Amiloride effects on abiraterone antiproliferative activity in prostate cancer cells in vitro and on clinical management of abiraterone induced mineralocorticoid excess syndrome.
175 Background: Abiraterone acetate (AA) deeply inhibits androgen synthesis but leads to an ACTH driven increase in mineralocorticoid hormones requiring glucocorticoid supplementation that may impair its antineoplastic efficacy. New strategies for the management of the AA induced mineral corticoid excess syndrome (MCES) are warranted. Methods: We analyzed in vitro the interaction in terms of proliferative activity of AA plus/minus prednisone with the steroid aldosterone receptor antagonists: eplerenone, spironolactone, a non-steroidal aldosterone receptor antagonist (PF-03882845) and the epithelial sodium channel antagonist amiloride. LNCaP were grown in a medium with charcoal-treated serum and concentration-response curves for each studied drug were performed. Besides, the activity of amiloride plus hydrochlorothiazide was assessed in the clinical management of AA induced MCES in 5 consecutive patients with castrate resistant prostate cancer. The recovery of AA induced MCES symptoms and signs was the primary end point. Results: Prednisone, spironolactone and eplerenone induced an increase in the LNCAP proliferation rate and antagonized the AA-induced reduction of the cell proliferation in a concentration-dependent manner, while PF-03882845 did not. Amiloride at high concentrations induced cell death. When combined with AA +/- prednisone, amiloride at low concentration did not interfere with AA anti-proliferative activity however an additive inhibitory effect was observed at higher concentrations. The association of amiloride with hydrochlorothiazide led to a complete disappearance of all clinical and biochemical signs of abiraterone induced MCES in the 5 treated patients. Conclusions: Amiloride and PF-03882845 do not negatively interfere with the AA inhibition of proliferative activity of prostate cancer cells in vitro. The association of amiloride plus hydrochlorothiazide is efficacious in the management AA induced MCES.