S3I-201 (NSC74859) is a cell-permeable, amidosalicylic acid based small molecule that inhibits Stat3 activity with IC50 of 86 µM¹. S3I-201 binds to the Stat3-SH2 domain and prevents its dimerization, inhibiting stat3 phosphorylation, translocation and Stat3-dependent transcription activities. S31-201 preferentially inhibits growth and induces apoptosis in tumor cells that contain persistently activated stat3¹. In addition, S3I-201 has been shown to retard stat3-dependent tumor growth in human breast tumor xenograft models, and to impair VZV infection of skin xenografts in vivo^1,2,3.