CYD0618 specifically suppresses the activation of STAT3.
A, HEK293T/STAT3-luciferase reporter cells were pre-treated with CYD0618 or CYD–NC at the indicated concentrations for 2 h. The luciferase activity was then assessed following stimulation with IL-6 (50 ng/ml) for 4 h. B and C, CYD0618 depresses the constitutive activation of STAT3. A2780 and OVCAR8 cells were treated with the indicated concentrations of CYD0618 for 24 h (B) or treated with CYD0618 for the indicated times (C). Whole-cell extracts were processed for Western blot analysis with the indicated antibodies. D, CYD0618 represses the inducible activation of STAT3. A2780 cells were pre-treated with CYD0618 at the indicated concentrations for 2 h, followed by stimulation with IL-6 (10 ng/ml), EGF (20 ng/ml), and IFN-γ (20 ng/ml) for 15 min. Whole-cell lysates from treated cells were measured by Western blotting using the antibodies as indicated. E, CYD0618 inhibits the constitutive activation of STAT3 in paclitaxel-resistant ovarian cancer cells (A2780/T) and other gynecological tumor cell lines (HeLa, MDA-MB-231, and MDA-MB-468). F and G, SRB staining assay showed that CYD0618 suppresses the growth of A2780/T, HeLa, MDA-MB-231, and MDA-MB-468 cells in vitro. Data are expressed as mean ± S.D., n = 3–6. *, p < 0.05; **, p < 0.01; and ***, p < 0.001 versus vehicle control.