Non randomized study on the potential of nitisinone to inhibit cytochrome P450 2C9, 2D6, 2E1 and the organic anion transporters OAT1 and OAT3 in healthy volunteers

Abstract

Purpose Nitisinone inhibits the cytochrome P450 (CYP) subfamilies CYP2C9, CYP2D6, and CYP2E1 and the organic anion transporter (OAT) isoforms OAT1 and OAT3 in vitro. Since the effect of nitisinone on these enzymes and transporters in humans is still unknown, the purpose of this study was to evaluate the effect of nitisinone on these CYP subfamilies and OAT isoforms. Methods This was an open-label, nonrandomized, two-arm, phase 1 study (EudraCT: 2016-004297-17) in healthy volunteers. The substrates (tolbutamide, metoprolol, and chlorzoxazone for the respective CYPs and furosemide for the OATs) were administered as single doses, before and after 15 days of once daily dosing of 80 mg nitisinone, to determine the AUC ∞ ratios ([substrate+nitisinone]/[substrate]). Nitisinone pharmacokinetics, safety, and tolerability were also assessed, and blood and urine were collected to determine substrate and nitisinone concentrations by LC-MS/MS. Results Thirty-six subjects were enrolled with 18 subjects included in each arm. The least square mean ratio (90% confidence interval) for AUC ∞ was 2.31 (2.11-2.53) for tolbutamide, 0.95 (0.88-1.03) for metoprolol, 0.73 (0.67-0.80) for chlorzoxazone, and 1.72 (1.63-1.81) for furosemide. Clinically relevant nitisinone steady-state concentrations were reached after 12 days: mean C av,ss of 94.08 μM. All treatments were well tolerated, and no safety concerns were identified. Conclusions Nitisinone did not affect CYP2D6 activity, was a weak inducer of CYP2E1, and was a weak inhibitor of OAT1 and OAT3. Nitisinone was a moderate inhibitor of CYP2C9, and treatment may therefore result in increased plasma concentrations of comedications metabolized primarily via this enzyme. Clinical trial registry identification EudraCT 2016-004297-17.

Inter‐laboratory analytical improvement of succinylacetone and nitisinone quantification from dried blood spot samples

“…It takes well over a month before SA in blood becomes unquantifiable and therefore within normal limits. For nitisinone on the other hand, the half‐life is approximately 2 days (1 day in newborns) . A steady‐state concentration is obtained after 12 days dosing …”

“…For nitisinone on the other hand, the half-life is approximately 2 days (1 day in newborns). 23,24 A steadystate concentration is obtained after 12 days dosing. 24 A limitation of the study is that time/stability and temperature stability studies were not performed, and data on time of analysis at each laboratory from preparation of samples were not collected for the calculation of recovery rates.…”

Repurposing the orphan drug nitisinone to control the transmission of African trypanosomiasis

“…Metabolic resistance due to increased rates of insecticide metabolism by P450s can cause resistance liabilities for new compounds. However, NTBC appears to only be moderately metabolised by CYP3A4 in humans [27], with little oxidative metabolism by other liver CYP enzymes [28]. We have incubated NTBC with microsomes extracted from tsetse, Aedes, and Anopheles and failed to detect evidence of metabolism as measured by substrate depletion/turnover (S2 Table ).…”

Interpretation of Cytochrome P‐450 Inhibition and Induction Effects From Clinical Data: Current Standards and Recommendations for Implementation

“…4 For example, CYP2C9 currently has no well-established and consistently supported sensitive substrates, so a moderate sensitive substrate, such as tolbutamide, is typically studied instead. 5,6 Studies using moderate sensitive and nonsensitive substrates are not explicitly included in the above inhibitor and inducer standards, but are in practice held to the same criteria as studies with sensitive substrates.…”

“…When sensitive index substrates are not known or suitable for study of an elimination pathway, moderate sensitive index substrates—those whose AUC is increased twofold to fivefold with strong inhibitors or is twofold to fivefold greater in PM‐type than normal metabolizer‐type subjects—are recommended for study instead 4 . For example, CYP2C9 currently has no well‐established and consistently supported sensitive substrates, so a moderate sensitive substrate, such as tolbutamide, is typically studied instead 5,6 …”