8-Epi-xanthatin induces the apoptosis of DU145 prostate carcinoma cells through signal transducer and activator of transcription 3 inhibition and reactive oxygen species generation

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in many human cancers. We tried to find STAT3 inhibitors from natural sources and found that Xanthium fruit extracts decreased phosphorylation of STAT3-Y705. 8-Epi-xanthatin (EXT) was isolated from the extracts. When DU145 cancer cells were treated with EXT, p-STAT3-Y705 was decreased with an IC50 of 3.2 mu M. EXT decreased the expression of STAT3 target genes, such as cyclin A, cyclin D1, and BCL-2, and induced PARP cleavage, indicating apoptotic cell death. Downregulation of EXT-induced p-STAT3-Y705 was rescued by pretreating DU145 cells with antioxidants, such as N-acetyl-L-cysteine (NAC), indicating that reactive oxygen species (ROS) were involved in the EXT-induced inhibition of STAT3 activation. Furthermore, we proved the association of EXT with STAT3 protein by using a drug affinity responsive target stability (DARTS) assay and a cellular thermal shift assay (CETSA). EXT inhibited proliferation of DU145 cells with a GI(50) of 6 mu M and reduced tumor growth in mice xenografted with DU145 cells. Immunoblotting showed that phosphorylation of STAT3-Y705 was lower in EXT-treated tumor tissue than in control tissues. Collectively, we found that EXT binds to, and inhibits, STAT3 activation and could be a lead compound for anticancer therapy.

Automated summary

STAT3 activation plays a crucial role in many human cancers. The compound 8-Epi-xanthatin (EXT) from Xanthium fruit inhibits STAT3 phosphorylation and induces apoptotic cell death in cancer cells. Antioxidants can reverse the EXT-induced suppression of STAT3 activation, indicating the involvement of reactive oxygen species (ROS) in this process.