213 Histone Deacetylase Inhibitor Vorinostat Is a Novel, Promising Treatment for Cushing Disease

INTRODUCTION: Recurrence (or remission failure) following transsphenoidal surgery in Cushing disease (CD) from pituitary corticotroph tumors (CtT) is a challenging clinical problem. Definitive therapy for recurrent/unremitting CD is limited to radiation, and medical/surgical adrenalectomy. Histone deacetylase inhibitors (HDACi) are drugs with potent antitumor activity approved for oral clinical use, with potential to affect adrenocorticotropin (ACTH) by inhibiting HDAC effect on proopiomelanocortin (POMC) transcription. METHODS: HDACi (Vorinostat/Valproate/Panabinostat) effect on cell survival (XTT/MTT), ACTH secretion (enzyme-linked immunosorbent assay), and apoptotic pathway (quantitative real-time polymerase chain reaction/Western blot) was tested on murine corticotroph tumor AtT20 cells. In vivo efficacy was tested in NCr nude mouse AtT20 xenograft model. Finally, HDACi efficacy against patient-derived CtT cells (n = 8) was tested in vitro. RESULTS: Vorinostat (1 µM) reduced AtT20 survival to 75% at 24 hours, 43% at 48 hours (analysis of variance, P = .002). Valproate/Panabinostat had no effect on survival. Vorinostat (1 µM/3-24 hours) resulted in significant reduction (70%, P < .001) of secreted ACTH in media. AtT20 survival and ACTH secretion was inversely associated with Vorinostat dose (0.5-4 µM) and time (3-72 hours). Vorinostat resulted in NFkB overexpression and decrease in POMC expression. Apoptosis activation was confirmed with increased BAX/Bcl2 ratio and cleaved PARP. Nude-mice xenograft AtT20 tumor involution (126 ± 33/160 ± 35 vs 337 ± 49 mm3, P = .001), protection from body weight loss (P < .001), and reversal of skin thinning was observed with intraperitoneal Vorinostat (50/25 mg/kg/24 hours) for 5 days. Corresponding reversal of elevated serum ACTH (P < .001) and cortisol (P = .003) occurred with Vorinostat. Effect on human CtT cells was confirmed with observation of decreased survival (78.92%, P = .001) and decreased ACTH secretion (83.64%, P = .03) with 1 µM Vorinostat exposure for 24 hours. CONCLUSION: Vorinostat is effective in reducing survival (via apoptosis activation) and ACTH secretion (via NFkB overexpression) in AtT20 and human tumors. Vorinostat may provide a novel strategy for recurrent/unremitting CD via antitumor and hormone effects.