Selective inhibitor of STAT3/JAK2 signaling. Inhibits the activation of STAT3 and JAK2 and displays no activity on Src, Akt, ERK and JNK. Suppresses phosphotyrosine levels of STAT3, inhibits STAT3 DNA binding and STAT3-mediated gene expression. Induces apoptosis in cell lines expressing constitutively active tyrosine-phosphorylated STAT3.