Screening and biological evaluation of a novel STAT3 signaling pathway inhibitor against cancer

It is now established that the specificity in signaling of signal transducer and activator of transcription 3 (STAT3) is mediated by the SH2 domain of STAT3, which mediates its interaction with the phosphopeptide docking sites displayed by receptors and JAKs, dimerization and subsequent DNA binding. Thus, we aimed to identify and design a class of strong potential small molecular inhibitors of STAT3 for the discovery and development of novel anticancer agents. Several classes of small molecules have been identified as STAT3 inhibitors after structure-based screening of the STAT3 SH2 domain. Next, we detected the activity of these inhibitors using fluorescence polarization (FP) and identified the growth inhibition of DU145 and MDA-MB-468 cells using the CCK-8 assay. Consequently, B9 inhibits the proliferation of tumor cells harboring abnormal activation of STAT3, such as, MDA-MB-468, MDA-MB-231 and DU145. However, there is little inhibition of MCF-7 cells. In addition, The Kd of B9 to STAT3 (I634S/Q635G) is 22.75 μM compared to 4.59 μM for WT as analyzed by SPR. The phosphorylation of STAT3 in MDA-MB-468 cells was obviously decreased after treatment with B9 at the preconceived concentration of 30 μM, as detected using immunoblotting. Here, we evaluated the effect of B9 on the migration of MDA-MB-468 cells. Taken together, our results indicate a novel small molecule that decreases STAT3 activation and function of the STAT3 signaling pathway, thereby inducing an antitumor response in human breast cancer cells harboring constitutively active STAT3.