Purity >95%. The mammalian transcription factor forkhead box M1 (FoxM1) is induced during G1 phase, with expression continuing through S phase and mitosis. Siomycin A is a peptide thiazole antibiotic, first isolated from S. sioyaensis, that interacts with the 23S rRNA of bacteria. It inhibits FoxM1 (IC50 = ~5 μM), preventing the expression of FoxM1-regulated genes, which includes FoxM1 itself. Through this mechanism, siomycin A prevents proliferation and induces apoptosis in certain types of stem cells as well as cancer cells.