title: Increased anti-tumour effects of doxorubicin and zoledronic acid in prostate cancer cells in vitro: supporting the benefits of combination therapy.
abstract: OBJECTIVE
  Combination treatment using the chemotherapy drug doxorubicin and the anti-resorptive agent zoledronic acid has shown to be very effective in inducing apoptosis in breast cancer cells, and also to eradicate breast tumour growth in vivo. Here, we investigated whether apoptotic cell death is increased when zoledronic acid and doxorubicin are given in sequence or in combination in prostate cancer cells in vitro.
  
  
  METHODS
  PC3, DU145 and LNCaP prostate cancer cells were treated with zoledronic acid or doxorubicin alone, in sequence or in combination, and apoptosis was measured by evaluation of nuclear morphology following staining with Hoechst and PI. The involvement of the mevalonate pathway in the induction of apoptosis was assessed through the addition of the mevalonate pathway intermediate geranylgeraniol.
  
  
  RESULTS
  Both agents induced PC3 cell death, with 5 microM zoledronic acid inducing 1.73% apoptosis and 50 nM doxorubicin 3.60% apoptosis following 24 h of exposure. In contrast, sequential exposure (doxorubicin followed by zoledronic acid) caused 8.87% apoptosis. Doxorubicin followed by zoledronic acid induced 4.77% apoptosis in LNCaP cells, compared to 1.53% caused by zol alone, 2.23% by dox alone and 2.5% following the reverse sequence (P < 0.001 in all cases). In DU145 cells doxorubicin followed by zoledronic acid induced 5.73% apoptosis, compared to 1.8% following zol alone, 2.93% by dox alone, and 3.20% following the reverse sequence (P < 0.001 in all cases).
  
  
  CONCLUSIONS
  This is the first detailed study to show that an increased anti-tumour effect is generated when doxorubicin and zoledronic acid are given in sequence in both hormone-sensitive and insensitive prostate cancer cells in vitro. Our results suggest that combined treatment with these agents is superior to single agent therapy, and should be explored in a tumour model of prostate cancer.
authors.affiliation: Academic Unit of Clinical Oncology, School of Medicine and Biomedical Sciences, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, UK.
authors.forename: Rhys D
authors.initials: RD
authors.lastname: Clyburn
authors.forename: Penny
authors.initials: P
authors.lastname: Reid
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Evans
authors.forename: Diane V
authors.initials: DV
authors.lastname: Lefley
authors.forename: Ingunn
authors.initials: I
authors.lastname: Holen
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D004164:Diphosphonates / Q000008:administration & dosage / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000008:administration & dosage / Q000627:therapeutic use*; D006801:Humans; D007093:Imidazoles / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D000077211:Zoledronic Acid
chemical_list: D004164:Diphosphonates; D007093:Imidazoles; D000077211:Zoledronic Acid; D004317:Doxorubicin