Medical treatment of Cushing's disease: somatostatin analogues and pasireotide.

Cushing's disease is Cushing's syndrome caused by an adrenocorticotropic hormone-secreting pituitary adenoma and, in the absence of adequate treatment, can be fatal. Cushing's disease represents an unmet medical need, with no approved medical therapies. Pasireotide is a novel multi-receptor-targeted somatostatin analogue with high affinity for sst(1,2,3) and sst(5). Compared with octreotide, pasireotide has an in vitro binding affinity 40-, 30- and 5-fold higher for sst(5,) sst(1) and sst(3), respectively, and 2-fold lower for sst(2). Adrenocorticotropic hormone-secreting pituitary adenomas predominantly express sst(5), followed by sst(2) and sst(1), suggesting that pasireotide may be effective in the treatment of Cushing's disease. In a 15-day phase II trial of pasireotide 600 μg s.c. b.i.d. in patients with de novo or persistent/recurrent Cushing's disease, 22 of 29 patients (76%) achieved reduced urinary free cortisol (UFC) levels, 5 of whom (17%) achieved normalized UFC. Patients who achieved normalized UFC had a significantly greater reduction in serum cortisol than those who did not (p = 0.04), and minimum pasireotide plasma concentrations appeared to be higher in responders. Based on these results, a randomized, double-blind phase III study comparing pasireotide 600 μg b.i.d. and 900 μg b.i.d. was initiated and is ongoing. This is the largest ever phase III study in patients with Cushing's disease. The primary end point of this study is normalization of UFC after 6 months of treatment. Finally, preliminary results from a study on 17 patients with Cushing's disease suggest that the combined use of pasireotide, cabergoline and low-dose ketoconazole may have additive beneficial effects in the medical treatment of Cushing's disease.