title: Combination treatment of malignant B cells using the anti-CD20 antibody rituximab and the anti-malarial artesunate.
abstract: Chemotherapy of non-Hodgkin's lymphoma is frequently hampered by drug resistance. The monoclonal antibody rituximab specifically targets the CD20 antigen and sensitizes B-cell lymphoma cells to standard anticancer drugs. In the present investigation, we analyzed, whether a combination of rituximab and artesunate may act in a complementary manner and eventually synergize in tumor cell killing. Artesunate is an anti-malarial drug, which also exerts profound activity towards cancer cells. While rituximab alone was minimally cytotoxic, rituximab increased cytotoxicity to artesunate in Ramos cells. Artesunate induced apoptosis, induced Fas/CD95 expression and the formation of reactive oxygen species (ROS) and resulted in a breakdown of mitochondrial membrane potential. This argues for the involvement of both receptor-driven extrinsic and mitochondrial intrinsic routes of apoptosis. Rituximab increased Fas/CD95 expression and ROS formation and decreased mitochondrial membrane potential ultimately leading to increased apoptosis induced by artesunate. The transcription factors YY1 and Sp1 are upstream regulators of apoptosis by controlling the expression of apoptosis-regulating genes. YY1 and Sp1 were down-regulated and Fas/CD95 was up-regulated by rituximab and artesunate indicating that artesunate activated the Fas/CD95 pathway and that rituximab increased the susceptibility of tumor cells to artesunate-induced apoptosis. Furthermore, rituximab affected the expression of antioxidant genes. The antibody decreased artesunate-induced up-regulation of catalase expression and increased artesunate-induced down-regulation of glutathione S-transferase-phi expression. Manganese-dependent superoxide dismutase expression was not changed by artesunate. Antioxidant proteins may help to detoxify artesunate-induced ROS. Rituximab reversed the artesunate-induced expression changes of antioxidant genes and, hence, reduced the detoxification capacity of Ramos cells. The effects of rituximab on antioxidant genes represent a novel mechanism of rituximab for chemosensitization.
authors.affiliation: German Cancer Research Center, Pharmaceutical Biology (C015), D-69120 Heidelberg, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Sieber
authors.forename: Georg
authors.initials: G
authors.lastname: Gdynia
authors.forename: Wilfried
authors.initials: W
authors.lastname: Roth
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bonavida
authors.forename: Thomas
authors.initials: T
authors.lastname: Efferth
mesh_terms: D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000276:immunology*; D000962:Antimalarials / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D037621:Artemisinins / Q000008:administration & dosage; D000077332:Artesunate; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D051549:Glutathione S-Transferase pi / Q000378:metabolism; D006801:Humans; D016393:Lymphoma, B-Cell / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D000069283:Rituximab; D016329:Sp1 Transcription Factor / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D050986:YY1 Transcription Factor / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000962:Antimalarials; D037621:Artemisinins; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C491901:FAS protein, human; D017382:Reactive Oxygen Species; D016329:Sp1 Transcription Factor; D050986:YY1 Transcription Factor; C494698:YY1 protein, human; D019014:fas Receptor; D000069283:Rituximab; D000077332:Artesunate; D002374:Catalase; D013482:Superoxide Dismutase; D051549:Glutathione S-Transferase pi