Generation 2.5 antisense oligonucleotides targeting the androgen receptor and its splice variants suppress enzalutamide-resistant prostate cancer cell growth

• Published in: Clinical cancer research 2015-04, Vol.21 (7), p.1675-1687
• Main Authors: Yamamoto, Yoshiaki, Loriot, Yohann, Beraldi, Eliana, Zhang, Fan, Wyatt, Alexander W, Al Nakouzi, Nader, Mo, Fan, Zhou, Tianyuan, Kim, Youngsoo, Monia, Brett P, MacLeod, A Robert, Fazli, Ladan, Wang, Yuzhuo, Collins, Colin C, Zoubeidi, Amina, Gleave, Martin
• Format: Article
• Language: English
• Subjects: Animals; Antineoplastic Agents - pharmacology; Blotting, Western; Drug Resistance, Neoplasm - genetics; Humans; Immunohistochemistry; Male; Mice; Oligonucleotides, Antisense - pharmacology; Phenylthiohydantoin - analogs & derivatives; Phenylthiohydantoin - pharmacology; Prostatic Neoplasms, Castration-Resistant - drug therapy; Prostatic Neoplasms, Castration-Resistant - genetics; Protein Isoforms; Receptors, Androgen - genetics; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering; Transfection; Xenograft Model Antitumor Assays
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.ccr-14-1108

Enzalutamide (ENZ) is a potent androgen receptor (AR) antagonist with activity in castration-resistant prostate cancer (CRPC); however, progression to ENZ-resistant (ENZ-R) CRPC frequently occurs with rising serum PSA levels, implicating AR full-length (ARFL) or variants (AR-Vs) in disease progression. To define functional roles of ARFL and AR-Vs in ENZ-R CRPC, we designed 3 antisense oligonucleotides (ASO) targeting exon-1, intron-1, and exon-8 in AR pre-mRNA to knockdown ARFL alone or with AR-Vs, and examined their effects in three CRPC cell lines and patient-derived xenografts. ENZ-R-LNCaP cells express high levels of both ARFL and AR-V7 compared with CRPC-LNCaP; in particular, ARFL levels were approximately 12-fold higher than AR-V7. Both ARFL and AR-V7 are highly expressed in the nuclear fractions of ENZ-R-LNCaP cells even in the absence of exogenous androgens. In ENZ-R-LNCaP cells, knockdown of ARFL alone, or ARFL plus AR-Vs, similarly induced apoptosis, suppressed cell growth and AR-regulated gene expression, and delayed tumor growth in vivo. In 22Rv1 cells that are inherently ENZ-resistant, knockdown of both ARFL and AR-Vs more potently suppressed cell growth, AR transcriptional activity, and AR-regulated gene expression than knockdown of ARFL alone. Exon-1 AR-ASO also inhibited tumor growth of LTL-313BR patient-derived CRPC xenografts. These data identify the AR as an important driver of ENZ resistance, and while the contributions of ARFL and AR-Vs can vary across cell systems, ARFL is the key driver in the ENZ-R LNCaP model. AR targeting strategies against both ARFL and AR-Vs is a rational approach for AR-dependent CRPC.