title: Role of P-glycoprotein inhibitors in ceramide-based therapeutics for treatment of cancer.
abstract: The anticancer properties of ceramide, a sphingolipid with potent tumor-suppressor properties, can be dampened via glycosylation, notably in multidrug resistance wherein ceramide glycosylation is characteristically elevated. Earlier works using the ceramide analog, C6-ceramide, demonstrated that the antiestrogen tamoxifen, a first generation P-glycoprotein (P-gp) inhibitor, blocked C6-ceramide glycosylation and magnified apoptotic responses. The present investigation was undertaken with the goal of discovering non-anti-estrogenic alternatives to tamoxifen that could be employed as adjuvants for improving the efficacy of ceramide-centric therapeutics in treatment of cancer. Herein we demonstrate that the tamoxifen metabolites, desmethyltamoxifen and didesmethyltamoxifen, and specific, high-affinity P-gp inhibitors, tariquidar and zosuquidar, synergistically enhanced C6-ceramide cytotoxicity in multidrug resistant HL-60/VCR acute myelogenous leukemia (AML) cells, whereas the selective estrogen receptor antagonist, fulvestrant, was ineffective. Active C6-ceramide-adjuvant combinations elicited mitochondrial ROS production and cytochrome c release, and induced apoptosis. Cytotoxicity was mitigated by introduction of antioxidant. Effective adjuvants markedly inhibited C6-ceramide glycosylation as well as conversion to sphingomyelin. Active regimens were also effective in KG-1a cells, a leukemia stem cell-like line, and in LoVo human colorectal cancer cells, a solid tumor model. In summary, our work details discovery of the link between P-gp inhibitors and the regulation and potentiation of ceramide metabolism in a pro-apoptotic direction in cancer cells. Given the active properties of these adjuvants in synergizing with C6-ceramide, independent of drug resistance status, stemness, or cancer type, our results suggest that the C6-ceramide-containing regimens could provide alternative, promising therapeutic direction, in addition to finding novel, off-label applications for P-gp inhibitors.
authors.affiliation: Department of Biochemistry and Molecular Biology, East Carolina University, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, Greenville, NC, United States; Department of Pharmacology, Faculty of Veterinary Medicine, South Valley University, Qena, Egypt.
authors.forename: Samy A F
authors.initials: SAF
authors.lastname: Morad
authors.affiliation: Department of Biochemistry and Molecular Biology, East Carolina University, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, Greenville, NC, United States.
authors.forename: Traci S
authors.initials: TS
authors.lastname: Davis
authors.affiliation: Department of Biochemistry and Molecular Biology, East Carolina University, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, Greenville, NC, United States.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: MacDougall
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA, United States.
authors.forename: Su-Fern
authors.initials: SF
authors.lastname: Tan
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA, United States; University of Virginia Cancer Center, University of Virginia, Charlottesville, VA, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Feith
authors.affiliation: Penn State University College of Medicine, Department of Pharmacology, University Drive, Hershey, PA, United States.
authors.forename: Dhimant H
authors.initials: DH
authors.lastname: Desai
authors.affiliation: Penn State University College of Medicine, Department of Pharmacology, University Drive, Hershey, PA, United States.
authors.forename: Shantu G
authors.initials: SG
authors.lastname: Amin
authors.affiliation: University of Virginia Cancer Center, University of Virginia, Charlottesville, VA, United States.
authors.forename: Mark
authors.initials: M
authors.lastname: Kester
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA, United States; University of Virginia Cancer Center, University of Virginia, Charlottesville, VA, United States.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Loughran
authors.affiliation: Department of Biochemistry and Molecular Biology, East Carolina University, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, Greenville, NC, United States. Electronic address: cabotm@ecu.edu.
authors.forename: Myles C
authors.initials: MC
authors.lastname: Cabot
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000970:Antineoplastic Agents / Q000737:chemistry / Q000627:therapeutic use*; D002518:Ceramides / Q000737:chemistry / Q000627:therapeutic use*; D018922:HL-60 Cells; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002518:Ceramides
keywords: C6-ceramide (CID: 5702613); Ceramide; Colon cancer; Cyclosporin A (CID: 5284373); Didesmethyltamoxifen (CID: 3036172); Fulvestrant (CID: 104741); Leukemia; N-Desmethyl tamoxifen-HCl (CID: 24200434); P-glycoprotein inhibitors; Sphingolipid metabolism; Tamoxifen-HCl (CID: 2733526); Tariquidar (CID: 148201); Verapamil-HCl (CID: 62969); Zosuquidar-3HCl (CID: 153997)