You have accessJournal of UrologyProstate Cancer: Basic Research (III)1 Apr 2013503 AUTOPHAGY IS A SURVIVAL MECHANISM IN MEDIATING RESISTANCE TO ANDROGENT RECEPTOR SIGNALING INHIBITORS IN CASTRATE RESISTANT PROSTATE CANCER CELLS Hao G. Nguyen, Joy C. Yang, Kung Hsing-Jien, Allen C. Gao, and Christopher P. Evans Hao G. NguyenHao G. Nguyen Sacramento, CA More articles by this author , Joy C. YangJoy C. Yang Sacramento, CA More articles by this author , Kung Hsing-JienKung Hsing-Jien Sacramento, CA More articles by this author , Allen C. GaoAllen C. Gao Sacramento, CA More articles by this author , and Christopher P. EvansChristopher P. Evans Sacramento, CA More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.1897AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES 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. Our hypothesis was: 1) autophagy is a cellular mechanism that confers resistance to the androgen receptor signaling inhibitor (ARSI), enzalutamide (MDV-3100) therapy and 2) blocking autophagy circumvents this survival mechanism to improve therapeutic response. METHODS To determine if autophagy was activated, we examined expression levels of LC3-I/II using Western Blotting in prostate cancer (CaP) cell lines, LNCaP, C4-2B, and CWR22 stably over-expressing LC3-GFP. Flow cytometry and fluorescence microscopy were used to quantify and visualize autophagy and to analyze cell cycle progression and apoptosis. Clonogenic assays were employed to evaluate cell survival. Enzalutamide (ENZA) and biclutamide were used as androgen receptor inhibitors. SiRNA to AMPK was transfected with Lipofectamine 2000. RESULTS Androgen deprivation or treatment with androgen receptor signaling inhibitors, ENZA or biclutamide induced autophagy in androgen-dependent and in castration resistant CaP (CRPC) cell lines. The autophagic cascade triggered by AR blockage, correlated with the increased LC3-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 or hydroxychloroquine increased apoptosis and significantly impaired cell viability. This autophagic process was mediated by AMPK activation and the suppression of mTOR through Raptor phosphorylation (Serine 792). Finally, si-RNA targeting AMPK significantly inhibited autophagy and promoted cell-death in CaP cells acutely or chronically exposed to ENZA or androgen deprived culturing condition, suggesting that autophagy is an important survival mechanism in CRPC cells. CONCLUSIONS These novel data support autophagy as an important mechanism of resistance to the androgen receptor signaling inhibitor in CRPC. Antiandrogen mediated autophagy is dependent on the activation of AMPK pathway and the suppression of mTOR pathway. Blocking autophagy pharmacologically or genetically significantly impairs prostate cancer cell survival, implying the therapeutics potential of autophagy inhibitors in the antiandrogen resistance setting. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e206 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Hao G. Nguyen Sacramento, CA More articles by this author Joy C. Yang Sacramento, CA More articles by this author Kung Hsing-Jien Sacramento, CA More articles by this author Allen C. Gao Sacramento, CA More articles by this author Christopher P. Evans Sacramento, CA More articles by this author Expand All Advertisement Advertisement PDF DownloadLoading ...