Effects of cytochrome P450 inhibitors on the biotransformation of fluorogenic substrates by adult male rat liver microsomes and cDNA-expressed rat cytochrome P450 isoforms

Physiologically-based pharmacokinetic modelling guided dose evaluations of nirmatrelvir/ritonavir in renal impairment for the management of COVID-19

We aimed to address factors contributing to the pharmacokinetic changes of nirmatrelvir/ritonavir in renal impaired (RI) patients and recommend dosing adjustment via a physiologically-based pharmacokinetic (PBPK) modelling approach. A PBPK model of nirmatrelvir/ritonavir was developed via Simcyp® Simulator. Sensitivity analysis of the influence of hepatic CYP3A4 intrinsic clearance and abundance, as well as hepatic non-CYP3A4 metabolism (other human liver microsomes [HLM] CLint) was performed to evaluate the effects of RI on oral clearance of nirmatrelvir. Other HLM CLint, the most sensitive parameter, was adjusted, and the simulated plasma concentration profiles of nirmatrelvir in severe RI subjects were within the therapeutic index of 292-10 000 ng/mL for dosing regimens of loading doses of 300/100 mg followed by 150/100 mg or 75/100 mg twice daily of nirmatrelvir/ritonavir. Considering that nirmatrelvir is available as a 150 mg tablet, we recommend 300/100 mg followed by 150/100 mg twice daily as the dosing regimen to be investigated in severe RI.

Development of a Dihydroquinoline-Pyrazoline GluN2C/2D-Selective Negative Allosteric Modulator of the N-Methyl-d-aspartate Receptor

Subunit-selective inhibition of N-methyl-d-aspartate receptors (NMDARs) is a promising therapeutic strategy for several neurological disorders, including epilepsy, Alzheimer's and Parkinson's disease, depression, and acute brain injury. We previously described the dihydroquinoline-pyrazoline (DQP) analogue 2a (DQP-26) as a potent NMDAR negative allosteric modulator with selectivity for GluN2C/D over GluN2A/B. However, moderate (<100-fold) subunit selectivity, inadequate cell-membrane permeability, and poor brain penetration complicated the use of 2a as an in vivo probe. In an effort to improve selectivity and the pharmacokinetic profile of the series, we performed additional structure-activity relationship studies of the succinate side chain and investigated the use of prodrugs to mask the pendant carboxylic acid. These efforts led to discovery of the analogue (S)-(-)-2i, also referred to as (S)-(-)-DQP-997-74, which exhibits >100- and >300-fold selectivity for GluN2C- and GluN2D-containing NMDARs (IC50 0.069 and 0.035 μM, respectively) compared to GluN2A- and GluN2B-containing receptors (IC50 5.2 and 16 μM, respectively) and has no effects on AMPA, kainate, or GluN1/GluN3 receptors. Compound (S)-(-)-2i is 5-fold more potent than (S)-2a. In addition, compound 2i shows a time-dependent enhancement of inhibitory actions at GluN2C- and GluN2D-containing NMDARs in the presence of the agonist glutamate, which could attenuate hypersynchronous activity driven by high-frequency excitatory synaptic transmission. Consistent with this finding, compound 2i significantly reduced the number of epileptic events in a murine model of tuberous sclerosis complex (TSC)-induced epilepsy that is associated with upregulation of the GluN2C subunit. Thus, 2i represents a robust tool for the GluN2C/D target validation. Esterification of the succinate carboxylate improved brain penetration, suggesting a strategy for therapeutic development of this series for NMDAR-associated neurological conditions.

ω-Functionalized Lipid Prodrugs of HIV NtRTI Tenofovir with Enhanced Pharmacokinetic Properties

Tenofovir (TFV) is the cornerstone nucleotide reverse transcriptase inhibitor (NtRTI) in many combination antiretroviral therapies prescribed to patients living with HIV/AIDS. Due to poor cell permeability and oral bioavailability, TFV is administered as one of two FDA-approved prodrugs, both of which metabolize prematurely in the liver and/or plasma. This premature prodrug processing depletes significant fractions of each oral dose and causes toxicity in kidney, bone, and liver with chronic administration. Although TFV exalidex (TXL), a phospholipid-derived prodrug of TFV, was designed to address this issue, clinical pharmacokinetic studies indicated substantial hepatic extraction, redirecting clinical development of TXL toward HBV. To circumvent this metabolic liability, we synthesized and evaluated ω-functionalized TXL analogues with dramatically improved hepatic stability. This effort led to the identification of compounds 21 and 23, which exhibited substantially longer t1/2 values than TXL in human liver microsomes, potent anti-HIV activity in vitro, and enhanced pharmacokinetic properties in vivo.

In Vitro and In Vivo Assessment of Metabolic Drug Interaction Potential of Dutasteride with Ketoconazole

Dutasteride (DUT) is a selective, potent, competitive, and irreversible inhibitor of both type-1 and type-2 5α-reductase (5AR) commonly used in the treatment of benign prostatic hyperplasia and androgenetic alopecia. In the present study, we developed a simple and sensitive high-performance liquid chromatography with fluorescence detection (HPLC-FL) method for simultaneous determination of DUT and its major active metabolite, 6β-hydroxydutasteride (H-DUT). Next, the pharmacokinetic interactions of DUT with ketoconazole (KET), a potent CYP3A inhibitor, were comprehensively investigated. In vivo rat intravenous and oral studies revealed that the pharmacokinetics of DUT and H-DUT were significantly altered by the co-administration of KET. Furthermore, the in vitro microsomal metabolism, blood distribution, and protein-binding studies suggest that the altered pharmacokinetics of DUT could be attributed primarily to the inhibition of the DUT metabolism by KET. To the best of our knowledge, this is the first study to show the drug interaction potential of DUT with azole antifungal drugs including KET, together with a newly developed HPLC-FL method for the simultaneous quantification of DUT and H-DUT.

Instability of the Human Cytochrome P450 Reductase A287P Variant Is the Major Contributor to Its Antley-Bixler Syndrome-like Phenotype

Human NADPH-cytochrome P450 oxidoreductase (POR) gene mutations are associated with severe skeletal deformities and disordered steroidogenesis. The human POR mutation A287P presents with disordered sexual development and skeletal malformations. Difficult recombinant expression and purification of this POR mutant suggested that the protein was less stable than WT. The activities of cytochrome P450 17A1, 19A1, and 21A2, critical in steroidogenesis, were similar using our purified, full-length, unmodified A287P or WT POR, as were those of several xenobiotic-metabolizing cytochromes P450, indicating that the A287P protein is functionally competent in vitro, despite its functionally deficient phenotypic behavior in vivo Differential scanning calorimetry and limited trypsinolysis studies revealed a relatively unstable A287P compared with WT protein, leading to the hypothesis that the syndrome observed in vivo results from altered POR protein stability. The crystal structures of the soluble domains of WT and A287P reveal only subtle differences between them, but these differences are consistent with the differential scanning calorimetry results as well as the differential susceptibility of A287P and WT observed with trypsinolysis. The relative in vivo stabilities of WT and A287P proteins were also examined in an osteoblast cell line by treatment with cycloheximide, a protein synthesis inhibitor, showing that the level of A287P protein post-inhibition is lower than WT and suggesting that A287P may be degraded at a higher rate. Current studies demonstrate that, unlike previously described mutations, A287P causes POR deficiency disorder due to conformational instability leading to proteolytic susceptibility in vivo, rather than through an inherent flavin-binding defect.

Omeprazole increases the efficacy of a soluble epoxide hydrolase inhibitor in a PGE₂ induced pain model

Epoxyeicosatrienoic acids (EETs) are potent endogenous analgesic metabolites produced from arachidonic acid by cytochrome P450s (P450s). Metabolism of EETs by soluble epoxide hydrolase (sEH) reduces their activity, while their stabilization by sEH inhibition decreases both inflammatory and neuropathic pain. Here, we tested the complementary hypothesis that increasing the level of EETs through induction of P450s by omeprazole (OME), can influence pain related signaling by itself, and potentiate the anti-hyperalgesic effect of sEH inhibitor. Rats were treated with OME (100mg/kg/day, p.o., 7 days), sEH inhibitor TPPU (3mg/kg/day, p.o.) and OME (100mg/kg/day, p.o., 7 days)+TPPU (3mg/kg/day, p.o., last 3 days of OME dose) dissolved in vehicle PEG400, and their effect on hyperalgesia (increased sensitivity to pain) induced by PGE2 was monitored. While OME treatment by itself exhibited variable effects on PGE2 induced hyperalgesia, it strongly potentiated the effect of TPPU in the same assay. The significant decrease in pain with OME+TPPU treatment correlated with the increased levels of EETs in plasma and increased activities of P450 1A1 and P450 1A2 in liver microsomes. The results show that reducing catabolism of EETs with a sEH inhibitor yielded a stronger analgesic effect than increasing generation of EETs by OME, and combination of both yielded the strongest pain reducing effect under the condition of this study.

Inhibitory effects and oxidation of 6-methylcoumarin, 7-methylcoumarin and 7-formylcoumarin via human CYP2A6 and its mouse and pig orthologous enzymes

1. Information about the metabolism of compounds is essential in drug discovery and development, risk assessment of chemicals and further development of predictive methods. 2. In vitro and in silico methods were applied to evaluate the metabolic and inhibitory properties of 6-methylcoumarin, 7-methylcoumarin and 7-formylcoumarin with human CYP2A6, mouse CYP2A5 and pig CYP2A19. 3. 6-Methylcoumarin was oxidized to fluorescent 7-hydroxy-6-methylcoumarin by CYP2A6 (Km: 0.64-0.91 µM; Vmax: 0.81-0.89 min(-1)) and by CYP2A5 and CYP2A19. The reaction was almost completely inhibited at 10 µM 7-methylcoumarin in liver microsomes of human and mouse, but in pig only 40% inhibition was obtained with the anti-CYP2A5 antibody or with methoxsalen and pilocarpine. 7-Methylcoumarin was a mechanism-based inhibitor for CYP2A6, but not for the mouse and pig enzymes. 7-Formylcoumarin was a mechanism-based inhibitor for CYP2As of all species. 4. Docking and molecular dynamics simulations of 6-methylcoumarin and 7-methylcoumarin in the active sites of CYP2A6 and CYP2A5 demonstrated a favorable orientation of the 7-position of 6-methylcoumarin towards the heme moiety. Several orientations of 7-methylcoumarin were possible in CYP2A6 and CYP2A5. 5. These results indicate that the active site of CYP2A6 has unique interaction properties for ligands and differs in this respect from CYP2A5 and CYP2A19.

Inhibition of cytochrome P450 2B4 by environmentally persistent free radical-containing particulate matter

Combustion processes generate particulate matter (PM) that can affect human health. The presence of redox-active metals and aromatic hydrocarbons in the post-combustion regions results in the formation of air-stable, environmentally persistent free radicals (EPFRs) on entrained particles. Exposure to EPFRs has been shown to negatively influence pulmonary and cardiovascular functions. Cytochromes P450 (P450/CYP) are endoplasmic reticulum resident proteins that are responsible for the metabolism of foreign compounds. Previously, it was shown that model EPFRs, generated by exposure of silica containing 5% copper oxide (CuO-Si) to either dicholorobenzene (DCB230) or 2-monochlorophenol (MCP230) at ≥ 230 °C, inhibited six forms of P450 in rat liver microsomes (Toxicol. Appl. Pharmacol. (2014) 277:200-209). In this study, the inhibition of P450 by MCP230 was examined in more detail by measuring its effect on the rate of metabolism of 7-ethoxy-4-trifluoromethylcoumarin (7EFC) and 7-benzyloxyresorufin (7BRF) by the purified, reconstituted CYP2B4 system. MCP230 inhibited the CYP2B4-mediated metabolism of 7EFC at least 10-fold more potently than non-EPFR controls (CuO-Si, silica, and silica generated from heating silica and MCP at 50 °C, so that EPFRs were not formed (MCP50)). The inhibition by EPFRs was specific for the P450 and did not affect the ability of the redox partner, P450 reductase (CPR) from reducing cytochrome c. All of the PM inhibited CYP2B4-mediated metabolism noncompetitively with respect to substrate. When CYP2B4-mediated metabolism of 7EFC was measured as a function of the CPR concentration, the mechanism of inhibition was competitive. EPFRs likely inhibit CYP2B4-mediated substrate metabolism by physically disrupting the CPR·P450 complex.

Environmentally persistent free radicals inhibit cytochrome P450 activity in rat liver microsomes

Combustion processes generate particulate matter that affects human health. When incineration fuels include components that are highly enriched in aromatic hydrocarbons (especially halogenated varieties) and redox-active metals, ultrafine particulate matter containing air-stable, environmentally persistent free radicals (EPFRs) is generated. The exposure to fine EPFRs (less than 2.5 μm in diameter) has been shown to negatively influence pulmonary and cardiovascular functions in living organisms. The goal of this study was to determine if these EPFRs have a direct effect on cytochrome P450 function. This was accomplished by direct addition of the EPFRs to rat liver microsomal preparations and measurement of several P450 activities using form-selective substrates. The EPFRs used in this study were formed by heating vapors from an organic compound (either monochlorophenol (MCP230) or 1,2-dichlorobenzene (DCB230)) and 5% copper oxide supported on silica (approximately 0.2 μm in diameter) to 230°C under vacuum. Both types of EPFRs (but not silica, physisorbed silica, or silica impregnated with copper oxide) dramatically inhibited the activities of CYP1A, CYP2B, CYP2E1, CYP2D2 and CYP3A when incubated at concentrations less than 0.1 mg/ml with microsomes and NADPH. Interestingly, at the same concentrations, the EPFRs did not inhibit HO-1 activity or the reduction of cytochrome c by NADPH-cytochrome P450 reductase. CYP2D2-selective metabolism by rat liver microsomes was examined in more detail. The inhibition of CYP2D2-selective metabolism by both DCB230- and MCP230-EPFRs appeared to be largely noncompetitive and was attenuated in the presence of catalase suggesting that reactive oxygen species may be involved in the mechanism of inhibition.

Cytochrome p450 inhibitory properties of common efflux transporter inhibitors

Drug transporter inhibitors are important tools to elucidate the contribution of transporters to drug disposition both in vitro and in vivo. These inhibitors are often unselective and affect several transporters as well as drug metabolizing enzymes, which can make experimental results difficult to interpret with confidence. We therefore tested 14 commonly used P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug-resistance associated protein (MRP) inhibitors as inhibitors of cytochrome P450 (P450) enzyme activities using recombinant enzymes. A subset of P-gp and/or CYP3A inhibitors were selected (cyclosporin A, elacridar, ketoconazole, quinidine, reserpine, and tacrolimus) for a comparison of P450 inhibition in human microsomes and hepatocytes. Most P-gp inhibitors showed CYP3A4 inhibition, with potencies often in a similar range as their P-gp inhibition, as well as less potent CYP2C19 inhibition. Other P450 enzymes were not strongly inhibited except a few cases of CYP2D6 inhibition. MRP and BCRP inhibitors showed limited P450 inhibition. Some inhibitors showed less P450 inhibition in human hepatocytes than human liver microsomes, for example, elacridar, probably due to differences in binding, permeability limitations, or active, P-gp mediated efflux of the inhibitor from the hepatocytes. Quinidine was a potent P450 inhibitor in hepatocytes but only showed weak inhibition in microsomes. Quinidine shows an extensive cellular uptake, which may potentiate intracellular P450 inhibition. Elacridar, described as a potent and selective P-gp inhibitor, displayed modest P450 inhibition in this study and is thus a useful model inhibitor to define the role of P-gp in drug disposition without interference with other processes.

Effects in Rats of Maternal Exposure to Raspberry Leaf and Its Constituents on the Activity of Cytochrome P450 Enzymes in the Offspring

The goal of our study was to determine whether maternal exposure to red raspberry leaf (RRL) and its constituents can permanently alter biotransformation of fluorogenic substrates by cytochrome P450 (CYP) in the livers of male and female offspring. Nulliparous female rats received vehicle, raspberry leaf, kaempferol, quercetin, or ellagic acid orally once breeding had been confirmed until parturition. Hepatic microsomes were prepared from animals at birth (postnatal day 1 [PND1]), weaning (PND21), PND65, and PND120 to determine the biotransformation of 8 fluorogenic substrates. The pattern of biotransformation of all but 2 of the substrates was gender specific. Maternal consumption of RRL increased biotransformation of 3 substrates by female offspring at PND120 resulting in a more masculine profile. Kaempferol and quercetin had a similar effect to RRL. These results suggest that maternal consumption of either RRL or some of its constituents leads to long-term alterations of CYP activity in female offspring.