Inhibition of Ceramide Kinase Is Effective against Cisplatin-Resistant Ovarian Cancer Cells by Regulating Ceramide and C1P Levels

Chemoresistance in ovarian cancer results in treatment failure, yet underlying mechanisms that regulate chemoresistance remain largely unclear. There is emerging evidence relating ovarian cancer drug resistance with bioactive sphingolipids and regulation of sphingolipid metabolism. This work investigated the expression and function of ceramide kinase (CerK), a lipid kinase that regulates central bioactive sphingolipids, in ovarian cancer, as well as the therapeutic potential of targeting CERK.The levels of ceramide, ceramide 1-phosphate (C1P), and Cerk in ovarian cancer and normal counterparts were measured. Functions of Cerk in ovarian cancer were examined.Immunohistochemistry, ELISA, and mass spectrometry methods were used to measure the level of ceramides, C1P, and CerK in primary tissues. Proliferation and apoptosis assays were performed in ovarian cancer cells after CERK depletion, CERK overexpression, and NVP-231 treatment in the absence or presence of cisplatin.Compared to normal ovarian cells, CerK and its mediating bioactive sphingolipids ceramide and C1P were decreased in ovarian cancer tissues. Interestingly, cisplatin-resistant ovarian cancer cells displayed increased CerK, decreased ceramide, and increased C1P, and furthermore, that CerK level was closely associated with ceramide and C1P levels in ovarian cancer cells. Functional analysis demonstrated that CerK overexpression was sufficient to promote growth and confer chemoresistance in ovarian cancer cells. CerK inhibition via both genetic and pharmacological approaches suppressed growth and induced apoptosis in cisplatin-resistant cells, and furthermore, this significantly augmented cisplatin's efficacy.The functional analysis of C1P was performed on in vitro ovarian cancer cells. In vivo studies were needed to further confirm the effects of CERK inhibition.Our work is the first to show the critical role of CerK as the underlying mechanism of ovarian cancer chemoresistance, through regulating ceramide and C1P.