Purity >98%. STA-21 is a natural antibiotic that potently inhibits STAT3 by preventing its dimerization and DNA binding when used at concentrations of 20-30 μM. It blocks the growth and survival of cancer cells that express constitutively active STAT3 (e.g., DU145 cells, IC50 = 12.2 μM). STAT3 inhibitors, including STA-21, prevent the proliferation of human keratinocytes and have value in improving psoriasis.