title: Prolonged treatment with bicalutamide induces androgen receptor overexpression and androgen hypersensitivity.
abstract: BACKGROUND
  Various hormone refractory prostate cancer cell models have been established with androgen depletion and have helped to clarify the mechanism for the transition into androgen-depletion independent status. However, the mechanism of bicalutamide resistance remains unclear because few cell models have been generated.
  
  
  METHODS
  We generated a bicalutamide-resistant subline, LNCaP-BC2, from LNCaP after prolonged treatment with bicalutamide. Androgen and/or bicalutamide responsiveness for proliferation and prostate-specific antigen (PSA) secretion were examined in vitro and in vivo. Testosterone and dihydrotestosterone (DHT) levels in xenografted tumors were analyzed by liquid chromatography-tandem mass spectrometry. Androgen receptor (AR) gene mutation and amplification and AR and pAR(210) expression were determined.
  
  
  RESULTS
  LNCaP-BC2 did not grow in an androgen-depleted medium and proliferation was stimulated in a tenfold lower concentration of androgen than that of LNCaP. LNCaP-BC2 grew in castrated male mice, and the DHT level in grafted LNCaP-BC2 tumors was 7.7-fold lower than in LNCaP tumors. Bicalutamide stimulated LNCaP-BC2 proliferation and PSA secretion in vitro and the antitumor activity of bicalutamide against LNCaP-BC2 was weaker than that of LNCaP in vivo. Additional AR mutation and AR gene amplification were not detected in LNCaP-BC2, but AR and pAR(210) expression and PSA secretion in LNCaP-BC2 were higher than in LNCaP.
  
  
  CONCLUSIONS
  Bicalutamide-resistant LNCaP-BC2 exhibited AR overexpression and hypersensitivity to low levels of androgen. Our data suggests that AR overexpression is a significant mechanism of bicalutamide resistance similar to resistance from chronic androgen depletion. In addition, pAR(210) overexpression could be a potential mechanism for hypersensitivity to low androgen in LNCaP-BC2.
authors.affiliation: Pharmaceutical Research Department 2, Kamakura Research Laboratories, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan. kawatahrm@chugai-pharm.co.jp
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Kawata
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Ishikura
authors.forename: Miho
authors.initials: M
authors.lastname: Watanabe
authors.forename: Ayako
authors.initials: A
authors.lastname: Nishimoto
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Tsunenari
authors.forename: Yuko
authors.initials: Y
authors.lastname: Aoki
mesh_terms: D000726:Androgen Antagonists / Q000008:administration & dosage; D000813:Anilides / Q000008:administration & dosage*; D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D013196:Dihydrotestosterone / Q000032:analysis; D004797:Enzyme-Linked Immunosorbent Assay; D008297:Male; D051379:Mice; D009570:Nitriles / Q000008:administration & dosage*; D011467:Prostate / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017430:Prostate-Specific Antigen / Q000032:analysis; D011944:Receptors, Androgen / Q000378:metabolism*; D013739:Testosterone / Q000032:analysis; D013997:Time Factors; D014105:Tosyl Compounds / Q000008:administration & dosage*
chemical_list: D000726:Androgen Antagonists; D000813:Anilides; D009570:Nitriles; D011944:Receptors, Androgen; D014105:Tosyl Compounds; D013196:Dihydrotestosterone; D013739:Testosterone; C053541:bicalutamide; D017430:Prostate-Specific Antigen