In vitro activity: Piceatannol displays ~10-fold selectivity for Syk over Lyn. Piceatannol treatment in RBL-2H3 cells strongly inhibits the antigen-stimulated phosphorylation of Syk and of most other cellular proteins but not the receptor β or γ subunit, in a dose-dependent manner. Piceatannol is also a potent inhibitor of histamine release in mast cells. Selective inhibition of Syk by Piceatannol blocks receptor-mediated down-stream cellular responses in mast cells including prevention of 1,4,5-IP3 synthesis, secretion and membrane ruffling and spreading. Piceatannol also potently inhibits PKA, PKC, MLCK, and CDPK with IC50 of 3 μM, 8 μM, 12 μM, and 19 μM, respectively. Piceatannol selectively prevents the IFNα-induced tyrosine phosphorylation of STAT3 and -5 but not STAT1 and -2, paralleled by the loss of Jak1 and IFNAR1 tyrosine phosphorylation but not Tyk2 and IFNAR2. Piceatannol potently induces apoptotic cell death in BJAB Burkitt-like lymphoma cells with ED50 of 25 μM, through the activation of caspase-3 and mitochondrial permeability transition independent of the CD95/Fas signaling pathway.

Kinase Assay: Recombinant Syk is expressed in baculovirus-infected St9 cells. Assays of recombinant Syk activity are carried out using angiotensin I peptide as substrate. The enzyme activities of recombinant Syk are measured by phosphorylation of angiotensin I peptide in the presence of various concentrations of Piceatannol.

Cell Assay: Cells (LNCaP, DU145, and PC-3) are exposed to increasing concentrations of Piceatannol. For the determination of cell proliferation, cells are assayed at 72 hours by trypan blue exclusion using a hemocytometer. After 1 week, colonies are stained with 1.25% crystal violet and quantified by measuring the absorbance at 595 nm.