Siomycin is a macrocyclic thiopeptide antibiotic with potent and selective antibacterial activity first isolated from the fermentation product of Streptomyces sioyaensis by Nishimura in 1959. This member of the thiostrepton family is a potent inhibitor of the oncogenic transcription factor, FoxM1. In vitro, siomycin inhibits FoxM1-induced cell growth on soft agar and selectively kills transformed cells. Siomycin has anti-cancer properties.
Siomycin is soluble in DMF and DMSO.