title: Rapamycin enhances docetaxel-induced cytotoxicity in a androgen-independent prostate cancer xenograft model by survivin downregulation.
abstract: BACKGROUND
  Docetaxel is a first-line treatment choice in castration-resistant prostate cancer (CRPC). However, the management of CRPC remains an important challenge in oncology. There have been many reports on the effects of rapamycin, which is an inhibitor of the mammalian target of rapamycin (mTOR), in the treatment of carcinogenesis. We assessed the cytotoxic effects of the combination treatment of docetaxel and rapamycin in prostate cancer cells. Furthermore, we examined the relationship between these treatments and survivin, which is a member of the inhibitory apoptosis family.
  
  
  METHODS
  Prostate cancer cells were cultured and treated with docetaxel and rapamycin. The effects on proliferation were evaluated with the MTS assay. In addition, we evaluated the effect on proliferation of the combination treatment induced knockdown of survivin expression by small interfering RNA transfection and docetaxel. Protein expression levels were assayed using western blotting. PC3 cells and xenograft growth in nude mice were used to evaluate the in vivo efficacy of docetaxel and its combination with rapamycin.
  
  
  RESULTS
  In vitro and in vivo, the combination of rapamycin with docetaxel resulted in a greater inhibition of proliferation than treatment with rapamycin or docetaxel alone. In addition, in vitro and in vivo, rapamycin decreased basal surviving levels, and cotreatment with docetaxel further decreased these levels. Transfection siRNA against survivin enhanced the cytotoxicity of docetaxel in PC3 cells.
  
  
  CONCLUSIONS
  The rapamycin-dependent enhancement of the cytotoxic effects of docetaxel was associated with the downregulation of survivin expression. Our results suggest that the combination of docetaxel and rapamycin is a candidate for the improved treatment of advanced prostate cancer.
authors.affiliation: Department of Urology, Gunma University Graduate School of Medicine, Maeabshi, Japan. yasu-m@med.gunma-u.ac.jp
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Morikawa
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Koike
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Sekine
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsui
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shibata
authors.forename: Kazuto
authors.initials: K
authors.lastname: Ito
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000728:Androgens / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D000077143:Docetaxel; D015536:Down-Regulation; D004357:Drug Synergism; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D011471:Prostatic Neoplasms / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D012097:Repressor Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D020123:Sirolimus / Q000494:pharmacology*; D000077022:Survivin; D043823:Taxoids / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000728:Androgens; D000970:Antineoplastic Agents; C117749:Birc5 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D000077022:Survivin; D043823:Taxoids; D000077143:Docetaxel; D020123:Sirolimus