Fostriecin (free base) is an inhibitor of the serine/threonine protein phosphatases 2A (PP2A) and 4 (PP4) (IC50s = 3.2 and 3 nM, respectively). It less effectively inhibits topoisomerase II and PP1 (IC50s = 40 and 131 microM, respectively) and does not inhibit PP2B. Through its effects on protein phosphatases, fostriecin increases the level of histone H3 phosphorylation and may alter epigenetic regulation of cell proliferation. On a related note, fostriecin was first identified as an antitumor antibiotic.
