Abstract MP11: Aldosterone Synthase Structure With Cushing’s Disease Drug Osilodrostat Provides Clues For Treatment Of Primary Aldosteronism

Abstract

Primary aldosteronism, the major form of secondary hypertension, often leads to cardiac disease. It develops due to excess steroid hormone aldosterone produced by aldosterone synthase, also known as cytochrome P450 11B2. CYP11B2 is 93% identical to cortisol-producing CYP11B1, which makes it difficult to design drugs specifically targeting CYP11B2. Osilodrostat (LCI699, Isturisa®) was initially developed as CYP11B2 inhibitor, but due to higher potency for CYP11B1 is now the first FDA-approved drug for CYP11B1-mediated Cushing’s disease. Thus, there is still no effective therapeutic option targeting CYP11B2 for primary aldosteronism. To determine aspects of the CYP11B2/osilodrostat interaction that could be improved to design a more selective CYP11B2 inhibitor, this project took a structure/function approach. First, osilodrostat affinity to CYP11B2 was examined using UV/vis spectroscopy. Osilodrostat induced a spectral change typical of ligand nitrogen coordination to the catalytic heme iron, establishing the binding location and mode, and revealed high CYP11B2 affinity. X-ray crystallography was used to solve the structure of CYP11B2 bound to osilodrostat. Consistent with the spectral analysis, osilodrostat binds in the active site with its imidazole nitrogen coordinating the heme iron. Additional interactions occur with the osilodrostat fluorinated benzonitrile. Osilodrostat binding was compared with that of its analog fadrozole to both CYP11B enzymes. CYP11B2 binding of osilodrostat is similar to (R) -fadrozole, but the fluorination of osilodrostat mediates additional active site interactions. Comparison with the previously-available CYP11B1 structure reveals CYP11B1 favors (S) -fadrozole due to distinct CYP11B active site architectures. These results suggest an opportunity to optimize inhibitor sterics to better discriminate between these two steroidogenic cytochrome P450 enzymes. Exploiting structural differences between the CYP11B enzymes should promote the design of therapeutics for the treatment of primary aldosteronism targeting CYP11B2, while reducing undesirable side effects due to off-target CYP11B1 inhibition.