Potent CYP3A4 Inhibitor Research Articles

Herb-drug interaction between Styrax and warfarin: Molecular basis and mechanism

BackgroundStyrax, one of the most famous folk medicines, has been frequently used for the treatment of cardiovascular diseases and skin problems in Asia and Africa. It is unclear whether Styrax or Styrax-related herbal medicines may trigger clinically relevant herb-drug interactions. PurposeThis study was carried out to investigate the inhibitory effects of Styrax on human cytochrome P450 enzymes (CYPs) and to clarify whether this herb may modulate the pharmacokinetic behavior of the CYP-substrate drug warfarin when co-administered. Study DesignThe inhibitory effects of Styrax on CYPs were assayed in human liver microsomes (HLM), while the pharmacokinetic interactions between Styrax and warfarin were investigated in rats. The bioactive constituents in Styrax with strong CYP3A inhibitory activity were identified and their inhibitory mechanisms were carefully investigated. MethodsThe inhibitory effects of Styrax on human CYPs were assayed in vitro, while the pharmacokinetic interactions between Styrax and warfarin were studied in rats. Fingerprinting analysis of Styrax coupled with LC-TOF-MS/MS profiling and CYP inhibition assays were used to identify the constituents with strong CYP3A inhibitory activity. The inhibitory mechanism of oleanonic acid (the most potent CYP3A inhibitor occurring in Styrax) against CYP3A4 was investigated by a panel of inhibition kinetics analyses and in silico analysis. ResultsIn vitro assays demonstrated that Styrax extract strongly inhibited human CYP3A and moderately inhibited six other tested human CYPs, as well as potently inhibited warfarin 10-hydroxylation in liver microsomes from both humans and rats. In vivo assays demonstrated that compared with warfarin given individually in rats, Styrax (100 mg/kg) significantly prolonged the plasma half-life of warfarin by 2.3-fold and increased the AUC(0-inf) of warfarin by 2.7-fold when this herb was co-administrated with warfarin (2 mg/kg) in rats. Two LC fractions were found with strong CYP3A inhibitory activity and the major constituents in these fractions were characterized by LC-TOF-MS/MS. Five pentacyclic triterpenoid acids (including epibetulinic acid, betulinic acid, betulonic acid, oleanonic acid and maslinic acid) present in Styrax were potent CYP3A inhibitors, and oleanonic acid was a competitive inhibitor against CYP3A-mediated testosterone 6β-hydroxylation. ConclusionStyrax and the pentacyclic triterpenoid acids occurring in this herb strongly modulate the pharmacokinetic behavior of warfarin via inhibition of CYP3A.

Inhibition of CYP1 by 7,8-dehydrorutaecarpine and its methoxylated derivatives

7,8-Dehydrorutaecarpine was a potent inhibitor of both CYP1A1 and CYP1A2. The introduction of methoxyl group reduced CYP1A1 inhibition and enhanced the relative inhibition selectivity to either CYP1A2 or CYP1B1. Among the synthesized derivatives, 2-methoxy-7,8-dehydrorutaecarpine had the best selectivity of CYP1A2 inhibition. In contrast, the introduction of 4-methoxyl group decreased the IC50 values for CYP1B1 and had the best selectivity of CYP1B1 inhibition. Results of molecular modeling showed that a hydrogen bond was formed between the 2-methoxyl group of 2-methoxy-7,8-dehydrorutaecarpine and Thr113 residue of CYP1A2. 2-Methoxy-7,8-dehydrorutaecarpine was a mixed type inhibitor of CYP1A2 with the inhibition constants of 9.5 ± 2.6 and 6.7 ± 2.6 nM for CYP1A2 and CYP1A2-substrate complex, respectively. For the 2-methoxyl derivatives of 7,8-dehydrorutaecarpine and rutaecarpine, the change of 2-methoxyl to an 2-ethoxyl group decreased and increased the IC50 values for CYP1A1 and CYP1A2, respectively. Our results demonstrated that introduction of alkoxyl modification to a heterocyclic compound, 7,8-dehydrorutaecarpine could change inhibitory selectivity among CYP1 enzymes. These results may provide important information for the interaction between CYP1 members and their inhibitors with a core structure of 7,8-dehydrorutaecarpine.

Relationship between plasma exposure of zolpidem and CYP2D6 genotype in healthy Korean subjects.

Zolpidem, a widely prescribed hypnotic agent, is extensively metabolized by cytochrome P450 (CYP) 3A4, and CYP2C9, CYP1A2 and CYP2D6 are also involved in the metabolism of zolpidem. The aim of the study was to investigate the effects of CYP2D6 genotypes on the exposure of zolpidem. The healthy male volunteers were divided into three different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, and CYP2D6*10/*10). Each subject received a single oral dose of zolpidem 5mg with or without a steady-state concentration of clarithromycin (a potent inhibitor of CYP3A4), and plasma concentrations of zolpidem were measured up to 12h after zolpidem dosing by using liquid chromatography-tandem mass spectrometry method. When zolpidem was administered alone, the exposure of zolpidem (the total areas under the curve and the mean peak plasma concentrations) was not significantly different among three different genotype groups. Even with the steady-state concentration of clarithromycin, a potent CYP3A4 inhibitor, there were no significant differences in the exposure of zolpidem in relation to CYP2D6 genotypes.

12 - Ritonavir, a potent inhibitor of CYP3A4, enhances the anticancer effects of panobinostat in bladder cancer cells

12 - Ritonavir, a potent inhibitor of CYP3A4, enhances the anticancer effects of panobinostat in bladder cancer cells

Cardiovascular Effects of Energy Drinks in the Pediatric Population.

Consumption of energy drinks in the pediatric population is correlated with more emergency department visits and causes adverse reactions, such as neurological, psychiatric, gastrointestinal, renal, and cardiovascular effects. These cardiovascular complications include increased cardiometabolic risk with high intake of sugar, short-term blood pressure increases and a decrease in cerebral blood flow due to the caffeine content, increased or decreased blood pressure from taurine, unmasked cardiac conditions, such as channelopathies, and atrial and ventral fibrillations. Cardiovascular complications can also arise when energy drinks are mixed with pharmaceutical drugs, such as amiodarone, potent CYP1A2 inhibitors, warfarin, digoxin, or corticosteroids. Combining energy drinks with alcohol also precipitates adverse cardiovascular events, posing a risk to the health of children and adolescents. This review further explores the ingredients in energy drinks and their mechanism of action in causing these cardiovascular complications.

CYP3A7 drug‐hormone Interactions in the Neonate: Adrenal Insufficiency and Low Birthweight in the HIV infected Neonate caused by Inhibition of CYP3A7 DHEA‐S Oxidation by Ritonavir

In the neonate and developing infant, CYP3A7 is the predominant CYP3A isoform and is responsible for the majority of metabolism of CYP3A substrates. However, its primary function is the 16α‐hydroxylation of the endogenous hormone DHEA‐S, which is important for maintenance of hormone homeostasis in the adrenal gland and production of estriol during the third trimester of pregnancy. Low maternal estriol levels have been reported to lead to low birth weight and premature birth. It has been previously reported that cohorts of HIV infected mothers and their newborns on a combined therapeutic regimen of Lopinavir and Ritonavir have increased adrenal insufficiency and low birth weight, as well as substantially elevated levels of DHEA‐S, leading to adverse outcomes in this fragile patient group. Since Ritonavir is a known potent inhibitor of CYP3A4, we hypothesized that it might also be an inhibitor of CYP3A7‐mediated DHEA‐S oxidation and that this inhibition might be responsible for the adrenal insufficiency and low birth weight associated with Lopinavir‐Ritonavir treatment. In order to test this hypothesis, we employed both recombinant CYP enzyme and neonatal human liver microsomes (nHLMs). We observed significant inhibition of CYP3A7 DHEA‐S hydroxylation activity in the presence of Ritonavir with an IC50 of 0.05 μM. Furthermore, Ritonavir displayed time‐dependent inhibition of DHEA‐S oxidation, with a Ki of 0.336 μM and a Kinact of 0.1077 min−1, suggesting that it may be a mechanism based inactivator of CYP3A7. Lopinavir was also capable of inhibiting CYP3A7, albeit to a much lesser extent than Ritonavir with an IC50 of 5.88 μM for DHEA‐S 16α‐hydroxylation, and without the associated time‐dependency. Interestingly, we observed that Lopinavir alone had a lower intrinsic clearance (Clint) rate in nHLMs compared to adult HLMs, suggesting that a pharmacokinetic enhancer adjuvant may not be necessary in this patient population in order to slow drug clearance and maintain efficacy. At a minimum, our results suggest that closer monitoring of the effective dose of the pharmacokinetic enhancer in neonatal HIV therapy may be required in order to prevent significant inhibition of CYP3A7 DHEA‐S oxidation and the associated adverse effects.Support or Funding InformationThis work was supported by the National Institutes of Health, Institute of General Medical Sciences [Grant R01 GM128508‐03] to JNL.

Synthesis of Spin-Labelled Bergamottin: A Potent CYP3A4 Inhibitor with Antiproliferative Activity.

Bergamottin (BM, 1), a component of grapefruit juice, acts as an inhibitor of some isoforms of the cytochrome P450 (CYP) enzyme, particularly CYP3A4. Herein, a new bergamottin containing a nitroxide moiety (SL-bergamottin, SL-BM, 10) was synthesized; chemically characterized, evaluated as a potential inhibitor of the CYP2C19, CYP3A4, and CYP2C9 enzymes; and compared to BM and known inhibitors such as ketoconazole (KET) (3A4), warfarin (WAR) (2C9), and ticlopidine (TIC) (2C19). The antitumor activity of the new SL-bergamottin was also investigated. Among the compounds studied, BM showed the strongest inhibition of the CYP2C9 and 2C19 enzymes. SL-BM is a more potent inhibitor of CYP3A4 than the parent compound; this finding was also supported by docking studies, suggesting that the binding positions of BM and SL-BM to the active site of CYP3A4 are very similar, but that SL-BM had a better ∆Gbind value than that of BM. The nitroxide moiety markedly increased the antitumor activity of BM toward HeLa cells and marginally increased its toxicity toward a normal cell line. In conclusion, modification of the geranyl sidechain of BM can result in new CYP3A4 enzyme inhibitors with strong antitumor effects.

In-Vitro assessment of the inhibitory effects of dietary flavones on the regulated metabolism of CYP 450: Potential for Herb-drug interactions

Background and objective: Dietary flavones like chrysin are found in foods and can contribute to human health through prevention of cardiovascular and cancer supplements. Recently, as herbal medicines and traditional allopathic medicines are used together, drug food or herbal drug interactions have become the target of our body and can lead to potential herbal-drug interactions. The present study aims to determine the metabolic stability and CYP inhibition liabilities in human liver microsomes in order to rule out the association between herb drugs and the dietary flavone chrysin. Methods: Standard procedures were used for metabolic stability study in human liver microsomes (Phase I) and metabolic stability study in cryopreserved human hepatocytes (Phase II). Human liver microsomes (HLMs) were added to each selective probe substrates of cytochrome P450 enzymes with or without of chrysin and IC50 was calculated. Results: Metabolic stability data reveals that Chrysin underwent phase II metabolism predominantly as it was highly stable in HLM and comparatively faster metabolism in hepatocytes. Chrysin was found to be a potent inhibitor of CYP1A2 and CYP2C9 with IC50 values of 0.6 μM and 1.6μM, respectively. Chrysin has weak inhibitory effect on other CYP isoforms such as CYP2C9, CY2D6 (~25μM) and no inhibition of CYP3A4 up to 100μM. Conclusion: These results could be useful in clinical practice for safely and effectively use of flavone chrysin. Our report showed that in vivo interactions of drugs and pharmaceuticals with dietary flavones must be examined for CYP1A2 and CYP2C9 substrates.

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

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

Clinically Significant Drug-Drug Interactions with Agents for Attention-Deficit/Hyperactivity Disorder.

This article provides an overview of the pharmacokinetic drug-drug interactions (DDIs) for agents prescribed for attention-deficit/hyperactivity disorder (ADHD). Polypharmacy in the treatment of patients with ADHD leads to high exposures to DDIs and possibly adverse safety outcomes. We performed a systematic search of DDI reports for ADHD agents in Embase and Medline. We also searched for agents in the pharmacological pipeline, which include (1) mazindol, molindone and viloxazine, which were previously prescribed for other indications; (2) centanafadine and AR-08, never before approved; and (3) two extracts (Polygala tenuifolia extract and the French maritime pine bark extracts). The identified literature included case reports, cross-sectional, cross-over and placebo-controlled studies of patient cohorts and healthy volunteers. The DDIs were classified as follows: ADHD agents acting as perpetrators, i.e., affecting the clearance of co-prescribed agents (victim drugs), or ADHD agents being the victim drugs, being affected by other agents. Ratios for changes in pharmacokinetic parameters before and after the DDI were used as a rough estimate of the extent of the DDI. Alcohol may increase plasma dextroamphetamine concentrations by presystemic effects. Until studies are done to orient clinicians regarding dosing changes, clinicians need to be aware of the potential for cytochrome P450 (CYP) 2D6 inhibitors to increase amphetamine levels, which is equivalent to increasing dosages. Atomoxetine is a wide therapeutic window drug. The CYP2D6 poor metabolizers who do not have CYP2D6 activity had better atomoxetine response, but also an increased risk of adverse effects. CYP2D6 inhibitors have been used to increase atomoxetine response in CYP2D6 extensive metabolizers. Guanfacine is mainly metabolized by CYP3A4, which can be induced and inhibited. The package insert recommends that in guanfacine-treated patients, after adding potent CYP3A4 inducers, the guanfacine dose should be doubled; after adding potent CYP3A4 inhibitors the guanfacine dose should be halved. Based on a phenobarbital case report and our experience with CYP3A4-metabolized antipsychotics, these correction factors may be too low. According to two case reports, carbamazepine is a clinically relevant inducer of methylphenidate (MPH). A case series study suggested that MPH may be associated with important elevations in imipramine concentrations. Due to the absence of or limitations in the data, no comments for clinicians can be provided on the pharmacokinetic DDIs for clonidine, centanafadine, mazindol, molindone, AR-08, P. tenuifolia extract and the French maritime pine bark extracts. According to currently available data, clinicians should not expect that ADHD drugs modify each other's serum concentrations. A summary table for clinicians provides our current recommendations on pharmacokinetic DDIs of ADHD agents based on our literature review and the package inserts; whenever it was possible, we provide information on serum concentrations and dose correction factors. There will be a need to periodically update these recommendations and these correction factors as new knowledge becomes available.

Population Pharmacokinetics of Ruxolitinib in Patients with aGVHD Who Had an Inadequate Response to Corticosteroids

Background: Jakafi® (ruxolitinib) is currently approved for the treatment of adult patients with intermediate- and high-risk myelofibrosis (MF) and for the treatment of adult patients with polycythemia vera (PV) who have had an inadequate response to or are intolerant to hydroxyurea. A prospective, open-label, single-cohort, Phase 2 study (REACH1) was conducted to evaluate the safety and efficacy of Jakafi® (ruxolitinib) in patients with acute graft versus host disease (aGVHD) who have had an inadequate response to corticosteroids. A population PK analysis was employed to characterize the PK of ruxolitinib in this patient population. Patients and Methods: REACH1, Study INCB 18424-251, and COMFORT-I are the 3 studies supporting the population PK of ruxolitinib; the first study is in participants with aGVHD who have had an inadequate response to corticosteroids, and the other 2 studies are in participants with MF. First, the final PK model for ruxolitinib in patients with MF was applied to the data in patients with MF and aGVHD. When significant biases were observed in this validation process, new population PK models were developed based on the pooled data. The accuracy and robustness of the final population PK model were assessed using a predictive check method. Results: An under-prediction bias was observed at the population level when existing PK model in MF was applied to pooled data in patients with MF and aGVHD. A new model was developed to account for the under prediction bias at the population level. The final population PK model for ruxolitinib was a 2 compartment disposition model with first order absorption, absorption lag time, and linear elimination. Body weight and gender were significant predictors of the volume of distribution of the central compartment and oral clearance, respectively. Patients with aGVHD showed lower oral clearance (66.7%) and slower rate of absorption (~28%) than that in patients with MF. The stage of liver involvement in GVHD and use of moderate or potent CYP3A4 inhibitors were identified as covariates for ruxolitinib CL. Conclusion: The population PK analysis supports the proposed dose regimen in patients with aGVHD who had an inadequate response to corticosteroids as well as dose recommendations for DDI and subjects with organ dysfunction. Disclosures Chen: Incyte Research Institute: Employment. Liu:Incyte Research Institute: Employment. Wang:Incyte Research Institute: Employment. Yeleswaram:Incyte Research Institute: Employment.

Evaluation of metabolic stability of antimalarial and antiretroviral drugs

The concomitant administration of drugs and antimalarial drugs is recommended for the treatment of HIV (Human Immunodeficiency Virus) patients with malaria resulting in drug-drug interactions (DDI) causing either lack of efficacy or toxicities. Drug metabolism is often the first step in understanding the DDI potential of either a new chemical entity or a combination of drugs. inhibitor (PI) such as is a potent CYP 3A4 inhibitor and may interact with these antimalarial drugs that are metabolized by CYP3A4 to cause metabolism-related DDI's. the present study is an attempt to evaluate the potential for a drug-drug interaction between and through metabolic stability studies. Metabolic stability of antimalarial and drugs alone and in combination with and without and was evaluated using human liver (HLM). The antimalarial drugs , and were metabolically unstable alone (% metabolism ≥ 80%) and in combination with other antimalarial drugs in HLM. , and were metabolically stable (% metabolism ≤ 30%). drug was metabolically unstable while was moderately stable. intrinsic clearance of antimalarial drugs , and decreased from 106.4, 290.6 and 230 ml/min/kg to 32, 44.8 and 49.5 ml/min/kg in the presence of . However, there was no change in the intrinsic clearance of , and in the presence of . did not alter the clearance of antimalarial drugs. This study suggests that affected the clearance of a few antimalarial drugs in HLM probably by the inhibition of CYP3A4 and findings may need to be further evaluated in clinical studies.

Effect of ritonavir on pharmacokinetics of antimalarial drug combinations in rats

The current treatment for Human Immunodeficiency Virus (HIV) patients coinfected with malaria involves the coadministration of antimalarial and antiretroviral (ARV) drugs. The World Health Organization (WHO) recommends artemisinin-based therapy for malaria that usually consists of artemether, artesunate or dihydroartemisinin with non-artemisinin derivatives such as amodiaquine, lumefantrine and mefloquine. Protease inhibitors (PI) such as ritonavir contribute to the improved health of HIV-positive individuals, and the inclusion of ritonavir in antiretroviral regimens is common in clinical practice. Ritonavir is a potent inhibitor of human CYP3A4, which is the primary enzyme involved in the metabolism of many of artemisinin-based drugs, as well as amodiaquine and proguanil. Upon co-administration, ritonavir can potentially influence the metabolism and thus increase the systemic exposure of these drugs. In order to understand this pharmacokinetic (PK) drug interaction, the current work evaluated the effect of ritonavir (50 mg/kg orally) on the PK of antimalarial drug combinations in Sprague Dawley (SD) rats. When co-administered with ritonavir, the exposure (AUC) of the antimalarial drugs artemether, artesunate and proguanil was increased by approximately 3.5-fold. Correspondingly, peak plasma concentrations (Cmax) of these drugs increased as well. There was no apparent influence of ritonavir on the PK of lumefantrine, amodiaquine and atovaquone. This study demonstrates the potential influence of ritonavir on the pharmacokinetics of at least some anti-malarial drugs, likely a result of inhibition of CYP3A. Further evaluation of clinically relevant drug interaction in humans may be warranted to ensure safe and effective use of anti-malarial and anti-HIV drugs concomitantly.

Potent CYP3A4 Inhibitors Derived from Dillapiol and Sesamol

Synthesis of 50 analogues of the natural insecticide synergists, dillapiol and sesamol, is reported. These were evaluated as potential insecticide synergists based on their inhibition of human CYP3A4. The most potent inhibitors have a relatively large hydrophobic substituent at either position 5 or 6 of these molecules. For example, 5-(benzyloxy)-6-(3-phenylsulfonyl)propyl)benzo[d][1,3]dioxole (18) and the diphenyl acetate of (6,7-dimethoxybenzo[d][1,3]dioxol-5-yl)propan-1-ol (5n) show inhibitory concentrations for 50% activity IC50 values of 0.086 and 0.2 μM, respectively. These compounds are 106 and 46 times more potent than dillapiol whose IC50 for the inhibition of CYP3A4 is 9.2 μM. The ortho-chloro analogue (8f), whose activity is 86 times the activity of dillapiol, is the most potent of the fourteen 5-(benzyloxy-6-(2 propenyl)benzo[d][1,3]dioxoles prepared for this study.

Physiologically Based Pharmacokinetic Modeling Suggests Limited Drug-Drug Interaction for Fesoterodine When Coadministered With Mirabegron.

5-Hydroxymethyl tolterodine (5-HMT; the active fesoterodine metabolite) is metabolized via the cytochrome P450 (CYP) 2D6 and CYP3A pathways. Mirabegron is a moderate CYP2D6 inhibitor and weak CYP3A inhibitor. Potential drug-drug interactions (DDIs) following coadministration of these 2 overactive bladder treatments were estimated using physiologically based pharmacokinetic models, developed and verified by comparing predicted and observed pharmacokinetic profiles from clinical studies. Models predicted and verified mirabegron and desipramine (CYP2D6 substrate) and 5-HMT and ketoconazole (strong CYP3A inhibitor) DDIs. Mirabegron model-predicted mean steady-state AUC and Cmax were within 11% of clinical observations. The predicted versus observed geometric mean ratio (GMR) of AUCinf for CYP2D6 substrates desipramine and metoprolol coadministered with mirabegron 100 or 160mg once daily were 3.47 versus 3.41 and 2.97 versus 3.29, respectively, indicating that the mirabegron model can be used to predict clinical CYP2D6 inhibition. 5-HMT fractional clearance by CYP3A and CYP2D6 was verified from clinical DDI studies with a potent CYP3A4 inhibitor (ketoconazole) and inducer (rifampicin) in CYP2D6 extensive and poor metabolizers and with a moderate CYP3A inhibitor (fluconazole) in healthy volunteers. 5-HMT AUCinf and Cmax GMRs for fesoterodine DDIs were all predicted within 1.26-fold of clinical observation, providing verification for the fesoterodine substrate model. The predicted changes in 5-HMT AUCinf and Cmax ratios for 8 mg fesoterodine when coadministered with 50 mg mirabegron were 1.22-fold and 1.17-fold, respectively, relative to 8 mg fesoterodine given alone. This modest increase in 5-HMT exposures by approximately 20% is considered clinically insignificant and would not require fesoterodine dose adjustment when coadministered with mirabegron within approved daily-dose ranges.

Effect of Serum Parathyroid Hormone on Tacrolimus Therapy in Kidney Transplant Patients: A Possible Biomarker for a Tacrolimus Dosage Schedule.

The mechanism responsible for the decreased extra-renal CYP3A activity in chronic kidney disease (CKD) patients remains unknown. Using an animal model, we previously found that elevated levels of serum intact parathyroid hormone (iPTH) caused a reduced CYP3A activity. This retrospective observational study assessed the relationship between serum iPTH levels and the blood concentration or dosage of tacrolimus, a CYP3A substrate, after oral administration in kidney transplant patients. Thirty-four patients were enrolled who had kidney transplants between April 2014 and March 2016 and who had been administrated once- daily prolonged-release tacrolimus (Graceptor®, Astellas Pharm Inc.). Among the 34 patients, 22 had taken a CYP3A inhibitor. These patients were excluded from the study. A significant positive correlation between serum iPTH and tacrolimus trough levels was found at 4 d before kidney transplantation in 12 patients who were not receiving potent CYP3A inhibitor. In addition, serum iPTH levels before transplantation could serve as a factor for the dose of tacrolimus up to 1 year after transplantation. Monitoring serum iPTH levels could predict the trough level for the initial administration of tacrolimus, and may serve as an index for the initial dose of tacrolimus in kidney transplantation patients.

MON-349 HIV and Asthma: What Could Go Wrong? A Case of Adrenal Insufficiency

Introduction: CYP3A4 is the principal enzyme of cytochrome P450 and is the primary metabolic step for the degradation of corticosteroids. Cobicistat is a potent CYP3A4 inhibitor, it is used to increase the levels of antiretrovirals in the treatment of HIV. It is currently available as part of a fixed-dose combination, where it is used to enhance the integrase inhibitor elvitegravir. The interaction of CYP3A4 inhibitors and substrates can lead to numerous side effects. We present a case of drug-drug interaction resulting in adrenal insufficiency. Case: A 34 y/o male with PMH HIV and asthma comes to the office for evaluation of low cortisol noticed on an AM serum blood test, at the time of visit reported being evaluated by his HIV specialist for complaints of stretch marks and facial swelling; at the time of our evaluation these symptoms had resolved, but prompted further evaluation and a cortisol level 0.2 ug/dl was found. He was diagnosed with HIV in 2015 and since 2016 had been on HAART therapy with a combination of elvitegravir/cobicistat/emtricitabine/tenofovir (Genvoya); additionally, was recently started on a Breo-Ellipta inhaler which consists of fluticasone and vilanterol. During an initial assessment, the patient complained of fatigue and lightheadedness. He denied weakness, weight loss, nausea or vomiting. It was suspected that the etiology of these findings was due to a drug-drug interaction between cobicistat and the inhaled steroids, as this could be causing adrenal insufficiency secondary to the interference of steroid metabolism. On a follow-up visit, an ACTH stimulation test was scheduled, measures of serum cortisol remained at 0.2 ug/dl confirming the diagnosis. He was prescribed prednisone 5 mg daily. Patient was recommended to suspend his inhaler and follow up with a pulmonologist. After discontinuing inhaled steroids, initial symptoms gradually improved, repeat ACTH stimulation test a month later showed regain of adrenal function. He is currently asymptomatic. Conclusion: This case report highlights the importance of recognizing potential interactions between medications in patients with chronic diseases. Clinicians should continuously consider drug-drug interactions when prescribing enzyme inhibitors; currently, the majority of the literature available focuses on protease inhibitors and less on integrase inhibitors. The management of patients with HIV and asthma requires an interdisciplinary approach to improve outcomes.

Regulation of drug metabolizing enzymes in the leukaemic bone marrow microenvironment

The bone marrow (BM) microenvironment contributes to drug resistance in acute myeloid leukaemia (AML) and multiple myeloma (MM). We have shown that the critical drug metabolizing enzymes cytochrome P450 (CYP) 3A4 and cytidine deaminase (CDA) are highly expressed by BM stroma, and play an important role in this resistance to chemotherapy. However, what factors influence the chemoprotective capacity of the BM microenvironment, specifically related to CYP3A4 and CDA expression, are unknown. In this study, we found that the presence of AML cells decreases BM stromal expression of CYP3A4 and CDA, and this effect appears to be at least partially the result of cytokines secreted by AML cells. We also observed that stromal CYP3A4 expression is up‐regulated by drugs commonly used in AML induction therapy, cytarabine, etoposide and daunorubicin, resulting in cross‐resistance. Cytarabine also up‐regulated CDA expression. The up‐regulation of CYP3A4 associated with disease control was reversed by clarithromycin, a potent inhibitor of CYP3A4. Our data suggest that minimal residual disease states are characterized by high levels of stromal drug metabolizing enzymes and thus, strong microenvironment‐mediated drug resistance. These results further suggest a potential role for clinically targeting drug metabolizing enzymes in the microenvironment.

Drug Transport across Porcine Intestine Using an Ussing Chamber System: Regional Differences and the Effect of P-Glycoprotein and CYP3A4 Activity on Drug Absorption.

Drug absorption across viable porcine intestines was investigated using an Ussing chamber system. The apparent permeability coefficients, Papp,pig, were compared to the permeability coefficients determined in humans in vivo, Peff,human. Eleven drugs from the different Biopharmaceutical Classification System (BCS) categories absorbed by passive diffusion with published Peff,human values were used to test the system. The initial experiments measured Papp,pig for each drug after application in a Krebs–Bicarbonate Ringer (KBR) buffer and in biorelevant media FaSSIF V2 and FeSSIF V2, mimicking fasted and fed states. Strong sigmoidal correlations were observed between Peff,human and Papp,pig. Differences in the segmental Papp,pig of antipyrine, cimetidine and metoprolol confirmed the discrimination between drug uptake in the duodenum, jejunum and ileum (and colon); the results were in good agreement with human data in vivo. The presence of the P-gp inhibitor verapamil significantly increased Papp,pig across the ileum of the P-gp substrates cimetidine and ranitidine (p < 0.05). Clotrimazole, a potent CYP3A4 inhibitor, significantly increased Papp,pig of the CYP3A4 substrates midazolam, verapamil and tamoxifen and significantly decreased the formation of their main metabolites. In conclusion, the results showed that this is a robust technique to predict passive drug permeability under fasted and fed states, to identify regional differences in drug permeability and to demonstrate the activity of P-gp and CYP3A4.

456 - Cobicistat, a potent CYP3A4 inhibitor, acts synergistically with oprozomib to cause endoplasmic reticulum stress in bladder cancer cells

456 - Cobicistat, a potent CYP3A4 inhibitor, acts synergistically with oprozomib to cause endoplasmic reticulum stress in bladder cancer cells