Related Experiment Videos
Bicalutamide functions as an androgen receptor antagonist by assembly of a transcriptionally inactive receptor
David Masiello1, Shinta Cheng, Glenn J Bubley
1Cancer Biology Program, Hematology-Oncology Division, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Abstract:
Prostate cancers (PCa) that relapse after androgen deprivation therapy invariably express high levels of androgen receptor (AR) and AR-regulated genes. Most do not respond to secondary hormonal therapies, including AR antagonists, and the mechanisms of AR activation in these clinically androgen-independent tumors are unclear. Bicalutamide, the most widely used AR antagonist, is a competitive antagonist shown previously to stabilize AR association with cytosolic heat shock protein complexes. This study found nuclear AR expression in bicalutamide-treated androgen-independent PCa and found that bicalutamide could stimulate AR nuclear translocation. Moreover, specific DNA binding by the bicalutamide-liganded AR was demonstrated in vivo using a VP16-AR fusion protein and was confirmed by chromatin immunoprecipitation showing binding to the prostate-specific antigen enhancer in LNCaP PCa cells. Nonetheless, bicalutamide could not stimulate interactions between the AR N and C termini or recruitment of steroid receptor coactivator proteins (SRC-1 or -2), although SRC transfection augmented AR activity in the presence of dihydrotestosterone and inhibitory concentrations of bicalutamide. These results demonstrate that bicalutamide stimulates the assembly of a transcriptionally inactive AR on DNA and support altered coactivator (or corepressor) expression as a mechanism of bicalutamide-resistant androgen-independent PCa.
Insights
Bicalutamide, an androgen receptor (AR) antagonist, can paradoxically activate AR in prostate cancer (PCa) cells, leading to resistance. This suggests altered coactivator expression drives treatment failure in advanced PCa.
Area of Science:
- Oncology
- Molecular Biology
- Endocrinology
Background:
- Prostate cancer (PCa) relapse after androgen deprivation therapy (ADT) is linked to high androgen receptor (AR) activity.
- Mechanisms of AR activation in ADT-resistant PCa are not fully understood.
- Bicalutamide, a common AR antagonist, typically inhibits AR but its role in resistant tumors requires clarification.
Purpose of the Study:
- To investigate the mechanism of AR activation by bicalutamide in androgen-independent PCa.
- To determine if bicalutamide can stimulate AR nuclear translocation and DNA binding in resistant PCa.
- To explore the role of coactivator recruitment in bicalutamide-mediated AR signaling.
Main Methods:
- Studied nuclear AR expression in bicalutamide-treated PCa cells.
- Utilized a VP16-AR fusion protein to assess AR DNA binding in vivo.
- Performed chromatin immunoprecipitation (ChIP) to confirm AR binding to the prostate-specific antigen enhancer.
- Assessed AR N- and C-terminal interactions and steroid receptor coactivator (SRC) recruitment.
Main Results:
- Bicalutamide induced nuclear AR expression and translocation in androgen-independent PCa cells.
- Bicalutamide-liganded AR demonstrated specific DNA binding in vivo and in LNCaP cells.
- Bicalutamide did not promote AR N/C-terminal interaction or SRC recruitment.
- SRC transfection partially restored AR activity in the presence of bicalutamide.
Conclusions:
- Bicalutamide can stimulate the binding of a transcriptionally inactive AR to DNA in PCa.
- Altered expression of coactivators or corepressors may be a key mechanism driving bicalutamide resistance in PCa.
- Findings provide insight into therapeutic resistance in advanced prostate cancer.