Abstract
In prostate cancer, blockade of androgen receptor (AR) signaling confers a therapeutic benefit. Nevertheless, this standard therapy allows relapse of hormone-refractory prostate cancer (HRPC) with a poor prognosis. HRPC cells often express variant ARs, such as point-mutated alleles and splicing isoforms, resulting in androgen-independent cell growth and resistance to antiandrogen (e.g., flutamide). However, a pharmacological strategy to block such aberrant ARs remains to be established. Here, we established a reporter system that monitors AR-mediated activation of a prostate-specific antigen (PSA) promoter. Our chemical library screening revealed that the antibiotic nigericin inhibits AR-mediated activation of the PSA promoter and PSA production in prostate cancer cells. Nigericin suppressed the androgen-dependent LNCaP cell growth even though the cells expressed a flutamide-resistant mutant AR. These effects were caused by AR suppression at the mRNA and post-translational levels. In HRPC 22Rv1 cells, which express the full-length AR and the constitutively active, truncated ARs lacking the carboxyl-terminal ligand-binding domain, small interfering RNA-mediated knockdown of both AR isoforms efficiently suppressed the androgen-independent cell growth, whereas knockdown of the full-length AR alone had no significant effect. It is noteworthy that nigericin was able to mimic the knockdown of both AR isoforms: it reduced the expression of the full-length and the truncated ARs, and it induced G1 cell-cycle arrest and apoptosis of 22Rv1 cells. These observations suggest that nigericin-like compounds that suppress AR expression at the mRNA level could be applied as new-type therapeutic agents that inhibit a broad spectrum of AR variants in HRPC.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan [Grant-in-Aid for Scientific Research on Priority Area “Cancer” 17016012]; and the Japanese Society for the Promotion of Science, Japan [Grant-in-Aid for Exploratory Research 20659024].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.064790.
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ABBREVIATIONS:
- AR
- androgen receptor
- HRPC
- hormone-refractory prostate cancer
- PSA
- prostate-specific antigen
- tAR
- truncated androgen receptor
- DHT
- dihydrotestosterone
- ARE
- androgen response element
- DBD
- DNA binding domain
- LBD
- ligand-binding domain
- SCADS
- Screening Committee of Anticancer Drugs
- CSS
- charcoal-stripped serum
- PCR
- polymerase chain reaction
- PARP
- poly(ADP-ribose) polymerase
- qRT-PCR
- quantitative reverse transcription-polymerase chain reaction
- siRNA
- small interfering RNA
- UTR
- untranslated region
- 17-AAG
- 17-demethoxy-17-(2-propenylamino)geldanamycin
- MG-132
- N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal
- PAGE
- polyacrylamide gel electrophoresis
- Hsp90
- 90-kDa heat shock protein
- PC-3/AR
- androgen receptor-transfected prostate cancer PC-3 cells.
- Received March 16, 2010.
- Accepted August 11, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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