title: Growth Inhibition by Testosterone in an Androgen Receptor Splice Variant-Driven Prostate Cancer Model.
abstract: Castration resistance creates a significant problem in the treatment of prostate cancer. Constitutively active splice variants of androgen receptor (AR) have emerged as drivers for resistance to androgen deprivation therapy, including the next-generation androgen-AR axis inhibitors abiraterone and enzalutamide. In this study, we describe the characteristics of a novel castration-resistant prostate cancer (CRPC) model, designated JDCaP-hr (hormone refractory).
  
  
  
  JDCaP-hr was established from an androgen-dependent JDCaP xenograft model after surgical castration. The expression of AR and its splice variants in JDCaP-hr was evaluated by immunoblotting and quantitative reverse transcription-polymerase chain reaction. The effects of AR antagonists and testosterone on JDCaP-hr were evaluated in vivo and in vitro. The roles of full-length AR (AR-FL) and AR-V7 in JDCaP-hr cell growth were evaluated using RNA interference.
  
  
  
  JDCaP-hr acquired a C-terminally truncated AR protein during progression from the parental JDCaP. The expression of AR-FL and AR-V7 mRNA was upregulated by 10-fold in JDCaP-hr compared with that in JDCaP, indicating that the JDCaP and JDCaP-hr models simulate castration resistance with some clinical features, such as overexpression of AR and its splice variants. The AR antagonist bicalutamide did not affect JDCaP-hr xenograft growth, and importantly, testosterone induced tumor regression. In vitro analysis demonstrated that androgen-independent prostate-specific antigen secretion and cell proliferation of JDCaP-hr were predominantly mediated by AR-V7. JDCaP-hr cell growth displayed a bell-shaped dependence on testosterone, and it was suppressed by physiological concentrations of testosterone. Testosterone induced rapid downregulation of both AR-FL and AR-V7 expression at physiological concentrations and suppressed expression of the AR target gene KLK3.
  
  
  
  Our findings support the clinical value of testosterone therapy, including bipolar androgen therapy, in the treatment of AR-overexpressed CRPC driven by AR splice variants that are not clinically actionable at present. Prostate 76:1536-1545, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Kanagawa, Japan. daisuke.nakata@takeda.com.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Nakata
authors.affiliation: Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Kanagawa, Japan.
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Kanagawa, Japan.
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Masaki
authors.affiliation: Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Kanagawa, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Tanaka
authors.affiliation: CMC Center, Takeda Pharmaceutical Company Limited, Yodogawa-ku, Osaka, Japan.
authors.forename: Masami
authors.initials: M
authors.lastname: Kusaka
authors.affiliation: Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Kanagawa, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D059002:Androgen Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000187:drug effects; D014644:Genetic Variation; D064593:Heterografts; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009919:Orchiectomy; D017430:Prostate-Specific Antigen / Q000378:metabolism; D064129:Prostatic Neoplasms, Castration-Resistant / Q000235:genetics* / Q000473:pathology*; D012326:RNA Splicing / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D011944:Receptors, Androgen / Q000235:genetics* / Q000502:physiology; D013739:Testosterone / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D059002:Androgen Receptor Antagonists; D012333:RNA, Messenger; D011944:Receptors, Androgen; D013739:Testosterone; D017430:Prostate-Specific Antigen
keywords: AR-V7; androgen deprivation therapy; castration-resistant prostate cancer; testosterone therapy