The ketoconazole legacy

Genotoxicity of pyrrolizidine alkaloids in metabolically inactive human cervical cancer HeLa cells co-cultured with human hepatoma HepG2 cells

Pyrrolizidine alkaloids (PAs) are secondary plant metabolites, which can be found as contaminant in various foods and herbal products. Several PAs can cause hepatotoxicity and liver cancer via damaging hepatic sinusoidal endothelial cells (HSECs) after hepatic metabolization. HSECs themselves do not express the required metabolic enzymes for activation of PAs. Here we applied a co-culture model to mimic the in vivo hepatic environment and to study PA-induced effects on not metabolically active neighbour cells. In this co-culture model, bioactivation of PA was enabled by metabolically capable human hepatoma cells HepG2, which excrete the toxic and mutagenic pyrrole metabolites. The human cervical epithelial HeLa cells tagged with H2B-GFP were utilized as non-metabolically active neighbours because they can be identified easily based on their green fluorescence in the co-culture. The PAs europine, riddelliine and lasiocarpine induced micronuclei in HepG2 cells, and in HeLa H2B-GFP cells co-cultured with HepG2 cells, but not in HeLa H2B-GFP cells cultured alone. Metabolic inhibition of cytochrome P450 enzymes with ketoconazole abrogated micronucleus formation. The efflux transporter inhibitors verapamil and benzbromarone reduced micronucleus formation in the co-culture model. Furthermore, mitotic disturbances as an additional genotoxic mechanism of action were observed in HepG2 cells and in HeLa H2B-GFP cells co-cultured with HepG2 cells, but not in HeLa H2B-GFP cells cultured alone. Overall, we were able to show that PAs were activated by HepG2 cells and the metabolites induced genomic damage in co-cultured HeLa cells.

Interaction of CYP3A4 with Rationally Designed Ritonavir Analogues: Impact of Steric Constraints Imposed on the Heme-Ligating Group and the End-Pyridine Attachment

Controlled inhibition of drug-metabolizing cytochrome P450 3A4 (CYP3A4) is utilized to boost bioavailability of anti-viral and immunosuppressant pharmaceuticals. We investigate structure–activity relationships (SARs) in analogues of ritonavir, a potent CYP3A4 inhibitor marketed as pharmacoenhancer, to determine structural elements required for potent inhibition and whether the inhibitory potency can be further improved via a rational structure-based design. This study investigated eight (series VI) inhibitors differing in head- and end-moieties and their respective linkers. SAR analysis revealed the multifactorial regulation of inhibitory strength, with steric constraints imposed on the tethered heme-ligating moiety being a key factor. Minimization of these constraints by changing the linkers’ length/flexibility and N-heteroatom position strengthened heme coordination and markedly improved binding and/or inhibitory strength. Impact of the end-pyridine attachment was not uniform due to influence of other determinants controlling the ligand-binding mode. This interplay between pharmacophoric determinants and the end-group enlargement can be used for further inhibitor optimization.

Rational Design of CYP3A4 Inhibitors: A One-Atom Linker Elongation in Ritonavir-Like Compounds Leads to a Marked Improvement in the Binding Strength

Inhibition of the major human drug-metabolizing cytochrome P450 3A4 (CYP3A4) by pharmaceuticals and other xenobiotics could lead to toxicity, drug–drug interactions and other adverse effects, as well as pharmacoenhancement. Despite serious clinical implications, the structural basis and attributes required for the potent inhibition of CYP3A4 remain to be established. We utilized a rational inhibitor design to investigate the structure–activity relationships in the analogues of ritonavir, the most potent CYP3A4 inhibitor in clinical use. This study elucidated the optimal length of the head-group spacer using eleven (series V) analogues with the R₁/R₂ side-groups as phenyls or R₁–phenyl/R₂–indole/naphthalene in various stereo configurations. Spectral, functional and structural characterization of the inhibitory complexes showed that a one-atom head-group linker elongation, from pyridyl–ethyl to pyridyl–propyl, was beneficial and markedly improved K_s, IC₅₀ and thermostability of CYP3A4. In contrast, a two-atom linker extension led to a multi-fold decrease in the binding and inhibitory strength, possibly due to spatial and/or conformational constraints. The lead compound, 3h, was among the best inhibitors designed so far and overall, the strongest binder (K_s and IC₅₀ of 0.007 and 0.090 µM, respectively). 3h was the fourth structurally simpler inhibitor superior to ritonavir, which further demonstrates the power of our approach.

The Effect of CYP3A Induction and Inhibition on the Pharmacokinetics of Laquinimod, a Novel Neuroimmunomodulator

Laquinimod, a neuroimmunomodulator, is extensively metabolized by cytochrome P450 (CYP) 3A4, and modulations of CYP3A4 activity may lead to alterations in the pharmacokinetics and/or clinical effects of laquinimod. To determine the drug-drug interaction potential of laquinimod with CYP3A inhibitors and inducers, interaction assessments were conducted in healthy volunteers using single-dose administration of laquinimod before and after multiple dosing of CYP3A inhibitors (ketoconazole, fluconazole, and cimetidine) or a CYP3A4 inducer (rifampin). For ketoconazole, subjects (n = 14) received laquinimod 0.6 mg following 1 day of ketoconazole (400 mg daily) pretreatment, a single concomitant dose, and 28 additional days. For fluconazole, subjects (n = 14) received laquinimod 0.6 mg after a single fluconazole dose of 400 mg followed by 200-mg daily fluconazole administration for 20 additional days. For cimetidine, subjects (n = 14) received laquinimod 0.6 mg following 1 day of cimetidine (800 mg twice daily) pretreatment, a single concomitant dose, and 21 additional days. For rifampin, subjects (n = 14) received laquinimod 0.6 mg following 9 days of rifampin (600 mg daily) pretreatment, a single concomitant dose, and 12 additional days. Coadministration of laquinimod with CYP3A inhibitors, ketoconazole, fluconazole, and cimetidine increased laquinimod area under the plasma concentration-time curve from time zero to infinity by approximately 3.1-, 2.5-, and 1.1-fold, respectively. Coadministration of laquinimod with rifampin decreased laquinimod area under the plasma concentration-time curve from time zero to infinity by 5-fold. These results indicate that coadministration of laquinimod with moderate to strong inhibitors of CYP3A or strong inducers of CYP3A may give rise to significant pharmacokinetic drug interactions.

Microphysiological heart-liver body-on-a-chip system with a skin mimic for evaluating topical drug delivery

Body-on-a-chip in vitro systems are a promising technology that aims to increase the predictive power of drug efficacy and toxicity in humans when compared to traditional animal models. Here, we developed a new heart-liver body-on-a-chip system with a skin surrogate to assess the toxicity of drugs that are topically administered. In order to test the utility of the system, diclofenac, ketoconazole, hydrocortisone and acetaminophen were applied topically through a synthetic skin surrogate (Strat-M membrane) and the toxicity results were compared to those of acute drug exposure from systemically applying the compounds. The heart-liver system was successful in predicting the effects for both cardiac and liver functions changes due to the compounds. The difference in the concentrations of drugs applied topically compared to systemically indicates that the barrier properties of the skin surrogate were efficient. One important advantage of this heart-liver system was the capability of showing differential effects of acute and chronic drug exposure which is necessary as part of the International Conference in Harmonisation (ICH) tri-partate guidelines. In conclusion, this work indicates a promising heart-liver body-on-a-chip system that can be used for the assessment of potential drug toxicity from dermal absorption as well as evaluate transport dynamics through the skin in the same system.

In silico and in vitro analysis of genetic variants of the equine CYP3A94, CYP3A95 and CYP3A97 isoenzymes

Cytochrome P450 enzymes (CYPs) of the equine CYP3A subfamily are predominantly involved in drug metabolism. In this study, genetic variants of the equine CYP3A94, CYP3A95, and CYP3A97 were identified and characterized using in silico modeling and in vitro enzyme kinetics. The genomes of 81 horses were sequenced to obtain the genetic variants. Structural CYP modifications of the most frequent variants were analyzed in silico using the 3D-structures predicted by homology modeling. Enzyme kinetic analyses were performed using testosterone as substrate. Twenty genetic variants were found including five missense variants (CYP3A94:p.Asp217Asn, CYP3A95:p.Asp214His, CYP3A95:p.Ser392Thr, CYP3A97:p.Ile119Thr, CYP3A97:p.Met500Val) with a higher percentage of minor allele frequency (MAF) (range 0.2-0.4). A splice-site variant (c.798 + 1G > A) in CYP3A94, likely to generate a truncated protein, was found in 50% of the horses. CYP3A94:p.Asp217Asn and CYP3A95:p.Asp214His were localized on the CYP F-α-helix, an important region for the substrate interactions in the human CYP3A4. Testosterone 2β-hydroxylation was diminished in CYP3A94²¹⁷Asn and CYP3A95³⁹²Thr. Ketoconazole inhibited 2β-hydroxylation differently in the five variants with the most pronounced inhibition obtained for CYP3A95³⁹²Thr. In vitro and in silico analyses of genetic variants allow unraveling structural features in equine CYPs that correlate with changes in the CYP activity.

No Increased Risk of Ketoconazole Toxicity in Drug-Drug Interaction Studies

In July 2013 the U.S. Food and Drug Administration (FDA) released a safety announcement regarding the use of ketoconazole and its adverse drug reactions. The FDA report advised against the use ketoconazole tablets as a first-line treatment for any fungal infections because of the risk of potentially serious drug-drug interactions and liver and adrenal gland complications. The European Medicines Agency (EMA) also proposed to limit the use of oral ketoconazole in fungal infections because of the same risk of harmful effects and interactions. In addition, the FDA also advised against the use of oral ketoconazole in drug interaction studies, in which it has been extensively used as an index inhibitor of drug metabolism. The aim of this investigation was to evaluate the risks of ketoconazole-induced hepatotoxicity described by the FDA and EMA in published drug interaction studies with ketoconazole and compare these data with the toxicity reported for ketoconazole when used as antifungal treatment. In the drug interaction studies (2355 participants; healthy volunteers and patients; median treatment duration, 6 days), only 40 participants were reported to have increased liver transaminase activity (1.7%), and no deaths were reported or associated with ketoconazole. In studies investigating ketoconazole treatment, patients were treated for 276 days (median), and 5.6% of patients had elevated liver enzyme activity. Because of the short treatment period in drug interaction studies the risk of drug-induced hepatic injury is considered very low. As such, we recommend that ketoconazole remain a safe CYP3A index inhibitor for use in drug interaction studies with healthy volunteers.

Characterization of chemical-induced sterile inflammation in vitro: application of the model compound ketoconazole in a human hepatic co-culture system

Liver injury as a result of a sterile inflammation is closely linked to the activation of immune cells, including macrophages, by damaged hepatocytes. This interaction between immune cells and hepatocytes is as yet not considered in any of the in vitro test systems applied during the generation of new drugs. Here, we established and characterized a novel in vitro co-culture model with two human cell lines, HepG2 and differentiated THP-1. Ketoconazole, an antifungal drug known for its hepatotoxicity, was used as a model compound in the testing of the co-culture. Single cultures of HepG2 and THP-1 cells were studied as controls. Different metabolism patterns of ketoconazole were observed for the single and co-culture incubations as well as for the different cell types. The main metabolite N-deacetyl ketoconazole was found in cell pellets, but not in supernatants of cell cultures. Global proteome analysis showed that the NRF2-mediated stress response and the CXCL8 (IL-8) pathway were induced by ketoconazole treatment under co-culture conditions. The upregulation and ketoconazole-induced secretion of several pro-inflammatory cytokines, including CXCL8, TNF-α and CCL3, was observed in the co-culture system only, but not in single cell cultures. Taking together, we provide evidence that the co-culture model applied might be suitable to serve as tool for the prediction of chemical-induced sterile inflammation in liver tissue in vivo.

The Use of Edoxaban in Patients with Nonvalvular Atrial Fibrillation and Venous Thromboembolism: A Pharmacist's Perspective

Until 2010, the vitamin K antagonist warfarin was the only available oral anticoagulant for the prevention of stroke or systemic embolic events (SEE) in patients with nonvalvular atrial fibrillation (NVAF) and the treatment of venous thromboembolism (VTE) in the United States. Despite its proven efficacy, the use of warfarin is limited by numerous disadvantages, including a delayed onset of action and variable efficacy resulting from interactions with genetic and environmental factors. Consequently, optimal anticoagulation with warfarin requires dose adjustments based on frequent monitoring. In contrast to warfarin, direct oral anticoagulants (DOACs) including dabigatran, rivaroxaban, apixaban, and edoxaban have predictable pharmacokinetic profiles, few drug-drug interactions, no known interactions with food, and can be administered at fixed doses without the requirement for routine monitoring. All DOACs have received US Food and Drug Administration (FDA) approval for the prevention of stroke or SEE in patients with NVAF and the treatment of VTE based on phase 3 trials demonstrating that they are at least as efficacious as warfarin. In addition, the incidence of clinically relevant bleeding associated with DOACs is comparable to or lower than with warfarin. In this article, the preclinical and clinical data that led to the FDA approval of once-daily edoxaban in January 2015 are presented. Furthermore, practical considerations for edoxaban use including dosing recommendations, transitions of care, reversal of anticoagulation, precautions, contraindications, and cost-effectiveness are discussed. Edoxaban is an important addition to oral anticoagulation options available for the therapeutic management of patients with NVAF or VTE.

Ritonavir is the best alternative to ketoconazole as an index inhibitor of cytochrome P450-3A in drug-drug interaction studies

AIMS

The regulatory prohibition of ketoconazole as a CYP3A index inhibitor in drug-drug interaction (DDI) studies has compelled consideration of alternative inhibitors.

METHODS

The biomedical literature was searched to identify DDI studies in which oral midazolam (MDZ) was the victim, and the inhibitory perpetrator was either ketoconazole, itraconazole, clarithromycin, or ritonavir. The ratios (RAUC ) of total area under the curve (AUC) for MDZ with inhibitor divided by MDZ AUC in the control condition were aggregated across individual studies for each inhibitor.

RESULTS

Mean (± SE) RAUC values were: ketoconazole (15 studies, 131 subjects), 11.5 (±1.2); itraconazole (five studies, 48 subjects), 7.3 (±1.0); clarithromycin (five studies, 73 subjects), 6.5 (±10.9); and ritonavir (13 studies, 159 subjects), 14.5 (±2.0). Differences among inhibitors were significant (F = 5.31, P < 0.005). RAUC values were not significantly related to inhibitor dosage or to duration of inhibitor pre-exposure prior to administration of MDZ.

CONCLUSIONS

Ritonavir produces CYP3A inhibition equivalent to or greater than ketoconazole, and is the best index CYP3A inhibitor alternative to ketoconazole. Cobicistat closely resembles ritonavir in structure and function, and can also be considered. Itraconazole and clarithromycin are not suitable alternatives since they do not produce inhibition comparable with ketoconazole or ritonavir, and have other significant disadvantages as well.

Liver injury associated with ketoconazole: review of the published evidence

The azole antifungal agent ketoconazole has been available since 1981 for the treatment of fungal infections. In 2013, the American Food and Drug Administration and the European Medicines Agency issued warnings or prohibitions against the clinical use of oral ketoconazole due to the risk of liver injury which may lead to liver transplantation or death. From the available published evidence it is difficult to determine the actual incidence or prevalence of liver injury during clinical use of ketoconazole as an antifungal. Hepatic injury, when it occurs, is generally evident as asymptomatic and reversible abnormalities of liver function tests. However, serious liver injury has been reported. Alternatives to ketoconazole (such as itraconazole, fluconazole, voriconazole, and terbinafine) are available, but improved safety with respect to liver injury risk is not clearly established. We are not aware of published reports of significant ketoconazole-associated liver injury in volunteer study participants when ketoconazole has been used as a CYP3A inhibitor in the context of clinical research on drug metabolism. Possible alternatives to ketoconazole as prototype CYP3A inhibitors include ritonavir and potentially itraconazole, but not clarithromycin.