title: Targeting autophagy overcomes Enzalutamide resistance in castration-resistant prostate cancer cells and improves therapeutic response in a xenograft model.
abstract: Macro-autophagy is associated with drug resistance in various cancers and can function as an adaptive response to maintain cell survival under metabolic stresses, including androgen deprivation. Androgen deprivation or treatment with androgen receptor (AR) signaling inhibitor (ARSI), Enzalutamide (MDV-3100, ENZA) or bicalutamide induced autophagy in androgen-dependent and in castration-resistant CaP (castration-resistant prostate cancer (CRPC)) cell lines. The autophagic cascade triggered by AR blockage, correlated with the increased light chain 3-II/I ratio and ATG-5 expression. Autophagy was observed in a subpopulation of C4-2B cells that developed insensitivity to ENZA after sustained exposure in culture. Using flow cytometry and clonogenic assays, we showed that inhibiting autophagy with clomipramine (CMI), chloroquine or metformin increased apoptosis and significantly impaired cell viability. This autophagic process was mediated by AMP-dependent protein kinase (AMPK) activation and the suppression of mammalian target of rapamycin (mTOR) through Raptor phosphorylation (Serine 792). Furthermore, small interfering RNA targeting AMPK significantly inhibited autophagy and promoted cell death in CaP cells acutely or chronically exposed to ENZA or androgen deprivation, suggesting that autophagy is an important survival mechanism in CRPC. Lastly, in vivo studies with mice orthotopically implanted with ENZA-resistant cells demonstrated that the combination of ENZA and autophagy modulators, CMI or metformin significantly reduced tumor growth when compared with control groups (P<0.005). In conclusion, autophagy is as an important mechanism of resistance to ARSI in CRPC. Antiandrogen-induced autophagy is mediated through the activation of AMPK pathway and the suppression of mTOR pathway. Blocking autophagy pharmacologically or genetically significantly impairs prostate cancer cell survival in vitro and in vivo, implying the therapeutics potential of autophagy inhibitors in the antiandrogen-resistance setting.
authors.affiliation: Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: H G
authors.initials: HG
authors.lastname: Nguyen
authors.affiliation: Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Yang
authors.affiliation: 1] Department of Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, CA, USA [2] UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: H-J
authors.initials: HJ
authors.lastname: Kung
authors.affiliation: Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: X-B
authors.initials: XB
authors.lastname: Shi
authors.affiliation: Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: D
authors.initials: D
authors.lastname: Tilki
authors.affiliation: UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: P N
authors.initials: PN
authors.lastname: Lara
authors.affiliation: 1] Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA [2] UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: DeVere White
authors.affiliation: 1] Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA [2] UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Gao
authors.affiliation: 1] Department of Urology, UC Davis School of Medicine, Sacramento, CA, USA [2] UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Sacramento, CA, USA.
authors.forename: C P
authors.initials: CP
authors.lastname: Evans
mesh_terms: D059002:Androgen Receptor Antagonists / Q000627:therapeutic use*; D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D001549:Benzamides; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000494:pharmacology*; D002997:Clomipramine / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D016513:Mice, SCID; D009570:Nitriles; D010669:Phenylthiohydantoin / Q000031:analogs & derivatives* / Q000627:therapeutic use; D064129:Prostatic Neoplasms, Castration-Resistant / Q000188:drug therapy / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D059002:Androgen Receptor Antagonists; D001549:Benzamides; D009570:Nitriles; D010669:Phenylthiohydantoin; D002738:Chloroquine; D008687:Metformin; C540278:enzalutamide; D002997:Clomipramine