title: Elevation of c-FLIP in castrate-resistant prostate cancer antagonizes therapeutic response to androgen receptor-targeted therapy.
abstract: OBJECTIVE
  To characterize the importance of cellular Fas-associated death domain (FADD)-like interleukin 1β-converting enzyme (FLICE) inhibitory protein (c-FLIP), a key regulator of caspase-8 (FLICE)-promoted apoptosis, in modulating the response of prostate cancer cells to androgen receptor (AR)-targeted therapy.
  
  
  METHODS
  c-FLIP expression was characterized by immunohistochemical analysis of prostatectomy tissue. The functional importance of c-FLIP to survival and modulating response to bicalutamide was studied by molecular and pharmacologic interventions.
  
  
  RESULTS
  c-FLIP expression was increased in high-grade prostatic intraepithelial neoplasia and prostate cancer tissue relative to normal prostate epithelium (P < 0.001). Maximal c-FLIP expression was detected in castrate-resistant prostate cancer (CRPC; P < 0.001). In vitro, silencing of c-FLIP induced spontaneous apoptosis and increased 22Rv1 and LNCaP cell sensitivity to bicalutamide, determined by flow cytometry, PARP cleavage, and caspase activity assays. The histone deacetylase inhibitors (HDACi), droxinostat and SAHA, also downregulated c-FLIP expression, induced caspase-8- and caspase-3/7-mediated apoptosis, and increased apoptosis in bicalutamide-treated cells. Conversely, the elevated expression of c-FLIP detected in the CRPC cell line VCaP underpinned their insensitivity to bicalutamide and SAHA in vitro. However, knockdown of c-FLIP induced spontaneous apoptosis in VCaP cells, indicating its relevance to cell survival and therapeutic resistance.
  
  
  CONCLUSIONS
  c-FLIP reduces the efficacy of AR-targeted therapy and maintains the viability of prostate cancer cells. A combination of HDACi with androgen deprivation therapy may be effective in early-stage disease, using c-FLIP expression as a predictive biomarker of sensitivity. Direct targeting of c-FLIP, however, may be relevant to enhance the response of existing and novel therapeutics in CRPC.
authors.affiliation: Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, Northern Ireland.
authors.forename: Clare
authors.initials: C
authors.lastname: McCourt
authors.forename: Pamela
authors.initials: P
authors.lastname: Maxwell
authors.forename: Roberta
authors.initials: R
authors.lastname: Mazzucchelli
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Montironi
authors.forename: Marina
authors.initials: M
authors.lastname: Scarpelli
authors.forename: Manuel
authors.initials: M
authors.lastname: Salto-Tellez
authors.forename: Joe M
authors.initials: JM
authors.lastname: O'Sullivan
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Longley
authors.forename: David J J
authors.initials: DJ
authors.lastname: Waugh
mesh_terms: D000813:Anilides / Q000008:administration & dosage; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage; D006801:Humans; D008297:Male; D058990:Molecular Targeted Therapy; D009367:Neoplasm Staging; D009570:Nitriles / Q000008:administration & dosage; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011944:Receptors, Androgen / Q000378:metabolism*; D015398:Signal Transduction; D014105:Tosyl Compounds / Q000008:administration & dosage
chemical_list: D000813:Anilides; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D056572:Histone Deacetylase Inhibitors; D009570:Nitriles; D011944:Receptors, Androgen; D014105:Tosyl Compounds; C053541:bicalutamide; D053181:Caspase 8