Abiraterone Acetate for Cushing Syndrome: Study in a Canine Primary Adrenocortical Cell Culture Model

Abiraterone acetate (AA) is a potent inhibitor of steroidogenic enzyme 17α-hydroxylase/17,20-lyase (CYP17A1). AA is approved for the treatment of prostate cancer but could also be used to treat patients with Cushing syndrome (CS). Similar to humans, canine glucocorticoid synthesis requires CYP17A1, providing a useful animal model. The objective of this study was to preclinically investigate the effect of AA on adrenocortical hormone production, cell viability, and mRNA expression of steroidogenic enzymes in canine primary adrenocortical cell cultures (n = 9) from the adrenal glands of nine healthy dogs. The cells were incubated with AA (0.125 nM to 10 μM) for 72 hours under basal conditions and with 100 nM ACTH(1-24). Adrenocortical hormone concentrations were measured in culture medium using liquid chromatography-mass spectrometry, RNA was isolated from cells for subsequent real-time quantitative PCR analysis, and cell viability was assessed with an alamarBlue™ assay. AA reduced cortisol (IC50, 21.4 ± 4.6 nM) without affecting aldosterone under basal and ACTH-stimulated conditions. AA increased progesterone under basal and ACTH-stimulated conditions but reduced corticosterone under basal conditions, suggesting concurrent inhibition of 21-hydroxylation. AA did not affect the mRNA expression of steroidogenic enzymes and did not inhibit cell viability. In summary, primary canine adrenocortical cell culture is a useful model system for drug testing. For the treatment of CS, AA may to be superior to other steroidogenesis inhibitors due to its low toxicity. For future in vivo studies, dogs with endogenous CS may provide a useful animal model.

Therapy of endocrine disease: steroidogenesis enzyme inhibitors in Cushing's syndrome

Steroidogenesis enzyme inhibitors are the mainstay of medical therapy in Cushing's syndrome (CS). Ketoconazole (KTZ) and metyrapone are the most commonly used agents. Although there is considerable experience of their use in individual specialist centres, these drugs have not been rigorously tested in prospective clinical trials. Clinicians face uncertainties and concerns with respect to the safety profile of these agents, and best means to monitor effect. We review steroidogenesis inhibitors in the management of CS, including older agents (KTZ, metyrapone, etomidate and mitotane) and those currently under development (LCI699, non-racemic KTZ), and offer a practical approach for their use in clinical practice.