Microtiter plate assays for inhibition of human, drug-metabolizing cytochromes P450

Acute exposure and biomarkers assessment in rainbow trout exposed to selected pharmaceuticals

Pharmaceuticals released from municipal effluents discharges pose a risk to aquatic organisms. The toxicity of 5 pharmaceuticals with distinct therapeutic actions were assessed in rainbow trout: olanzapine (antipsychotic), erythromycin (antibiotic), mycophenoate (immunosuppression), pinaverium (anti-inflammatory) and trazodone (sedative). Juveniles were exposed to these drugs for 96 h at concentrations between 64 µg/L up to 40 mg/L to reach lethality. Survival was determined and a suite of biomarkers was analyzed for drug biotransformation, oxidative stress/damage and metabolic activity at sublethal concentrations. The data revealed the following toxicity: olanzapine >trazodone>mycophenolate>pinaverium∼erythromycin based on mortality. The data also revealed that toxicity was associated to mass, pKa and hydrophobicity and the following sublethal effects: GST, LPO and DNA strand breaks. Pharmaceuticals with lower molecular weight, physiological pKa, moderate hydrophobicity, low biotransformation and DNA strand breaks were generally more toxic to fish. However, this should be considered as a general guide in identifying toxic pharmaceuticals in non-target organisms.

Evaluation of Lippia scaberrima Sond. and Aspalathus linearis (Burm.f.) R. Dahlgren extracts on human CYP enzymes and gold nanoparticle synthesis: implications for drug metabolism and cytotoxicity

BACKGROUND

Metabolism is an important component of the kinetic characteristics of herbal constituents, and it often determines the internal dose and concentration of these effective constituents at the target site. The metabolic profile of plant extracts and pure compounds need to be determined for any possible herb-drug metabolic interactions that might occur.

METHODS

Various concentrations of the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with fermented and unfermented Aspalathus linearis extract were used to determine the inhibitory potential on placental, microsomal and recombinant human hepatic Cytochrome P450 enzymes. Furthermore, the study investigated the synthesis and characterization of gold nanoparticles from the ethanolic extract of Lippia scaberrima as a lead sample. Confirmation and characterization of the synthesized gold nanoparticles were conducted through various methods. Additionally, the cytotoxic properties of the ethanolic extract of Lippia scaberrima were compared with the gold nanoparticles synthesized from Lippia scaberrima using gum arabic as a capping agent.

RESULTS

All the samples showed varying levels of CYP inhibition. The most potent inhibition took place for CYP2C19 and CYP1B1 with 50% inhibitory concentration (IC50) values of less than 0.05 µg/L for the essential oil tested and IC50-values between 0.05 µg/L-1 µg/L for all the other combinations and extracts tested, respectively. For both CYP1A2 and CYP2D6 the IC50-values for the essential oil, the extracts and combinations were found in the range of 1 - 10 µg/L. The majority of the IC50 values found were higher than 10 µg/L and, therefore, were found to have no inhibition against the CYP enzymes tested.

CONCLUSION

Therefore, the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with Aspalathus linearis do not possess any clinically significant CYP interaction potential and may be further investigated for their adjuvant potential for use in the tuberculosis treatment regimen. Furthermore, it was shown that the cytotoxic potential of the Lippia scaberrima gold nanoparticles was reduced by twofold when compared to the ethanolic extract of Lippia scaberrima.

Preclinical Characterization and Development on NAQ as a Mu Opioid Receptor Partial Agonist for Opioid Use Disorder Treatment

Mu opioid receptor (MOR) selective antagonists and partial agonists have clinical utility for the treatment of opioid use disorders (OUDs). However, the development of many has suffered due to their poor pharmacokinetic properties and/or rapid metabolism. Our recent efforts to identify MOR modulators have provided 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(isoquinoline-3-carboxamido)morphinan (NAQ), a low-efficacy partial agonist, that showed sub-nanomolar binding affinity to the MOR (K i 0.6 nM) with selectivity over the delta opioid receptor (δ/μ 241) and the kappa opioid receptor (κ/μ 48). Its potent inhibition of the analgesic effect of morphine (AD50 0.46 mg/kg) and precipitation of significantly less withdrawal symptoms even at 100-fold greater dose than naloxone represents a promising molecule for further development as a novel OUD therapeutic agent. Therefore, further in vitro and in vivo characterization of its pharmacokinetics and pharmacodynamics properties was conducted to fully understand its pharmaceutical profile. NAQ showed favorable in vitro ADMET properties and no off-target binding to several classes of GPCRs, enzymes, and ion channels. Following intravenous administration, 1 mg/kg dose of NAQ showed a similar in vivo pharmacokinetic profile to naloxone; however, orally administered 10 mg/kg NAQ demonstrated significantly improved oral bioavailability over both naloxone and naltrexone. Abuse liability assessment of NAQ in rats demonstrated that NAQ functioned as a less potent reinforcer than heroin. Chronic 5 day NAQ pretreatment decreased heroin self-administration in a heroin-vs-food choice procedure similar to the clinically used MOR partial agonist buprenorphine. Taken together, these studies provide evidence supporting NAQ as a promising lead to develop novel OUD therapeutics.

Probing PXR activation and modulation of CYP3A4 by Tinospora crispa and Tinospora sinensis

ETHNOPHARMACOLOGICAL RELEVANCE

The two Tinospora species, T. crispa and T. sinensis, native to Southeast Asia, are integral components of various traditional preparations with structure-function claims to treat various disorders, including diabetes and inflammation.

AIM OF THE STUDY

To assure the safety of the botanicals finished products, herb-drug interaction potential of T. crispa and T. sinensis was investigated by testing their extracts and compounds for in vitro activation of the pregnane X-receptor (PXR) and the modulation of CYP3A4 isozyme, selectively.

MATERIALS AND METHODS

A total of sixteen fully characterized phytochemicals from T. crispa and T. sinensis were evaluated for PXR activation by luciferase reporter gene assay. CYP3A4 inhibition studies were carried out for eleven compounds. In addition, docking studies were performed to elucidate the possible binding modes to the PXR by the compounds using computational methods.

RESULTS

Significant activation of PXR (2-fold) was observed for both extracts and non-polar fractions of T. crispa. Among the pure compounds, columbin showed highest activation of PXR (3-fold), which was comparable with the positive control, rifampicin. Vital interactions were predicted with docking simulation of PXR-columbin complex with critical amino acid residues (Trp-299) that are known for the activation of PXR. The methanolic extracts of T. crispa and T. sinensis also showed considerable CYP3A4 inhibition.

CONCLUSION

T. crispa and T. sinensis, both demonstrated the potential to mediate herb-drug interaction through PXR activation and inhibition of CYP3A4 isozyme. Moreover, the elucidation of the potential to induce herb-drug interaction, by the phytochemicals of these Tinospora plants, thereby supports the need for further investigation to establish the clinical relevancy of these constituents for possible adverse interactions with pharmaceutical drugs.

Sulfated extract of Abelmoschus esculentus: A potential cancer chemopreventive agent

BACKGROUND

Abelmoschus esculentus (AE) (okra), is an edible plant used in many food applications.

OBJECTIVE

This study explored whether sulfated AE (SAE) has promising cancer chemopreventive activities that may recommend it as a functional food supplement ‎instead of (or in addition to) AE for the population at risk of cancer and in the health food industry.

METHODS

Cytochrome P450-1A (CYP1A)‎ was estimated by fluorescence enzymatic reaction, using β-naphthoflavone-treated cells (CYP1A inducer). Peroxyl and hydroxyl radical scavenging was assayed by an oxygen radical absorbance capacity assay. Flow cytometry was used to analyze apoptosis/necrosis in MCF-7 cells, cell cycle phases in MCF-7 cells, and macrophage binding to fluorescein isothiocyanate-lipopolysaccharide (FITC-LPS)‎. Nitric oxide was determined by Griess assay in LPS-stimulated macrophages, and cytotoxicity was determined by MTT assay. Diethylnitrosamine (DEN) was used to induce hepatic tumor initiation in rats. Placental glutathione-S-transferase (GSTP; an initiation marker) was stained in a fluorescence immunohistochemical analysis of liver sections, and histopathological changes were examined.

RESULTS

SAE exhibited strong antitumor initiation and antitumor promotion activities. It suppressed CYP1A, ‎scavenged peroxyl and hydroxyl radicals, induced macrophage proliferation, suppressed ‎macrophage binding to FITC-LPS, inhibited nitric oxide generation, showed specific cytotoxicity to ‎human breast MCF-7 adenocarcinoma cells, and disturbed the cell cycle phases (S and G2/M phases) ‎in association with an increased percentage of apoptotic/necrotic MCF-7 cells. Over a short time period, DEN stimulated liver cancer initiation, but SAE treatment reduced the DEN-induced histopathological alterations and ‎inhibited CYP1A and GSTP.

CONCLUSION

SAE extract has the potential for use as an alternative to AE in health foods to provide cancer chemoprevention in populations at risk for cancer.

Preliminary in vitro approach to evaluate the drug-drug interaction potential of EST73502, a dual µ-opioid receptor partial agonist and σ1 receptor antagonist

The potential for drug-drug interactions (DDI) of EST73502 was preliminary explored in vitro. EST73502 is a new chemical entity intended for oral pain treatment with dual sigma-1 receptor (σ1R) antagonism and μ-opioid receptor (MOR) partial agonism, that presents a promising potent analgesic activity.Several enzymes were involved in EST73502 metabolism catalysing the formation of different metabolites, CYP3A4 and CYP2D6 being the main ones.Fraction unbound was determined due to its impact in interactions, a considerable proportion of EST73502 being available.EST73502 showed a low potential for CYP inhibition, except for CYP2D6 that showed time-dependent inhibition.No induction potential was found for CYP1A2 and 3A4, while CYP2B6 was induced at high concentration.EST73502 seemed to be a potential efflux transporter substrate (efflux ratio ≥ 2) but a negligible in vivo impact would be expected due to its high solubility and permeability in Caco-2 cells. P-gp inhibition was observed while no BCRP inhibition was detected.Preliminary in vitro interaction studies suggested that neither CYPs nor efflux transporters interactions would preclude further development of EST73502 to thoroughly assess the clinical relevance of these findings.

Potential chemopreventive, anticancer and anti-inflammatory properties of a refined artocarpin-rich wood extract of Artocarpus heterophyllus Lam

Colorectal cancer (CRC) represents the third leading cause of death among cancer patients below the age of 50, necessitating improved treatment and prevention initiatives. A crude methanol extract from the wood pulp of Artocarpus heterophyllus was found to be the most bioactive among multiple others, and an enriched extract containing 84% (w/v) artocarpin (determined by HPLC–MS–DAD) was prepared. The enriched extract irreversibly inhibited the activity of human cytochrome P450 CYP2C9, an enzyme previously shown to be overexpressed in CRC models. In vitro evaluations on heterologously expressed microsomes, revealed irreversible inhibitory kinetics with an IC₅₀ value of 0.46 µg/mL. Time- and concentration-dependent cytotoxicity was observed on human cancerous HCT116 cells with an IC₅₀ value of 4.23 mg/L in 72 h. We then employed the azoxymethane (AOM)/dextran sodium sulfate (DSS) colitis-induced model in C57BL/6 mice, which revealed that the enriched extract suppressed tumor multiplicity, reduced the protein expression of proliferating cell nuclear antigen, and attenuated the gene expression of proinflammatory cytokines (Il-6 and Ifn-γ) and protumorigenic markers (Pcna, Axin2, Vegf, and Myc). The extract significantly (p = 0.03) attenuated (threefold) the gene expression of murine Cyp2c37, an enzyme homologous to the human CYP2C9 enzyme. These promising chemopreventive, cytotoxic, anticancer and anti-inflammatory responses, combined with an absence of toxicity, validate further evaluation of A. heterophyllus extract as a therapeutic agent.

Innovation in bioanalytical strategies and in vitro drug-drug interaction study approaches in drug discovery

Failure to evaluate actual toxicities of investigational molecules in drug discovery is majorly due to inadequate evaluation of their pharmacokinetics. Limitation of conventional drug metabolism profiling procedure demands advancement of existing approaches. Various techniques such as 3D cell culture system, bio microfluidic OoC model, sandwich culture model is in pipeline to be employed at their full potential in drug discovery phase. Although they outweigh the conventional techniques in various aspects, a more detailed exploration of applicability in terms of automation and high throughput analysis is required. This review extensively discusses various ongoing innovations in bioanalytical techniques. The review also proposed various scientific strategies to be adopted for prior assessment of interaction possibilities in translational drug discovery research.

Coumarin-Based Profluorescent and Fluorescent Substrates for Determining Xenobiotic-Metabolizing Enzyme Activities In Vitro

Activities of xenobiotic-metabolizing enzymes have been measured with various in vitro and in vivo methods, such as spectrophotometric, fluorometric, mass spectrometric, and radioactivity-based techniques. In fluorescence-based assays, the reaction produces a fluorescent product from a nonfluorescent substrate or vice versa. Fluorescence-based enzyme assays are usually highly sensitive and specific, allowing measurements on small specimens of tissues with low enzyme activities. Fluorescence assays are also amenable to miniaturization of the reaction mixtures and can thus be done in high throughput. 7-Hydroxycoumarin and its derivatives are widely used as fluorophores due to their desirable photophysical properties. They possess a large π-π conjugated system with electron-rich and charge transfer properties. This conjugated structure leads to applications of 7-hydroxycoumarins as fluorescent sensors for biological activities. We describe in this review historical highlights and current use of coumarins and their derivatives in evaluating activities of the major types of xenobiotic-metabolizing enzyme systems. Traditionally, coumarin substrates have been used to measure oxidative activities of cytochrome P450 (CYP) enzymes. For this purpose, profluorescent coumarins are very sensitive, but generally lack selectivity for individual CYP forms. With the aid of molecular modeling, we have recently described several new coumarin-based substrates for measuring activities of CYP and conjugating enzymes with improved selectivity.

Cancer Chemopreventive Properties of Sulfated Enterolobium cyclocarpum Extract

Enterolobium cyclocarpum (EC) is an edible plant and a gum source for food industries. Its sulfated polysaccharide extract (SEC) was examined for cancer chemopreventive properties to estimate its anti-tumor activity. The modulation of carcinogen metabolism and the antioxidant activity revealed that SEC is a potent tumor anti-initiator since it inhibited cytochrome P450-1A (CYP1A) and induced carcinogen detoxification enzyme glutathione-S-transferase. SEC is also a weak scavenger for hydroxyl and peroxyl radicals. SEC was found to modulate macrophage functions into an anti-inflammatory pattern, where it enhanced macrophage proliferation and phagocytosis of fluorescein isothiocyanate-lipopolysaccharide (FITC-LPS). In addition, SEC strongly inhibited the nitric oxide (NO) generation in LPS-stimulated macrophages and induced the binding affinity of FITC-LPS to macrophages. SEC exhibited specific cytotoxicity against human hepatocellular Hep G2 carcinoma cells. SEC disturbed the cell cycle phase, as indicated by the concomitant arrest in S- and G2/M-phases that was associated with necrosis induction. A short-term initiation model for liver cancer was prepared using diethylnitrosamine (DEN) in rats. SEC inhibited the DEN-histopathological findings and reduced both CYP1A and the tumor initiation marker placental glutathione S-transferase (GSTP). Taken together, SEC could be used as an alternative gum in health food industries to provide cancer prevention in high-risk populations.

Constitutive androstane receptor (CAR) mediates dieldrin-induced liver tumorigenesis in mouse

Dieldrin has been shown to induce liver tumors selectively in mice. Although the exact mechanism is not fully understood, previous studies from our laboratory and others have shown that dieldrin induced liver tumors in mice through a non-genotoxic mechanism acting on tumor promotion stage. Two studies were performed to examine the role of nuclear receptor activation as a possible mode of action (MOA) for dieldrin-induced mouse liver tumors. In the initial study, male C57BL/6 mice (6- to 8-week old) were treated with dieldrin in diet (10 ppm) for 7, 14, and 28 days. Phenobarbital (PB), beta-naphthoflavone (BNF) and Di (2-ethylhexyl) phthalate (DEHP) were included as positive controls in this study for evaluating the involvement of CAR (constitutive androstane receptor), AhR (aryl hydrocarbon receptor) or PPARα (peroxisome proliferator activated receptor alpha) in the MOA of dieldrin hepatocarcinogenesis. A significant increase in hepatocyte DNA synthesis (BrdU incorporation) was seen in treated mice compared with the untreated controls. Analysis of the expression of the nuclear receptor responsive genes revealed that dieldrin induced a significant increase in the expression of genes specific to CAR activation (Cyp2b10, up to 400- to 2700-fold) and PXR activation (Cyp3a11, up to 5- to 11-fold) over untreated controls. The AhR target genes Cyp1a1 and Cyp1a2 were also slightly induced (2.0- to 3.7-fold and 1.7- to 2.8-fold, respectively). PPARα activation was not seen in the liver following dieldrin treatment. In addition, consistent with previous studies in our lab, treatment with dieldrin produced significant elevation in the hepatic oxidative stress. In a subsequent study using CAR, PXR, and CAR/PXR knockout mice, we confirmed that the dieldrin-induced liver effects in mouse were only mediated by the activation of CAR receptor. Based on these findings, we propose that dieldrin induced liver tumors in mice through a nuclear receptor CAR-mediated mode of action. The previously observed oxidative stress/damage may be an associated or modifying factor in the process of dieldrin-induced liver tumor formation subsequent to the CAR activation.

Sensitive CometChip assay for screening potentially carcinogenic DNA adducts by trapping DNA repair intermediates

Genotoxicity testing is critical for predicting adverse effects of pharmaceutical, industrial, and environmental chemicals. The alkaline comet assay is an established method for detecting DNA strand breaks, however, the assay does not detect potentially carcinogenic bulky adducts that can arise when metabolic enzymes convert pro-carcinogens into a highly DNA reactive products. To overcome this, we use DNA synthesis inhibitors (hydroxyurea and 1-β-d-arabinofuranosyl cytosine) to trap single strand breaks that are formed during nucleotide excision repair, which primarily removes bulky lesions. In this way, comet-undetectable bulky lesions are converted into comet-detectable single strand breaks. Moreover, we use HepaRG™ cells to recapitulate in vivo metabolic capacity, and leverage the CometChip platform (a higher throughput more sensitive comet assay) to create the 'HepaCometChip', enabling the detection of bulky genotoxic lesions that are missed by current genotoxicity screens. The HepaCometChip thus provides a broadly effective approach for detection of bulky DNA adducts.

Investigation of the inhibition of eight major human cytochrome P450 isozymes by a probe substrate cocktail in vitro with emphasis on CYP2E1

1. A protocol has been developed and validated for the high-throughput screening of eight major human cytochrome P450 (CYP) isozymes inhibition (CYP 1A2, 2C9, 2C19, 2D6, 3A4, 2B6, 2C8 and 2E1) using an in vitro probe cocktail containing eight substrates by overcoming the unfavorable effect of assay conditions on CYP2E1 inhibition data. 2. The cocktail consisting of selective probe substrates like tacrine (CYP1A2), diclofenac (CYP2C9), S-mephenytoin (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A4), bupropion (CYP2B6), paclitaxel (CYP2C8) and chlorzoxazone (CYP2E1) was incubated with human liver microsomes. 3. The method was investigated by incubating well-known CYP inhibitors {alphanaphthoflavone (CYP1A2), sulfaphenazole (CYP2C9), N-3-benzylnirvanol (CYP2C19), quinidine (CYP2D6), ketoconazole (CYP3A4), ticlopidine (CYP2B6), quercetin (CYP2C8) and 4-methylpyrazole (CYP2E1)} with the substrate cocktail. A fast gradient liquid chromatography tandem mass spectrometry (LC-MS/MS) was used for this study. 4. The IC₅₀ values determined for typical CYP inhibitors were reproducible and consistent with those in the literature. DMSO has significant effect and itself inhibits CYP2E1. DMSO should not exceed 0.1% for the determination of reliable CYP2E1 inhibition profile. This cocktail assay offers an efficient and robust method to determine the CYP450 isoforms inhibition profiles of large numbers of compounds in a quick turnaround time.

In Vitro Human Metabolism and Inhibition Potency of Verbascoside for CYP Enzymes

Verbascoside is found in many medicinal plant families such as Verbenaceae. Important biological activities have been ascribed to verbascoside. Investigated in this study is the potential of verbascoside as an adjuvant during tuberculosis treatment. The present study reports on the in vitro metabolism in human hepatic microsomes and cytosol incubations as well as the presence and quantity of verbascoside within Lippia scaberrima. Additionally, studied are the inhibitory properties on human hepatic CYP enzymes together with antioxidant and cytotoxic properties. The results yielded no metabolites in the hydrolysis or cytochrome P450 (CYP) oxidation incubations. However, five different methylated conjugates of verbascoside could be found in S-adenosylmethionine incubation, three different sulphate conjugates with 3'-phosphoadenosine 5'-phosphosulfate (PAPS) incubation with human liver samples, and very low levels of glucuronide metabolites after incubation with recombinant human uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A7, UGT1A8, and UGT1A10. Additionally, verbascoside showed weak inhibitory potency against CYP1A2 and CYP1B1 with IC50 values of 83 µM and 86 µM, respectively. Potent antioxidant and low cytotoxic potential were observed. Based on these data, verbascoside does not possess any clinically relevant CYP-mediated interaction potential, but it has effective biological activity. Therefore, verbascoside could be considered as a lead compound for further drug development and as an adjuvant during tuberculosis treatment.

Inhibition of Cytochrome P450 Activities by Extracts of Hyptis verticillata Jacq.: Assessment for Potential HERB-Drug Interactions

Understanding the potential for adverse drug reactions (ADRs), from herb-drug interactions, is a key aspect of medicinal plant safety, with particular relevance for public health in countries where medicinal plant use is highly prevalent. We undertook an in-depth assessment of extracts of Hyptis verticillata Jacq., via its impact on activities of key cytochrome P450 (CYP) enzymes (CYPs 1A1, 1A2, 1B1, 3A4 and 2D6), its antioxidant properties (determined by DPPH assays) and chemical characterisation (using LC-MS). The dried plant aqueous extract demonstrated potent inhibition of the activities of CYPs 1A1 (7.6 µg/mL), 1A2 (1.9 µg/mL), 1B1 (9.4 µg/mL) and 3A4 (6.8 µg/mL). Further analysis of other crude extracts demonstrated potent inhibition of CYP1A2 activity for a dried plant ethanol extract (1.5 µg/mL), fresh plant ethanol extract (3.9 µg/mL), and moderate activity for a fresh plant aqueous extract (27.8 µg/mL). All four extracts demonstrated strong antioxidant activity, compared to the positive control (ascorbic acid, 1.3 µg/mL), with the dried plant ethanol extract being the most potent (1.6 µg/mL). Analysis of the dried plant aqueous extract confirmed the identity of seven phytochemicals, five lignans and two triterpenes. Individual screening of these phytochemicals against the activity of CYP1A2 identified yatein as a moderate inhibitor (71.9 μM), likely to contribute to the plant extract’s potent bioactivity. Further analysis on the impact of this plant on key drug metabolizing enzymes in vivo appears warranted for likely ADRs, as well as furthering development as a potential chemopreventive agent.

Discovery and Preclinical Development of IIIM-290, an Orally Active Potent Cyclin-Dependent Kinase Inhibitor

Rohitukine (1), a chromone alkaloid isolated from Indian medicinal plant Dysoxylum binectariferum, has inspired the discovery of flavopiridol and riviciclib, both of which are bioavailable only via intravenous route. With the objective to address the oral bioavailability issue of this scaffold, four series of rohitukine derivatives were prepared and screened for Cdk inhibition and cellular antiproliferative activity. The 2,6-dichloro-styryl derivative IIIM-290 (11d) showed strong inhibition of Cdk-9/T1 (IC₅₀ 1.9 nM) kinase and Molt-4/MIAPaCa-2 cell growth (GI₅₀ < 1.0 μM) and was found to be highly selective for cancer cells over normal fibroblast cells. It inhibited the cell growth of MIAPaCa-2 cells via caspase-dependent apoptosis. It achieved 71% oral bioavailability with in vivo efficacy in pancreatic, colon, and leukemia xenografts at 50 mg/kg, po. It did not have CYP/efflux-pump liability, was not mutagenic/genotoxic or cardiotoxic, and was metabolically stable. The preclinical data presented herein indicates the potential of 11d for advancement in clinical studies.

Modulation of Cytochrome P450, P-glycoprotein and Pregnane X Receptor by Selected Antimalarial Herbs-Implication for Herb-Drug Interaction

Seven medicinal plants popularly used for treating malaria in West Africa were selected to assess herb-drug interaction potential through a series of in vitro methods. Fluorescent cytochrome P450 (CYP) assays were conducted using the recombinant CYP enzymes for CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 to assess the effect of the methanolic extracts on the metabolic activity of CYPs. Secondly, the inhibitory effect of the extracts was evaluated on P-glycoproteins (P-gp) using calcein-AM, a fluorescent substrate, in MDCK-II and hMDR1-MDCK-II cells. The inhibition of P-gp activity was determined as a reflection of increase in calcein-AM uptake. Additionally, the enzyme induction potential of the extracts was assessed through the modulation of PXR activity in HepG2 cells transiently transfected with pSG5-PXR and PCR5 plasmid DNA. Significant inhibition of CYP activity (IC₅₀ < 10 µg/mL) was observed with the following herbs: A. muricata [CYP2C9, 3A4 and CYP2D6]; M. indica [CYP2C9]; M. charantia [CYP2C9 and CYP2C19]; P. amarus [CYP2C19, CYP2C9 and CYP3A4]; T. diversifolia [CYP2C19 and CYP3A4]. Extracts of four herbs (P. amarus, M. charantia, T. diversifolia and A. muricata) exhibited significant inhibition of P-gp with IC₅₀ values (µg/mL) of 17 ± 1, 16 ± 0.4, 26 ± 1, and 24 ± 1, respectively. In addition, four herbs (A. mexicana, M. charantia, P. amarus and T. diversifolia) showed a >two-fold increase in induction in PXR activity. These findings suggest that these herbs may be capable of eliciting herb-drug interactions if consumed in high quantities with concomitant use of conventional therapies.

Toxicological evaluation of the flavour ingredient N-(1-((4-amino-2,2-dioxido-1H-benzo[c][1,2,6]thiadiazin-5-yl)oxy)-2-methylpropan-2-yl)-2,6-dimethylisonicotinamide (S2218)

A toxicological evaluation of N-(1-((4-amino-2,2-dioxido-1H-benzo[c][1,2,6]thiadiazin-5-yl)oxy)-2-methylpropan-2-yl)-2,6-dimethylisonicotinamide (S2218; CAS 1622458-34-7), a flavour with modifying properties, was completed for the purpose of assessing its safety for use in food and beverage applications. S2218 exhibited minimal oxidative metabolism in vitro, and in rat pharmacokinetic studies, the compound was poorly orally bioavailable and rapidly eliminated. S2218 was not found to be mutagenic in an in vitro bacterial reverse mutation assay, and was found to be neither clastogenic nor aneugenic in an in vitro mammalian cell micronucleus assay. In subchronic oral toxicity studies in male and female rats, the NOAEL was 140 mg/kg bw/day (highest dose tested) for S2218 sulfate salt (S8069) when administered as a food ad-mix for 13 consecutive weeks. Furthermore, S2218 sulfate salt demonstrated a lack of maternal toxicity, as well as adverse effects on fetal morphology at the highest dose tested, providing a NOAEL of 1000 mg/kg bw/day for both maternal toxicity and embryo/fetal development when administered orally during gestation to pregnant rats.

Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease

Monoamine oxidase B (MAO-B) has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased MAO-B expression in astroglia has been observed adjacent to amyloid plaques in AD patient brains. This phenomenon is hypothesized to lead to increased production of hydrogen peroxide and reactive oxygen species (ROS), thereby contributing to AD pathology. Therefore, reduction of ROS-induced oxidative stress via inhibition of MAO-B activity may delay the progression of the disease. In the present study we report the pharmacological properties of sembragiline, a novel selective MAO-B inhibitor specifically developed for the treatment of AD, and on its effect on ROS-mediated neuronal injury and astrogliosis in MAO-B transgenic animals. Sembragiline showed potent and long-lasting MAO-B-selective inhibition and did not inhibit MAO-A at doses where full inhibition of MAO-B was observed. Such selectivity should translate into a favorable clinical safety profile. Indeed, sembragiline neither induced the serotonin syndrome when administered together with the serotonin precursor l-5-hydroxytryptophan in combination with antidepressants such as fluoxetine, nor potentiated the pressor effect of tyramine. Additionally, in experiments using a transgenic animal model conditionally overexpressing MAO-B in astroglia, sembragiline protected against neuronal loss and reduced both ROS formation and reactive astrogliosis. Taken together, these findings warrant further investigation of the potential therapeutic benefit of MAO-B inhibitors in patients with AD and other neurologic disorders.

Glaucarubulone glucoside from Castela macrophylla suppresses MCF-7 breast cancer cell growth and attenuates benzo[a]pyrene-mediated CYP1A gene induction

Quassinoids often exhibit antioxidant and antiproliferative activity. Emerging evidence suggests that these natural metabolites also display chemopreventive actions. In this study, we investigated the potential for the quassinoid glaucarubulone glucoside (Gg), isolated from the endemic Jamaican plant Castela macrophylla (Simaroubaceae), to display potent cytotoxicity and inhibit human cytochrome P450s (CYPs), particularly CYP1A enzymes, known to convert polyaromatic hydrocarbons into carcinogenic metabolites. Gg reduced the viability of MCF-7 breast adenocarcinoma cells (IC₅₀ = 121 nm) to a greater extent than standard of care anticancer agents 5-fluorouracil, tamoxifen (IC₅₀ >10 μm) and the tamoxifen metabolite 4-hydroxytamoxifen (IC₅₀ = 2.6 μm), yet was not cytotoxic to non-tumorigenic MCF-10A breast epithelial cells. Additionally, Gg induced MCF-7 breast cancer cell death. Gg blocked increases in reactive oxygen species in MCF-10A cells mediated by the polyaromatic hydrocarbon benzo[a]pyrene (B[a]P) metabolite B[a]P 1,6-quinone, yet downregulated the expression of genes that promote antioxidant activity in MCF-7 cells. This implies that Gg exhibits antioxidant and cytoprotective actions in non-tumorigenic breast epithelial cells and pro-oxidant, cytotoxic actions in breast cancer cells. Furthermore, Gg inhibited the activities of human CYP1A according to non-competitive kinetics and attenuated the ability of B[a]P to induce CYP1A gene expression in MCF-7 cells. These data indicate that Gg selectively suppresses MCF-7 breast cancer cell growth without impacting non-tumorigenic breast epithelial cells and blocks B[a]P-mediated CYP1A induction. Taken together, our data provide a rationale for further investigations of Gg and similar plant isolates as potential agents to treat and prevent breast cancer. Copyright © 2017 John Wiley & Sons, Ltd.

Evaluation of the Effects of S-Allyl-L-cysteine, S-Methyl-L-cysteine, trans-S-1-Propenyl-L-cysteine, and Their N-Acetylated and S-Oxidized Metabolites on Human CYP Activities

Three major organosulfur compounds of aged garlic extract, S-allyl-L-cysteine (SAC), S-methyl-L-cysteine (SMC), and trans-S-1-propenyl-L-cysteine (S1PC), were examined for their effects on the activities of five major isoforms of human CYP enzymes: CYP1A2, 2C9, 2C19, 2D6, and 3A4. The metabolite formation from probe substrates for the CYP isoforms was examined in human liver microsomes in the presence of organosulfur compounds at 0.01-1 mM by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Allicin, a major component of garlic, inhibited CYP1A2 and CYP3A4 activity by 21-45% at 0.03 mM. In contrast, a CYP2C9-catalyzed reaction was enhanced by up to 1.9 times in the presence of allicin at 0.003-0.3 mM. SAC, SMC, and S1PC had no effect on the activities of the five isoforms, except that S1PC inhibited CYP3A4-catalyzed midazolam 1'-hydroxylation by 31% at 1 mM. The N-acetylated metabolites of the three compounds inhibited the activities of several isoforms to a varying degree at 1 mM. N-Acetyl-S-allyl-L-cysteine and N-acetyl-S-methyl-L-cysteine inhibited the reactions catalyzed by CYP2D6 and CYP1A2, by 19 and 26%, respectively, whereas trans-N-acetyl-S-1-propenyl-L-cysteine showed weak to moderate inhibition (19-49%) of CYP1A2, 2C19, 2D6, and 3A4 activities. On the other hand, both the N-acetylated and S-oxidized metabolites of SAC, SMC, and S1PC had little effect on the reactions catalyzed by the five isoforms. These results indicated that SAC, SMC, and S1PC have little potential to cause drug-drug interaction due to CYP inhibition or activation in vivo, as judged by their minimal effects (IC₅₀>1 mM) on the activities of five major isoforms of human CYP in vitro.

Human P450 Microarrays for In Vitro Toxicity Analysis: Toward Complete Automation of Human Toxicology Screening

The development of a tool that can provide early-stage predictive toxicology data may accelerate the identification of safer drug candidates, and thereby improve the clinical progression of drug candidates to pharmaceuticals. Such a system would require an accurate and reliable technique that is amenable to the large number of drug candidates that must be screened in the lead discovery and optimization stages of drug development. A key component of predictive toxicology is the ability to harness the metabolite-generating capacity of human cytochromes P450, which are involved in first-pass drug metabolism function of the liver. We have miniaturized P450 catalysis into a microarray format consisting of up to 11,200 isolated P450 reactions, each in 5 nL sol-gel spots, on a single functionalized glass microscope-size biochip. This dramatic scale down from more conventional 96 and 384-well plate scales (at least a 1000-fold reduction in volume) did not adversely affect P450 catalytic activity. Based on the functionality of the P450-containing microarray, we developed the metabolizing enzyme toxicology assay Chip (MetaChip), which combines high-throughput P450 catalysis with cell-based screening on a microscale platform. Proof of concept was demonstrated using anticancer prodrugs cyclophosphamide and Tegafur, as well as the analgesic acetaminophen. The MetaChip may provide a high-throughput microscale alternative to currently used in vitro methods for human metabolism and toxicology screening.

Measuring Drug Metabolism Kinetics and Drug-Drug Interactions Using Self-Assembled Monolayers for Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry

The competition of two drugs for the same metabolizing enzyme is a common mechanism for drug-drug interactions that can lead to altered kinetics in drug metabolism and altered elimination rates in vivo. With the prevalence of multidrug therapy, there is great potential for serious drug-drug interactions and adverse drug reactions. In an effort to prevent adverse drug reactions, the FDA mandates the evaluation of the potential for metabolic inhibition by every new chemical entity. Conventional methods for assaying drug metabolism (e.g., those based on HPLC) have been established for measuring drug-drug interactions; however, they are low-throughput. Here we describe an approach to measure the catalytic activity of CYP2C9 using the high-throughput technique self-assembled monolayers for matrix-assisted laser desorption-ionization (SAMDI) mass spectrometry. We measured the kinetics of CYP450 metabolism of the substrate, screened a set of drugs for inhibition of CYP2C9 and determined the Ki values for inhibitors. The throughput of this platform may enable drug metabolism and drug-drug interactions to be interrogated at a scale that cannot be achieved with current methods.

Highly Miniaturized Formats for In Vitro Drug Metabolism Assays Using Vivid® Fluorescent Substrates and Recombinant Human Cytochrome P450 Enzymes

Highly miniaturized P450 screening assays designed to enable facile analysis of P450 drug interactions in a 1536-well plate format with the principal human cytochrome P450 enzymes (CYP3A4, 2D6, 2C9, 2C19, and 1A2) and Vivid® fluorogenic substrates were developed. The detailed characterization of the assays included stability, homogeneity, and reproducibility of the recombinant P450 enzymes and the kinetic parameters of their reactions with Vivid® fluorogenic substrates, with a focus on the specific characteristics of each component that enable screening in a low-volume 1536-well plate assay format. The screening assays were applied for the assessment of individual cytochrome P450 inhibition profiles with a panel of selected assay modifiers, including isozyme-specific substrates and inhibitors. IC50values obtained for the modifiers in 96- and 1536-well plate formats were similar and comparable with values obtained in assays with conventional substrates. An overall examination of the 1536-well assay statistics, such as signal-to-background ratio and Z′ factor, demonstrated that these assays are a robust, successful, and reliable tool to screen for cytochrome P450 metabolism and inhibition in an ultra-high-throughput screening format. ( Journal of Biomolecular Screening 2005:56-66)

A High-Throughput Method for Enzyme Kinetic Studies

A simple and flexible setup for conducting drug metabolism studies is described in this report. A heating block was designed for the Multimek liquid handler platform for incubation of multiple samples at 37 °C in a 96-well format. This setup enables the rapid performance of drug metabolism experiments on a large number of samples. In this report, the authors present the validation of the system by 1) showing reproducible and consistent determination of the in vitro half-life of midazolam in every well across the entire plate and 2) determination of metabolic parameter values of midazolam, testosterone, diclofenac, warfarin, and dextromethorphan and inhibition parameter values of quinidine and ketoconazole, all comparable to literature values. In addition, the authors demonstrate the application of the setup to determining the metabolic stability of a set of proprietary compounds, the inhibition of activity of cytochrome P450 (CYP) enzymes, and the conduct of a single combination experiment that can simultaneously determine the metabolic stability and CYP inhibition activity. Overall, the system represents a simple, high-throughput and useful tool for drug metabolism screening in drug discovery. ( Journal of Biomolecular Screening 2003:544-554)

Toxicological evaluation of a novel umami flavour compound: 2-(((3-(2,3-Dimethoxyphenyl)-1H-1,2,4-triazol-5-yl)thio)methyl)pyridine

A toxicological evaluation of a umami flavour compound, 2-(((3-(2,3-dimethoxyphenyl)-1H-1,2,4-triazol-5-yl)thio)methyl)pyridine (S3643; CAS 902136-79-2), was completed for the purpose of assessing its safety for use in food and beverage applications. S3643 undergoes extensive oxidative metabolism in vitro with rat microsomes producing the S3643-sulfoxide and 4′-hydroxy-S3643 as the major metabolites. In incubations with human microsomes, the O-demethyl-S3643 and S3643-sulfoxide were produced as the major metabolites. In pharmacokinetic studies in rats, the S3643-sulfoxide represents the dominant biotransformation product. S3643 was not found to be mutagenic or clastogenic in vitro, and did not induce micronuclei in CHO-WB_L cells. In subchronic oral toxicity studies in rats, the no-observed-adverse-effect-level (NOAEL) for S3643 was 100 mg/kg bw/day (highest dose tested) when administered in the diet for 90 consecutive days.

Synthesis and Structure-Activity Relationships of 2-Aminoacetamide Derivatives as Peroxisome Proliferator-Activated Receptor α/γ Dual Agonists

We describe the design, syntheses, and structure-activity relationships of novel zwitterionic compounds as nonthiazolidinedion-based peroxisome proliferator-activated receptor (PPAR) α/γ dual agonists. In our previous report, we obtained compound 1 showing potent PPARα/γ dual agonistic activities, together with a sufficient glucose-lowering effect in db/db mice. However, this compound possessed an issue, i.e., the 1,3,4-oxadiazole ring was not stable in acidic conditions. Thus, we carried out further optimization to improve the stability while maintaining the other favorable profile features including potent PPARα/γ dual agonistic activity. We addressed the issue by changing the oxadiazole ring to a bioisostere amide group. These amide derivatives were stable in acidic conditions and decreased plasma glucose and plasma triglyceride levels significantly without marked weight gain.

Significant inhibitory impact of dibenzyl trisulfide and extracts of Petiveria alliacea on the activities of major drug-metabolizing enzymes in vitro: An assessment of the potential for medicinal plant-drug interactions

Dibenzyl trisulfide (DTS) is the major active ingredient expressed in Petiveria alliacea L., a shrub widely used for a range of conditions, such as, arthritis, asthma and cancer. Given its use alone and concomitantly with prescription medicines, we undertook to investigate its impact on the activities of important drug metabolizing enzymes, the cytochromes P450 (CYP), a key family of enzymes involved in many adverse drug reactions. DTS and seven standardized extracts from the plant were assessed for their impact on the activities of CYPs 1A2, 2C19, 2C9, 2D6 and 3A4 on a fluorometric assay. DTS revealed significant impact against the activities of CYPs 1A2, 2C19 and 3A4 with IC50 values of 1.9, 4.0 and 3.2μM, respectively, which are equivalent to known standard inhibitors of these enzymes (furafylline, and tranylcypromine), and the most potent interaction with CYP1A2 displayed irreversible enzyme kinetics. The root extract, drawn with 96% ethanol (containing 2.4% DTS), displayed IC50 values of 5.6, 3.9 and 4.2μg/mL respectively, against the same isoforms, CYPs 1A2, 2C19 and 3A4. These investigations identify DTS as a valuable CYP inhibitor and P. alliacea as a candidate plant worthy of clinical trials to confirm the conclusions that extracts yielding high DTS may lead to clinically relevant drug interactions, whilst extracts yielding low levels of DTS, such as aqueous extracts, are unlikely to cause adverse herb-drug interactions.

Toxicological evaluation of two novel bitter modifying flavour compounds: 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)imidazolidine-2,4-dione and 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)-5,5-dimethylimidazolidine-2,4-dione

A toxicological evaluation of two novel bitter modifying flavour compounds, 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)imidazolidine-2,4-dione (S6821, CAS 1119831-25-2) and 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)-5,5-dimethylimidazolidine-2,4-dione (S7958, CAS 1217341-48-4), were completed for the purpose of assessing their safety for use in food and beverage applications. S6821 undergoes oxidative metabolism in vitro, and in rat pharmacokinetic studies both S6821 and S7958 are rapidly converted to the corresponding O-sulfate and O-glucuronide conjugates. S6821 was not found to be mutagenic or clastogenic in vitro, and did not induce micronuclei in bone marrow polychromatic erythrocytes in vivo. S7958, a close structural analog of S6821, was also found to be non-mutagenic in vitro. In short term and subchronic oral toxicity studies in rats, the no-observed-adverse-effect-level (NOAEL) for both S7958 and S6821 was 100 mg/kg bw/day (highest dose tested) when administered as a food ad-mix for either 28 or 90 consecutive days, respectively. Furthermore, S6821 demonstrated a lack of maternal toxicity, as well as adverse effects on fetal morphology at the highest dose tested, providing a NOAEL of 1000 mg/kg bw/day for both maternal toxicity and embryo/fetal development when administered orally during gestation to pregnant rats.

Discovery of 4-acetyl-3-(4-fluorophenyl)-1-(p-tolyl)-5-methylpyrrole as a dual inhibitor of human P-glycoprotein and Staphylococcus aureus Nor A efflux pump

Polysubstituted pyrrole natural products, lamellarins, are known to overcome multi-drug resistance in cancer via the inhibition of p-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) efflux pumps. Herein, a series of simplified polysubstituted pyrroles, prepared via a one-pot domino protocol, were screened for P-gp inhibition in P-gp overexpressing human adenocarcinoma LS-180 cells using a rhodamine 123 efflux assay. Several compounds showed the significant inhibition of P-gp at 50 μM, as indicated by increase in the intracellular accumulation of Rh123 in LS-180 cells. Furthermore, pyrrole 5i decreased the efflux of digoxin, a FDA approved P-gp substrate in MDCK-MDR1 cells with an IC50 of 11.2 μM. In in vivo studies, following the oral administration of a P-gp substrate drug, rifampicin, along with compound , the Cmax and AUC0-∞ of rifampicin was enhanced by 31% and 46%, respectively. All the compounds were then screened for their ability to potentiate ciprofloxacin activity via the inhibition of Staphylococcus aureus Nor A efflux pump. Pyrrole showed the significant inhibition of S. aureus Nor A efflux pump with 8- and 4-fold reductions in the MIC of ciprofloxacin at 50 and 6.25 μM, respectively. The molecular docking studies of compound with the human P-gp and S. aureus Nor A efflux pump identified its plausible binding site and key interactions. Thus, the results presented herein strongly indicate the potential of this scaffold for its use as multi-drug resistance reversal agent or bioavailability enhancer.

Strain differences in cytochrome P450 mRNA and protein expression, and enzymatic activity among Sprague Dawley, Wistar, Brown Norway and Dark Agouti rats

Rat cytochrome P450 (CYP) exhibits inter-strain differences, but their analysis has been scattered across studies under different conditions. To identify these strain differences in CYP more comprehensively, mRNA expression, protein expression and metabolic activity among Wistar (WI), Sprague Dawley (SD), Dark Agouti (DA) and Brown Norway (BN) rats were compared. The mRNA level and enzymatic activity of CYP1A1 were highest in SD rats. The rank order of Cyp3a2 mRNA expression mirrored its protein expression, i.e., DA>BN>SD>WI, and was similar to the CYP3A2-dependent warfarin metabolic activity, i.e., DA>SD>BN>WI. These results suggest that the strain differences in CYP3A2 enzymatic activity are caused by differences in mRNA expression. Cyp2b1 mRNA levels, which were higher in DA rats, did not correlate with its protein expression or enzymatic activity. This suggests that the strain differences in enzymatic activity are not related to Cyp2b1 mRNA expression. In conclusion, WI rats tended to have the lowest CYP1A1, 2B1 and 3A2 mRNA expression, protein expression and enzymatic activity among the strains. In addition, SD rats had the highest CYP1A1 mRNA expression and activity, while DA rats had higher CYP2B1 and CYP3A2 mRNA and protein expression. These inter-strain differences in CYP could influence pharmacokinetic considerations in preclinical toxicological studies.

Relationships of Echium plantagineum L. bee pollen, dietary flavonoids and their colonic metabolites with cytochrome P450 enzymes and oxidative stress

Echium plantagineumL. bee pollen is a dietary source of flavonoids, which can play a protective role in the gastrointestinal tract by modulating cytochrome P450 (CYP) biotransformation enzymes and by opposing oxidative stress.

Determining the IC 50 Values for Vorozole and Letrozole, on a Series of Human Liver Cytochrome P450s, to Help Determine the Binding Site of Vorozole in the Liver

Vorozole and letrozole are third-generation aromatase (cytochrome P450 19A1) inhibitors. [¹¹C]-Vorozole can be used as a radiotracer for aromatase in living animals but when administered by IV, it collects in the liver. Pretreatment with letrozole does not affect the binding of vorozole in the liver. In search of finding the protein responsible for the accumulation of vorozole in the liver, fluorometric high-throughput screening assays were used to test the inhibitory capability of vorozole and letrozole on a series of liver cytochrome P450s (CYP1A1, CYP1A2, CYP2A6, and CYP3A4). It was determined that vorozole is a potent inhibitor of CYP1A1 (IC₅₀ = 0.469 μM) and a moderate inhibitor of CYP2A6 and CYP3A4 (IC₅₀ = 24.4 and 98.1 μM, resp.). Letrozole is only a moderate inhibitor of CYP1A1 and CYP2A6 (IC₅₀ = 69.8 and 106 μM) and a very weak inhibitor of CYP3A4 (<10% inhibition at 1 mM). Since CYP3A4 makes up the majority of the CYP content found in the human liver, and vorozole inhibits it moderately well but letrozole does not, CYP3A4 is a good candidate for the protein that [¹¹C]-vorozole is binding to in the liver.