Differential Inhibition of Cytochrome P450 3A4, 3A5 and 3A7 by Five Human Immunodeficiency Virus (HIV) Protease Inhibitors in vitro

Development of a physiologically-based pharmacokinetic model for Ritonavir characterizing exposure and drug interaction potential at both acute and steady-state conditions

Ritonavir (RTV) is a potent CYP3A inhibitor that is widely used as a pharmacokinetic (PK) enhancer to increase exposure to select protease inhibitors. However, as a strong and complex perpetrator of CYP3A interactions, RTV can also enhance the exposure of other co-administered CYP3A substrates, potentially causing toxicity. Therefore, the prediction of drug-drug interactions (DDIs) and estimation of dosing requirements for concomitantly administered drugs is imperative. In this study, we aimed to develop a physiologically-based PK (PBPK) model for RTV using the PK-sim® software platform. A total of 13 clinical PK studies of RTV covering a wide dose range (100 to 600 mg including both single and multiple dosing), and eight clinical DDI studies with RTV on CYP3A and P-gp substrates, including alprazolam, midazolam, rivaroxaban, clarithromycin, fluconazole, sildenafil, and digoxin were used for the model development and evaluation. Chronopharmacokinetic differences (between morning vs. evening doses) and limitations in parameter estimation for biochemical processes of RTV from in vitro studies were incorporated in the PBPK model. The final developed PBPK model predicted 100% of RTV AUClast and Cmax within a twofold dimension error. The geometric mean fold error (GMFE) from all PK datasets was 1.275 and 1.194, respectively. In addition, 97% of the DDI profiles were predicted with the DDI ratios within a twofold dimension error. The GMFE values from all DDI datasets were 1.297 and 1.212, respectively. Accordingly, this model could be applied to the prediction of DDI profiles of RTV and CYP3A substrates and used to estimate dosing requirements for concomitantly administered drugs.

Human Data on Pharmacokinetic Interactions of Cannabinoids: A Narrative Review

Concomitant use of cannabinoids with other drugs may result in pharmacokinetic drug-drug interactions, mainly due to the mechanism involving Phase I and Phase II enzymes and/or efflux transporters. Cannabinoids are not only substrates but also inhibitors or inducers of some of these enzymes and/or transporters. This narrative review aims to provide the available information reported in the literature regarding human data on the pharmacokinetic interactions of cannabinoids with other medications. A search on Pubmed/Medline, Google Scholar, and Cochrane Library was performed. Some studies were identified with Google search. Additional articles of interest were obtained through cross-referencing of published literature. All original research papers discussing interactions between cannabinoids, used for medical or recreational/adult-use purposes, and other medications in humans were included. Thirty-two studies with medicinal or recreational/adult-use cannabis were identified (seventeen case reports/series, thirteen clinical trials, and two retrospective analyses). In three of these studies, a bidirectional pharmacokinetic drug-drug interaction was reported. In the rest of the studies, cannabinoids were the perpetrators, as in most of them, concentrations of cannabinoids were not measured. In light of the widespread use of prescribed and non-prescribed cannabinoids with other medications, pharmacokinetic interactions are likely to occur. Physicians should be aware of these potential interactions and closely monitor drug levels and/or responses. The existing literature regarding pharmacokinetic interactions is limited, and for some drugs, studies have relatively small cohorts or are only case reports. Therefore, there is a need for high-quality pharmacological studies on cannabinoid-drug interactions.

The involvement of hepatic cytochrome P450s in the cytotoxicity of lapatinib

Lapatinib, an oral tyrosine kinase inhibitor used as a first-line treatment for HER2-positive breast cancer, has been reported to be associated with hepatotoxicity; however, the underlying mechanisms remain unclear. In this study, we report that lapatinib causes cytotoxicity in multiple types of hepatic cells, including primary human hepatocytes, HepaRG cells, and HepG2 cells. A 24-h treatment with lapatinib induced cell cycle disturbances, apoptosis, and DNA damage, and decreased the protein levels of topoisomerase in HepG2 cells. We investigated the role of cytochrome P450 (CYP)-mediated metabolism in lapatinib-induced cytotoxicity using our previously established HepG2 cell lines, which express each of 14 CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrate that lapatinib is metabolized by CYP1A1, 3A4, 3A5, and 3A7. Among these, lapatinib-induced cytotoxicity and DNA damage were attenuated in cells overexpressing CYP3A5 or 3A7. Additionally, we measured the production of three primary metabolites of lapatinib (O-dealkylated lapatinib, N-dealkylated lapatinib, and N-hydroxy lapatinib) in CYP1A1-, 3A4-, 3A5-, and 3A7-overexpressing HepG2 cells. We compared the cytotoxicity of lapatinib and its 3 metabolites in primary human hepatocytes, HepaRG cells, and HepG2 cells and demonstrated that N-dealkylated lapatinib is more toxic than the parent drug and the other metabolites. Taken together, our results indicate that lapatinib-induced cytotoxicity involves multiple mechanisms, such as apoptosis and DNA damage; that N-dealkylated lapatinib is a toxic metabolite contributing to the toxic effect of lapatinib; and that CYP3A5- and 3A7-mediated metabolism plays a role in attenuating the cytotoxicity of lapatinib.

A model-based pharmacokinetic assessment of drug-drug interaction between tacrolimus and nirmatrelvir/ritonavir in a kidney transplant patient with COVID-19

We experienced a patient with a remarkable and prolonged increase in tacrolimus blood concentrations when nirmatrelvir/ritonavir was concomitantly used. The inhibitory intensity and duration of nirmatrelvir/ritonavir on tacrolimus pharmacokinetics were examined using a model-based analysis. A renal transplant patient taking oral tacrolimus continuously was treated with nirmatrelvir/ritonavir for 5 days. The baseline tacrolimus trough blood concentration was 4.2 ng/mL. Tacrolimus was discontinued on Day 6 after the concomitant administration of nirmatrelvir/ritonavir, and the trough concentration increased to 96.4 ng/mL on Day 7. The model-based analysis showed that tacrolimus clearance decreased to 35% and bioavailability increased by 18.7-fold after the coadministration of nirmatrelvir/ritonavir, compared with before the coadministration. Therefore, nirmatrelvir/ritonavir drastically decreased both the apparent clearance and apparent volume of distribution. Simulated tacrolimus concentrations could be best fitted to the observed concentrations when the inhibitory effects of nirmatrelvir/ritonavir were modeled to disappear over about 10 days by first-order elimination. In conclusion, nirmatrelvir/ritonavir greatly increases tacrolimus concentrations by not only reducing clearance, but also increasing bioavailability. Interactions between nirmatrelvir/ritonavir and low-bioavailability drugs which are substrates for CYP3A and P-glycoprotein, such as tacrolimus, are harmful, and concomitant use of these medicines should be avoided.

Human cytochrome P450 3A7 binding four copies of its native substrate dehydroepiandrosterone 3-sulfate

Human fetal cytochrome P450 3A7 (CYP3A7) is involved in both xenobiotic metabolism and the estriol biosynthetic pathway. Although much is understood about cytochrome P450 3A4 and its role in adult drug metabolism, CYP3A7 is poorly characterized in terms of its interactions with both categories of substrates. Herein, a crystallizable mutated form of CYP3A7 was saturated with its primary endogenous substrate dehydroepiandrosterone 3-sulfate (DHEA-S) to yield a 2.6 Å X-ray structure revealing the unexpected capacity to simultaneously bind four copies of DHEA-S. Two DHEA-S molecules are located in the active site proper, one in a ligand access channel, and one on the hydrophobic F'-G' surface normally embedded in the membrane. While neither DHEA-S binding nor metabolism exhibit cooperative kinetics, the current structure is consistent with cooperativity common to CYP3A enzymes. Overall, this information suggests that mechanism(s) of CYP3A7 interactions with steroidal substrates are complex.

Leveraging physiologically based pharmacokinetic modeling to optimize dosing for lopinavir/ritonavir with rifampin in pediatric patients

STUDY OBJECTIVE

Treatment of HIV and tuberculosis co-infection leads to significant mortality in pediatric patients, and treatment can be challenging due to the clinically significant drug-drug interaction (DDI) between lopinavir/ritonavir (LPV/RTV) and rifampin. Doubling LPV/RTV results in insufficient lopinavir trough concentrations in pediatric patients. The objective of this study was to leverage physiologically based pharmacokinetic (PBPK) modeling to optimize the adjusted doses of LPV/RTV in children receiving the WHO-revised doses of rifampin (15 mg/kg daily).

DESIGN

Adult and pediatric PBPK models for LPV/RTV with rifampin were developed, including CYP3A and P-glycoprotein inhibition and induction.

SETTING (OR DATA SOURCE)

Data for LPV/RTV model development and evaluation were available from the pediatric AIDS Clinical Trials Group.

PATIENTS

Dosing simulations were next performed to optimize dosing in children (2 months to 8 years of age).

INTERVENTION

Exposure following super-boosted LPV/RTV with 10 and 15 mg/kg PO daily rifampin was simulated.

MEASUREMENTS AND MAIN RESULTS

Simulated parameters were within twofold observations for LPV, RTV, and rifampin in adults and children ≥2 weeks old. The model predicted that, in healthy adults receiving 400/100 mg oral LPV/RTV twice daily (BID), co-treatment with 600 mg oral rifampin daily decreased the steady-state area under the concentration vs. time curve of LPV by 79%, in line with the observed change of 75%. Simulated and observed concentration profiles were comparable for LPV/RTV (230/57.5 mg/m2 ) PO BID without rifampin and 230/230 mg/m2 LPV/RTV PO BID with 10 mg/kg PO daily rifampin in pediatric patients. Sixteen mg/kg of super-boosted LPV (LPV/RTV 1:1) PO BID with 15 mg/kg PO daily rifampin achieved simulated LPV troughs >1 mg/L in ≥93% of virtual children weighing 3.0-24.9 kg, which was comparable with 10 mg/kg PO daily rifampin.

CONCLUSIONS

Super-boosted LPV/RTV with 15 mg/kg rifampin achieves therapeutic LPV troughs in HIV/TB-infected simulated children.

A Comprehensive Analysis of Human CYP3A4 Crystal Structures as a Potential Tool for Molecular Docking-Based Site of Metabolism and Enzyme Inhibition Studies

The notable ability of human liver cytochrome P450 3A4 (CYP3A4) to metabolize diverse xenobiotics encourages researchers to explore in-depth the mechanism of enzyme action. Numerous CYP3A4 protein crystal structures have been deposited in protein data bank (PDB) and are majorly used in molecular docking analysis. The quality of the molecular docking results depends on the three-dimensional CYP3A4 protein crystal structures from the PDB. Present review endeavors to provide a brief outline of some technical parameters of CYP3A4 PDB entries as valuable information for molecular docking research. PDB entries between 22 April 2004 and 2 June 2021 were compiled and the active sites were thoroughly observed. The present review identified 76 deposited PDB entries and described basic information that includes CYP3A4 from human genetic, Escherichia coli (E. coli) use for protein expression, crystal structure obtained from X-ray diffraction method, taxonomy ID 9606, Uniprot ID P08684, ligand–protein structure description, co-crystal ligand, protein site deposit and resolution ranges between 1.7[Formula: see text]Å and 2.95[Formula: see text]Å. The observation of protein–ligand interactions showed the various residues on the active site depending on the ligand. The residues Ala305, Ser119, Ala370, Phe304, Phe108, Phe213 and Phe215 have been found to frequently interact with ligands from CYP3A4 PDB. Literature surveys of 17 co-crystal ligands reveal multiple mechanisms that include competitive inhibition, noncompetitive inhibition, mixed-mode inhibition, mechanism-based inhibition, substrate with metabolite, inducer, or combination modes of action. This overview may help researchers choose a trustworthy CYP3A4 protein structure from the PDB database to apply the protein in molecular docking analysis for drug discovery.

Unraveling the Structural Basis of Selective Inhibition of Human Cytochrome P450 3A5

The human cytochrome P450 (CYP) CYP3A4 and CYP3A5 enzymes metabolize more than one-half of marketed drugs. They share high structural and substrate similarity and are often studied together as CYP3A4/5. However, CYP3A5 preferentially metabolizes several clinically prescribed drugs, such as tacrolimus. Genetic polymorphism in CYP3A5 makes race-based dosing adjustment of tacrolimus necessary to minimize acute rejection after organ transplantation. Moreover, the differential tissue distribution and expression levels of CYP3A4 and CYP3A5 can aggravate toxicity during treatment. Therefore, selective inhibitors of CYP3A5 are needed to distinguish the role of CYP3A5 from that of CYP3A4 and serve as starting points for potential therapeutic development. To this end, we report the crystal structure of CYP3A5 in complex with a previously reported selective inhibitor, clobetasol propionate (CBZ). This is the first CYP3A5 structure with a type I inhibitor, which along with the previously reported substrate-free and type II inhibitor-bound structures, constitute the main CYP3A5 structural modalities. Supported by structure-guided mutagenesis analyses, the CYP3A5-CBZ structure showed that a unique conformation of the F-F' loop in CYP3A5 enables selective binding of CBZ to CYP3A5. Several polar interactions, including hydrogen bonds, stabilize the position of CBZ to interact with this unique F-F' loop conformation. In addition, functional and biophysical assays using CBZ analogs highlight the importance of heme-adjacent moieties for selective CYP3A5 inhibition. Our findings can be used to guide further development of more potent and selective CYP3A5 inhibitors.

Adrenal insufficiency in HIV/AIDS: a review

INTRODUCTION

Adrenal insufficiency (AI) is one of the most common potentially life-threatening endocrine complications in people living with human immunodeficiency virus (PLHIV) infection and acquired immunodeficiency syndrome (AIDS).

AREAS COVERED

In this review, the authors explore the definitions of relative AI, primary AI, secondary AI and peripheral glucocorticoid resistance in PLHIV. It also focuses on the pathophysiology, etiology, diagnosis and management of this endocrinopathy in PLHIV. A literature review was conducted through Medline and Google Scholar search on the subject.

EXPERT OPINION

Physicians need to be aware of the endocrinological implications of HIV infection and its treatment, especially CYP3A4 enzyme inhibitors. A high index of clinical suspicion is needed in the detection of AI, especially in PLHIV, as it may present insidiously with nonspecific signs and symptoms and may be potentially life threatening if left untreated. Patients with overt primary and secondary AI require glucocorticoid replacement therapy. Overt primary AI also necessitates mineralocorticoid replacement. On the other hand, the management of relative AI remains controversial. In order to reduce the risk of adrenal crisis during periods of stress, the short-term use of glucocorticoids may be necessary in relative AI.

Characterization of fluorescent probe substrates to develop an efficient high-throughput assay for neonatal hepatic CYP3A7 inhibition screening

CYP3A7 is a member of the cytochrome P450 (CYP) 3A enzyme sub-family that is expressed in the fetus and neonate. In addition to its role metabolizing retinoic acid and the endogenous steroid dehydroepiandrosterone sulfate (DHEA-S), it also has a critical function in drug metabolism and disposition during the first few weeks of life. Despite this, it is generally ignored in the preclinical testing of new drug candidates. This increases the risk for drug-drug interactions (DDI) and toxicities occurring in the neonate. Therefore, screening drug candidates for CYP3A7 inhibition is essential to identify chemical entities with potential toxicity risks for neonates. Currently, there is no efficient high-throughput screening (HTS) assay to assess CYP3A7 inhibition. Here, we report our testing of various fluorescent probes to assess CYP3A7 activity in a high-throughput manner. We determined that the fluorescent compound dibenzylfluorescein (DBF) is superior to other compounds in meeting the criteria considered for an efficient HTS assay. Furthermore, a preliminary screen of an HIV/HCV antiviral drug mini-library demonstrated the utility of DBF in a HTS assay system. We anticipate that this tool will be of great benefit in screening drugs that may be used in the neonatal population in the future.

Environmental Pollutants, Mucosal Barriers, and Pathogen Susceptibility; The Case for Aflatoxin B1 as a Risk Factor for HIV Transmission and Pathogenesis

HIV transmission risk is dependent on the infectivity of the HIV+ partner and personal susceptibility risk factors of the HIV- partner. The mucosal barrier, as the internal gatekeeper between environment and self, concentrates and modulates the internalization of ingested pathogens and pollutants. In this review, we summarize the localized effects of HIV and dietary toxin aflatoxin B1 (AFB1), a common pollutant in high HIV burden regions, e.g., at the mucosal barrier, and evidence for pollutant-viral interactions. We compiled literature on HIV and AFB1 geographic occurrences, mechanisms of action, related co-exposures, personal risk factors, and HIV key determinants of health. AFB1 exposure and HIV sexual transmission hotspots geographically co-localize in many low-income countries. AFB1 distributes to sexual mucosal tissues generating inflammation, microbiome changes and a reduction of mucosal barrier integrity, effects that are risk factors for increasing HIV susceptibility. AFB1 exposure has a positive correlation to HIV viral load, a risk factor for increasing the infectivity of the HIV+ partner. The AFB1 exposure and metabolism generates inflammation that recruits HIV susceptible cells and generates chemokine/cytokine activation in tissues exposed to HIV. Although circumstantial, the available evidence makes a compelling case for studies of AFB1 exposure as a risk factor for HIV transmission, and a modifiable new component for combination HIV prevention efforts.

A scaffolded approach to unearth potential antibacterial components from epicarp of Malaysian Nephelium lappaceum L

The emergence and spread of antimicrobial resistance have been of serious concern to human health and the management of bacterial infectious diseases. Effective treatment of these diseases requires the development of novel therapeutics, preferably free of side effects. In this regard, natural products are frequently conceived to be potential alternative sources for novel antibacterial compounds. Herein, we have evaluated the antibacterial activity of the epicarp extracts of the Malaysian cultivar of yellow rambutan fruit (Nephelium lappaceum L.) against six pathogens namely, Bacillus subtilis, methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pyogenes, Pseudomonas aeruginosa, Klebsiella pneumoniae and Salmonella enterica. Among a series of solvent extracts, fractions of ethyl acetate and acetone have revealed significant activity towards all tested strains. Chemical profiling of these fractions, via HPLC, LC-MS and GC-MS, has generated a library of potentially bioactive compounds. Downstream virtual screening, pharmacological prediction, and receptor-ligand molecular dynamics simulation have eventually unveiled novel potential antibacterial compounds, which can be extracted for medicinal use. We report compounds like catechin, eplerenone and oritin-4-beta-ol to be computationally inhibiting the ATP-binding domain of the chaperone, DnaK of P. aeruginosa and MRSA. Thus, our work follows the objective to propose new antimicrobials capable of perforating the barrier of resistance posed by both the gram positives and the negatives.

A Semimechanistic Pharmacokinetic Model for Depot Medroxyprogesterone Acetate and Drug-Drug Interactions With Antiretroviral and Antituberculosis Treatment

Depot medroxyprogesterone acetate is an injectable hormonal contraceptive, widely used by women of childbearing potential living with HIV and/or tuberculosis. As medroxyprogesterone acetate is a cytochrome P450 (CYP3A4) substrate, drug-drug interactions (DDIs) with antiretroviral or antituberculosis treatment may lead to subtherapeutic medroxyprogesterone acetate concentrations (< 0.1 ng/mL), resulting in contraception failure, when depot medroxyprogesterone is dosed at 12-week intervals. A pooled population pharmacokinetic analysis with 744 plasma medroxyprogesterone acetate concentrations from 138 women treated with depot medroxyprogesterone and antiretroviral/antituberculosis treatment across three clinical trials was performed. Monte Carlo simulations were performed to predict the percentage of participants with subtherapeutic medroxyprogesterone acetate concentrations and to derive alternative dosing strategies. Medroxyprogesterone acetate clearance increased by 24.7% with efavirenz coadministration. Efavirenz plus antituberculosis treatment (rifampicin + isoniazid) increased clearance by 52.4%. Conversely, lopinavir/ritonavir and nelfinavir decreased clearance (28.7% and 15.8%, respectively), but lopinavir/ritonavir also accelerated medroxyprogesterone acetate's appearance into the systemic circulation, thus shortening the terminal half-life. A higher risk of subtherapeutic medroxyprogesterone acetate concentrations at Week 12 was predicted on a typical 60-kg woman on efavirenz (4.99%) and efavirenz with antituberculosis treatment (6.08%) when compared with medroxyprogesterone acetate alone (2.91%). This risk increased in women with higher body weight. Simulations show that re-dosing every 8 to 10 weeks circumvents the risk of subtherapeutic medroxyprogesterone acetate exposure associated with these DDIs. Dosing depot medroxyprogesterone every 8 to 10 weeks should eliminate the risk of subtherapeutic medroxyprogesterone acetate exposure caused by coadministered efavirenz and/or antituberculosis treatment, thus reducing the risk of contraceptive failure.

Recombinant expression and characterization of novel P450s from Actinosynnema mirum

Cytochrome P450 monooxygenases (P450s) are the major contributor in the metabolism of xenobiotics, including therapeutic agents. Thus, P450s find broad application in the pharmaceutical industry to synthesize metabolites of new active pharmaceutical ingredients in order to evaluate toxicity and pharmacokinetics. As an alternative to human hepatic P450s, microbial P450s offer several advantages, such as an easier and more efficient heterologous expression as well as higher stability under process conditions. Recently, the wild-type strain Actinosynnema mirum has been reported to catalyze hydroxylation reactions with high activity on a broad range of substrates. In this study, one of these substrates, ritonavir, was used to analyze the transcriptional response of the wild-type strain. Analysis of the differential gene expression pattern allowed the assignment of genes potentially responsible for ritonavir conversion. Heterologous expression of these candidates and activity testing led to the identification of a novel P450 that efficiently converts ritonavir resembling the activity of the human CYP3A4.

Clinically relevant enantiomer specific R- and S-praziquantel pharmacokinetic drug-drug interactions with efavirenz and ritonavir

We conducted a clinical study to determine the effect of efavirenz and ritonavir on the pharmacokinetics of R- and S-PZQ in healthy male participants. This was toward evaluating the risk of drug-drug interactions, which may occur after PZQ administration to HIV patients on efavirenz or ritonavir containing regimens. A non-randomized, open-label, single-dose, one sequence crossover study with 2 arms was conducted. We gave 26 healthy volunteers a single oral dose of 40 mg/kg PZQ followed by a daily oral dose of either 400 mg efavirenz or 100 mg ritonavir for 14 consecutive days. On day 14, they ingested a single 40 mg/kg dose of PZQ. We measured plasma levels up to 12 h on day 1 and day 14. Samples were analyzed by LC-MS. Pharmacokinetic analysis was conducted in WinNonlin to determine the primary endpoints (plasma T_1/2 , C_min , and AUC). Efavirenz had a significant effect on the pharmacokinetics of PZQ (p < .05), reducing the AUC by 4-fold (1213.15 vs. 281.35 h·ng/ml for R-PZQ and 5669 vs. 871.84 h·ng/ml for S-PZQ). Ritonavir had no significant effect on R-PZQ but increased the AUC 2-fold for S-PZQ (p < .05) (4154.79 vs. 7291.05 h·ng/ml). Using PZQ in HIV patients needs investigation, as there is a risk of both treatment failure and adverse effects because of induction and inhibition, respectively.

Inhibition of CYP3A7 DHEA-S Oxidation by Lopinavir and Ritonavir: An Alternative Mechanism for Adrenal Impairment in HIV Antiretroviral-Treated Neonates

Prophylactic antiretroviral therapy (ART) in HIV infected pregnant mothers and their newborns can dramatically reduce mother-to-child viral transmission and seroconversion in the neonate. The ritonavir-boosted lopinavir regimen, known as Kaletra, has been associated with premature birth and transient adrenal insufficiency in newborns, accompanied by increases in plasma dehydroepiandrosterone 3-sulfate (DHEA-S). In the fetus and neonates, cytochrome P450 CYP3A7 is responsible for the metabolism of DHEA-S into 16α-hydroxy DHEA-S, which plays a critical role in growth and development. In order to determine if CYP3A7 inhibition could lead to the adverse outcomes associated with Kaletra therapy, we conducted in vitro metabolic studies to determine the extent and mechanism of CYP3A7 inhibition by both ritonavir and lopinavir and the relative intrinsic clearance of lopinavir with and without ritonavir in both neonatal and adult human liver microsomes (HLMs). We identified ritonavir as a potent inhibitor of CYP3A7 oxidation of DHEA-S (IC₅₀ = 0.0514 μM), while lopinavir is a much weaker inhibitor (IC₅₀ = 5.88 μM). Furthermore, ritonavir is a time-dependent inhibitor of CYP3A7 with a K_I of 0.392 μM and a k_inact of 0.119 min^–1, illustrating the potential for CYP3A mediated drug–drug interactions with Kaletra. The clearance rate of lopinavir in neonatal HLMs was much slower and comparable to the rate observed in adult HLMs in the presence of ritonavir, suggesting that the addition of ritonavir in the cocktail therapy may not be necessary to maintain effective concentrations of lopinavir in neonates. Our results suggest that several of the observed adverse outcomes of Kaletra therapy may be due to the direct inhibition of CYP3A7 by ritonavir and that the necessity for the inclusion of this drug in the therapy may be obviated by the lower rate of lopinavir clearance in the neonatal liver. These results may lead to a reconsideration of the use of ritonavir in neonatal antiretroviral therapy.

Evaluation of the effects of atazanavir-ritonavir on the pharmacokinetics of lumefantrine in patients living with HIV in Lagos University Teaching Hospital, South-Western Nigeria

PURPOSE

Atazanavir-ritonavir (ATVr)-based antiretroviral therapy and artemether-lumefantrine (AL) are commonly used drugs for the treatment of human immune deficiency virus (HIV) infection and malaria respectively. However, interaction of both drugs, with Cytochrome P 3A4 (CYP 3A4) isoenzyme, may spawn clinically significant pharmacokinetic interactions. This study evaluated the effects of atazanavir-ritonavir on the pharmacokinetics of lumefantrine.

METHOD

In a case-control study, twenty participants having Plasmodium falciparum malaria were recruited and divided into two groups (ATVr-arm, n=10; and control-arm, n= 10). All the participants were administered six oral doses of AL 80-480 mg (Coartem). Thereafter, their blood samples were collected at different time intervals over seven days. The concentration of lumefantrine in each sample was quantified with high-performance liquid chromatography (HPLC) and used to determine its pharmacokinetic parameters which were compared between the test and control groups.

RESULTS

ATVr increased the mean day 7 concentration of lumefantrine (ATVr 3847.09 ± 893.35 ng/mL, control 1374.53 ± 265.55 ng/mL, p = 0.016) and the area under its plasma concentration-time curve (ATVr 670529.57 ± 157172.93 ng.h/mL, control 447976.28 ± 80886.99 ng.h/mL, p = 0.224) by 179.88 % and 49.68 %, respectively, but decreased its mean maximum plasma drug concentration (Cmax) (ATVr 13725.70 ± 2658.44 ng/mL, control 15380.48 ± 2332.62 ng/mL, p = 0.645) by 10.76 %.

CONCLUSION

ATVr increased drug exposure and day 7 plasma concentration of lumefantrine. AL is therefore considered effective for the treatment of malaria in patients taking ATVr-based regimen. However, the safety associated with the interaction requires further elucidation.

TRIAL REGISTRATION

Clin ClinicalTrials.gov Identifier: NCT04531072, August 27, 2020. "Retrospectively registered".

Investigating the influence of relevant pharmacogenetic variants on the pharmacokinetics and pharmacodynamics of orally administered docetaxel combined with ritonavir

The anticancer drug docetaxel exhibits large interpatient pharmacokinetic and pharmacodynamic variability. In this study, we aimed to assess the functional significance of 14 polymorphisms in the CYP3A, CYP1B1, ABCB1, ABCC2, and SLCO1B3 genes for the pharmacokinetics and pharmacodynamics of oral docetaxel, co-administered with ritonavir. None of the tested CYP3A, ABCB1, ABCC2, and SLCO1B3 genotypes and diplotypes showed a significant relation with an altered bioavailability or clearance of either docetaxel or ritonavir. Similarly, no clear effect of CYP1B1 genotype on clinical outcomes was observed in a subgroup of non-small cell lung cancer (NSCLC) patients. Our post hoc power analysis indicated that our pharmacogenetic-pharmacokinetic analysis was only powered for relatively high effect sizes, which were to be expected given the high interpatient variability. This makes it unlikely that future studies will explain the high observed interpatient variability in oral docetaxel pharmacokinetics as a result of any of these separate polymorphisms and diplotypes.

Differential effects of antiretroviral drug toxicity in male versus female children who are HIV-exposed but uninfected

: In recent years, widespread use of antiretroviral therapy (ART) during pregnancy has been increasingly effective in reducing risk of vertical transmission of HIV, with over 80% of pregnant women living with HIV now accessing ART, and a 41% reduction in new infections in children between 2010 and 2018. Despite these strides, the developmental toxicity of widely administered antiretroviral drugs (ARVs) remains poorly described and existing literature often fails to account for fetal and infant sex as a variable. Recent reports have identified associations between in-utero exposure to commonly used antiretroviral regimens and alteration in neurodevelopment, growth, and metabolism amongst children who are HIV-exposed but uninfected, with findings of sex differences in the prevalence and severity of ARV toxicity. These differences are potentially explained by variable exposure to ARV drugs in utero or exacerbation of existing sex-linked risk factors. Fetal ARV exposure is mediated by placental and fetal drug transporters and metabolic enzymes, which may contribute to the manifestation of sex differences. Existing evidence of sex differences in ARV toxicity in fetal development is concerning, and demands further research to guide optimal treatment options for maternal health and prevention of vertical HIV transmission.

Clobetasol Propionate Is a Heme-Mediated Selective Inhibitor of Human Cytochrome P450 3A5

The human cytochrome P450 (CYP) enzymes CYP3A4 and CYP3A5 metabolize most drugs and have high similarities in their structure and substrate preference. Whereas CYP3A4 is predominantly expressed in the liver, CYP3A5 is upregulated in cancer, contributing to drug resistance. Selective inhibitors of CYP3A5 are, therefore, critical to validating it as a therapeutic target. Here we report clobetasol propionate (clobetasol) as a potent and selective CYP3A5 inhibitor identified by high-throughput screening using enzymatic and cell-based assays. Molecular dynamics simulations suggest a close proximity of clobetasol to the heme in CYP3A5 but not in CYP3A4. UV-visible spectroscopy and electron paramagnetic resonance analyses confirmed the formation of an inhibitory type I heme-clobetasol complex in CYP3A5 but not in CYP3A4, thus explaining the CYP3A5 selectivity of clobetasol. Our results provide a structural basis for selective CYP3A5 inhibition, along with mechanistic insights, and highlight clobetasol as an important chemical tool for target validation.

Structural Perspectives of the CYP3A Family and Their Small Molecule Modulators in Drug Metabolism

Cytochrome P450 enzymes function to catalyze a wide range of reactions, many of which are critically important for drug response. Members of the human cytochrome P450 3A (CYP3A) family are particularly important in drug clearance, and they collectively metabolize more than half of all currently prescribed medications. The ability of these enzymes to bind a large and structurally diverse set of compounds increases the chances of their modulating or facilitating drug metabolism in unfavorable ways. Emerging evidence suggests that individual enzymes in the CYP3A family play discrete and important roles in catalysis and disease progression. Here we review the similarities and differences among CYP3A enzymes with regard to substrate recognition, metabolism, modulation by small molecules, and biological consequence, highlighting some of those with clinical significance. We also present structural perspectives to further characterize the basis of these comparisons.

Neonatal cytochrome P450 CYP3A7: A comprehensive review of its role in development, disease, and xenobiotic metabolism

The human cytochrome P450 CYP3A7, once thought to be an enzyme exclusive to fetal livers, has more recently been identified in neonates and developing infants as old as 24 months post-gestational age. CYP3A7 has been demonstrated to metabolize two endogenous compounds that are known to be important in the growth and development of the fetus and neonate, namely dehydroepiandrosterone sulfate (DHEA-S) and all-trans retinoic acid (atRA). In addition, it is also known to metabolize a variety of drugs and xenobiotics, albeit generally to a lesser extent relative to CYP3A4/5. CYP3A7 is an important component in the development and protection of the fetal liver and additionally plays a role in certain disease states, such as cancer and adrenal hyperplasia. Ultimately, a full understanding of the expression, regulation, and metabolic properties of CYP3A7 is needed to provide neonates with appropriate individualized pharmacotherapy. This article summarizes the current state of knowledge of CYP3A7, including its discovery, distribution, alleles, RNA splicing, expression and regulation, metabolic properties, substrates, and inhibitors.

Indinavir Increases Midazolam N-Glucuronidation in Humans: Identification of an Alternate CYP3A Inhibitor Using an In Vitro to In Vivo Approach

Midazolam is a widely used index substrate for assessing effects of xenobiotics on CYP3A activity. A previous study involving human hepatocytes showed the primary route of midazolam metabolism, 1'-hydroxylation, shifted to N-glucuronidation in the presence of the CYP3A inhibitor ketoconazole, which may lead to an overprediction of the magnitude of a xenobiotic-midazolam interaction. Because ketoconazole is no longer recommended as a clinical CYP3A inhibitor, indinavir was selected as an alternate CYP3A inhibitor to evaluate the contribution of the N-glucuronidation pathway to midazolam metabolism. The effects of indinavir on midazolam 1'-hydroxylation and N-glucuronidation were first characterized in human-derived in vitro systems. Compared with vehicle, indinavir (10 μM) inhibited midazolam 1'-hydroxylation by recombinant CYP3A4, human liver microsomes, and high-CYP3A activity cryopreserved human hepatocytes by ≥70%; the IC₅₀ obtained with hepatocytes (2.7 μM) was within reported human unbound indinavir C_max (≤5 μM). Midazolam N-glucuronidation in hepatocytes increased in the presence of indinavir in both a concentration-dependent (1-33 μM) and time-dependent (0-4 hours) manner (by up to 2.5-fold), prompting assessment in human volunteers (n = 8). As predicted by these in vitro data, indinavir was a strong inhibitor of the 1'-hydroxylation pathway, decreasing the 1'-hydroxymidazolam/midazolam area under the plasma concentration versus time curve (AUC)_0-12h ratio by 80%. Although not statistically significant, the midazolam N-glucuronide/midazolam AUC_0-12h ratio increased by 40%, suggesting a shift to the N-glucuronidation pathway. The amount of midazolam N-glucuronide recovered in urine increased 4-fold but remained <10% of the oral midazolam dose (2.5 mg). A powered clinical study would clarify whether N-glucuronidation should be considered when assessing the magnitude of a xenobiotic-midazolam interaction.

Pharmacokinetics and pharmacodynamics of cytochrome P450 inhibitors for HIV treatment

INTRODUCTION

Drugs used in HIV treatment; all protease inhibitors, some non-nucleoside reverse transcriptase inhibitors, and pharmacoenhancers ritonavir and cobicistat can inhibit cytochrome P450 (CYP) enzymes. CYP inhibition can cause clinically significant drug-drug interactions (DDI), leading to increased drug exposure and potential toxicity. Areas covered: A complete understanding of pharmacodynamics and CYP-mediated DDI is crucial to prevent adverse side effects and to achieve optimal efficacy. We summarized the pharmacodynamics of all the CYP inhibitors used for HIV treatment, followed by a discussion of drug interactions between these CYP inhibitors and other drugs, and a discussion on the effect of CYP polymorphisms. We also discussed the potential advancements in improving the pharmacodynamics of these CYP inhibitors by using nanotechnology strategy. Expert opinion: The drug-interactions in HIV patients receiving ARV drugs are complicated, especially when patients are on CYP inhibitors-based ART regimens. Therefore, evaluation of CYP-mediated drug interactions is necessary prior to prescribing ARV drugs to HIV subjects. To improve the treatment efficacy and minimize DDI, novel approaches such as nanotechnology may be the potential alternative approach. However, further studies with large cohort need to be conducted to provide strong evidence for the use of nano-formulated ARVs to effectively treat HIV patients.

CYP3A4/5 Activity Probed with Testosterone and Midazolam: Correlation between Two Substrates at the Microsomal and Enzyme Levels

Testosterone (TST) and midazolam (MDZ) are widely used as probes to detect CYP3A4/5 activity, but the data acquired with these two substrates do not correlate well at the microsomal level (per milligram of microsomal protein), and the reason is unclear. In this study, CYP3A4/5 activity was probed with TST and MDZ at the microsomal and enzyme levels (per picomole of CYP3A4/5) in 72 human liver samples. Correlation coefficients were lower in V_max and CL_int at the microsomal level, as compared with those at the enzyme level ( V_max 0.658 vs 0.883; CL_int no correlation vs 0.796). Compared with TST, MDZ was found to correlate better with the content of CYP3A4/5 (no correlation vs 0.431) and CYP3A5 (no correlation vs 0.447), and huge variations in enzyme content existed among different genotypes, which explained the lower degree of correlation at the microsomal level. In addition, different genotypes had varying effects on activity at the enzyme level, whereas the difference between activity at the enzyme level probed with TST and that probed with MDZ was not obvious ( P > 0.05), indicating that the effect of gene polymorphisms on correlation between activity probed with these two substrates was limited at the enzyme level. In conclusion, our study demonstrates a high degree of correlation between CYP3A4/5 activity probed with TST and MDZ at the enzyme level but not at the microsomal level and allows us to correctly understand the influence of gene polymorphisms on the correlations.

Managing antiretroviral therapy in the elderly HIV patient

Introduction: Owing to more effective and less toxic antiretroviral therapy (ART), people living with HIV (PLWH) live longer, a phenomenon expected to grow in the next decades. With advancing age, effectively treated PLWH experience not only a heightened risk for non-infective comorbidities and multimorbidity, but also for geriatric syndromes and frailty. In addition, older adults living with HIV (OALWH) have a higher prevalence of so-called iatrogenic triad described as polypharmacy (PP), potentially inappropriate medication use, and drug-drug interactions. Areas covered: This review will focus the management of ART in OALWH. We will discuss iatrogenic triad and best way to address PP. Special focus will be given to pharmacokinetic and pharmacodynamic aspects of ART in the elderly, evaluation of ART toxicities, and specific ART strategies commonly used in this population. Expert commentary: Research should be focused on recruiting more OALWH, frail individuals in particular, into the clinical trials and specific geriatric outcome need to be considered together with traditional viroimmunological outcomes.

Minor contribution of CYP3A5 to the metabolism of hepatitis C protease inhibitor paritaprevir in vitro

Paritaprevir (PTV) is a non-structural protein 3/4A protease inhibitor developed for the treatment of hepatitis C disease as a fixed dose combination of ombitasvir (OBV) and ritonavir (RTV) with or without dasabuvir. The aim of this study was to evaluate the effects of cytochrome P450 (CYP) 3A5 on in vitro PTV metabolism using human recombinant CYP3A4, CYP3A5 (rCYP3A4, rCYP3A5) and human liver microsomes (HLMs) genotyped as either CYP3A5*1/*1, CYP3A5*1/*3 or CYP3A5*3/*3. The intrinsic clearance (CL_int, V_max/K_m) for the production of a metabolite from PTV in rCYP3A4 was 1.5 times higher than that in rCYP3A5. The PTV metabolism in CYP3A5*1/*1 and CYP3A5*1/*3 HLMs expressing CYP3A5 was comparable to that in CYP3A5*3/*3 HLMs, which lack CYP3A5. CYP3A4 expression level was significantly correlated with PTV disappearance rate and metabolite formation. In contrast, there was no such correlation found for CYP3A5 expression level. This study represents that the major CYP isoform involved in PTV metabolism is CYP3A4, with CYP3A5 having a minor role in PTV metabolism. The findings of the present study may provide foundational information on PTV metabolism, and may further support dosing practices in HCV-infected patients prescribed PTV-based therapy.

A novel cytochrome P450 mono-oxygenase from Streptomyces platensis resembles activities of human drug metabolizing P450s

Cytochrome P450 mono-oxygenases (P450) are versatile enzymes which play essential roles in C-source assimilation, secondary metabolism, and in degradations of endo- and exogenous xenobiotics. In humans, several P450 isoforms constitute the largest part of phase I metabolizing enzymes and catalyze oxidation reactions which convert lipophilic xenobiotics, including drugs, to more water soluble species. Recombinant human P450s and microorganisms are applied in the pharmaceutical industry for the synthesis of drug metabolites for pharmacokinetics and toxicity studies. Compared to the membrane-bound eukaryotic P450s, prokaryotic ones exhibit some advantageous features, such as high stability and generally easier heterologous expression. Here, we describe a novel P450 from Streptomyces platensis DSM 40041 classified as CYP107L that efficiently converts several commercial drugs of various size and properties. This P450 was identified by screening of actinobacterial strains for amodiaquine and ritonavir metabolizing activities, followed by genome sequencing and expression of the annotated S. platensis P450s in Escherichia coli. Performance of CYP107L in biotransformations of amodiaquine, ritonavir, amitriptyline, and thioridazine resembles activities of the main human metabolizing P450s, namely CYPs 3A4, 2C8, 2C19, and 2D6. For application in the pharmaceutical industry, an E. coli whole-cell biocatalyst expressing CYP107L was developed and evaluated for preparative amodiaquine metabolite production.

Comparison of Antifungal Azole Interactions with Adult Cytochrome P450 3A4 versus Neonatal Cytochrome P450 3A7

Adult drug metabolism is dominated by cytochrome P450 3A4 (CYP3A4), which is often inhibited by antifungal azole drugs, resulting in potential alterations in drug metabolism and adverse drug/drug interactions. In the fetal and neonatal stages of life, the 87% identical cytochrome P450 3A7 (CYP3A7) is expressed but not CYP3A4. Azole antifungals developed for adults are also used in neonates, assuming they interact similarly with both enzymes, but systematic information is lacking. Herein a method was developed for generating recombinant purified CYP3A7. Thirteen different azoles were then evaluated for binding and inhibition of purified human CYP3A4 versus CYP3A7. All imidazole-containing azoles bound both enzymes via coordination to the heme iron and inhibited both with IC₅₀ values ranging from 180 nM for clotrimazole to the millimolar range for imidazole itself. Across this wide range of potencies, CYP3A4 was consistently inhibited more strongly than CYP3A7, with clotrimazole being the least selective (1.5-fold) inhibitor and econazole the most selective (12-fold). Observations for 1,2,4-triazole-containing azoles were more varied. Most bound to CYP3A4 via coordination to the heme iron, but several also demonstrated evidence of a distinct binding mode at low concentrations. However, only posaconazole inhibited CYP3A4. Of the triazoles, only posaconazole inhibited CYP3A7, again less potently than CYP3A4. Spectral evidence for binding was weak or nonexistent for all triazoles. Overall, although the details of binding interactions do vary, the same azole compounds inhibit both enzymes, albeit with weaker interactions with CYP3A7 compared with CYP3A4.

Biosynthesis and Identification of Metabolites of Maraviroc and Their Use in Experiments to Delineate the Relative Contributions of Cytochrome P4503A4 versus 3A5

Maraviroc (MVC) is a CCR5 coreceptor antagonist indicated in combination with other antiretroviral agents for the treatment of CCR5-tropic human immunodefinciency virus-1 infection. In this study, the metabolism of MVC was investigated in human liver microsomes to delineate the relative roles of CYP3A4 and CYP3A5. MVC is metabolized to five hydroxylated metabolites, all of which were biosynthesized and identified using mass and NMR spectroscopy. The sites of metabolism were the 2- and 3-positions of the 4,4-difluorocyclohexyl moiety and the methyl of the triazole moiety. Absolute configurations were ultimately ascertained by comparison to authentic standards. The biosynthesized metabolites were used for quantitative in vitro experiments in liver microsomes using cyp3cide, a selective inactivator of CYP3A4. (1S,2S)-2-OH-MVC was the main metabolite representing approximately half of the total metabolism, and CYP3A5 contributed approximately 40% to that pathway in microsomes from CYP3A5*1/*1 donors. The other four metabolites were almost exclusively metabolized by CYP3A4. (1S,2S)-2-hydroxylation also correlated to T-5 N-oxidation, a CYP3A5-specific activity. These data are consistent with clinical pharmacokinetic data wherein CYP3A5 extensive metabolizer subjects showed a modestly lower exposure to MVC.

The challenge of polypharmacy in an aging population and implications for future antiretroviral therapy development

: It is estimated that by 2030 nearly three-quarters of persons living with HIV will be 50 years and older. The aging HIV population presents a new clinical concern for HIV providers: adverse effects from polypharmacy. An aging population means more comorbidities and potentially more drug-drug interactions for providers to manage. This review discusses major comorbidities including cardiovascular disease, anticoagulation, hypertension, diabetes mellitus and malignancy and considerations for drug-interactions with antiretrovirals.

Fluticasone furoate induced iatrogenic Cushing syndrome in a pediatric patient receiving anti-retroviral therapy

Summary

We present a case of iatrogenic Cushing’s syndrome, induced by treatment with fluticasone furoate (1–2 dd, 27.5 µg in each nostril) in a pediatric patient treated for congenital HIV. The pediatric patient described in this case report is a young girl of African descent, treated for congenital HIV with a combination therapy of Lopinavir/Ritonavir (1 dd 320/80 mg), Lamivudine (1 dd 160 mg) and Abacavir (1 dd 320 mg). Our pediatric patient presented with typical Cushingoid features (i.e. striae of the upper legs, full moon face, increased body and facial hair) within weeks after starting fluticasone furoate therapy, which was exacerbated after increasing the dose to 2 dd because of complaints of unresolved rhinitis. Biochemical analysis fitted iatrogenic Cushing’s syndrome, with a repeatedly low cortisol (<0.03 µM, ref 0.14–0.60 µM) and low ACTH (9 pg/mL, ref 9–52 pg/mL) without signs of adrenal insufficiency. No other biochemical abnormalities that could point to adrenal or pituitary dysfunction were detected; electrolytes, thyroid and gonadal function, and IGF-1 were within the normal range. Pharmacogenetic analysis revealed that the pediatric patient carried the CYP3A4 *1B/*1G and CYP3A5 *3/*3 genotype (associated with a partial and complete loss of enzyme activity, respectively) which is associated with the development of iatrogenic Cushing’s syndrome in patients treated for HIV due to the strong inhibition of CYP3 enzymes by Ritonavir. Upon discontinuation of fluticasone treatment, the pediatric patient improved both clinically and biochemically with normalisation of cortisol and ACTH within a couple of weeks.

Learning points:

Neurotoxicity in the Post-HAART Era: Caution for the Antiretroviral Therapeutics

Despite the advent of highly active antiretroviral therapy (HAART), HIV-associated neurological disorders (HAND) remain a major challenge in human immunodeficiency virus (HIV) treatment. The early implementation of HAART in the infected individuals helps suppress the viral replication in the plasma and other compartments. Several studies also report the beneficial effect of drugs that successfully penetrate central nervous system (CNS). However, recent data in both clinical setup and in in vitro studies indicate CNS toxicity of the antiretrovirals (ARVs). Although the evidence is limited, correlation between prolonged use of ARVs and neurotoxicity strongly suggests that it is essential to study the underlying mechanisms responsible for such toxicity. Furthermore, closer attention toward clinical outcomes is required to screen various ARV regimens for their association with HAND and other comorbidities. A growing body of literature also indicates a possible role of accelerated aging in the antiretroviral therapy-associated neurotoxicity. Lastly, owing to high pill burden, multiple drugs in the HIV treatment also invite a possible role of drug-drug interaction via various cytochrome P450 enzymes. The particular emphasis of this review is to highlight the need to identify alternative approaches in reducing the CNS toxicity of the ARV drugs in HIV-infected individuals.

Parasite Cathepsin D-Like Peptidases and Their Relevance as Therapeutic Targets

Inhibition of aspartic cathepsin D-like peptidases (APDs) has been often discussed as an antiparasite intervention strategy. APDs have been considered as virulence factors of Trypanosoma cruzi and Leishmania spp., and have been demonstrated to have important roles in protein trafficking mechanisms of apicomplexan parasites. APDs also initiate blood digestion as components of multienzyme proteolytic complexes in malaria, platyhelminths, nematodes, and ticks. Increasing DNA and RNA sequencing data indicate that parasites express multiple APD isoenzymes of various functions that can now be specifically evaluated using new functional-genomic and biochemical tools, from which we can further assess the potential of APDs as targets for novel effective intervention strategies against parasitic diseases that still pose an alarming threat to mankind.

Antiretroviral drug toxicity in relation to pharmacokinetics, metabolic profile and pharmacogenetics

INTRODUCTION

Besides therapeutic effectiveness, drug tolerability is a key issue for treatments that must be taken indefinitely. Given the high prevalence of toxicity in HIV therapy, the factors implicated in drug-induced morbidities should be identified in order to improve the safety, tolerability and adherence to the treatments. Current approaches have focused almost exclusively on parent drug concentrations; whereas recent evidence suggests that drug metabolites resulting from complex genetic and environmental influences can also contribute to treatment outcome. Pharmacogenetic variations have shown to play a relevant role in the variability observed in antiretroviral drug exposure, clinical response and sometimes toxicity. The integration of pharmacokinetic, pharmacogenetic and metabolic determinants will more probably address current therapeutic needs in patients.

AREAS COVERED

This review offers a concise description of three classes of antiretroviral drugs. The review looks at the metabolic profile of these drugs and gives a comprehensive summary of the existing literature on the influence of pharmacogenetics on their pharmacokinetics and metabolic pathways, and the associated drug or metabolite toxicity.

EXPERT OPINION

Due to the high prevalence of toxicity and the related risk of low adherence to the treatments, association of kinetic, genetic and metabolic markers predictive of therapeutic or toxicity outcomes could represent a more complete approach for optimizing antiretroviral therapy.

Effect of Ethanol on the Metabolic Characteristics of HIV-1 Integrase Inhibitor Elvitegravir and Elvitegravir/Cobicistat with CYP3A: An Analysis Using a Newly Developed LC-MS/MS Method

Elvitegravir (EVG), an integrase inhibitor for the treatment HIV infection, is increasingly becoming the part of first-line antiretroviral therapy (ART) regimen. EVG is mainly metabolized through cytochrome P450 (CYP) 3A4. Previously, we have shown that ethanol alters ART-CYP3A4 interactions with protease inhibitors thereby altering their metabolisms. However, as EVG is a fairly new class of drug, its kinetic characteristics and the effect of ethanol on EVG-CYPP3A4 interaction is poorly understood. In this study, we characterized EVG and cobicistat (COBI)-boosted EVG metabolism in human microsomes followed by ethanol-EVG, ethanol-COBI-EVG interaction with CYP3A. First, we developed and validated a simple, sensitive, and robust liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of EVG in the human liver microsomes. The lower limit of quantification for the drug was at 0.003 μM (1.34ng/ml). Extraction yield, matrix effects, drug stability, and calibration curves for the proposed method were validated according to the FDA guidelines. Time dependent kinetics data showed that 20mM ethanol decreases the apparent half-life of EVG degradation by ~50% compared to EVG alone. Our substrate kinetic results revealed that ethanol mildly decreases the catalytic efficiency for EVG metabolism. Inhibition studies demonstrated that EVG inhibits CYP3A4, and 20 mM ethanol causes a decrease in the IC₅₀ of EVG. However, in the presence of COBI we were unable to determine these parameters effectively because COBI, being a strong inhibitor of CYP3A4, blocked the EVG/ethanol-CYP3A4 interactions. Docking studies predicted a shift of EVG or COBI binding to the active site of CYP3A4 in the presence of ethanol. Taken together, these results suggest that ethanol interacts with microsomal CYP3A and alters EVG-CYP3A4 interaction thereby altering EVG metabolism and inhibition of CYP3A4 by EVG. This finding has clinical significance because alcohol use is highly prevalent in HIV population, and there are no separate guidelines for these patients while they are on ART medication.

Clinical use of cobicistat as a pharmacoenhancer of human immunodeficiency virus therapy

The pharmacoenhancement of plasma concentrations of protease inhibitors by coadministration of so-called boosters has been an integral part of antiretroviral therapy for human immunodeficiency virus (HIV) for 1.5 decades. Nearly all HIV protease inhibitors are combined with low-dose ritonavir or cobicistat, which are able to effectively inhibit the cytochrome-mediated metabolism of HIV protease inhibitors in the liver and thus enhance the plasma concentration and prolong the dosing interval of the antiretrovirally active combination partners. Therapies created in this way are clinically effective regimens, being convenient for patients and showing a high genetic barrier to viral resistance. In addition to ritonavir, which has been in use since 1996, cobicistat, a new pharmacoenhancer, has been approved and is widely used now. The outstanding property of cobicistat is its cytochrome P450 3A-selective inhibition of hepatic metabolism of antiretroviral drugs, in contrast with ritonavir, which not only inhibits but also induces a number of cytochrome P450 enzymes, UDP-glucuronosyltransferase, P-glycoprotein, and other cellular transporters. This article reviews the current literature, and compares the pharmacokinetics, pharmacodynamics, and safety of both pharmacoenhancers and discusses the clinical utility of cobicistat in up-to-date and future HIV therapy.

Risk factors for pre-term birth in a Canadian cohort of HIV-positive women: role of ritonavir boosting?

BACKGROUND

The risk of pre-term birth (PTB) associated with the use of protease inhibitors (PIs) during pregnancy remains a subject of debate. Recent data suggest that ritonavir boosting of PIs may play a specific role in the initiation of PTB, through an effect on the maternal-fetal adrenal axis. The primary objective of this study is to compare the risk of PTB among women treated with boosted PI versus non-boosted PIs during pregnancy.

METHODS

Between 1988 and 2011, 705 HIV-positive women were enrolled into the Centre Maternel et Infantile sur le SIDA mother-infant cohort at Centre Hospitalier Universitaire Sainte-Justine in Montreal, Canada. Inclusion criteria for the study were: 1) attendance at a minimum of two antenatal obstetric visits and 2) singleton live birth, at 24 weeks gestational or older. The association between PTB (defined as delivery at <37 weeks gestational age), antiretroviral drug exposure and maternal risk factors was assessed retrospectively using logistic regression.

RESULTS

A total of 525 mother-infant pairs were included in the analysis. Among them, PI-based combination anti-retroviral therapy was used in 37.4%, boosted PI based in 24.4%, non-nucleoside reverse transcriptase inhibitor (NNRTI) or nucleoside reverse transcriptase inhibitor based in 28.1%, and no treatment was given in 10.0% of cases. Overall, 13.5% of women experienced PTB. Among women treated with antiretroviral therapy, the risk of PTB was significantly higher among women who received boosted versus non-boosted PI (OR 2.01, 95% CI 1.02-3.97). This remained significant after adjusting for maternal age, delivery CD4 count, hepatitis C co-infection, history of previous PTB, and parity (aOR 2.17, 95% CI 1.05-4.51). There was no increased risk of PTB with the use of unboosted PIs as compared to NNRTI- or NRTI-based regimens.

CONCLUSION

While previous studies on the association between PTB and PI use have generally considered all PIs the same, our results would indicate a possible role of ritonavir boosting as a risk factor for PTB. Further work is needed to understand the pathophysiologic mechanisms involved, and to identify the safest ARV regimens to be used in pregnancy.

Influence of HIV antiretrovirals on methadone N-demethylation and transport

Drug interactions involving methadone and/or HIV antiretrovirals can be problematic. Mechanisms whereby antiretrovirals induce clinical methadone clearance are poorly understood. Methadone is N-demethylated to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) by CYP2B6 and CYP3A4 in vitro, but by CYP2B6 in vivo. This investigation evaluated human hepatocytes as a model for methadone induction, and tested the hypothesis that methadone and EDDP are substrates for human drug transporters. Human hepatocyte induction by several antiretrovirals of methadone N-demethylation, and CYP2B6 and CYP3A4 transcription, protein expression and catalytic activity, and pregnane X receptor (PXR) activation were evaluated. Methadone and EDDP uptake and efflux by overexpressed transporters were also determined. Methadone N-demethylation was generally not significantly increased by the antiretrovirals. CYP2B6 mRNA and activity (bupropion N-demethylation) were induced by several antiretrovirals, as were CYP3A4 mRNA and protein expression, but only indinavir increased CYP3A activity (alfentanil dealkylation). CYP upregulation appeared related to PXR activation. Methadone was not a substrate for uptake (OCT1, OCT2, OCT3, OATP1A2, OATP1B1, OATP1B3, OATP2B1) or efflux (P-gp, BCRP) transporters. EDDP was a good substrate for P-gp, BCRP, OCT1, OCT3, OATP1A2, and OATP1B1. OATP1A2- and OCT3-mediated EDDP uptake, and BCRP-mediated EDDP efflux transport, was inhibited by several antiretrovirals. Results show that hepatocyte methadone N-demethylation resembles expressed and liver microsomal metabolism more than clinical metabolism. Compared with clinical studies, hepatocytes underreport induction of methadone metabolism by HIV drugs. Hepatocytes are not a good predictive model for clinical antiretroviral induction of methadone metabolism and not a substitute for clinical studies. EDDP is a transporter substrate, and is susceptible to transporter-mediated interactions.

CYP3A5 genotype impacts maraviroc concentrations in healthy volunteers

CYP3A5 plays a prominent role in the metabolism of maraviroc, an approved drug for human immunodeficiency virus (HIV)-1 treatment and a candidate for HIV-1 prevention. We studied the effect of the CYP3A5 genotype on pharmacokinetics of maraviroc and a primary CYP3A5-dependent metabolite of maraviroc denoted as metabolite 1 (M1). Volunteers were screened for health status and CYP3A5 genotype (wild-type allele *1 and dysfunctional alleles *2, *3, *6, and *7) to obtain 24 evaluable subjects in three groups (n = 8 each): homozygous dysfunctional (two dysfunctional alleles), heterozygous (one *1 allele and one dysfunctional allele), and homozygous wild-type (two *1 alleles). Subjects received 300 mg maraviroc orally followed by blood collection for 32 hours. The homozygous wild-type group exhibited lower mean plasma maraviroc concentrations at almost all sampling times. The median (interquartile range) maraviroc area under the plasma concentration-time curves from time 0 to infinity (AUC0-inf) were 2099 (1422-2568) ng⋅h/ml, 1761 (931-2640) ng⋅h/ml, and 1238 (1065-1407) ng⋅h/ml for the homozygous dysfunctional, heterozygous, and homozygous wild-type groups, respectively. The homozygous wild-type group had 41% lower maraviroc AUC0-inf and 66% higher apparent clearance compared with the homozygous dysfunctional group (P = 0.02). The AUC0-inf ratios of maraviroc to M1 in heterozygous and homozygous wild-type subjects were lower by 51 and 64% relative to the homozygous dysfunctional group, respectively (P < 0.001). In conclusion, the lower maraviroc concentrations in the homozygous wild-type group indicate that maraviroc may be underdosed in people homozygous for the CYP3A5*1 allele, including almost one-half of African Americans.

Etravirine: a good option for concomitant use with chemotherapy for Hodgkin's lymphoma

The treatment of malignancies in HIV patients is challenged by the issue of drug-drug interactions between antiretroviral therapy and antineoplastic agents. While protease inhibitors have been shown to increase the incidence and severity of cancer therapy-related side effects, the impact of other antiretroviral agents on the tolerability and response to chemotherapy is less well documented. We report the successful use of an etravirine-based regimen in a patient treated with BEACOPP chemotherapy for advanced Hodgkin's lymphoma. Etravirine constitutes a valuable option for concomitant use with chemotherapy due to its moderate inducing effect on drug metabolising enzymes.

Drug-drug interactions between HMG-CoA reductase inhibitors (statins) and antiviral protease inhibitors

The HMG-CoA reductase inhibitors are a class of drugs also known as statins. These drugs are effective and widely prescribed for the treatment of hypercholesterolemia and prevention of cardiovascular morbidity and mortality. Seven statins are currently available: atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin. Although these drugs are generally well tolerated, skeletal muscle abnormalities from myalgia to severe lethal rhabdomyolysis can occur. Factors that increase statin concentrations such as drug-drug interactions can increase the risk of these adverse events. Drug-drug interactions are dependent on statins' pharmacokinetic profile: simvastatin, lovastatin and atorvastatin are metabolized through cytochrome P450 (CYP) 3A, while the metabolism of the other statins is independent of this CYP. All statins are substrate of organic anion transporter polypeptide 1B1, an uptake transporter expressed in hepatocyte membrane that may also explain some drug-drug interactions. Many HIV-infected patients have dyslipidemia and comorbidities that may require statin treatment. HIV-protease inhibitors (HIV PIs) are part of recommended antiretroviral treatment in combination with two reverse transcriptase inhibitors. All HIV PIs except nelfinavir are coadministered with a low dose of ritonavir, a potent CYP3A inhibitor to improve their pharmacokinetic properties. Cobicistat is a new potent CYP3A inhibitor that is combined with elvitegravir and will be combined with HIV-PIs in the future. The HCV-PIs boceprevir and telaprevir are both, to different extents, inhibitors of CYP3A. This review summarizes the pharmacokinetic properties of statins and PIs with emphasis on their metabolic pathways explaining clinically important drug-drug interactions. Simvastatin and lovastatin metabolized through CYP3A have the highest potency for drug-drug interaction with potent CYP3A inhibitors such as ritonavir- or cobicistat-boosted HIV-PI or the hepatitis C virus (HCV) PI, telaprevir or boceprevir, and therefore their coadministration is contraindicated. Atorvastatin is also a CYP3A substrate, but less potent drug-drug interactions have been reported with CYP3A inhibitors. Non-CYP3A-dependent statin concentrations are also affected although to a lesser extent when coadministered with HIV or HCV PIs, mainly through interaction with OATP1B1, and treatment should start with the lowest available statin dose. Effectiveness and occurrence of adverse effects should be monitored at regular time intervals.

A conceptually new treatment approach for relapsed glioblastoma: coordinated undermining of survival paths with nine repurposed drugs (CUSP9) by the International Initiative for Accelerated Improvement of Glioblastoma Care

To improve prognosis in recurrent glioblastoma we developed a treatment protocol based on a combination of drugs not traditionally thought of as cytotoxic chemotherapy agents but that have a robust history of being well-tolerated and are already marketed and used for other non-cancer indications. Focus was on adding drugs which met these criteria: a) were pharmacologically well characterized, b) had low likelihood of adding to patient side effect burden, c) had evidence for interfering with a recognized, well-characterized growth promoting element of glioblastoma, and d) were coordinated, as an ensemble had reasonable likelihood of concerted activity against key biological features of glioblastoma growth. We found nine drugs meeting these criteria and propose adding them to continuous low dose temozolomide, a currently accepted treatment for relapsed glioblastoma, in patients with recurrent disease after primary treatment with the Stupp Protocol. The nine adjuvant drug regimen, Coordinated Undermining of Survival Paths, CUSP9, then are aprepitant, artesunate, auranofin, captopril, copper gluconate, disulfiram, ketoconazole, nelfinavir, sertraline, to be added to continuous low dose temozolomide. We discuss each drug in turn and the specific rationale for use- how each drug is expected to retard glioblastoma growth and undermine glioblastoma's compensatory mechanisms engaged during temozolomide treatment. The risks of pharmacological interactions and why we believe this drug mix will increase both quality of life and overall survival are reviewed.

Population pharmacokinetic modeling and simulation of amprenavir following fosamprenavir/ritonavir administration for dose optimization in HIV infected pediatric patients

Fosamprenavir (FPV) is the phosphate ester prodrug of the HIV-1 protease inhibitor amprenavir (APV). A pediatric population pharmacokinetic model for APV was developed and simulation was used to identify dosing regimens for pediatric patients receiving FPV in combination with ritonavir (RTV) which resulted in concentrations similar to those in adults receiving FPV/RTV 700/100 mg BID. Pharmacokinetic data was obtained from HIV infected subjects aged 2 months to 18 years receiving either FPV or FPV/RTV. A two-compartment model with first order absorption and elimination was an appropriate structural model. Significant covariates in the model included RTV coadministration on clearance, fed status on bioavailability for the oral suspension, body weight on clearance and volume terms, black race on clearance, and age on clearance. The following FPV/RTV twice daily dosing regimens in pediatric patients delivered plasma APV exposure similar to adults: 45/7 mg/kg in patients weighing <11 kg, 30/3 mg/kg in patients weighing 11 to <15 kg, 23/3 mg/kg in patients weighing 15 to <20 kg, and 18/3 mg/kg in patients weighting ≥20 kg. Additionally children weighing ≥39 kg can receive the adult regimen.

How best to approach endocrine evaluation in patients with HIV in the era of combined antiretroviral therapy?

Endocrine and metabolic dysfunction has been documented throughout the history of clinical experience with HIV and AIDS. Opportunistic infections such as CMV and TB adrenalitis, tumours affecting endocrine organs, and cachexia and wasting can still be seen, particulary in severely immunocompromised individuals who may be noncompliant with, resistant to, or without access to effective antiretroviral therapy (ART). However, in those with good control of their HIV infection, the profile of endocrinopathy in HIV has largely changed with the advent of highly effective combination ART. The problems that we now more frequently see in people living for many years with low viral loads and good CD4 counts relate to side effects or interactions of therapy. These included adverse metabolic effects of antiretrovirals, most notably dyslipidaemia and lipodystrophy with protease inhibitors, drug-drug interactions, including marked CYP3A4 inhibition with protease inhibitors and autoimmune endocrinopathy as part of an immune reconstitution syndrome after initiation of antiretrovirals. In addition, chronic endocrine and metabolic disorders, including hypogonadism and osteoporosis, occur at higher levels than in the background population, associated with chronic illness, lower body weight and use of both prescribed and nonprescribed drugs.