Identification of a non-phosphorylated, cell permeable, small molecule ligand for the Stat3 SH2 domain
Signal transducer and activator of transcription 3 (Stat3) protein is a cytosolic transcription factor that is aberrantly activated in numerous human cancers. Inhibitors of activated Stat3–Stat3 protein complexes have been shown to hold therapeutic promise for the treatment of human cancers harboring activated Stat3. Herein, we report the design and synthesis of a focused library of salicylic acid containing Stat3 SH2 domain binders. The most potent inhibitor, 17o, effectively disrupted Stat3–phosphopeptide complexes (Ki = 13 Î¼M), inhibited Stat3–Stat3 protein interactions (IC50 = 19 Î¼M) and silenced intracellular Stat3 phosphorylation and Stat3-target gene expression profiles. Inhibition of Stat3 function in both breast and multiple myeloma (MM) tumor cells correlated with induced cell death (EC50 = 10 and 16 Î¼M, respectively).