Biotransformation of prednisone and dexamethasone by cytochrome P450 based systems – Identification of new potential drug candidates

Abstract

Prednisone and dexamethasone are synthetic glucocorticoids widely used as anti-inflammatory and immunosuppressive drugs. Since their hydroxylated derivatives could serve as novel potential drug candidates, our aim was to investigate their biotransformation by the steroid hydroxylase CYP106A2 from Bacillus megaterium ATCC13368. In vitro we were able to demonstrate highly selective 15β-hydroxylation of the steroids with a reconstituted CYP106A2 system. The reactions were thoroughly characterized, determining the kinetic parameters and the equilibrium dissociation constant. The observed lower conversion rate in the case of dexamethasone hydroxylation was clarified by quantum chemical calculations, which suggest a rearrangement of the intermediately formed radical species. To identify the obtained conversion products with NMR, CYP106A2-based Bacillus megaterium whole-cell systems were applied resulting in an altered product pattern for prednisone, yet no significant change for dexamethasone conversion compared to in vitro. Even the MS941 control strain performed a highly selective biotransformation of prednisone producing the known metabolite 20β-dihydrocortisone. The identified novel prednisone derivatives 15β, 17, 20β, 21-tetrahydroxy-preg-4-en-3,11-dione and 15β, 17, 20β, 21-tetrahydroxy-preg-1,4-dien-3,11-dione as well as the 15β-hydroxylated variants of both drugs are promising candidates for drug-design and development approaches.