title: [Killing and proapoptotic effects of topoisomerase I inhibitor on K562 cells].
abstract: OBJECTIVE
  Recently, it has been demonstrated that topoisomerase I(Topo I) inhibitor is a useful alternative for treatment of the patients with chronic myelogenous leukemia(CML) in accelerated or blast crisis. In order to get insight into pharmalogic activity of Topo I inhibitor, this study was designed to investigate the killing and proapoptotic activity of Topo I inhibitor(Topotecan, TPT) using K562 cell line, which carry abnormal chromosome[t(9;22)] of characteristics of CML.
  
  
  METHODS
  The cytotoxic effect of TPT on K562 cells was determined using MTT assay; TPT-induced apoptosis in K562 cells was identified by morphological analysis and Annexin V FITC staining; correlation between TPT-mediated killing or apoptosis and caspase-8 activation was investigated using caspase-8 inhibitor IETD-fmk.
  
  
  RESULTS
  After incubation of K562 cells with 0.15 mumol/L TPT for 12, 24, 48, and 72 h, the survival rates, compared with control, progressively reduced to (92 +/- 36)% [P > 0.05 vs (94 +/- 27)%], (68 +/- 21)% [P < 0.05 vs (119 +/- 13)%], (54 +/- 15)% [P < 0.05 vs (132 +/- 31)%], and (21 +/- 10)% [P < 0.01 vs (114 +/- 19)%]. Targeted cells meanwhile demonstrated phosphatidylserine externalization, cell shrinkage, chromatin margination, karyorrehxis and eventually disintegrate into numerous apoptotic bodies. After exposure to TPT in combination with IETD-fmk for 24 h and 48 h, K562 cells were still survival at viability of (95 +/- 29)% and (87 +/- 11)%, the latter was significantly higher than that of to TPT only [P < 0.05 vs (54 +/- 15)%].
  
  
  CONCLUSIONS
  Topoisomerase I inhibitor TPT possess killing activity and was induce apoptosis to K562 cells, which could be dependent on activation of caspase-8.
authors.affiliation: Department of Hematology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, P. R. China.
authors.forename: Xie-qun
authors.initials: XQ
authors.lastname: Chen
authors.forename: You-feng
authors.initials: YF
authors.lastname: Wan
authors.forename: Qing-xian
authors.initials: QX
authors.lastname: Bai
authors.forename: Yun-xin
authors.initials: YX
authors.lastname: Cao
mesh_terms: D017209:Apoptosis; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D020014:K562 Cells; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000494:pharmacology*
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D019772:Topotecan; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases