title: Synergistic effects of verapamil on pingyangmycin-induced cytotoxicity and apoptosis in KB cells.
abstract: OBJECTIVE
  Previous studies have shown that pingyangmycin (PYM; bleomycin A5) can induce two distinct modes of cell death (necrosis, apoptosis). At high concentrations, PYM can be considered as an apoptosis mimetic drug. In this study, we explored the possibility that the membrane-modifying agent verapamil might affect the transport function of PYM through the plasma membrane, resulting in inducing apoptosis of tumor cells at low concentration of PYM.
  
  
  METHODS
  Cytotoxicity, flow cytometry and DNA fragmentation assays were used to detect the interaction of verapamil and PYM in human oral carcinoma cell line KB cells.
  
  
  RESULTS
  Our results indicated that verapamil can enhance the cytotoxicity of PYM against KB cells with the non-toxic doses (P<0.05). The cell viability at a concentration of 500 microg ml-1 of PYM was 35+/-2% compared with control and 10 microg ml-1 verapamil decreased the cell viability lower to 28+/-1%. In addition, because of the synergistic effect of verapamil, KB cells apoptosis was found to be induced when treated with a lower concentration of PYM (50 microg ml-1) for 24 h by flow cytometry and DNA fragmentation assays.
  
  
  CONCLUSIONS
  Verapamil was found to enhance PYM-induced cytotoxicity and apoptosis in KB cells. The responsiveness of PYM might be explained by the effective accumulation of PYM by verapamil in KB cells mediated by the inhibition of PYM efflux function of the cells.
authors.affiliation: School of Applied Chemistry, Department of Oral and Maxillofacial Surgery, Institute of Stomatology, Chung Shan Medical University, Taichungt, Taiwan.
authors.forename: Y-C
authors.initials: YC
authors.lastname: Ho
authors.forename: K-W
authors.initials: KW
authors.lastname: Tai
authors.forename: Y-C
authors.initials: YC
authors.lastname: Chang
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D001761:Bleomycin / Q000008:administration & dosage / Q000031:analogs & derivatives*; D002121:Calcium Channel Blockers / Q000008:administration & dosage*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000473:pathology; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D004357:Drug Synergism; D005434:Flow Cytometry; D006801:Humans; D007624:KB Cells; D009062:Mouth Neoplasms / Q000188:drug therapy* / Q000473:pathology; D014700:Verapamil / Q000008:administration & dosage*
chemical_list: D000903:Antibiotics, Antineoplastic; D002121:Calcium Channel Blockers; D001761:Bleomycin; C025703:bleomycetin; D014700:Verapamil