Suppression of mutant androgen receptors by flutamide

Objectives: To examine the effects of flutamide and hydroxyflutamide on the transactivation of mutant androgen receptors. Methods: Androgen-independent human prostate cancer cell line PC3 was transfected with plasmids expressing wild-type, W741C mutant, T877A mutant or W741C+T877A mutant androgen receptors. The effects of bicalutamide, hydroxyflutamide or flutamide on the basal and dihydrotestosterone-induced transcriptional activities of the wild-type and mutant androgen receptors were evaluated by luciferase assays using a reporter plasmid containing the prostate-specific antigen (PSA) promoter. The effects of the antiandrogens on the transcription and translation of the PSA gene in LNCaP cells expressing a mutant (T877A) androgen receptor were assessed by real-time reverse transcription-polymerase chain reaction and radioimmunoassays. Affinity of the antiandrogens to each androgen receptor construct was evaluated by ligand-binding assay. Results: Flutamide, but not hydroxyflutamide, successfully suppressed the transcription of all of the mutant androgen receptors examined in this study and also showed suppressive effects on PSA secretion by LNCaP cells treated with dihydrotestosterone. These inhibitory effects were probably not the result of competitive inhibition by flutamide given its low affinity to the androgen receptor constructs. Conclusions: Flutamide, with its suppressive effects on mutant androgen receptors, may be an alternative to conventional antiandrogens for hormone refractory prostate cancer.