The antiandrogen bicalutamide activates the androgen receptor (AR) with a mutation in codon 741 through the mitogen activated protein kinase (MARK) pathway in human prostate cancer PC3 cells

Abstract

Abstract. The objective of this study was to assess the effect of antiandrogen on the activation of mutated androgen receptor (AR) and its signaling pathway in prostate cancer. We transfected the AR gene with a point mutation at codon 741 (tryptophan to leucine; W741L) into human androgenindependent prostate cancer PC3 cells lacking the expression of AR, and established PC3 cells overexpressing mutant type AR (PC3/W741L). Changes in the phenotype in these cells were compared to those in PC3 cells transfected with wildtype AR (PC3/Wild) and control vector alone (PC3/Co). There was no significant differences in the growth among PC3/Co, PC3/Wild and PC3/W741L cells. A transactivation assay using these cells showed that bicalutamide activated W741L mutant type AR, but not wild-type AR, while hydroxyflutamide failed to activate either type of ARs. Treatment with specific inhibitors of the MAPK or STST3 pathway (UO126 or AG490, respectively), in contrast to treatment with the Akt pathway inhibitor LY294002, significantly inhibited the dihydrotestosterone-induced activation of both wild-type and mutant ARs; however, activation of W741L mutant AR by bicalutamide was significantly inhibited by treatment with UO126, in contrast to treatment with AG490 or LY294002. Furthermore, treatment of PC3/W741L with bicalutamide, in contrast to treatment with hydroxyflutamide, resulted in significant upregulation of phosphorylated p44/42 MAPK. These findings suggest that the MAPK pathway might be involved in the activation of the AR with a point mutation at codon 741 induced by treatment with the antiandrogen bicalutamide. IntroductionProstate cancer is the most frequently diagnosed malignancy and the second leading cause of cancer-specific deaths in men in Western industrialized countries. Despite intensive efforts in the field of prostate cancer research, androgen withdrawal therapy has continued to be the mainstay of treatment for men with advanced prostate cancer since the report by Huggins and Hodges in 1941 (1). In recent years, a novel therapeutic strategy of androgen ablation by combining luteinizing hormone-releasing hormone analog and antiandrogen was introduced as 'maximal androgen blockade (MAB)'. Initially, ~90% of patients with advanced prostate cancer favorably respond to MAB therapy; however, androgenindependent (AI) progression ultimately occurs within a few years in the majority of these patients (1,2). During the course of AI progression, a paradoxical phenomenon, 'antiandrogen withdrawal syndrome (AWS)', which is characterized by the improvement of clinical findings associated with prostate cancer following discontinuation of therapeutic antiandrogen, has been shown to occur in 25-50% of patients treated with androgen ablation therapy (3,4).Several investigators have reported the activation of some types of mutant androgen receptors (ARs) by anti-androgens (5-9). For example, Fenton et al reported that flutamide works as an agonist for T877S and H874Y mutant ARs (6), while Hara et al showed the stimulation of W741...

Antiandrogen withdrawal syndrome (AAWS) in the treatment of patients with prostate cancer

“…This finding was further confirmed by a structural analysis of the interaction between bicalutamide and W741L AR LBD, with a 2-fold increase in binding affinity (Bohl et al 2005). W741L AR-positive tumor cells, if stimulated by bicalutamide, show a significant upregulation of the MAPK pathway compared to tumor cells carrying wildtype AR (Terakawa et al 2010). Even before bicalutamide, flutamide was reported to act as an agonist for T877S and H874Y AR (Fenton et al 1997).…”