title: [Effects of mammalian-target-of-rapamycin pathway on lapatinib resistance in breast cancer MDA-MB-231 cells].
abstract: OBJECTIVE
  To establish a lapatinib resistance cell line for elucidating the mechanisms of drug resistance of lapatinib in human breast cancer cells.
  
  
  METHODS
  The human breast cancer MDA-MB-231 cells were exposed in an incremental dose of lapatinib to establish a lapatinib resistance rMDA-MB-231 cell line. The assay of methyl thiazolyl tetrazolium (MTT) was used to detect the cytotoxic activity of lapatinib against MDA-MB-231 and rMDA-MB-231 cells. The protein expression was detected by Western blot. Small interfering RNA was used to specifically knock down mammalian-target-of-rapamycin (mTOR) in rMDA-MB-231 cells. Apoptosis was determined by fluorescein isothiocyanate (FITC)-annexin V/PI staining and flow cytometry.
  
  
  RESULTS
  The human breast cancer lapatinib resistance cell line rMDA-MB-231 was induced by lapatinib. The half maximal inhibitory concentration (IC50) values of lapatinib against MDA-MB-231 and rMDA-MB-231 cells were (6.1 ± 0.6) and (34.9 ± 2.7) µmol/L respectively (P < 0.01). Compared with MDA-MB-231 cells, the protein expression of mTOR in rMDA-MB-231 cells was significantly up-regulated. The protein expression of mTOR was significantly down-regulated by specific siRNA duplexes in rMDA-MB-231 cells. After siRNA interference, 20 µmol/L lapatinib was added into control, negative siRNA control and mTOR-targeted siRNA groups respectively. The percents of cell apoptosis in control, negative control and targeted siRNA groups were 13.4% ± 2.5%, 14.2% ± 2.8% and 34.6% ± 5.8% respectively, there was no significance between the first two groups (P > 0.05) , and there was significant difference between the control and targeted siRNA group (P < 0.01) .
  
  
  CONCLUSIONS
  The up-regulation of mTOR plays an important role in the lapatinib-resistant phenotype of human breast cancer rMDA-MB-231 cells. And the down-regulation of mTOR increases the apoptotic death of lapatinib against rMDA-MB-231 cells.
authors.affiliation: Department of Surgery, General PLA Hospital, Beijing 100853, China. Email: vicky1968@163.com.
authors.forename: Jian-dong
authors.initials: JD
authors.lastname: Wang
authors.forename: Quan-sheng
authors.initials: QS
authors.lastname: Wang
authors.forename: Yi-zhou
authors.initials: YZ
authors.lastname: Bai
authors.forename: De-qiang
authors.initials: DQ
authors.lastname: Kou
authors.forename: Xi-ru
authors.initials: XR
authors.lastname: Li
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.forename: Rong
authors.initials: R
authors.lastname: Li
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D000077341:Lapatinib; D011799:Quinazolines / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D011799:Quinazolines; D000077341:Lapatinib; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases