title: The effect of quercetin on topotecan cytotoxicity in MCF-7 and MDA-MB 231 human breast cancer cells.
abstract: BACKGROUND
  Topotecan, which is a Camptothecin derivative, shows a large spectrum in anti-tumor activity. Topotecan exerts its cytotoxic effect on tumor cells mainly by inhibition of topoisomerase I activity resulting in double-strand DNA breaks. In our study, we investigated the combined cytotoxic action of Topotecan and Quercetin in MCF-7 and MDA-MB 231 human breast cancer cells. To examine the possible relation between the cytotoxic activity of Topotecan and oxidative stress, we measured ROS and nitrite levels in both human breast cell lines.
  
  
  METHODS
  MCF-7 and MDA-MB 231 cells were exposed to Topotecan, Quercetin, or a combination of both agents for 24 h at 37 degrees C. The viability of the cells was measured using the colorimetric MTT (3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. We determined reactive oxygen species and nitrite levels as indicators of oxidative stress in both cell lines with and without Topotecan and/or Quercetin incubations using fluorometric dichlorofluorescin diacetate (DCFH-DA) and diaminonaphtalene (DAN) assay.
  
  
  RESULTS
  The IC(50) concentration of Topotecan was 100 ng/ml in MCF-7 cell line and 160 ng/ml in MDA-MB231 cell line. Treatment with Quercetin enhanced cytotoxicity of Topotecan as 1.4-fold in MCF-7 and 1.3-fold in MDA-MB-231 cell line. A significant increment on ROS and nitrite levels was found in MCF-7 and MDA-MB-231 cells following Topotecan incubation.
  
  
  CONCLUSIONS
  Our results suggest that Topotecan has cytotoxic activity against both of the breast cancer cell lines in vitro. A combination with Quercetin increases efficacy of Topotecan in the treatment of breast cancers. Our results indicate that increased oxidative stress plays a role in the cytotoxic action of Topotecan.
authors.affiliation: Department of Biochemistry, Akdeniz University, Faculty of Medicine, Antalya, Turkey. halideakbas@akdeniz.edu.tr
authors.forename: S Halide
authors.initials: SH
authors.lastname: Akbas
authors.forename: Mujgan
authors.initials: M
authors.lastname: Timur
authors.forename: Tomris
authors.initials: T
authors.lastname: Ozben
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D006801:Humans; D009573:Nitrites / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology*; D017382:Reactive Oxygen Species; D019772:Topotecan / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D009573:Nitrites; D017382:Reactive Oxygen Species; D019772:Topotecan; D011794:Quercetin