Inhibitor of the STAT3 signaling pathway; inhibits the activation, nuclear translocation and transactivation of STAT3. Displays selectivity for STAT3 over STAT1, STAT5, JAK1, JAK2 and Src kinases. Inhibits the transcription of STAT3 target genes and induces cell growth inhibition, apoptosis and cell cycle arrest of cancer cells with constitutively active STAT3. Also reversibly inhibits mTORC1 signaling and stimulates autophagy in vitro; displays antineoplastic effects in acute myelogenous leukemia (AML) stem cells.