Purity >95%. Rubratoxin A is a natural mycotoxin and competitive inhibitor of protein phosphatase 2A (PP2A; IC50 = 170 nM). It has no significant effect on several other phosphatases, including PP1, PP2B, and protein tyrosine phosphatase 1B. Rubratoxin A drives overphosphorylation of PP2A substrate proteins in cultured cells treated for three hours at 20 μM. It causes suppression of tumor metastasis and reduction of primary tumor volume in mouse xenografts.