Niclosamide is a salicylanilide compound with antihelminthic actions. It specifically inhibits the signal transducer and activator of transcription 3 (STAT3) with an IC50 value of 0.25 μM. It does not decrease the level or activity of the related STAT1, STAT5, JAK, or Src kinases. Through its effects on STAT3, niclosamide inhibits the proliferation and colony formation of Du145 prostate cancer cells, which have constitutively active STAT3, with IC50 values of 0.7 and 0.1 μM, respectively.
