Blocking the JAG1-Notch1 signaling axis by either re-expression of miR-199b-5p, siRNA-mediated JAG1 knockdown or treatment with the Notch-specific inhibitor γ-secretase (GSI) dramatically abrogated tumor growth and enhance cisplatin-induced cytotoxicity in vitro and in vivo in ovarian cancer cells. The gene discussed is JAG1; the disease is ovarian cancer.