title: The effects of terbium on the cellular accumulation of cisplatin in MDA-MB-231 human breast tumor cells.
abstract: OBJECTIVE
  Cisplatin (DDP) is an effective antitumor agent limited in its efficacy by the development of tumor cell resistance. The defective accumulation of DDP has been shown to be a prominent feature in many DDP-resistant cell lines. In an effort to circumvent this problem, we examined the cellular accumulation of DDP in the presence of terbium (Tb3+). We also examined the effects of verapamil on the cellular accumulation of DDP in order to delineate the specific interaction of Tb3+ and DDP. All experiments were performed on DDP-sensitive or DDP-resistant MDA-MB-231 human breast tumor cells.
  
  
  METHODS
  The cellular accumulation of DDP and verapamil were determined by electrothermal atomic absorption spectrophotometry. Time-resolved luminescence spectroscopy was used to obtain equilibrium binding constants for the Tb3+/MDA cell complexes.
  
  
  RESULTS
  We found that 100 microM Tb3+ increased DDP accumulation in the parent MDA cell line, 5.7-fold resistant MDA/A13 and 10-fold resistant MDA/CH cells by 56.2 +/- 7.4, 71.9 +/- 9.4 and 50.8 +/- 9.4%, respectively (P < 0.0001 for all MDA cell types). In contrast, 20 microM verapamil had no significant effect on DDP accumulation in the MDA cell lines. In addition, a positive correlation between the membrane binding of Tb3+ and the cellular accumulation of DDP was found to exist in the parent cell line and sublines (r = 0.9).
  
  
  CONCLUSIONS
  In agreement with earlier studies, the plasma membrane of MDA cell lines contain a specific Tb(3+)-binding protein. Our findings suggest that the Tb(3+)-binding protein may be intimately associated with the accumulation of DDP in breast tumor cells.
authors.affiliation: Department of Natural Sciences, University of Maryland Eastern Shore, Princes Anne 21853, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Mack
authors.forename: R G
authors.initials: RG
authors.lastname: Canada
authors.forename: P A
authors.initials: PA
authors.lastname: Andrews
mesh_terms: D000704:Analysis of Variance; D000970:Antineoplastic Agents / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002945:Cisplatin / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D008875:Middle Aged; D013725:Terbium / Q000378:metabolism / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D013725:Terbium; D014700:Verapamil; D002945:Cisplatin