore, STAT3 is a therapeutic target of cancer drug discovery. We previously reported that natural products inhibited constitutively activated STAT3 in human prostate tumor cells. We used a dual-luciferase assay to screen 200 natural products isolated from herbal medicines and we identified ginkgetin obtained from the leaves of Ginkgo biloba L. as a STAT3 inhibitor. Ginkgetin inhibited both inducible and constitutively activated STAT3 and blocked the nuclear translocation of p-STAT3 in DU-145 prostate cancer cells. Furthermore, ginkgetin selectively inhibited the growth of prostate tumor cells stimulated with activated STAT3. Ginkgetin induced STAT3 dephosphorylation at Try705 and inhibited its localization to the nucleus, leading to the inhibition of expression of STAT3 target genes such as cell survival-related genes (cyclin D1 and survivin) and anti-apoptotic proteins (Bcl-2 and Bcl-xL). Therefore, ginkgetin inhibited the growth of STAT3-activated tumor cells. We also found that ginkgetin inhibited tumor growth in xenografted nude mice and downregulated p-STAT3(Tyr705) and survivin in tumor tissues. This is the first report that ginkgetin exerts antitumor activity by inhibiting STAT3. Therefore, ginkgetin is a good STAT3 inhibitor and may be a useful lead molecule for development of a therapeutic STAT3 inhibitor.

Artocarpus altilis (Parkinson) Fosberg Extracts and Geranyl Dihydrochalcone Inhibit STAT3 Activity in Prostate Cancer DU145 Cells.

Artocarpus altilis (Parkinson) Fosberg has traditionally been used in Indonesia for the treatment of liver cirrhosis, hypertension, and diabetes. In many other countries, it is used for the treatment of malaria, yellow fever, and dengue fever. It has been reported that A. altilis extracts have antiatherosclerotic and cytoprotective effects, but its molecular targets in tumor cells are not yet fully understood. The A. altilis extracts and the partially purified fraction have been shown to inhibit STAT3 activity and the phosphorylation of STAT3 in a dose-dependent manner. To identify the active components, a bioassay-guided isolation of the partially purified fraction resulted in the identification of a geranyl dihydrochalcone, CG901. Its chemical structure was established on the basis of spectroscopic evidence and comparison with published data. The partially purified fraction and the isolated a geranyl dihydrochalcone, CG901, down-regulated the expression of STAT3 target genes, induced apoptosis in DU145 prostate cancer cells via caspase-3 and PARP degradation, and inhibited tumor growth in human prostate tumor (DU145) xenograft initiation model. These results suggest that A. altilis could be a good natural source and that the isolated compound will be a potential lead molecule for developing novel therapeutics against STAT3-related diseases, including cancer and inflammation.

Geranylnaringenin (CG902) inhibits constitutive and inducible STAT3 activation through the activation of SHP-2 tyrosine phosphatase.

The roles and significance of signal transducer and activator of transcription 3 (STAT3) in human cancers have been extensively studied and STAT3 is a promising therapeutic target for cancer drug discovery. During the screening of natural products to identify STAT3 inhibitors, we identified geranylnaringenin (CG902), which decreased luciferase activity in a dose-dependent manner. CG902 specifically inhibited STAT3 phosphorylation at Tyr-705 in DU145 prostate cancer cells and decreased the expression levels of STAT3 target genes, such as cyclin D1, cyclin A, and survivin. Notably, the knockdown of the SHP-2 gene by small interfering RNA suppressed the ability of CG902 to inhibit STAT3 activation and CG902 activated the phosphatase activity of SHP-2 through direct interaction with SHP-2 and induced the phosphorylation of SHP-2. The interactions between CG902 and SHP-2 were confirmed by pull-down assay using biotinylated CG902. The interactions were also further validated by the drug affinity responsive target stability (DARTS) and cellular thermal shift assay (CETSA). The inhibitory effect of CG902 on cell growth was confirmed using the DU145 mouse xenograft model. We propose that CG902 inhibits STAT3 activity through a mechanism that involves the interactions between CG902 and SHP-2, and the phosphorylation of SHP-2, which leads to SHP-2 activation in DU145 cells. CG902 is the first compound to regulate STAT3 activity via the modulation of SHP-2 activity, and our results suggest that CG902 is a novel inhibitor of the STAT3 pathway and an activator of SHP-2, and may be a useful lead molecule for the development of a therapeutic STAT3 inhibitor.

Antiobesity Effects of Salvia plebeia R. Br. Extract in High-Fat Diet-Induced Obese Mice.

This study was designed to investigate the antiobesity effects of Salvia plebeia R. Br. ethanolic extracts (SPE) in mice fed high-fat diets (HFD). Male C57BL/6J mice were randomly assigned to four groups: normal diet (Chow), high-fat diet (HFD, 45% fat), HFD+SPE 200 (200 mg/kg b.w.), and HFD+SPE 400 (400 mg/kg b.w.). Extracts were administered orally every day for 8 weeks. Increases in body/fat weight and feed efficiency ratio were monitored in all mice. In addition, obesity resulting from feeding HFD to the mice was confirmed by the increase of glucose level, aspartate transaminase, alanine transaminase, triglyceride (TG), high-density lipoprotein cholesterol, very low-density lipoprotein-c, leptin, and adiponectin in blood. The SPE-treated mice gained less body and mesenteric/subcutaneous adipose tissues weights and had lower TG, very low-density lipoprotein cholesterol, leptin, and glucose level in serum, compared to the HFD group. Moreover, histopathological examinations revealed that the size of adipocytes in liver and adipose tissue was significantly decreased by SPE, compared to the HFD group. The expression of adipogenesis transcription factors (e.g., peroxisome proliferator activated receptor γ and CCAAT/enhancer binding protein α) and lipogenesis-related target genes (adipocyte fatty acid-binding protein 2, lipoprotein lipase, fatty acid synthase, and sterol regulatory element-binding transcription factor 1c) in HFD-induced obese mice was decreased by SPE treatment. These results suggest that SPE attenuates the fat accumulation in HFD-induced obese mice by suppressing the expressions of genes related to adipogenesis and lipogenesis activity. Therefore, SPE could be developed as a potential therapy for reduction of body weight and antiobesity intervention.

Sugiol inhibits STAT3 activity via regulation of transketolase and ROS-mediated ERK activation in DU145 prostate carcinoma cells.

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in various human cancers and has been used as a therapeutic target for tumors. This study screened natural products to identify compounds that inhibit STAT3 activity using a STAT3-dependent luciferase reporter system. Sugiol was identified as a compound that decreased luciferase activity in a dose-dependent manner. Sugiol specifically inhibited STAT3 phosphorylation at Tyr-705 in DU145 prostate cells, and this inhibition was independent of the STAT3 upstream kinase. Sugiol induced cell cycle arrest and decreased the expression levels of STAT3 target genes, such as cyclin D1, cyclin A, and survivin. Notably, we observed that sugiol interacted with transketolase, an enzyme in central metabolism, and increased ROS levels leading to the activation of ERK, which inhibits STAT3 activity. The protein phosphatase MEG2 was also responsible for sugiol-induced STAT3 dephosphorylation. The inhibitory effect of sugiol on cell growth was confirmed using the DU145 mouse xenograft model. We propose that sugiol inhibits STAT3 activity through a mechanism that involves the inhibition of transketolase, which leads to increased ROS levels and MEG2 activation in DU145 cells. Therefore, sugiol is the first compound regulating STAT3 activity via modulation of cancer metabolic pathway and we suggest the use of sugiol as an inhibitor of the STAT3 pathway for the treatment of human solid tumors with activated STAT3.