Fenretinide metabolism in humans and mice: utilizing pharmacological modulation of its metabolic pathway to increase systemic exposure

Abstract

BACKGROUND AND PURPOSEHigh plasma levels of fenretinide [N-(4-hydroxyphenyl)retinamide (4-HPR)] were associated with improved outcome in a phase II clinical trial. Low bioavailability of 4-HPR has been limiting its therapeutic applications. This study characterized metabolism of 4-HPR in humans and mice, and to explore the effects of ketoconazole, an inhibitor of CYP3A4, as a modulator to increase 4-HPR plasma levels in mice and to increase the low bioavailability of 4-HPR.EXPERIMENTAL APPROACH4-HPR metabolites were identified by mass spectrometric analysis and levels of 4-HPR and its metabolites [N-(4-methoxyphenyl)retinamide (4-MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR)] were quantified by high-performance liquid chromatography (HPLC). Kinetic analysis of enzyme activities and the effects of enzyme inhibitors were performed in pooled human and pooled mouse liver microsomes, and in human cytochrome P450 (CYP) 3A4 isoenzyme microsomes. In vivo metabolism of 4-HPR was inhibited in mice.KEY RESULTSSix 4-HPR metabolites were identified in the plasma of patients and mice. 4-HPR was oxidized to 4-oxo-4-HPR, at least in part via human CYP3A4. The CYP3A4 inhibitor ketoconazole significantly reduced 4-oxo-4-HPR formation in both human and mouse liver microsomes. In two strains of mice, co-administration of ketoconazole with 4-HPR in vivo significantly increased 4-HPR plasma concentrations by > twofold over 4-HPR alone and also increased 4-oxo-4-HPR levels.CONCLUSIONS AND IMPLICATIONSMice may serve as an in vivo model of human 4-HPR pharmacokinetics. In vivo data suggest that the co-administration of ketoconazole at normal clinical doses with 4-HPR may increase systemic exposure to 4-HPR in humans.

Anti-cancer potency of tasquinimod is enhanced via albumin-binding facilitating increased uptake in the tumor microenvironment

“…The liver is the major site of metabolism for quinoline-3-carboxamide compounds via Cytochrome P450 3A (CYP-3A) which can be inhibited by ketoconazole [29]. This conclusion is confirmed by the demonstration that co-treatment of mice with ketoconazole, at an oral dose of 25mg/kg/day which inhibits CYP-3A by > 90% [32], decreases tasquinimod's β-elimination phase resulting in an increase in the plasma elimination half-life by more than 8 fold, Figure1D. Metabolically, tasquinimod can be: 1) hydroxylated in the aromatic quinoline scaffold in multiple sites, 2) N-demethylated at the quinoline nitrogen, 3) N-demethylated at the carboxamide nitrogen, or 4) O-demethylated at the quinoline methoxy group, Figure1E.…”

“…To confirm this conclusion, castrated male nude mice were xenografted with the castrate resistant CWR-22RH human prostate cancer tissue and the animals immediately randomized into groups (n=10) which were: 1) left untreated as controls; 2) given daily oral treatment with tasquinimod alone via the drinking water (10mg/kg/day); 3) given oral ketoconazole alone via oral gavage at a daily dose which inhibits cytochrome P450 3A4 (i.e., 25 mg/kg/day) [32]; or 4) given a combination of the two drugs. The ability of this ketoconazole dosing regimen to inhibit tasquinimod metabolism was validated by the demonstration that it prolong (p<0.05) the plasma clearance of tasquinimod, Figures 1B&C.…”

The Bioactive Lipid 4-Hydroxyphenyl Retinamide Inhibits Flavivirus Replication

“…The in vivo anti-DENV-2 activity of 4-HPR was comparable to that of celgosivir (50 mg/kg/ day, 0.80 log 10 ), which was previously shown to be efficacious in murine models of lethal DENV-2 infection (43,44) and which is currently in a phase Ib clinical trial as an anti-DENV-2 agent. The coadministration of ketoconazole improves 4-HPR pharmacokinetics by slowing the conversion of 4-HPR into 4-oxo-4-HPR (61) and led to slightly reduced plasma viremia compared to that in mice treated with 4-HPR alone. This interpretation is supported by the observation that 4-oxo-4-HPR was a less potent inhibitor of DENV-2 than 4-HPR and that ketoconazole had no anti-DENV-2 activity in cell culture (see Fig.…”

Lecithin:Retinol Acyltransferase Is Critical for Cellular Uptake of Vitamin A from Serum Retinol-binding Protein

“…Furthermore, the synthetic retinoid FHR also reduced RBP levels in wild type but not Lrat Ϫ/Ϫ mice, but FHR, unlike ATRA, displays a longer half-life and does not show evidence of autoinduced increased metabolism by Cyp26a1 (see Ref. 35 and references therein). Indeed, RBP serum levels were still reduced after 24 h in wild type mice after FHR treatment, whereas Lrat Ϫ/Ϫ mice showed no such reduction.…”