title: Cell-cycle synchronization reverses Taxol resistance of human ovarian cancer cell lines.
abstract: BACKGROUND
  Taxol is a powerful chemotherapy agent leading to mitotic arrest and cell death; however, its clinical efficacy has been hampered due to the development of drug resistance. Taxol specifically targets the cell cycle. Progress through mitosis (M stage) is an absolute requirement for drug-induced death because cell death is markedly reduced in cells blocked at the G1-S transition. The measured doubling time for ovarian cancer cells is about 27 h. As such, during treatment with Taxol most of the cells are not in the M stage of the cell cycle. Thus, the effect of cell-cycle synchronization was investigated in regard to reversing Taxol resistance in ovarian cancer cells.
  
  
  METHODS
  Giemsa-Wright staining was used for assessing the morphology of the cells. The doubling time of the cells was calculated using formula as follows: Td = In2/slope. The resistant index and cell cycle were measured via MTT assays and flow cytometry. Thymidine was used to induce cell-cycle synchronization, and cell apoptosis rates following exposure to Taxol were measured using a flow cytometer.
  
  
  RESULTS
  The growth doubling time of two Taxol-resistant cell lines were longer than that of Taxol-sensitive cells. Apoptotic rates in Taxol-sensitive and -resistant cell lines after synchronization and exposure to Taxol were all higher compared to unsynchronized controls (p <0.05).
  
  
  CONCLUSIONS
  Synchronization of the cell-cycle resulted in an increased effectiveness of Taxol toward ovarian cancer cell lines. We speculated that formation of drug resistance toward Taxol in ovarian cancer could be partly attributed to the longer doubling time of these cells.
authors.affiliation: Department of Obstetrics and Gynecology, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Peking, China. lingyapan@hotmail.com.
authors.forename: Xueqing
authors.initials: X
authors.lastname: Wang
authors.forename: Lingya
authors.initials: L
authors.lastname: Pan
authors.forename: Ning
authors.initials: N
authors.lastname: Mao
authors.forename: Lifang
authors.initials: L
authors.lastname: Sun
authors.forename: Xiangjuan
authors.initials: X
authors.lastname: Qin
authors.forename: Jie
authors.initials: J
authors.lastname: Yin
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