Spironolactone: A Selective Androgen Receptor Modulator In Castration-Resistant Prostate Cancer

212 Background: Spironolactone is an effective drug to treat arterial hypertension as well as fluid retention and hypokalemia. Recently, some data suggested that spironolactone might induce progression in castration-resistant prostate cancer (CRPC) patients treated by abiraterone acetate, a recently approved selective CYP17 inhibitor. Nevertheless, no biological data are available to explain these clinical observations. The purpose of this study was to identify the potential underlying molecular mechanism. Methods: Effect of spironolactone with or without Abiraterone acetate (AA) on androgen receptor (AR) was assessed on LNCaP cells in this study. We performed a yeast-based functional assay with different levels of spironolactone with and without AA. The nuclear localization and activation of androgen receptor (AR) were detected by immunofluorescence and luciferase assays. Results: Results from the yeast-based functional assay show that the wild type androgen receptor is activated by high concentrations of spironolactone in an androgen-depleted environment. Moreover, spironolactone-induced AR transcriptional activity is downregulated by different AR antagonists as well as high concentrations of AA. These results suggest that spironolactone is possibly a potential AR modulator. Luciferase reporter assays showed that AR transcriptional activity in LNCaP cells was upregulated by spironolactone as well. Finally, AR immunoreactivity was almost nuclear in spironolactone-exposed cells. Taken together, these results suggest that spironolactone is a selective androgen receptor modulator. Conclusions: Spironolactone is a selective androgen receptor modulator and should be used with caution in routine practice in patient with metastatic prostate cancer treated by hormonotherapy especially AA.