Siomycin is a macrocyclic antibiotic with potent and selective antibacterial activity discovered in 1969. Recently, siomycin was discovered to be a potent inhibitor of the oncogenic transcription factor-forkhead box M1, FoxM1 (previously known as HFH-11B, Trident, WIN or MPP2). The reduced transcription activity was reflected in the down regulation of protein and mRNA levels of FoxM1 and effects on down stream genes – Cdc25B, Survivin and CENPB. In vitro, siomycin was demonstrated to inhibit FoxM1 induced cell growth on soft agar and selectively kill transformed but not normal cells.
