Combined Usage of MDK Inhibitor Augments Interferon-γ Anti-Tumor Activity in the SKOV3 Human Ovarian Cancer Cell Line

Ovarian cancer (OC) is a particularly lethal disease due to intratumoral heterogeneity, resistance to traditional chemotherapy, and poor response to targeted therapy and immunotherapy. Interferon-gamma (IFN-gamma) is an attractive therapeutic cytokine, with positive responses achieved in multiple OC clinical trials. However, clinical application of IFN-gamma in OC is still hindered, due to the severe toxicity when used at higher levels, as well as the considerable pro-metastatic adverse effect when used at lower levels. Thus, an effective combined intervention is needed to enhance the anti-tumor efficacy of IFN-gamma and to suppress the IFN-gamma-induced metastasis. Here, we uncovered that OC cells develop an adaptive strategy by upregulating midkine (MDK) to counteract the IFN-gamma-induced anti-tumor activity and to fuel IFN-gamma-induced metastasis. We showed that MDK is a critical downstream target of IFN-gamma in OC, and that this regulation acts in a dose-dependent manner and is mediated by STAT1. Gain-of-function studies showed that MDK overexpression promotes cell proliferation and metastasis in OC, indicating that IFN-gamma-activated MDK may antagonize IFN-gamma in inhibiting OC proliferation but synergize IFN-gamma in promoting OC metastasis. Subsequently, we assessed the influence of MDK inhibition on IFN-gamma-induced anti-proliferation and pro-metastasis effects using an MDK inhibitor (iMDK), and we found that MDK inhibition robustly enhanced IFN-gamma-induced growth inhibition (all CIs < 0.1) and reversed IFN-gamma-driven epithelial-to-mesenchymal transition (EMT) and metastasis in OC in vitro. Collectively, these data identify an IFN-gamma responsive protein, MDK, in counteracting anti-proliferation while endowing the pro-metastatic role of IFN-gamma in cancer treatment, and we therefore propose the combined utilization of the MDK inhibitor in IFN-gamma-based therapies in future OC treatment.