title: Antiproliferative and proapoptotic effects of topotecan in combination with thymoquinone on acute myelogenous leukemia.
abstract: BACKGROUND
  Topotecan has shown promising antineoplastic activity in solid tumors and acute leukemia. Because of the primary dose-limiting toxicity of topotecan, it is necessary to identify other agents that can work synergistically with topotecan, potentially increasing its efficacy while limiting its toxicity. Many studies showed synergism in combination of topotecan with gemcitabine and bortezomib. Other studies report the increase in growth inhibition of gemcitabine or oxaliplatin when cells were preexposed to naturally occurring drugs such as thymoquinone. The aim of this project was to study the mode of action of topotecan along with thymoquinone, on survival and apoptosis pathways in acute myelogenous leukemia (AML) cell lines, and to investigate the potential synergistic effect of thymoquinone on topotecan.
  
  
  METHODS
  U937 cells were incubated with different topotecan and thymoquinone concentrations for 24 and 48 hours, separately and in combination. Cell proliferation was determined using WST-1 (Roche) reagent. The effect of the compounds on protein expression of Bax, Bcl2, p53, caspase-9, -8, and -3 was determined using Western blot analysis. Cell cycle analysis was performed in addition to annexin/propidium iodide staining.
  
  
  RESULTS
  Thymoquinone and topotecan exhibited antiproliferative effects on U937 cells when applied separately. In combination, the reduction in proliferation was extremely significant with a major increase in the expression levels of Bax/Bcl2, p53, and caspase-3 and -9. Preexposure with thymoquinone resulted in an increase in cell growth inhibition compared with topotecan treatment.
  
  
  CONCLUSIONS
  Thymoquinone, when combined with topotecan in noncytotoxic doses, produced synergistic antiproliferative and proapoptotic effects in AML cells. Preexposure to thymoquinone seems to be more effective than simultaneous application with topotecan.
authors.affiliation: Department of Natural Sciences, Lebanese American University of Beirut, Beirut, Lebanon.
authors.forename: Rana
authors.initials: R
authors.lastname: Khalife
authors.forename: Stephany
authors.initials: S
authors.lastname: El-Hayek
authors.affiliation: Department of Natural Sciences, Lebanese American University of Beirut, Beirut, Lebanon.
authors.forename: El-Hayek
authors.initials: el-H
authors.lastname: Stephany
authors.affiliation: Department of Natural Sciences, Lebanese American University of Beirut, Beirut, Lebanon.
authors.forename: Omayr
authors.initials: O
authors.lastname: Tarras
authors.affiliation: Department of Natural Sciences, Lebanese American University of Beirut, Beirut, Lebanon.
authors.forename: Mohammad Hassan
authors.initials: MH
authors.lastname: Hodroj
authors.affiliation: Department of Natural Sciences, Lebanese American University of Beirut, Beirut, Lebanon. Electronic address: Sandra.rizk@lau.edu.lb.
authors.forename: Sandra
authors.initials: S
authors.lastname: Rizk
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D016227:Benzoquinones / Q000494:pharmacology*; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology; D019772:Topotecan / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D016227:Benzoquinones; D059004:Topoisomerase I Inhibitors; D019772:Topotecan; C003466:thymoquinone
keywords: AML; Anticancer; Apoptosis; Combined therapy; p53