Enhanced cisplatin resistance of ovarian cancer cells in three-dimensional (3D) culture system through activation of Notch1/HES1 signaling

Abstract

Ovarian cancer is a lethal malignancy among females worldwide. A combination treatment of surgery and chemotherapy has been adopted in clinical practice, however, many patients developed resistance to platinum based regimen even if they responded initially. Conventionally, in vitro studies on chemoresistance have been performed in 2D cell culture systems. Emerging evidence has pointed out the restrictions of 2D system due to its poor imitating in vivo environment with cell-cell and cell-extracellular matrix interactions. Therefore, 3D cell culture system, which recapitulates in vivo structures and reflects more closely the real gene expression pattern and drug responses, has become a reliable tool in cancer researches.

Previous studies reported that cancer cells cultured in the 3D system showed higher resistance to cisplatin, a common platinum agent, than cells cultured in the 2D system. In this study, cisplatin-resistance of two main subtypes of ovarian cancer, serous carcinoma and clear cell carcinoma, was found to be enhanced in the 3D system. Gene profiling analysis and q-PCR confirmed that HES1, a key downstream effector of Notch1 signaling with high association with cisplatinresistance and patient survival, was significantly up-regulated in ovarian cancer cells cultured in the 3D system. Notch1 was found to be activated in ovarian cancer cells cultured in the 3D culture system by Western Blot analysis. Inhibition of Notch1 signaling by γ-Secretase Inhibitor (GSI) and knockdown restored cisplatin induced cytotoxicity in ovarian cancer cells in both 2D and 3D systems, suggesting Notch1/HES1 signaling is activated and involved in cisplatin resistance of ovarian cancer cells in 3D system.

Previous studies have suggested that low-level of Reactive Oxygen Species (ROS) may increase chemoresistance. In this study, an accumulation of ROS was found in ovarian cancer cells in the 3D system. Consistently, phosphorylation of p38 MAPK, which was activated by ROS, was found to be increased in ovarian cancer cells cultured in the 3D system accompanying with an increased expression of Notch1. These results suggested that ROS might be involved in activation of Notch1 signaling through phosphorylation of p38 MAPK in ovarian cancer cells in 3D system.

Taken together, this study demonstrated that the aberrant activation of Notch1/HES1 signaling led to enhanced cisplatin resistance of ovarian cancers in 3D cell culture system and could be a putative target for treatment of ovarian cancers.