Novel 2-Carbonylbenzo[b]thiophene 1,1-Dioxide Derivatives as Potent Inhibitors of STAT3 Signaling Pathway.

Signal transducer and activator of transcription 3 (STAT3) is considered to be an attractive therapeutic target for cancer therapy. In this study, a series of 2-carbonylbenzo[b]thiophene 1,1-dioxide derivatives (CBT) were designed to inhibit the STAT3 SH2 domain phosphorylation site Try 705. We demonstrated that incorporation of basic flexible groups through amide bond linkage to benzo[b]thiophene 1,1-dioxide (BTP) achieved compounds with higher antiproliferative potency than BTP itself. The most potent compound 6o, as indicated from luciferase reporter gene assay, inhibited the STAT3 pathway by decreasing the phosphorylation level of STAT3 Tyr705, while the phosphorylation level of other upstream tyrosine kinases in this pathway was not significantly inhibited. Compound 6o was also shown to trigger ROS generation and accumulation, thus consequently attributed partially to the observed cell apoptosis. This study provided important structural information for the development of inhibitors targeting the STAT3 pathway.