Role of rat liver cytochrome P450 3A and 2D in metabolism of imrecoxib

Comparative Pharmacokinetics and Safety of Imrecoxib, a Novel Selective Cyclooxygenase-2 Inhibitor, in Elderly Healthy Subjects

Background

Imrecoxib is a novel and moderately selective cyclooxygenase-2 inhibitor with properties of anti-inflammation and alleviating pain, which is widely applied in osteoarthritis patients. The pharmacokinetic data supporting imrecoxib’s rational use in elderly population are not available.

Purpose

The study aims to investigate the pharmacokinetics of imrecoxib and its main metabolites and explore the safety of imrecoxib in elderly healthy subjects.

Methods

A total of 19 healthy subjects including 10 non-elderly and 9 elderly subjects received single dose of 100 mg imrecoxib under fasting condition. Pharmacokinetics, safety and tolerability profiles were assessed.

Results

After oral administration of single dose of 100 mg imrecoxib, it was absorbed into plasma with median time to reach peak concentration (T_max) around 2 hours. The concentration–time curves of imrecoxib (M0) showed higher interindividual variability in elderly subjects compared with non-elderly subjects. Peak concentration (C_max) of M0, its hydroxyl metabolite M1 and carboxylated metabolite M2 in plasma increased by 39%, 21% and 17%, and area under concentration–time curve from time 0 to time t (AUC_0-t) of M0, M1 and M2 in plasma increased by 34%, 13% and 27%, respectively, in elderly subjects compared with non-elderly subjects. The 90% CIs of geometric mean ratios of C_max, AUC_0-t and AUC_0-∞ of M0, M1 and M2 between the two groups were not located within 80–125%, indicating C_max, AUC_0-t and AUC_0-∞ were not completely equivalent between non-elderly and elderly healthy subjects. However, comparison of pharmacokinetic data of M0, M1 and M2 between the two groups showed no significant difference (P>0.05). Imrecoxib was well tolerated in both non-elderly and elderly healthy subjects, especially with favorable gastrointestinal and cardiovascular safety profiles.

Conclusion

Pharmacokinetic and safety profiles of imrecoxib in elderly healthy subjects indicated that no dose adjustment should be required for elderly population.

Inhibition of imrecoxib on mRNA and protein expression of CYP2C11 enzyme in rats

PURPOSE

To evaluate the effect of imrecoxib on CYP2C11 enzyme activity, mRNA and protein expression.

METHOD

An ultra-performance liquid chromatography (UPLC) method was established. Tolbutamide was selected as CYP2C11 enzyme-specific probe drug and incubated with imrecoxib in rat liver microsomes. The amount of 4-hydroxytolbutamide produced was measured by UPLC to investigate the effect of imrecoxib on CYP2C11 enzyme activity. Imrecoxib (10 mg/kg) was given by intragastric administration twice daily. After 1, 7 and 14 days of administration, liver tissues were taken. The expression of CYP2C11 enzyme mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR), and its protein expression was determined by Western Blot.

RESULTS

Imrecoxib concentration was inversely proportional to the production of 4-hydroxytolbutamide in liver microsomes. Imrecoxib demonstrated dose-dependent inhibitory effect on CYP2C11 activity with IC50=74.77 μM. After administration, RT-PCR showed CYP2C11 enzyme mRNA expressions were 65% (P<0.05), 35%, and 34% of control group, respectively (P<0.01). Western Blot showed CYP2C11 enzyme protein expressions were 80%, 37%, and 34% of control group, respectively (P<0.01).

CONCLUSION

Imrecoxib can reduce mRNA and protein expression of CYP2C11 enzyme in rat liver and inhibit the activity of CYP2C11 enzyme in a dose-dependent manner. However, it will not produce clinically significant drug interactions.

Dose investigation of imrecoxib in patients with renal insufficiency based on modelling and simulation

OBJECTIVE

Imrecoxib is a new moderately selective cyclooxygenase-2 (COX-2) inhibitor. A previous study has shown that drug exposure differs significantly in renally impaired patients. We aim to describe the population pharmacokinetics (PPK) of imrecoxib (M0) and its two metabolites (M1, M2) to provide a theoretical basis for investigating imrecoxib doses for renally impaired patients.

METHODS

Using PPK analysis, 24 patients with 257 different plasma concentrations were studied. Of these, 12 had severe renal impairment and 12 had normal renal function. The dose regimen was simulated based on the final model to compare the ratio (Cu,ss/IC50) of the average unbound concentration at steady state (Cu,ss) to the half-maximal inhibitory concentration (IC50) of COX-2.

RESULTS

Imrecoxib and its metabolite concentrations were satisfactorily described by a two-compartment with first-order transit absorption model for imrecoxib and a one-compartment model for its metabolites. Renal function was a significant binary covariate. Scenarios of '75 mg q12h' and '50 mg q8h' in renally impaired patients had similar Cu,ss/IC50 values with a '100 mg q12h' regimen in subjects with normal renal function.

CONCLUSION

A PPK model of imrecoxib and its two metabolites is presented. The renal insufficiency regimen should be reduced to '75 mg q12h' or '50 mg q8h'.

Biotransformation and bioactivation reactions - 2018 literature highlights

In the past three decades, ADME sciences have become an integral component of the drug discovery and development process. At the same time, the field has continued to evolve, thus, requiring ADME scientists to be knowledgeable of and engage with diverse aspects of drug assessment: from pharmacology to toxicology, and from in silico modeling to in vitro models and finally in vivo models. Progress in this field requires deliberate exposure to different aspects of ADME; however, this task can seem daunting in the current age of mass information. We hope this review provides a focused and brief summary of a wide array of critical advances over the past year and explains the relevance of this research ( Table 1 ). We divided the articles into categories of (1) drug optimization, (2) metabolites and drug metabolizing enzymes, and (3) bioactivation. This annual review is the fourth of its kind (Baillie et al. 2016 ; Khojasteh et al. 2017 , 2018 ). We have followed the same format we used in previous years in terms of the selection of articles and the authoring of each section. This effort in itself also continues to evolve. I am pleased that Rietjens, Miller, and Mitra have again contributed to this annual review. We would like to welcome Namandjé N. Bumpus, James P. Driscoll, and Donglu Zhang as authors for this year's issue. We strive to maintain a balance of authors from academic and industry settings. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. Cyrus Khojasteh, on behalf of the authors.

Formation of 4'-carboxyl acid metabolite of imrecoxib by rat liver microsomes

AIM

Imrecoxib is a novel and moderately selective COX-2 inhibitor. The aim of the present in vitro investigation was to study the formation of the major metabolite 4'-carboxylic acid imrecoxib (M2) and identify the enzyme(s) involved in the reaction.

METHODS

The formation of M2 was studied in rat liver cytosol in the absence or presence of liver microsome. The formed metabolite was identified and quantified by LC/MS(n). In addition, to characterize the cytochrome P450 (CYP) isozymes involved in M2 formation, the effects of typical CYP inhibitors (such as ketoconazle, quinine, alpha-naphthoflavone, methylpyrazole, and cimetidine) on the formation rate of M2 were investigated.

RESULTS

The formation of M2 from 4-hydroxymethyl imrecoxib (M4) was completely dependent on rat liver microsomes and NADPH. Enzyme kinetic studies demonstrated that the formation rate of M2 conformed to monophasic Michaelis-Menten kinetics. Additional experiments showed that the formation of M2 was induced significantly by dexamethasone and lowered by ketoconazole strongly and concentration-dependently. By comparison, other CYP inhibitors, such as alpha-naphthoflavone, cimetidine, quinine, and methylpyrazole had no inhibitory effects on this metabolic pathway.

CONCLUSION

These biotransformation studies of imrecoxib in rat liver at the subcellular level showed that the formation of M2 occurs in rat liver microsomes and is NADPH-dependent. The reaction was mainly catalyzed by CYP 3A in untreated rats and in dexamethasone-induced rats. Other CYP, such as CYP 1A, 2C, 2D, and 2E, seem unlikely to participate in this metabolic pathway.