Amiodarone analog-dependent effects on CYP2C9-mediated metabolism and kinetic profiles

G-quadruplex binder pyridostatin as an effective multi-target ZIKV inhibitor

At present, there are still no anti-Zika virus (ZIKV) drugs or vaccines approved by FDA with accurate targets and antiviral mechanisms. Considering the RNA G-quadruplex sequences in ZIKV genome, it is very meaningful to develop G-quadruplex binders as potential anti-ZIKV drugs with novel and accurate targets. In this paper, five classical G-quadruplex binders including Ber, Braco 19, NiL, 360A and PDS have been chosen to discuss their interaction with ZIKV RNA G-quadruplexes. PDS shows higher binding affinity and thermal stability than the other G-quadruplex binders. This property is further evidenced in cells by immunofluorescence microscopy. And PDS shows higher anti-ZIKV activity (EC₅₀ = 4.2 ± 0.4 μM) than the other G-quadruplex binders as well as the positive control ribavirin, with a low cytotoxicity. By time-of-addition assay, PDS exerts antiviral activity at the post-entry process of ZIKV replication cycle, thus inhibiting ZIKV mRNA replication and protein expression. Furthermore, PDS combines with ZIKV NS2B-NS3 protease and reduces its catalytic activity. This study suggests that G-quadruplex binder PDS is an effective multi-target ZIKV inhibitor, which provides more guidance to design some novel anti-ZIKV drugs targeting ZIKV RNA G-quadruplexes.

The detoxification effect of cytochrome P450 3A4 on gelsemine-induced toxicity

Gelsemine (GA), the principal alkaloid in Gelsemium elegans Benth, exhibits potent and specific antinociception in chronic pain without the induction of apparent tolerance. However, GA also exerts neurotoxicity and hepatotoxicity when overdosed, and potential detoxification pathways are urgently needed. Cytochrome P450 enzymes (CYPs) are important phase I enzymes involved in the detoxification of xenobiotic compounds. The study aimed to investigate the role of CYPs-mediated metabolism in GA-induced toxicity. Microsomes, chemical special inhibitors and human recombinant CYPs indicated that GA was mainly metabolized by CYP3A4/5. The major metabolite of GA was isolated and identified as 4-N-demethyl-GA by high-resolution mass spectrometry and nuclear magnetic resonance technology. The CYP3A4 inhibitor ketoconazole significantly inhibited the metabolism of GA. This drastically increased GA toxicity which is caused by increasing the level of malondialdehyde and decreasing the level of the superoxide dismutase in mice. In contrast, the CYP3A4 inducer dexamethasone significantly increased GA metabolism and markedly decreased GA toxicity in mice. Notably, in CYP3A4-humanized mice, the toxicity of GA was significantly reduced compared to normal mice. These findings demonstrated that CYP3A4-mediated metabolism is a robust detoxification pathway for GA-induced toxicity.

The cytochrome P450 metabolic profiling of SMU-B in vitro, a novel small molecule tyrosine kinase inhibitor

A novel small molecule tyrosine kinase inhibitor 6-[6-Amino-5-[(1R)-1-(2,6-dichloro-3-fluorophenyl)ethoxy]-3-pyridyl]-1'-methylspiro[indoline-3,4'-piperidine]-2-one (SMU-B) had good activity against ALK (anaplastic lymphoma kinase) and ROS1 (c-ros oncogene 1) targets in non-small-cell lung cancer. The excellent bioactivity of SMU-B highlights the importance of determining its metabolic traits, which could provide meaningful information for further pharmacokinetic studies of SMU-B. In this work, we studied the metabolism of SMU-B in human liver microsomes. Three metabolites of SMU-B were identified by a quadrupole-time of flight tandem mass spectrometer (Q-TOF-MS), and the metabolic pathways of SMU-B were demethylation, dehydrogenation and oxidation. CYP3A4/5 was the principal isoform involved in SMU-B metabolism, as shown by chemical inhibition and recombination human enzyme studies. Additionally, a predication with a molecular docking model confirmed that SMU-B could interact with the active sites of CYP3A4 and CYP3A5. This study illuminates the metabolic profile of the anti-tumor drug SMU-B, which will accelerate its clinical use.

Impact of CYP2C9-Interacting Drugs on Warfarin Pharmacogenomics

Precise dosing of warfarin is important to achieve therapeutic benefit without adverse effects. Pharmacogenomics explains some interindividual variability in warfarin response, but less attention has been paid to drug‐drug interactions in the context of genetic factors. We investigated retrospectively the combined effects of cytochrome P450 (CYP)2C9 and vitamin K epoxide reductase complex (VKORC)1 genotypes and concurrent exposure to CYP2C9‐interacting drugs on long‐term measures of warfarin anticoagulation. Study participants predicted to be sensitive responders to warfarin based on CYP2C9 and VKORC1 genotypes, had significantly greater international normalized ratio (INR) variability over time. Participants who were concurrently taking CYP2C9‐interacting drugs were found to have greater INR variability and lesser time in therapeutic range. The associations of INR variability with genotype were driven by the subgroup not exposed to interacting drugs, whereas the effect of interacting drug exposure was driven by the subgroup categorized as normal responders. Our findings emphasize the importance of considering drug interactions in pharmacogenomic studies.

CYP3A4/5 mediates the metabolic detoxification of humantenmine, a highly toxic alkaloid from Gelsemium elegans Benth

Gelsemium elegans Benth., a well-known toxic herbal plant, is widely used to treat rheumatic arthritis, inflammation and other diseases. Gelsemium contains humantenmine (HMT), which is an important bioactive and toxic alkaloid. Cytochrome P450 enzymes (CYPs) play important roles in the elimination and detoxification of exogenous substances. This study aimed to investigate the roles of CYPs in the metabolism and detoxification of HMT. First, metabolic studies were performed in vitro by using human liver microsomes, selective chemical inhibitors and recombinant human CYPs. Results indicated that four metabolites, including hydroxylation and oxidation metabolites, were found in human liver microsomes and identified based on their high-resolution mass spectrum. The isoform responsible for HMT metabolism was mainly CYP3A4/5. Second, the toxicity of HMT on L02 cells in the presence of the nicotinamide adenine dinucleotide phosphate system (NADPH) was significantly less than that without NADPH system. A CYP3A4/5 activity inhibition model was established by intraperitoneally injecting ketoconazole in mice and used to evaluate the role of CYP3A4/5 in HMT detoxification. In this model, the 14-day survival rate of the mice decreased to 17% after they were intragastrically treated with HMT, along with hepatic injury and increasing alanine aminotransferase (ALT) /aspartate aminotransferase (AST) levels. Overall, CYP3A4/5 mediated the metabolism and detoxification of HMT.

Oxidative metabolism of koumine is mainly catalyzed by microsomal CYP3A4/3A5

1. Gelsemium elegans Benth (Loganiaceae) is a toxic plant that can be used for committing suicide besides alleviating pains. Its anti-inflammatory and analgesic effect mainly come from its active ingredient, namely koumine. Koumine, an indole alkaloid, possesses widely pharmacological effects especially inhibition of neuropathic pain. 2. This study aimed to investigate the metabolic profile of koumine using human liver microsomes (HLMs), selective chemical inhibitors and recombinant human CYP isoforms. Ultra-performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS) was used to detect and identify metabolites. 3. Four major metabolites of koumine were found after incubation with HLMs or individual CYP isoforms. The metabolic pathways of koumine included demethylation, dehydrogenation, oxidation and demethyl-dehydrogenation. Chemical inhibition study showed that the inhibitor of CYP3A4/3A5 significantly decreased (93%) the formation of koumine metabolites. Further, CYP3A4/3A5 was shown as the most efficient isoform in biotransformation of koumine, among a series of CYP isoforms tested. 4. In conclusion, koumine was metabolized into four oxidative metabolites in HLMs. And CYP3A4/3A5 was probably the main contributor to the hepatic oxidative metabolism of koumine.

Nanoscale electron transport measurements of immobilized cytochrome P450 proteins

Gold nanopillars, functionalized with an organic self-assembled monolayer, can be used to measure the electrical conductance properties of immobilized proteins without aggregation. Measurements of the conductance of nanopillars with cytochrome P450 2C9 (CYP2C9) proteins using conducting probe atomic force microscopy demonstrate that a correlation exists between the energy barrier height between hopping sites and CYP2C9 metabolic activity. Measurements performed as a function of tip force indicate that, when subjected to a large force, the protein is more stable in the presence of a substrate. This agrees with the hypothesis that substrate entry into the active site helps to stabilize the enzyme. The relative distance between hopping sites also increases with increasing force, possibly because protein functional groups responsible for electron transport (ETp) depend on the structure of the protein. The inhibitor sulfaphenazole, in addition to the previously studied aniline, increased the barrier height for electron transfer and thereby makes CYP2C9 reduction more difficult and inhibits metabolism. This suggests that P450 Type II binders may decrease the ease of ETp processes in the enzyme, in addition to occupying the active site.

Molecular functionality of CYP2C9 polymorphisms and their influence on drug therapy

metabolizes approximately 20% of clinically used drugs, including the narrow therapeutic window drugs warfarin and phenytoin. More than 16,000 variants have been reported in the National Center for Biotechnology Information

Warfarin-amiodarone drug-drug interactions: determination of [I](u)/K(I,u) for amiodarone and its plasma metabolites

A retrospective clinical evaluation in a cohort of 73 patients receiving stable anticoagulation therapy showed that the addition/elimination of amiodarone resulted in a 6–65% change in warfarin dose requirement. To evaluate the roles of amiodarone and its circulating metabolites in this highly variable inhibitory drug interaction, an LC-ESI⁺ MS/MS assay was developed for the quantitation of low concentrations of these compounds in human plasma, utilizing newly synthesized deuterated analogs as internal standards. K_I’s were determined for the inhibition of (S)-warfarin 7-hydroxylation in human liver microsomes, by parent drug and metabolites, and unbound drug fractions (f_u) were measured so that the ratio of unbound plasma concentration to the microsomal K_I for unbound drug ([I]_u/K_I,_u) could be calculated. From these ratios, we predict a minor metabolite, N,N-didesethylamiodarone, to be a major contributor to the drug interaction between warfarin and amiodarone.

Pharmacogenetic effect of the UGT polymorphisms on mycophenolate is modified by calcineurin inhibitors

BACKGROUND

Mycophenolic acid (MPA) is glucuronidated primarily by uridine diphosphate glucuronosyltransferase enzymes (UGT) 1A9 and 1A8. These enzymes are highly polymorphic resulting in low activity and high expression phenotypes. We hypothesized that polymorphisms of UGT1A9 and 1A8 may alter MPA pharmacokinetics in kidney transplantation.

METHODS

One hundred seventeen kidney (n = 93), pancreas (n = 11), or simultaneous kidney and pancreas (SPK) (n = 13) transplant recipients were studied for the effect of UGT1A9 and UGT1A8 polymorphisms on MPA dose-corrected trough concentrations. Individuals were genotyped for UGT1A8 and UGT1A9 polymorphisms (1A8*2, 1A8*3, 1A9*3, 1A9-275 and 1A9-2152). Linear regression was used to estimate the effect of UGT polymorphisms on the individual's mean MPA dose-corrected trough concentration with and without stratification by calcineurin inhibitor. A multiple linear regression analysis was performed to assess the dependence between the average MPA dose-corrected trough concentration and age, gender, UGT genotype (1A8*2, 1A8*3, 1A9*3, 1A9-275, 1A9-2152), serum albumin, hemoglobin (Hgb), hematocrit (HCT), liver transaminases (AST, ALT), serum creatinine, and bilirubin.

RESULTS

Mycophenolic acid dose-corrected trough concentrations were 60% higher in subjects heterozygous or homozygous for UGT1A8*2 than in those with the wild type (p = 0.02); however, this effect was dependent on concomitant calcineurin inhibitor. When subjects were stratified by calcineurin inhibitor status, the UGT1A8*2 effect was only apparent in the tacrolimus group (p < 0.01). Mycophenolic acid dose-corrected trough concentrations were 70% lower in carriers of the UGT1A9 -275T>A/-2152 C>T polymorphism who received cyclosporine (p < 0.01). There was no effect of the UGT1A9 -275T>A/-2152C>T polymorphism in the tacrolimus group.

CONCLUSIONS

The effect of UGT1A8 and UGT1A9 variants on MPA metabolism appears to be modified by concomitant calcineurin inhibitor therapy. Confirmatory in vivo and in vitro studies are needed.

Differential genotype dependent inhibition of CYP2C9 in humans

The effects of genetic polymorphisms in drug-metabolizing enzymes (e.g., CYP2C9(*)3) on drug clearance have been well characterized but much less is known about whether these polymorphisms alter susceptibility to drug-drug interactions. Previous in vitro work has demonstrated that genotype-dependent inhibition of CYP2C9 mediated flurbiprofen metabolism, suggesting the possibility of genotype-dependent inhibition interactions in vivo. In the current study, flurbiprofen was used as a probe substrate and fluconazole as a prototypical inhibitor to investigate whether genotype-dependent inhibition of CYP2C9 occurs in vivo. From 189 healthy volunteers who were genotyped for CYP2C9 polymorphisms, 11 control subjects (CYP2C9(*)1/(*)1), 9 heterozygous and 2 homozygous for the CYP2C9(*)3 allele participated in the pharmacokinetic drug interaction study. Subjects received a single 50-mg oral dose of flurbiprofen alone or after administration of either 200 or 400 mg of fluconazole for 7 days using an open, randomized, crossover design. Flurbiprofen and fluconazole plasma concentrations along with flurbiprofen and 4'-hydroxyflurbiprofen urinary excretion were monitored. Flurbiprofen apparent oral clearance differed significantly among the three genotype groups (p < 0.05) at baseline but not after pretreatment with 400 mg of fluconazole for 7 days. Changes in flurbiprofen apparent oral clearance after fluconazole coadministration were gene dose-dependent, with virtually no change occurring in (*)3/(*)3 subjects. Analysis of fractional clearances suggested that the fraction metabolized by CYP2C9, as influenced by genotype, determined the degree of drug interaction observed. In summary, the presence of CYP2C9(*)3 alleles (either one or two alleles) can alter the degree of drug interaction observed upon coadministration of inhibitors.

Polymorphic variants of CYP2C9: mechanisms involved in reduced catalytic activity

CYP2C9 catalyzes the demethylation of the biphasic kinetics substrate (S)-naproxen, and the CYP2C9*2 (R144C) and CYP2C9*3 (I359L) variants are associated with lower rates of (S)-naproxen demethylation. To assess the reasons for these reductions in catalytic activity of the two variants and potential substrate concentration-dependent differences in a biphasic kinetics substrate, cytochrome P450 (P450) cycle coupling and uncoupling were monitored during coincubation of (S)-naproxen and CYP2C9 over a range of P450 reductase concentrations. Coupling was greatest in the CYP2C9.1 enzyme, followed by CYP2C9.2, and then CYP2C9.3. Uncoupling in CYP2C9.1 and CYP2C9.3 was primarily to H(2)O(2). In contrast, CYP2C9.2 uncoupled to excess water preferentially. The conversion of enzyme to the high spin state was similar in CYP2C9.1 and CYP2C9.2, but lower in CYP2C9.3. It is noteworthy that neither altered substrate binding nor altered interaction with reductase seemed to be involved in reduced catalysis. These results suggest that in addition to coupling differences, differential uncoupling to shunt products and differences in spin state help explain the reduced catalytic activity in these enzymes.

Use of simple docking methods to screen a virtual library for heteroactivators of cytochrome P450 2C9

Several laboratories have demonstrated that activation of drug metabolism by P450s may occur via a mechanism that resembles allosterism from an enzyme kinetic standpoint. Because the effector drug binding site may be located in the same P450 binding pocket where the drug substrate is located, the ability to find and characterize novel effectors (aka heteroactivators) will prove to be important in probing the mechanism of activation. We have used analogues of the prototypical CYP2C9 heteroactivator dapsone to validate a simple docking method that can be used to predict heteroactivators based on ligand binding location in a P450 crystal structure. As proof of concept for the described docking method, a protocol was developed to discover potential heteroactivators from a virtual chemical library through efficient sorting of >40,000 compounds. One of the top-scoring compounds identified was verified to be a CYP2C9 heteroactivator in vitro, and it possessed activity similar to dapsone.