Metabolite V, an epoxide species is a minor circulating metabolite in humans following a single oral dose of deflazacort

In vitro cytochrome P450- and transporter-mediated drug interaction potential of 6β-hydroxy-21-desacetyl deflazacort-A major human metabolite of deflazacort

6β-Hydroxy-21-desacetyl deflazacort (6β-OH-21-desDFZ) is a major circulating but not biologically active metabolite of deflazacort (DFZ). In vitro studies were performed to evaluate cytochrome P450 (CYP)- and transporter-mediated drug interaction potentials of 6β-OH-21-desDFZ. Up to 50 µM, the highest soluble concentration in the test system, 6β-OH-21-desDFZ weakly inhibited (IC₅₀  > 50 µM) the enzyme activity of CYPs 1A2, 2B6, 2C8, 2C9, and 2D6, while moderately inhibiting CYP2C19 and CYP3A4 with IC₅₀ values of approximately 50 and 35 μM, respectively. The inhibition was neither time-dependent nor metabolism-based. Incubation of up to 50 µM 6β-OH-21-desDFZ with plated cryopreserved human hepatocytes for 48 h resulted in no meaningful concentration-dependent induction of either mRNA levels or enzyme activity of CYP1A2, CYP2B6, or CYP3A4. In transporter inhibition assays, 6β-OH-21-desDFZ, up to 50 µM, did not show interaction with human OAT1, OAT3, and OCT2 transporters. It weakly inhibited (IC₅₀  > 50 µM) human MATE1, MATE2-K, and OCT1 transporter activity, and moderately inhibited human MDR1, OATP1B1, and OATP1B3 transporter activity with IC₅₀ values of 19.81 μM, 37.62 μM, and 42.22 μM, respectively. ¹⁴ C-6β-OH-21-desDFZ was biosynthesized using bacterial biotransformation and the subsequent study showed that 6β-OH-21-desDFZ was not a substrate for human BCRP, MDR1, MATE1, MATE2-K, OAT1, OATP1B1, OATP1B3, and OCT2 transporters, but appeared to be an in vitro substrate for the human OAT3 uptake transporter. At plasma concentrations of 6β-OH-21-desDFZ seen in the clinic, CYP- and transporter-mediated drug-drug interactions are not expected following administration of a therapeutic dose of DFZ in Duchenne muscular dystrophy (DMD) patients.