In vitro activity: HO-3867 produces significant cytotoxicity in A2780 and other tested ovarian cancer cell lines, with less toxic to noncancerous ovarian surface epithelial cells. HO-3867 induces G(2)-M cell cycle arrest in A2780 cells and promotes apoptosis by caspase-8 and caspase-3 activation. HO-3867 blocks the JAK/STAT3 pathway in human ovarian cancer cell lines.

Kinase Assay: HO-3867 is a selective and potent STAT3 inhibitor and shows good antitumor activity.

Cell Assay: Cell viability is determined by a colorimetric assay using MTT. In the mitochondria of living cells, yellow MTT undergoes a reductive conversion to formazan, producing a purple color. Cells, grown to ~80% confluence in 75-mm flasks, are trypsinized, counted, seeded in 96-well plates with an average population of 7,000 cells/well, incubated overnight, and then treated with HO-3867 for 24 h. All experiments are done using 8 replicates and repeated at least three times.