Guggulsterone and bexarotene induce secretion of exosome‐associated breast cancer resistance protein and reduce doxorubicin resistance in MDA‐MB‐231 cells |
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| Authors: | Ji Na Kong Qian He Guanghu Wang Somsankar Dasgupta Michael B. Dinkins Gu Zhu Austin Kim Stefka Spassieva Erhard Bieberich |
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| Affiliation: | 1. Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA;2. Saint James School of MedicineCane Hall, Saint Vincent and the Grenadines;3. Division of Hematology/Oncology, Department of Medicine, Medical University of South Carolina, Charleston, SC |
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| Abstract: | Many breast cancer cells acquire multidrug resistance (MDR) mediated by ABC transporters such as breast cancer resistance protein (BCRP/ABCG2). Here we show that incubation of human breast cancer MDA‐MB‐231 cells with farnesoid X receptor antagonist guggulsterone (gug) and retinoid X receptor agonist bexarotene (bex) elevated ceramide, a sphingolipid known to induce exosome secretion. The gug+bex combination reduced cellular levels of BCRP to 20% of control cells by inducing its association and secretion with exosomes. Exogenous C6 ceramide also induced secretion of BCRP‐associated exosomes, while siRNA‐mediated knockdown or GW4869‐mediated inhibition of neutral sphingomyelinase 2 (nSMase2), an enzyme generating ceramide, restored cellular BCRP. Immunocytochemistry showed that ceramide elevation and concurrent loss of cellular BCRP was prominent in Aldefluor‐labeled breast cancer stem‐like cells. These cells no longer excluded the BCRP substrate Hoechst 33342 and showed caspase activation and apoptosis induction. Consistent with reduced BCRP, ABC transporter assays showed that gug+bex increased doxorubicin retention and that the combination of gug+bex with doxorubicin enhanced cell death by more than fivefold. Taken together, our results suggest a novel mechanism by which ceramide induces BCRP secretion and reduces MDR, which may be useful as adjuvant drug treatment for sensitizing breast cancer cells and cancer stem cells to chemotherapy. |
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| Keywords: | doxorubicin nuclear receptors breast cancer resistance protein bile acid sphingolipids cancer stem cells multidrug resistance exosomes |
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