Short hairpin RNA knockdown of the androgen receptor attenuates ligand-independent activation and delays tumor progression.
Progression to androgen independence is the lethal end stage of prostate cancer. We used expression of androgen receptor (AR)-targeted short hairpin RNAs (shRNA) to directly test the requirement for AR in ligand-independent activation of androgen-regulated genes and hormone-independent tumor progression. Transient transfection of LNCaP human prostate cancer cells showed that AR shRNA decreased R1881 induction of the prostate-specific antigen (PSA)-luciferase reporter by 96%, whereas activation by forskolin, interleukin-6, or epidermal growth factor was inhibited 48% to 75%. Whereas the antiandrogen bicalutamide provided no further suppression, treatment with the mitogen-activated protein kinase (MAPK) inhibitor U0126 completely abrogated the residual activity, indicating a MAPK-dependent, AR-independent pathway for regulating the PSA promoter. Expression of doxycycline-inducible AR shRNA expression in LNCaP cells resulted in decreased levels of AR and PSA as well as reduced proliferation in vitro. When these cells were grown as xenografts in immunocompromised mice, induction of AR shRNA decreased serum PSA to below castration nadir levels and significantly retarded tumor growth over the entire 55-day experimental period. This is the first demonstration that, by inducibly suppressing AR expression in vivo, there is an extensive delay in progression to androgen independence as well as a dramatic inhibition of tumor growth and decrease in serum PSA, which exceeds that seen with castration alone. Based on these findings, we propose that suppressing AR expression may provide superior therapeutic benefit in reducing tumor growth rate than castration and may additionally be very effective in delaying progression to androgen independence.
Cheng
Helen
H
The Prostate Center at Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada.
Snoek
Rob
R
Ghaidi
Fariba
F
Cox
Michael E
ME
Rennie
Paul S
PS
D059002:Androgen Receptor Antagonists; D000728:Androgens / Q000494:pharmacology*; D045744:Cell Line, Tumor; D018450:Disease Progression; D004317:Doxorubicin / Q000494:pharmacology; D006801:Humans; D008297:Male; D011401:Promoter Regions, Genetic; D017430:Prostate-Specific Antigen / Q000097:blood / Q000235:genetics; D011471:Prostatic Neoplasms / Q000473:pathology / Q000628:therapy*; D034741:RNA, Small Interfering / Q000494:pharmacology*; D011944:Receptors, Androgen / Q000235:genetics; D015533:Transcriptional Activation
D059002:Androgen Receptor Antagonists; D000728:Androgens; D034741:RNA, Small Interfering; D011944:Receptors, Androgen; D004317:Doxorubicin; D017430:Prostate-Specific Antigen