Conversion of the HIV protease inhibitor nelfinavir to a bioactive metabolite by human liver CYP2C19

Construction of a fused grid-based CYP2C19-Template system and the application

A ligand-accessible space in the CYP2C19 active site was reconstituted as a fused grid-based Template with the use of structural data of the ligands. An evaluation system of CYP2C19-mediated metabolism has been developed on Template with the introduction of the idea of Trigger-residue initiated ligand-movement and fastening. Reciprocal comparison of the data of simulation on Template with experimental results suggested a unified way of the interaction of CYP2C19 and its ligands through the simultaneous plural-contact with Rear-wall of Template. CYP2C19 was expected to have a room for ligands between vertically standing parallel walls termed Facial-wall and Rear-wall, which were separated by a distance corresponding to 1.5-Ring (grid) diameter size. The ligand sittings were stabilized through contacts with Facial-wall and the left-side borders of Template including specific Position 29 or Left-end after Trigger-residue initiated ligand-movement. Trigger-residue movement is suggested to force ligands to stay firmly in the active site and then to initiate CYP2C19 reactions. Simulation experiments for over 450 reactions of CYP2C19 ligands supported the system established.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

The role of pharmacogenetics in Efficacy and safety of protease inhibitor based therapy in human immunodeficiency virus type (HIV) infection

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). HIV can now be classified as a chronic disease; until a cure is found, patients are likely to require life-long therapy. However, despite these undoubted advances, there are many issues that need to be resolved, including the problems associated with long-term efficacy and toxicity. Moreover, pharmacotherapy of patients infected with HIV is challenging because a great number of comorbidities increase polypharmacy and the risk for drug-drug interactions. There is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. HIV-infected population consists of ethnically diverse individuals on complex and potentially toxic antiretroviral regimens on a long-term basis. These individuals would benefit greatly from predictive tests that identify the most durable regimens. Pharmacogenetics holds that promise. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of antiHIV therapeutics of the protease inhibitors Lopinavir and Ritonavir and the impact of genetic variation in drug metabolism and transport on the treatment of HIV.

Prioritization of Anti-SARS-Cov-2 Drug Repurposing Opportunities Based on Plasma and Target Site Concentrations Derived from their Established Human Pharmacokinetics

There is a rapidly expanding literature on the in vitro antiviral activity of drugs that may be repurposed for therapy or chemoprophylaxis against severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). However, this has not been accompanied by a comprehensive evaluation of the target plasma and lung concentrations of these drugs following approved dosing in humans. Accordingly, concentration 90% (EC90 ) values recalculated from in vitro anti-SARS-CoV-2 activity data was expressed as a ratio to the achievable maximum plasma concentration (Cmax ) at an approved dose in humans (Cmax /EC90 ratio). Only 14 of the 56 analyzed drugs achieved a Cmax /EC90 ratio above 1. A more in-depth assessment demonstrated that only nitazoxanide, nelfinavir, tipranavir (ritonavir-boosted), and sulfadoxine achieved plasma concentrations above their reported anti-SARS-CoV-2 activity across their entire approved dosing interval. An unbound lung to plasma tissue partition coefficient (Kp Ulung ) was also simulated to derive a lung Cmax /half-maximal effective concentration (EC50 ) as a better indicator of potential human efficacy. Hydroxychloroquine, chloroquine, mefloquine, atazanavir (ritonavir-boosted), tipranavir (ritonavir-boosted), ivermectin, azithromycin, and lopinavir (ritonavir-boosted) were all predicted to achieve lung concentrations over 10-fold higher than their reported EC50 . Nitazoxanide and sulfadoxine also exceeded their reported EC50 by 7.8-fold and 1.5-fold in lung, respectively. This analysis may be used to select potential candidates for further clinical testing, while deprioritizing compounds unlikely to attain target concentrations for antiviral activity. Future studies should focus on EC90 values and discuss findings in the context of achievable exposures in humans, especially within target compartments, such as the lungs, in order to maximize the potential for success of proposed human clinical trials.

Pharmacogenomics of Antiretroviral Drug Metabolism and Transport

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). Individual tailoring of antiretroviral regimens has the potential to further improve the long-term management of HIV through the mitigation of treatment failure and drug-induced toxicities. While the mechanisms underlying anti-HIV drug adverse outcomes are multifactorial, the application of drug-specific pharmacogenomic knowledge is required in order to move toward the personalization of HIV therapy. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of anti-HIV therapeutics and the impact of genetic variation in drug metabolism and transport on the treatment of HIV. Future perspectives on and current challenges in pursuing personalized HIV treatment are also discussed.

Group-based pharmacogenetic prediction: is it feasible and do current NHS England ethnic classifications provide appropriate data?

Inter-individual variation of drug metabolising enzymes (DMEs) leads to variable efficacy of many drugs and even adverse drug responses. Consequently, it would be desirable to test variants of many DMEs before drug treatment. Inter-ethnic differences in frequency mean that the choice of SNPs to test may vary across population groups. Here we examine the utility of testing representative groups as a way of assessing what variants might be tested. We show that publicly available population information is potentially useful for determining loci for pre-treatment genetic testing, and for determining the most prevalent risk haplotypes in defined groups. However, we also show that the NHS England classifications have limitations for grouping for these purposes, in particular for people of African descent. We conclude: (1) genotyping of hospital patients and people from the hospital catchment area confers no advantage over using samples from appropriate existing ethnic group collections or publicly available data, (2) given the current NHS England Black African grouping, a decision as to whether to test, would have to apply to all patients of recent Black African ancestry to cover reported risk alleles and (3) the current scarcity of available genome and drug effect data from Africans is a problem for both testing and treatment decisions.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Pharmacokinetics of Increased Nelfinavir Plasma Concentrations in Women During Pregnancy and Postpartum

This study aims to evaluate the safety, acceptability, and pharmacokinetics (PK) of an increased dose of nelfinavir (NFV) during the third trimester of pregnancy. The study was registered as part of the International Maternal Pediatric Adolescent AIDS Clinical Trials network (IMPAACT-P1026s), an ongoing multicenter prospective cohort study of antiretroviral PK during pregnancy (NCT00042289). NFV intensive PK evaluations were performed at steady state during the third trimester of pregnancy and 2-3 weeks postpartum. Plasma concentrations of NFV and its active metabolite, hydroxyl-tert-butylamide (M8) were measured using high-performance liquid chromatography with ultraviolet detection. A total of 18 women are included in the analysis. NFV area under the concentration-time curve (AUC) with the increased dose during the third trimester was nearly identical to the standard dose postpartum, with a geometric mean ratio for third trimester to postpartum AUC of 0.98 (90%CI 0.71-1.35). Despite the increased dose, M8 AUC was lower during the third trimester compared to postpartum (0.53, IQR [0.38-0.75]), as was the M8/NFV AUC ratio (0.51, IQR [0.42-0.63]). NFV AUC_0-12 was above target in 15 of 18 (83%) of participants during the third trimester compared to 14 of 16 (88%) postpartum. No major safety concerns were noted. Increasing the NFV dose to 1875 mg twice daily during the third trimester achieved similar concentrations postpartum compared to standard dosing (1250 mg twice daily). Increased NFV dose regimens may still have some benefit to human immunodeficiency virus (HIV)-positive pregnant women living in countries where novel protease inhibitors are currently unavailable or in individuals who are intolerant to ritonavir-boosted HIV medications.

Pharmacokinetic alterations in poloxamer 407-induced hyperlipidemic rats

1. Plasma lipid profile abnormalities in hyperlipidemia can potentially alter the pharmacokinetics of a drug in a complex manner. To evaluate these pharmacokinetic alterations in hyperlipidemia and to determine the underlying mechanism(s), poloxamer 407-induced hyperlipidemic rats (HL rats), a well-established animal model of hyperlipidemia have been used. 2. In this review, we summarize findings on the pathophysiological and gene expression changes in drug-metabolizing enzymes and transporters in HL rats. We discuss pharmacokinetic changes in drugs metabolized primarily via hepatic cytochrome P450 (CYPs) in terms of alterations in hepatic intrinsic clearance (CL^'_int), free fraction in plasma (f_u) and hepatic blood flow rate (Q_H), depending on the hepatic excretion ratio, as well as drugs eliminated primarily by mechanisms other than hepatic CYPs. 3. For lipoprotein-bound drugs, increased binding to lipoproteins resulted in lower f_u values and volumes of distribution, with some exceptions. Generally, slower non-renal clearance (or total body clearance) of drugs that are substrates of hepatic CYP3A and CYP2C is well explained by the following factors: alterations in CL^'_int (due to down-regulation of hepatic CYPs), decreased f_u and/or possible decreased Q_H. 4. These consistent findings across studies in HL rats suggest more studies are needed at the clinical level for optimal pharmacotherapies for hyperlipidemia.

Accessing Drug Metabolites via Transition-Metal Catalyzed C-H Oxidation: The Liver as Synthetic Inspiration

Can classical and modern chemical C-H oxidation reactions complement biotransformation in the synthesis of drug metabolites? We have surveyed the literature in an effort to try to answer this important question of major practical significance in the pharmaceutical industry. Drug metabolites are required throughout all phases of the drug discovery and development process; however, their synthesis is still an unsolved problem. This Review, not intended to be comprehensive or historical, highlights relevant applications of chemical C-H oxidation reactions, electrochemistry and microfluidic technologies to drug templates in order to access drug metabolites, and also highlights promising reactions to this end. Where possible or appropriate, the contrast with biotransformation is drawn. In doing so, we have tried to identify gaps where they exist in the hope to spur further activity in this very important research area.

Strengths, weaknesses, opportunities and challenges for long acting injectable therapies: Insights for applications in HIV therapy

Advances in solid drug nanoparticle technologies have resulted in a number of long-acting (LA) formulations with the potential for once monthly or longer administration. Such formulations offer great utility for chronic diseases, particularly when a lack of medication compliance may be detrimental to treatment response. Two such formulations are in clinical development for HIV but the concept of LA delivery has its origins in indications such as schizophrenia and contraception. Many terms have been utilised to describe the LA approach and standardisation would be beneficial. Ultimately, definitions will depend upon specific indications and routes of delivery, but for HIV we propose benchmarks that reflect perceived clinical benefits and available data on patient attitudes. Specifically, we propose dosing intervals of ≥1week, ≥1month or ≥6months, for oral, injectable or implantable strategies, respectively. This review focuses upon the critical importance of potency in achieving the LA outcome for injectable formulations and explores established and emerging technologies that have been employed across indications. Key technological challenges such as the need for consistency and ease of administration for drug combinations, are also discussed. Finally, the review explores the gaps in knowledge regarding the pharmacology of drug release from particulate-based LA injectable suspensions. A number of hypotheses are discussed based upon available data relating to local drug metabolism, active transport systems, the lymphatics, macrophages and patient-specific factors. Greater knowledge of the mechanisms that underpin drug release and protracted exposure will help facilitate further development of this strategy to achieve the promising clinical benefits.

Effect of Methamphetamine on Spectral Binding, Ligand Docking and Metabolism of Anti-HIV Drugs with CYP3A4

Cytochrome P450 3A4 (CYP3A4) is the major drug metabolic enzyme, and is involved in the metabolism of antiretroviral drugs, especially protease inhibitors (PIs). This study was undertaken to examine the effect of methamphetamine on the binding and metabolism of PIs with CYP3A4. We showed that methamphetamine exhibits a type I spectral change upon binding to CYP3A4 with δA_max and K_D of 0.016±0.001 and 204±18 μM, respectively. Methamphetamine-CYP3A4 docking showed that methamphetamine binds to the heme of CYP3A4 in two modes, both leading to N-demethylation. We then studied the effect of methamphetamine binding on PIs with CYP3A4. Our results showed that methamphetamine alters spectral binding of nelfinavir but not the other type I PIs (lopinavir, atazanavir, tipranavir). The change in spectral binding for nelfinavir was observed at both δA_max (0.004±0.0003 vs. 0.0068±0.0001) and K_D (1.42±0.36 vs.2.93±0.08 μM) levels. We further tested effect of methamphetamine on binding of 2 type II PIs; ritonavir and indinavir. Our results showed that methamphetamine alters the ritonavir binding to CYP3A4 by decreasing both the δA_max (0.0038±0.0003 vs. 0.0055±0.0003) and K_D (0.043±0.0001 vs. 0.065±0.001 nM), while indinavir showed only reduced K_D in presence of methamphetamine (0.086±0.01 vs. 0.174±0.03 nM). Furthermore, LC-MS/MS studies in high CYP3A4 human liver microsomes showed a decrease in the formation of hydroxy ritonavir in the presence of methamphetamine. Finally, CYP3A4 docking with lopinavir and ritonavir in the absence and presence of methamphetamine showed that methamphetamine alters the docking of ritonavir, which is consistent with the results obtained from spectral binding and metabolism studies. Overall, our results demonstrated differential effects of methamphetamine on the binding and metabolism of PIs with CYP3A4. These findings have clinical implication in terms of drug dose adjustment of antiretroviral medication, especially with ritonavir-boosted antiretroviral therapy, in HIV-1-infected individuals who abuse methamphetamine.

Inhibition Profiling of Retroviral Protease Inhibitors Using an HIV-2 Modular System

Retroviral protease inhibitors (PIs) are fundamental pillars in the treatment of HIV infection and acquired immunodeficiency syndrome (AIDS). Currently used PIs are designed against HIV-1, and their effect on HIV-2 is understudied. Using a modular HIV-2 protease cassette system, inhibition profiling assays were carried out for protease inhibitors both in enzymatic and cell culture assays. Moreover, the treatment-associated resistance mutations (I54M, L90M) were introduced into the modular system, and comparative inhibition assays were performed to determine their effect on the susceptibility of the protease. Our results indicate that darunavir, saquinavir, indinavir and lopinavir were very effective HIV-2 protease inhibitors, while tipranavir, nelfinavir and amprenavir showed a decreased efficacy. I54M, L90M double mutation resulted in a significant reduction in the susceptibility to most of the inhibitors with the exception of tipranavir. To our knowledge, this modular system constitutes a novel approach in the field of HIV-2 protease characterization and susceptibility testing.

Application of a novel regulatable Cre recombinase system to define the role of liver and gut metabolism in drug oral bioavailability

The relative contribution of hepatic compared with intestinal oxidative metabolism is a crucial factor in drug oral bioavailability and therapeutic efficacy. Oxidative metabolism is mediated by the cytochrome P450 mono-oxygenase system to which cytochrome P450 reductase (POR) is the essential electron donor. In order to study the relative importance of these pathways in drug disposition, we have generated a novel mouse line where Cre recombinase is driven off the endogenous Cyp1a1 gene promoter; this line was then crossed on to a floxed POR mouse. A 40 mg/kg dose of the Cyp1a1 inducer 3-methylcholanthrene (3MC) eliminated POR expression in both liver and small intestine, whereas treatment at 4 mg/kg led to a more targeted deletion in the liver. Using this approach, we have studied the pharmacokinetics of three probe drugs--paroxetine, midazolam, nelfinavir--and show that intestinal metabolism is a determinant of oral bioavailability for the two latter compounds. The Endogenous Reductase Locus (ERL) mouse represents a significant advance on previous POR deletion models as it allows direct comparison of hepatic and intestinal effects on drug and xenobiotic clearance using lower doses of a single Cre inducing agent, and in addition minimizes any cytotoxic effects, which may compromise interpretation of the experimental data.

Pharmacokinetics of Nelfinavir in Subjects With Hepatic Impairment

HIV-seronegative subjects with hepatic impairment (6 mild, 6 moderate) and 12 matched healthy controls received nelfinavir 1250 mg every 12 hours with food for 2 weeks. Mild impairment did not significantly change nelfinavir or major metabolite (M8) steady-state exposures compared with controls. In subjects with moderate impairment, steady-state area under the plasma concentration time-curve over the dosing interval and maximum observed plasma concentrations were 62% and 22% higher for nelfinavir than for controls, and for M8 were 46% and 35% of control values. With increasing degree of impairment, no trend toward increase in unbound nelfinavir was observed, but there was an increase in unbound M8 levels. Nelfinavir was safe and well tolerated. One subject with moderate impairment was discontinued because of transient leucopenia. Observed changes are unlikely to affect nelfinavir efficacy or markedly influence safety. Dose reduction of nelfinavir does not appear necessary for subjects with mild/moderate impairment. Further long-term evaluations of nelfinavir pharmacokinetics and safety in HIV-seropositive subjects with hepatic impairment may be useful.

Clinical implications of the nelfinavir-proton pump inhibitor drug interaction in patients with human immunodeficiency virus

STUDY OBJECTIVE

To determine if the concomitant use of nelfinavir and proton pump inhibitors (PPIs) in patients with human immunodeficiency virus (HIV) infection results in the loss of virologic control.

DESIGN

Retrospective cohort study.

DATA SOURCE

Pharmacy, laboratory, and administrative databases of a large integrated health care system in northern California.

PATIENTS

A total of 1147 HIV-positive adults who started nelfinavir therapy between November 1, 1998, and June 20, 2003; within this cohort, 141 patients (12.3%) were also prescribed PPIs.

MEASUREMENTS AND MAIN RESULTS

The effects on two virologic outcomes--achievement of undetectable HIV viral load and subsequent virologic rebound--were compared between patients receiving nelfinavir alone and those receiving nelfinavir with PPIs. Cox proportional hazards models were used, with adjustments for age, sex, race, HIV risk factors, hepatitis B or C coinfection, and other concurrent drugs known to affect the metabolism of nelfinavir. The use of PPIs had little effect on the ability to achieve an undetectable HIV viral load (adjusted hazard ratio [HR] 0.82, 95% confidence interval [CI] 0.58-1.19, p=0.29), but there was an approximate 50% increased risk of virologic rebound with the concurrent use of PPIs (adjusted HR 1.53, 95% CI 1.06-2.19, p=0.02). Short-term use of PPIs (defined as within 30 days of initial PPI dispensation) was not associated with increased risk of virologic rebound (HR 1.07, 95% CI 0.26-4.41, p=0.93) compared with no use of PPIs.

CONCLUSION

Use of PPIs should be minimized or avoided in patients who have attained an undetectable HIV viral load while taking a nelfinavir-based antiretroviral regimen. However, concomitant use of these drugs may be acceptable for indications where PPIs are required for fewer than 30 days.

Twenty-six years of HIV science: an overview of anti-HIV drugs metabolism

From the identification of HIV as the agent causing AIDS, to the development of effective antiretroviral drugs, the scientific achievements in HIV research over the past twenty-six years have been formidable. Currently, there are twenty-five anti-HIV compounds which have been formally approved for clinical use in the treatment of AIDS. These compounds fall into six categories: nucleoside reverse transcriptase inhibitors (NRTIs), nucleotide reverse transcriptase inhibitors (NtRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), cell entry inhibitors or fusion inhibitors (FIs), co-receptor inhibitors (CRIs), and integrase inhibitors (INIs). Metabolism by the host organism is one of the most important determinants of the pharmacokinetic profile of a drug. Formation of active or toxic metabolites will also have an impact on the pharmacological and toxicological outcomes. Therefore, it is widely recognized that metabolism studies of a new chemical entity need to be addressed early in the drug discovery process. This paper describes an overview of the metabolism of currently available anti-HIV drugs.

Effect of ethanol on spectral binding, inhibition, and activity of CYP3A4 with an antiretroviral drug nelfinavir

Cytochrome P450 3A4 (CYP3A4) is the most abundant CYP enzyme in the liver and metabolizes approximately 50% of the drugs, including antiretrovirals. Although CYP3A4 induction by ethanol and impact of CYP3A4 on drug metabolism and toxicity is known, CYP3A4-ethanol physical interaction and its impact on drug binding, inhibition, or metabolism is not known. Therefore, we studied the effect of ethanol on binding and inhibition of CYP3A4 with a representative protease inhibitor, nelfinavir, followed by the effect of alcohol on nelfinavir metabolism. Our initial results showed that methanol, ethanol, isopropanol, isobutanol, and isoamyl alcohol bind in the active site of CYP3A4 and exhibit type I spectra. Among these alcohol compounds, ethanol showed the lowest K(D) (5.9±0.34mM), suggesting its strong binding affinity with CYP3A4. Ethanol (20mM) decreased the K(D) of nelfinavir by >5-fold (0.041±0.007 vs. 0.227±0.038μM). Similarly, 20mM ethanol decreased the IC(50) of nelfinavir by >3-fold (2.6±0.5 vs. 8.3±3.1μM). These results suggest that ethanol facilitates binding of nelfinavir with CYP3A4. Furthermore, we performed nelfinavir metabolism using LCMS. Although ethanol did not alter k(cat), it decreased the K(m) of nelfinavir, suggesting a decrease in catalytic efficiency (k(cat)/K(m)). This is an important finding because alcoholism is prevalent in HIV-1-infected persons and alcohol is shown to decrease the response to antiretroviral therapy.

CYP2C19 genetic variants affect nelfinavir pharmacokinetics and virologic response in HIV-1-infected children receiving highly active antiretroviral therapy

BACKGROUND

The objective of this research was to identify the impact of genetic variants of P-glycoprotein (ABCB1) and cytochrome P450 (CYP) on nelfinavir pharmacokinetics and response to highly active antiretroviral therapy (HAART) in HIV-1-infected children.

METHODS

HIV-1-infected children (n = 152) from Pediatric AIDS Clinical Trial Group 366 or 377 receiving nelfinavir as a component of HAART were evaluated. Genomic DNA was assayed for ABCB1 and CYP genetic variants using real-time polymerase chain reaction Nelfinavir oral clearance (CL/F), M8 to nelfinavir ratios, CD4 T cells, and HIV-1-RNA were measured during HAART.

RESULTS

Nelfinavir CL/F and M8 to nelfinavir ratios were significantly associated with the CYP2C19-G681A genotypes (P < 0.001). Furthermore, the CYP2C19-G681A genotype was related to virologic responses at week 24 (P = 0.01). A multivariate analysis demonstrated that age (P = 0.03), concomitant protease inhibitor use (P < 0.001), and the CYP2C19-G681A genotype (P < 0.001) remained significant covariates associated with nelfinavir CL/F.

CONCLUSIONS

CYP2C19 genotypes altered nelfinavir pharmacokinetics and the virologic response to HAART in HIV-1-infected children. These findings suggest that CYP2C19 genotypes are important determinants of nelfinavir pharmacokinetics and virologic response in HIV-1-infected children.

Influence of CYP2C19 polymorphism on the pharmacokinetics of nelfinavir and its active metabolite

AIMS

This study reports the pharmacokinetics of nelfinavir, its active metabolite, M8, and active moiety (nelfinavir + M8) in volunteers genotyped for CYP2C19 as extensive metabolizer (*1*1; n = 38), heterozygous poor metabolizer (PM) (*1*2; n = 22) and homozygous PM (*2*2; n = 6).

METHODS

Subjects received nelfinavir at normal dose (3.5 days of 1250 mg q12h) or high dose (1250 mg q12h for 3 days and single dose of 3125 mg on day 4). Steady-state plasma samples were analysed by high-performance liquid chromatography/ultraviolet assay to determine pharmacokinetics.

RESULTS

At steady state, the mean C(max) was 42% [95% confidence interval (CI) 19, 69] and 63% (95% CI 20, 122) higher, and mean AUC was 51% (95% CI 24, 83) and 85% (95% CI 32, 159) higher for *1*2 and *2*2 compared with *1*1 subjects, respectively. For M8, the mean C(max) and AUC were 35% (95% CI 6, 55) and 33% (95% CI -3, 56), respectively, lower for *1*2 compared with *1*1 subjects. M8 was not detectable in *2*2 subjects. The mean C(max) and AUC values for the active moiety were higher by 30-35% for the *1*2 and *2*2 compared with *1*1 subjects.

CONCLUSIONS

Mutation in CYP2C19 increased the systemic exposure of nelfinavir and reduced the exposure of M8. No significant differences were noted among the heterozygous (*1*2) and homozygous (*2*2) PMs. These changes are not considered to be clinically relevant and hence the use of nelfinavir does not require prior assessment of CYP2C19 genotype.

Formed and preformed metabolites: facts and comparisons

The administration of metabolites arising from new drug entities is often employed in drug discovery to investigate their associated toxicity. It is expected that administration of metabolites can predict the exposure of metabolites originating from the administration of precursor drug. Whether exact and meaningful information can be obtained from this has been a topic of debate. This communication summarizes observations and theoretical relationships based on physiological modelling for the liver, kidney and intestine, three major eliminating organs/tissues. Theoretical solutions based on physiological modelling of organs were solved, and the results suggest that deviations are expected. Here, examples of metabolite kinetics observed mostly in perfused organs that did not match predictions are provided. For the liver, discrepancies in fate between formed and preformed metabolites may be explained by the heterogeneity of enzymes, the presence of membrane barriers and whether transporters are involved. For the kidney, differences have been attributed to glomerular filtration of the preformed but not the formed metabolite. For the intestine, the complexity of segregated flows to the enterocyte and serosal layers and differences in metabolism due to the route of administration are addressed. Administration of the metabolite may or may not directly reflect the toxicity associated with drug use. However, kinetic data on the preformed metabolite will be extremely useful to develop a sound model for modelling and simulations; in-vitro evidence on metabolite handling at the target organ is also paramount. Subsequent modelling and simulation of metabolite data arising from a combined model based on both drug and preformed metabolite data are needed to improve predictions on the behaviours of formed metabolites.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

Effects of standard and supratherapeutic doses of nelfinavir on cardiac repolarization: a thorough QT study

This was a randomized, 4-way crossover, third-party-blinded study in 68 healthy subjects to assess the effect of nelfinavir on QTc interval. Treatments included (A) nelfinavir 1250 mg every 12 hours on days 1-4, (B) nelfinavir 1250 mg every 12 hours on days 1-3 plus 3125 mg on day 4, (C) placebo, and (D) moxifloxacin 400 mg every 24 hours on days 1-4. Pharmacokinetics and triplicate 12-lead electrocardiograms were performed over 12 hours on days 1 and 4. Time-matched, placebo-subtracted, baseline-adjusted changes in QT intervals with Fridericia's (QTcF) correction were determined following nelfinavir and moxifloxacin administration. Neither dose of nelfinavir had a clinically relevant effect on the QTcF interval on day 4 (primary endpoint) and day 1 because at every time point the upper 90% confidence limit was below 10 milliseconds and, furthermore, the mean difference was below 5 milliseconds. Additionally, there was no clinically relevant effect on QTcB (Bazett's correction), uncorrected QT, or the RR interval on days 1 or 4. Pharmacokinetics confirmed adequate systemic exposure to nelfinavir and moxifloxacin. While nelfinavir exposure was higher in poor compared with extensive metabolizers of CYP2C19 isozyme, there were no corresponding significant differences in QTcF change from placebo. At clinically relevant, doses nelfinavir is unlikely to cause QTc prolongation.

Significant decrease in nelfinavir systemic exposure after omeprazole coadministration in healthy subjects

STUDY OBJECTIVES

To assess the effect of omeprazole on the multiple-dose (steady-state) pharmacokinetics and safety of nelfinavir, and to evaluate the safety and tolerability of nelfinavir when administered alone and with omeprazole.

DESIGN

Open-label, two-period, single-fixed-sequence study.

SETTING

Clinical research unit of a large, teaching hospital.

PARTICIPANTS

Twenty healthy volunteers (mean age 26 +/- 9 yrs, range 18-48 yrs). Intervention. Subjects received nelfinavir 1250 mg every 12 hours for 4 days (period 1). After a 7-day washout period, subjects were coadministered nelfinavir 1250 mg every 12 hours and omeprazole 40 mg every 24 hours for 4 days (period 2).

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of nelfinavir and its active metabolite M8 were determined on day 4 of both periods. Plasma samples were assayed by a high-performance liquid chromatography-ultraviolet method for nelfinavir and M8 concentrations, and noncompartmental pharmacokinetic analysis was performed by using analytical software. In the presence of omeprazole, nelfinavir area under the concentration-time curve over the dosing interval (AUC(tau)), maximum observed plasma concentration (C(max)), and minimum observed plasma concentration (C(min)) were reduced by an average of 36%, 37%, and 39%, respectively, relative to administration of nelfinavir alone. The AUC(tau), C(max), and C(min) of M8 were reduced by an average of 92%, 89%, and 75%, respectively. The slopes of the terminal elimination phase of nelfinavir and M8 plasma concentration-time curves were similar between treatments. Nelfinavir was well tolerated when administered alone and when coadministered with omeprazole.

CONCLUSION

The observed reduction in the systemic exposure to both nelfinavir and its active metabolite M8 after coadministration with omeprazole could result in loss of virologic control and potential emergence of drug resistance. Hence, omeprazole should not be coadministered to patients taking nelfinavir.

Pharmacogenetic Considerations in the Management of HIV Infection

Potent combination antiretroviral drug therapy has now been available to HIV-infected patients for more than a decade, resulting in a significant decline in disease-related morbidity and mortality. Nonetheless, a number of HIV-infected individuals fail to experience the full benefit of their antiretroviral medications; some lack a robust virologic response, while others experience treatment-limiting toxicities. A number of factors may contribute to variable drug response in patients with HIV infection. Virologic, immunologic, pharmacologic, and pharmacokinetic differences between HIV-infected patients have all been noted to contribute to interpatient variability in drug response. Recent data suggest that pharmacogenetic differences among HIV-infected individuals may also be an important variable that contributes to antiretroviral drug response. Pharmacogenetic studies of antiretroviral drug therapy have explored the influence of single nucleotide polymorphisms in genes responsible for key proteins involved in antiretroviral drug metabolism (cytochrome P50 enzymes) and drug transport (P-glycoprotein). In addition, the human leukocyte antigen genotype (HLA-B*57) has been found to predict abacavir-associated hypersensitivity reactions. Antiretroviral pharmacogenetics offers the possibility of optimizing virologic response and minimizing drug toxicity by individualizing anti-HIV pharmacotherapy. The authors review those genetic polymorphisms that have been shown, or are strongly suspected, to influence antiretroviral drug metabolism, transport, and toxicity.

Saquinavir, nelfinavir and M8 pharmacokinetics following combined saquinavir, ritonavir and nelfinavir administration

OBJECTIVES

This study evaluated the steady-state pharmacokinetic interaction between ritonavir-boosted saquinavir and nelfinavir.

METHODS

Open label, multiple-dose, two parallel-groups, single crossover study conducted in 24 HIV-infected patients (12 in each group). Patients in the nelfinavir group added saquinavir/ritonavir, 1000/100 mg twice daily to their ongoing stable treatment regimen consisting of nelfinavir, 1250 mg twice daily and two nucleoside reverse transcriptase inhibitors (NRTIs). Patients in the saquinavir group added nelfinavir, 1250 mg twice daily to their ongoing stable treatment regimen consisting of saquinavir/ritonavir, 1000/100 mg twice daily and two NRTIs. Pharmacokinetic assessments were performed before and 7 days after the start of combined treatment with nelfinavir/saquinavir/ritonavir. Blood samples were collected before and 1, 2, 3, 4, 6, 8, 10 and 12 h after dosing for measurement of nelfinavir, the nelfinavir metabolite M8 and saquinavir using liquid chromatography tandem mass spectrometry (LC-MS/MS).

RESULTS

The addition of saquinavir/ritonavir to the nelfinavir-containing regimen resulted in significant increases in the M8 pharmacokinetic parameters AUC(0-12), Cmax and C12; geometric mean ratios (90% confidence intervals) of 2.25 ng.h/mL (1.47-3.44), 1.74 ng/mL (1.25-2.40) and 4.21 ng/mL (2.10-8.47), respectively. The intra-individual changes in nelfinavir and saquinavir concentrations were highly variable. Statistical analysis could not discard a relevant interaction but includes the possibility that some parameters may be halved, others more than doubled. At the same time the analysis failed to show any directed change.

CONCLUSIONS

The co-administration of nelfinavir and saquinavir/ritonavir leads to unpredictable changes in concentrations of both drugs. It is unclear whether the increased concentrations of M8 are associated with a clinical benefit.

Depo-medroxyprogesterone in women on antiretroviral therapy: effective contraception and lack of clinically significant interactions

We conducted an open-label, steady-state pharmacokinetic (PK) study of drug interactions among HIV-infected women treated with depo-medroxyprogesterone acetate (DMPA) while on nucleoside analogues plus nelfinavir (N=21), efavirenz (N=17), or nevirapine (N=16); or nucleosides only or no antiretroviral therapy as a control group (N=16). PK parameters were estimated using non-compartmental analysis, with between-group comparisons of medroxyprogesterone acetate (MPA) PKs and within-subject comparisons of ARV PKs before and 4 weeks after DMPA dosing. Plasma progesterone levels were measured at baseline and at 2, 4, 6, 8, 10, and 12 weeks after DMPA dosing. There were no significant changes in MPA area under the concentration curve, peak or trough concentrations, or apparent clearance in the nelfinavir, efavirenz, or nevirapine groups compared to the control group. Minor changes in nelfinavir and nevirapine drug exposure were seen after DMPA, but were not considered clinically significant. Suppression of ovulation was maintained.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades

There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).

A review of nelfinavir for the treatment of HIV infection

Nelfinavir (NFV) is a protease inhibitor that has been widely used for several years for the treatment of HIV infection. This has led to extensive experience with NFV-containing regimens, in which the drug has shown prolonged viral suppression, good tolerability and a unique resistance profile. In recent years, several antiretroviral drugs with some advantages over NFV have been developed. Nevertheless, NFV has favourable characteristics that make it a suitable antiretroviral compound for many HIV-infected patients. It can be used in patients who do not tolerate ritonavir even at low doses, and it is well tolerated in pregnant women, has a low-grade interaction with methadone and may be well tolerated in hepatitis C virus-co-infected patients. In addition, its new simplified posology may contribute to improved adherence.