Identification of human liver cytochrome P450 enzymes involved in biotransformation of vicriviroc, a CCR5 receptor antagonist

Tandem mass spectrometry of small-molecule antiviral drugs: 1. HIV-related antivirals

Antiviral drugs are a class of compounds developed specifically for the treatment of viral infections. In the development and subsequent application of antiviral drugs, like for any other class of drugs, quantitative analysis in biological matrix is important, e.g., to establish bioavailability, to study pharmacokinetics, and later on possibly for therapeutic drug monitoring. Liquid chromatography-mass spectrometry (LC-MS) with tandem mass spectrometry (MS-MS) operated in selected-reaction monitoring (SRM) mode is the method of choice in quantitative bioanalysis. As information of the fragmentation of antiviral drugs in MS-MS is very much scattered in the scientific literature, it was decided to collect this information and to review it, not only to understand which product ions are actually used in SRM, but also to assist in other studies, e.g., in the identification of drug metabolites or (forced) degradation products. In this first study, attention is paid to antiviral agents used against HIV infection. The review provides fragmentation schemes of ca. 40 antiviral agents as well as several phosphorylated anabolites. The identity of the product ions used in SRM, i.e., elemental composition and exact-m/z, is tabulated, and more detailed fragmentation schemes are provided.

Targeting CCR5 for anti-HIV research

Highly active antiretroviral therapy (HAART) is the only approach for human immunodeficiency virus (HIV) infection treatment at present. Although HAART is effective in controlling the progression of infection, it is impossible to eradicate the virus from patients. The patients have to live with the virus. Alternative ways for the cure of HIV infection have been investigated. As the major co-receptor for HIV-1 infection, C-C motif chemokine receptor 5 (CCR5) is naturally an ideal target for anti-HIV research. The first CCR5 antagonist, maraviroc, has been approved for the treatment of HIV infection. Several other CCR5 antagonists are in clinical trials. CCR5 delta32 is a natural genotype, conferring resistance to CCR5 using HIV-1 strains. Gene therapy research targeting this mutant has been conducted for HIV infection treatment. A Berlin patient has been cured of HIV infection by the transplantation of stem cells from a CCR5 delta32 genotype donor. The infusion of an engineered zinc finger nuclease (ZFN)-modified autologous cluster of differentiation 4 (CD4) T cells has been proved to be a promising direction recently. In this study, the anti-HIV research targeting CCR5 is summarized, including CCR5 antagonist development, stem cell transplantation, and gene therapy.

CYP2J2 and CYP2C19 are the major enzymes responsible for metabolism of albendazole and fenbendazole in human liver microsomes and recombinant P450 assay systems

Albendazole and fenbendazole are broad-spectrum anthelmintics that undergo extensive metabolism to form hydroxyl and sulfoxide metabolites. Although CYP3A and flavin-containing monooxygenase have been implicated in sulfoxide metabolite formation, the enzymes responsible for hydroxyl metabolite formation have not been identified. In this study, we used human liver microsomes and recombinant cytochrome P450s (P450s) to characterize the enzymes involved in the formation of hydroxyalbendazole and hydroxyfenbendazole from albendazole and fenbendazole, respectively. Of the 10 recombinant P450s, CYP2J2 and/or CYP2C19 was the predominant enzyme catalyzing the hydroxylation of albendazole and fenbendazole. Albendazole hydroxylation to hydroxyalbendazole is primarily mediated by CYP2J2 (0.34 μl/min/pmol P450, which is a rate 3.9- and 8.1-fold higher than the rates for CYP2C19 and CYP2E1, respectively), whereas CYP2C19 and CYP2J2 contributed to the formation of hydroxyfenbendazole from fenbendazole (2.68 and 1.94 μl/min/pmol P450 for CYP2C19 and CYP2J2, respectively, which are rates 11.7- and 8.4-fold higher than the rate for CYP2D6). Correlation analysis between the known P450 enzyme activities and the rate of hydroxyalbendazole and hydroxyfenbendazole formation in samples from 14 human liver microsomes showed that albendazole hydroxylation correlates with CYP2J2 activity and fenbendazole hydroxylation correlates with CYP2C19 and CYP2J2 activities. These findings were supported by a P450 isoform-selective inhibition study in human liver microsomes. In conclusion, our data for the first time suggest that albendazole hydroxylation is primarily catalyzed by CYP2J2, whereas fenbendazole hydroxylation is preferentially catalyzed by CYP2C19 and CYP2J2. The present data will be useful in understanding the pharmacokinetics and drug interactions of albendazole and fenbendazole in vivo.

Pharmacokinetic interaction of vicriviroc with other antiretroviral agents: results from a series of fixed-sequence and parallel-group clinical trials

BACKGROUND

Vicriviroc is a next-generation antiretroviral compound that blocks HIV from entering uninfected cells by binding to the virus's cellular co-receptor chemokine receptor 5 (CCR5). A potent inhibitor of HIV infection of human cells both in vitro and in vivo, vicriviroc is in development for use in treatment-naïve HIV-1-infected individuals. These patients often receive antiretroviral therapy regimens that include a ritonavir-enhanced protease inhibitor. Such regimens have a high potential for drug-drug interactions because many of the antiretroviral agents inhibit or induce elements of drug elimination pathways, such as the hepatic cytochromes, which may alter drug concentrations and affect both safety and efficacy. The aim of this set of studies was to determine what, if any, dose adjustments or monitoring would be required to use vicriviroc in regimens containing the most common antiretroviral agents.

METHODS

Drug-drug interactions between vicriviroc and 11 other antiretroviral compounds were investigated in fixed-sequence or parallel-group clinical trials lasting 12-35 days. Fixed-sequence studies were conducted with the protease inhibitors atazanavir, darunavir, fosamprenavir, indinavir, nelfinavir, saquinavir and tipranavir. In these studies vicriviroc was administered with ritonavir for a fixed duration, followed by administration of vicriviroc with ritonavir plus the protease inhibitor. Parallel-group studies conducted with lopinavir, zidovudine/lamivudine and tenofovir disoproxil fumarate randomized subjects to receive vicriviroc with or without the study drug. All subjects enrolled in the studies were healthy male and female adults.

STATISTICAL METHODS

The log-transformed data for vicriviroc primary pharmacokinetic parameters on appropriate days were statistically analysed using a one-way analysis of variance (ANOVA) model extracting the effects due to treatment. Steady state was evaluated by an ANOVA model on trough concentrations using day and subject as class variables.

RESULTS

Vicriviroc exposure was not affected by the concurrently administered antiretroviral drugs in any clinically relevant manner, nor did vicriviroc have a clinically relevant effect on the exposure of other drugs. The drug combinations studied were safe and well tolerated, with most adverse events reported as mild to moderate. Aside from the known toxicities of the other antiretroviral drugs, no clinically relevant changes in blood chemistry, haematological parameters, ECGs or vital signs were associated with either vicriviroc or combination treatment.

CONCLUSIONS

No dose modification or monitoring of vicriviroc concentrations is necessary when vicriviroc is co-administered with any of the antiretroviral agents reviewed here. The lack of drug-drug interactions suggests that it will be possible to add vicriviroc at the single clinically prescribed dose level to various background regimens that include a boosted protease inhibitor, with all other drugs also prescribed at their standard doses.

Vicriviroc, a new CC-chemokine receptor 5 inhibitor for treatment of HIV: properties, promises and challenges

IMPORTANCE OF THE FIELD

Although HIV has become a treatable disease with near to normal life expectancy, the quest for the development of better tolerated drugs with simple dosing schedules and a high barrier to the emergence of drug resistance remains. Vicriviroc is a small-molecule chemokine receptor antagonist that inhibits the binding of R5-tropic HIV-1 to host cells at the CC-chemokine receptor 5 (CCR5) co-receptor, thus, preventing viral entry. CCR5 inhibitors are believed to possibly decrease inflammation from the immune system and thereby offer additional properties further to their antiretroviral efficacy.

AREAS COVERED IN THIS REVIEW

This review is based on a PubMed search covering the years 2005 - 2010 for pharmacokinetic, pharmacological and clinical data of vicriviroc.

WHAT THE READER WILL GAIN

In this review, the pharmacokinetic, pharmacological and clinical data of vicriviroc are presented. Moreover, the potential role of vicriviroc in the growing HIV armamentarium is discussed.

TAKE HOME MESSAGE

Vicriviroc is being developed to be administered in combination with a ritonavir-boosted protease inhibitor for patients with R5-tropic virus. Early clinical trials have established the safety of vicriviroc in both treatment-naive and -experienced R5-tropic HIV-1 infected individuals. Recently, two Phase III clinical trials in treatment-experienced patients failed to prove its superiority over available HIV medications. Phase III trials for treatment-naive patients are still under planning. Clearly, more favorable study results are needed to move vicriviroc into drug registration and approval.

Potential of novel antiretrovirals to modulate expression and function of drug transporters in vitro

OBJECTIVES

The chemokine receptor antagonists maraviroc and vicriviroc and the integrase inhibitors elvitegravir and raltegravir are novel antiretroviral agents for the treatment of HIV-1 infections. ATP-binding cassette (ABC) transporters as modulators of the effectiveness and safety of therapy can mediate viral resistance and drug-drug interactions. To expand knowledge on drug-drug interactions of these antiretrovirals we investigated whether these compounds are substrates, inhibitors or inducers of important ABC transporters.

METHODS

We evaluated P-glycoprotein (P-gp/ABCB1) inhibition by the calcein assay in P388/dx and L-MDR1 cells, breast cancer resistance protein (BCRP/ABCG2) inhibition in MDCKII-BCRP cells by pheophorbide A efflux, and inhibition of the multidrug resistance-associated protein 2 (MRP2/ABCC2) by using the MRP2 PREDIVEZ™ Vesicular Transport Kit. Substrate characteristics were evaluated by growth inhibition assays in MDCKII cells overexpressing particular ABC transporters. Induction of transporters was quantified by real-time RT-PCR in LS180 cells and for ABCB1 also at the functional level.

RESULTS

Elvitegravir and vicriviroc inhibited ABCB1 in P388/dx and L-MDR1 cells (f2 values 1.9±0.2 µmol/L and 8.5±3.6 µmol/L, respectively). The IC50 for ABCG2 inhibition was 15.7±5.7 µmol/L for elvitegravir and 236.7±93.3 µmol/L for vicriviroc. Raltegravir and maraviroc showed no evidence of ABCB1 or ABCG2 inhibition. Maraviroc and vicriviroc stimulated ABCC2 transport function. Growth inhibition assays suggest that elvitegravir, raltegravir and vicriviroc are substrates of ABCB1. Induction assays demonstrate that mRNA expression of several ABC transporters is induced by these antiretrovirals in LS180 cells.

CONCLUSIONS

The new antiretrovirals bear the potential to modulate expression and function of several ABC transporters, with elvitegravir revealing the highest interaction potential.

Renal insufficiency has no effect on the pharmacokinetics of vicriviroc in a ritonavir-containing regimen

BACKGROUND AND OBJECTIVE

Vicriviroc is a small-molecule CCR5 antagonist currently in development for the treatment of HIV in patients on a regimen containing a ritonavir-boosted protease inhibitor. As renal disease and renal dysfunction are prevalent in the HIV-infected population, patients with varying degrees of renal insufficiency may receive vicriviroc, which is metabolized by cytochrome P450 (CYP) 3A4. The present study therefore examined the impact of renal insufficiency on the pharmacokinetics and safety of vicriviroc alone and in the presence of ritonavir, a strong CYP3A4 inhibitor.

SUBJECTS AND METHODS

This study was an open-label, randomized, two-treatment crossover trial conducted in HIV-negative subjects with haemodialysis-dependent end-stage renal disease (ESRD) and healthy subjects with normal renal function matched by age, height, bodyweight and sex. Subjects received a single dose of vicriviroc 75 mg alone in one period, and in another period they received a single dose of vicriviroc 15 mg after 4 days of ritonavir 100 mg once daily. Ritonavir treatment was then continued for an additional 13 days. The two trial periods were separated by an interval of at least 3 weeks. The primary endpoints were the log-transformed area under the plasma concentration-time curve (AUC) and the maximum plasma concentration (C(max)), and the 90% confidence intervals (CIs) of the mean differences between subjects with ESRD and matched healthy subjects. The protocol provided the option of dose modification and further study if the vicriviroc C(max) and AUC values were at least twice as high in subjects with ESRD compared with healthy subjects, or if warranted by other safety and tolerability observations.

RESULTS

Twelve subjects (six with ESRD, six healthy) completed the study. When vicriviroc was administered alone, the mean vicriviroc C(max) and AUC ratio estimates (90% CI) for subjects with ESRD versus healthy subjects were 74% (53, 103) and 84% (49, 145), respectively. When ritonavir was added to the regimen, the ratio estimates (90% CI) were 81% (59, 111) and 134% (105, 171), respectively. Ritonavir plasma concentrations were substantially higher in subjects with ESRD than in healthy subjects. Treatment-emergent adverse events considered possibly or probably related to treatment occurred only during the ritonavir period of the study and in one healthy subject and two subjects with ESRD; all were of mild or moderate severity.

CONCLUSIONS

ESRD had no clinically relevant impact on exposure of vicriviroc when vicriviroc was administered alone or in the presence of ritonavir. In this single-dose study, vicriviroc was well tolerated both by healthy subjects and by those with ESRD. Dose adjustment of vicriviroc is therefore not necessary in renally impaired populations.

Pharmacokinetic/pharmacodynamic modeling of the antiretroviral activity of the CCR5 antagonist Vicriviroc in treatment experienced HIV-infected subjects (ACTG protocol 5211)

OBJECTIVE

This substudy of AIDS Clinical Trials Group (ACTG) Protocol 5211 explored the relationship between antiretroviral effect and plasma concentrations of vicriviroc, an investigational CCR5 antagonist for HIV infection.

METHODS

Eighty-six treatment-experienced subjects failing their current antiretroviral regimens were randomized to add vicriviroc 5, 10, or 15 mg once daily or placebo for 2 weeks. Beyond week 2, subjects were changed to optimized background antiretroviral treatment while continuing vicriviroc or placebo. Plasma samples collected at weeks 2 and 8 were assayed for vicriviroc concentrations and combined with vicriviroc concentration data from 110 seronegatives enrolled in 5 phase 1 studies. An inhibitory Emax model was used to assess pharmacokinetic (PK)/pharmacodynamic relationships and recursive partitioning was applied to determine the breakpoint in vicriviroc PK parameters associated with virologic suppression.

RESULTS

A 2-compartment model was fitted to the drug concentration data. At week 2, a higher vicriviroc Cmin was associated with a greater mean drop in HIV RNA (viral load) and a higher percentage of subjects experiencing a >1 log10 copies/mL drop in viral load. In subjects with Cmin > 54 ng/mL, the mean viral load decrease was 1.35 log10 copies/mL vs. 0.76 log10 with Cmin < 54 ng/mL (P = 0.003, Student t test). At this Cmin breakpoint, 70% of subjects with the higher Cmin had a >1 log drop in HIV RNA, compared with 44% with a lower Cmin (P = 0.048, Fisher exact test). Similar results were seen with an area under the curve breakpoint of 1460 ng h/mL. At weeks 16 and 24, all vicriviroc-treated subjects experienced better viral load responses than placebo recipients, but there was no apparent relationship between PK and change in viral load among these vicriviroc-treated subjects.

CONCLUSIONS

There was a positive correlation between vicriviroc Cmin, area under the curve, and viral load changes at week 2 in treatment-experienced HIV-infected subjects receiving no other new active antiretroviral drugs. This correlation did not persist beyond week 16, probably because treatment response at that point also depended on having other active drugs in the regimen.

Pharmacologic characteristics of investigational and recently approved agents for the treatment of HIV

PURPOSE OF REVIEW

Two agents from antiretroviral classes with novel mechanisms of action against HIV received regulatory approval in 2007. Maraviroc is the first in the class of chemokine coreceptor 5 antagonists and raltegravir is the first in the class of integrase inhibitors. There are other compounds in these two new classes in later stages of clinical development, as well as several protease inhibitors and nonnucleoside reverse transcriptase inhibitors that have been recently approved or are under investigation for use in treatment-experienced patients. The purpose of this article is to review the pharmacologic characteristics of these newly approved and investigational antiretroviral drugs, with particular emphasis on data presented or published within the past year.

RECENT FINDINGS

Several pivotal studies describing the efficacy, safety, and pharmacologic properties of maraviroc, vicriviroc, etravirine, rilpivirine, raltegravir, elvitegravir, darunavir/ritonavir, and tipranavir/ritonavir have begun to emerge.

SUMMARY

To date, these agents have demonstrated promising virologic activity with primarily excellent tolerability, but there is still much to learn about their pharmacology. Future studies should evaluate their potential for drug-drug interactions and elucidate their concentration-effect relationships. An appreciation for the pharmacology of these drugs is critical to their optimal use.

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.

Pharmacokinetics and drug-drug interactions of antiretrovirals: an update

Current antiretroviral treatment has allowed HIV infection to become a chronic manageable condition with many HIV patients living longer. However, available antiretrovirals are not without limitations, for example the development of resistance and adverse effects. Consequently, new drugs in existing and novel classes are urgently required to provide viable treatment options to patients with few remaining choices. Darunavir, etravirine, maraviroc and raltegravir have been recently approved for treatment-experienced patients and other agents such as rilpivirine, vicriviroc and elvitegravir are currently under phase III study. Clinical studies are necessary to optimise potential treatment combinations and to manage drug-drug interactions to help avoid toxicity or therapy failure. This review aims to summarise the pharmacokinetics and key drug-drug interaction studies for newly available antiretrovirals and those in development. Further information regarding drug-drug interactions of well established antiretrovirals and those recently approved are readily available online at sites such as http://www.hiv-druginteractions.org, http://www.clinicaloptions.com/hiv, http://hivinsite.ucsf.edu. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

The chemokine system and CCR5 antagonists: potential in HIV treatment and other novel therapies

Since the recognition of human acquired immune deficiency syndrome, numerous classes of pharmacologic therapeutics have been developed to manage the disease. Current therapy includes co-administration of combinations of drugs classified by their mechanism of action as 'transcriptase inhibitors', 'protease inhibitors', 'integrase inhibitors' and the more recent 'fusion inhibitors'. This review focuses on the chemokine system and the recognition of chemokine receptors as targets for anti-human immunodeficiency virus (HIV) therapy. The FDA-approved chemokine (C-C motif) receptor 5 (CCR5) antagonist maraviroc (Selzentry) is discussed in detail, along with another compound vicriviroc, currently in clinical trials. The mechanism of action, pharmacokinetics, toxicity and current status of research on CCR5 antagonists is described. Further, potential therapeutic uses of these agents other than anti-HIV therapy are discussed.

Drug interactions with new and investigational antiretrovirals

More than 20 individual and fixed-dose combinations of antiretrovirals are approved for the treatment of human immunodeficiency virus (HIV) infection. However, owing to the ongoing limitations of drug resistance and adverse effects, new treatment options are still required. A number of promising new agents in existing or new drug classes are in development or have recently been approved by the US FDA. Since these agents will be used in combination with other new and existing antiretrovirals, understanding the potential for drug interactions between these compounds is critical to their appropriate use. This article summarizes the drug interaction potential of new and investigational protease inhibitors (darunavir), non-nucleoside reverse transcriptase inhibitors (etravirine and rilpivirine), chemokine receptor antagonists (maraviroc, vicriviroc and INCB 9471), integrase inhibitors (raltegravir and elvitegravir) and maturation inhibitors (bevirimat).