Abstract B095: Tackling chemotherapy resistance of cancer cells: Inhibition of diacylglycerol O-acyltransferase 2 increases ceramide and cancer cell apoptosis
Authors: Raquib Rideeta , Hernández-Corbacho Maria J. , Obeid Lina M. 
Published: September 2020

Abstract
Cellular stress induced by chemotherapy results in the activation of cell death pathways. The efficacy of chemotherapy can be hindered by the upregulation of proteins that inhibit pro-apoptotic effectors. Ceramide sits at the center of the sphingolipid pathway and Obeid et al demonstrated that exogenous treatment of ceramide induced apoptosis in leukemic cells, whereas cell stressors increase endogenous ceramide levels upstream of caspase activation. The enzyme, diacylglycerol O-acyltransferase 2 (DGAT2), can cause O-acylation of ceramide to 1-O-acylceramide, which is then accumulated in lipid droplets and does not have pro-cell death function. Senkal et al. illustrated that the conversion of ceramide to 1-O-acylceramide causes HCT-116 colon cancer cells to become resistant to chemotherapy 5-fluorouracil (5-FU). Knockdown of the DGAT2 gene showed increased levels of ceramide, decreased levels of 1-O-acylceramides, and sensitized cancer cells to 5FU indicated by a higher caspase 3/7 activation in knockdown cells treated with 5FU than control. Mouse models were employed to demonstrate that a four-week oleate high-fat diet resulted in greater lipid droplet formation and accumulation of acylceramide in the liver versus a control diet, as detected by light chromatography and mass spectrometry (LC-MS). These data demonstrate that the conversion of ceramide to 1-O-acylceramide might act as a survival mechanism and promote chemotherapy resistance and that diet upregulates this process. Thus, we hypothesize that utilizing the commercially available DGAT2 inhibitor (PF-06424439) can increase ceramide in cancer cell lines, hence increase cell death. Treatments of various cancer cell lines, such as MDA-MB-231, MCF-7, and PC3 cells with a chemotherapeutic (cisplatin, doxorubicin, or paclitaxel) were administered alone or paired with PF-06424439 for various time points. Cell viability was quantified via an MTT assay. Oxidoreductase enzymes reduce the MTT dye to insoluble formazan, which exhibits a purple color and represents the reductive activity present in the mitochondria of living cells. Cell death was quantified via lactate dehydrogenase (LDH) release from damaged cells. Greater cell death was observed when both chemotherapy and PF-06424439 were administered in combination versus chemotherapy alone. Ceramide levels were quantified with LC-MS and greater ceramide levels were seen in the combination treatment, hence affirming that ceramide may have a role in mediating cell death. The physiological implications of the combination treatment and factors such as diet will be evaluated via in vivo models in future studies.
Citation Format: Rideeta Raquib, Maria J. Hernández-Corbacho, Lina M. Obeid. Tackling chemotherapy resistance of cancer cells: Inhibition of diacylglycerol O-acyltransferase 2 increases ceramide and cancer cell apoptosis [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr B095.