title: In vitro evaluation of zoledronic acid resistance developed in MCF-7 cells.
abstract: BACKGROUND
  Zoledronic acid is an important osteotropic compound used in combination with anticancer agents to reduce the incidence of hypercalcemia and skeletal morbidity in patients with advanced breast cancer and bone metastases. Ineffectiveness of anticancer drugs during chemotherapy is a frequently observed situation in cancer chemotherapy. The resistance of tumor cells to more than one cytotoxic drugs is defined as multidrug resistance. Drug resistance may be caused by altered gene expression levels and altered activities of proteins related to drug transport or cell death.
  
  
  METHODS
  To investigate the potential development of zoledronic acid resistance in breast cancer, parental MCF-7 cells were selected by increasing doses of zoledronic acid. MTT cytotoxicity assays, RT-PCR and Western blot were performed. The anticancer drugs paclitaxel, docetaxel, vincristine and doxorubicin were tested in combination to assess their combined antiproliferative effects and cross-resistance profiles.
  
  
  RESULTS
  Results demonstrated that the drug-adapted cells are resistant to zoledronic acid compared to parental MCF-7 and de novo expression of resistance genes, such as BCRP and LRP, were found. Up-regulation of Bcl-2 gene expression in resistant cells was also found. Synergistic cytotoxic effects of the combination of zoledronic acid with paclitaxel, docetaxel and vincristine were confirmed by fractional inhibitory indices, and zoledronic acid resistant cells were also found to be cross-resistant to these agents.
  
  
  CONCLUSIONS
  Zoledronic acid may cause resistance in MCF-7 cells. Overexpression of BCRP and LRP genes and an increase in Bcl-2 gene expression may have roles in the development of zoledronic acid resistance in the MCF-7 cell line. On the other hand, MDR1 and MRP1 genes do not seem to contribute to the zoledronic acid resistance significantly.
authors.affiliation: Department of Biological Sciences, Middle East Technical University, 06531 Ankara, Turkey.
authors.forename: Meltem Demirel
authors.initials: MD
authors.lastname: Kars
authors.forename: Ozlem Darcansoy
authors.initials: OD
authors.lastname: Işeri
authors.forename: Ali Ugur
authors.initials: AU
authors.lastname: Ural
authors.forename: Ufuk
authors.initials: U
authors.lastname: Gündüz
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D015153:Blotting, Western; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D004164:Diphosphonates / Q000494:pharmacology*; D000077143:Docetaxel; D004317:Doxorubicin / Q000008:administration & dosage; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis / Q000235:genetics; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D017239:Paclitaxel / Q000008:administration & dosage; D020133:Reverse Transcriptase Polymerase Chain Reaction; D043823:Taxoids / Q000008:administration & dosage; D020394:Vault Ribonucleoprotein Particles / Q000096:biosynthesis / Q000235:genetics; D014750:Vincristine / Q000008:administration & dosage; D000077211:Zoledronic Acid; D000099187:Major Vault Protein
chemical_list: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D000077143:Docetaxel; D004317:Doxorubicin; D007093:Imidazoles; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D017239:Paclitaxel; D043823:Taxoids; D020394:Vault Ribonucleoprotein Particles; D014750:Vincristine; D000077211:Zoledronic Acid; D000099187:Major Vault Protein; C116614:ABCG2 protein, human; C421109:multidrug resistance-associated protein 1