An Electrochemical Microfluidic Platform for Human P450 Drug Metabolism Profiling

Bioelectrochemical platform with human monooxygenases: FMO1 and CYP3A4 tandem reactions with phorate

It is highly advantageous to devise an in vitro platform that can predict the complexity of an in vivo system. The first step of this process is the identification of a xenobiotic whose monooxygenation is carried out by two sequential enzymatic reactions. Pesticides are a good model for this type of tandem reactions since in specific cases they are initially metabolised by human flavin-containing monooxygenase 1 (hFMO1), followed by cytochrome P450 (CYP). To assess the feasibility of such an in vitro platform, hFMO1 is immobilised on glassy carbon electrodes modified with graphene oxide (GO) and cationic surfactant didecyldimethylammonium bromide (DDAB). UV-vis, contact angle and AFM measurements support the effective decoration of the GO sheets by DDAB which appear as 3 nm thick structures. hFMO1 activity on the bioelectrode versus three pesticides; fenthion, methiocarb and phorate, lead to the expected sulfoxide products with K_M values of 29.5 ± 5.1, 38.4 ± 7.5, 29.6 ± 4.1 µM, respectively. Moreover, phorate is subsequently tested in a tandem system with hFMO1 and CYP3A4 resulting in both phorate sulfoxide as well as phoratoxon sulfoxide. The data demonstrate the feasibility of using bioelectrochemical platforms to mimic the complex metabolic reactions of xenobiotics within the human body.

Biotransformation of phenytoin in the electrochemically-driven CYP2C19 system

The possibility of the detection of atypical kinetic profiles of drug biotransformation using electrochemical systems based on immobilized cytochromes P450 with phenytoin hydroxylation by cytochrome P450 2C19 (CYP2C19) as an example was evaluated for the first time. For this purpose, we developed an electrochemical system, where one of the electrodes was modified by didodecyldimethylammonium bromide (DDAB) and was used as an electron donor for reduction of heme iron ion of the immobilized CYP2C19 and initiation of the catalytic reaction, while the second electrode was not modified and served for an electrochemical quantitation of 4-hydroxyphenytoin, which is a metabolite of antiepileptic drug phenytoin, by its oxidation peak. It was revealed that the dependence of the rate of 4-hydroxyphenytoin formation on phenytoin concentration is described by the equation for two enzymes or two binding sites indicating the existing of high- and low-affinity forms of the enzyme. The atypical kinetics and the kinetic parameters of CYP2C19-mediated phenytoin hydroxylation in the electrochemical system correlate to the same characteristics obtained by other authors in an alternative enzymatic system. Our results demonstrate the possibility of electrochemical systems based on cytochromes P450 to be applied for the detection of atypical kinetic profiles of drug metabolism.

Cytochrome P450 enzymes: a review on drug metabolizing enzyme inhibition studies in drug discovery and development

Assessment of drug candidate's potential to inhibit cytochrome P450 (CYP) enzymes remains crucial in pharmaceutical drug discovery and development. Both direct and time-dependent inhibition of drug metabolizing CYP enzymes by the concomitant administered drug is the leading cause of drug-drug interactions (DDIs), resulting in the increased toxicity of the victim drug. In this context, pharmaceutical companies have grown increasingly diligent in limiting CYP inhibition liabilities of drug candidates in the early stages and examining risk assessments throughout the drug development process. This review discusses different strategies and decision-making processes for assessing the drug-drug interaction risks by enzyme inhibition and lays particular emphasis on in vitro study designs and interpretation of CYP inhibition data in a stage-appropriate context.

Electrochemistry of cytochrome P450 17α-hydroxylase/17,20-lyase (P450c17)

Within the superfamily of cytochrome P450 enzymes (P450s), there is a small class which is functionally employed for steroid biosynthesis. The enzymes in this class appear to have a small active site to accommodate the steroid substrates specifically and snuggly, prior to the redox transformation or hydroxylation to form a product. Cytochrome P450c17 is one of these and is also a multi-functional P450, with two activities, the first 17α-hydroxylation of pregnenolone is followed by a subsequent 17,20-lyase transformation to dehydroepiandrosterone (DHEA) as the dominant pathways to cortisol precursors or androgens in humans, respectively. How P450c17 regulates these two redox reactions is of special interest. There is a paucity of direct electrochemical studies on steroidogenic P450s, and in this mini-review we provide an overview of these studies with P450c17. Historical consideration as to the difficulties in obtaining reliable electrochemistry due to issues of handling proteins on an electrode, together with advances in the electrochemical techniques are addressed. Recent work using Fourier transformed alternating current voltammetry is highlighted as this technique can provide both catalytic information simultaneously with the underlying redox transfer with the P450 haem.

A Cytochrome P450 3A4 Biosensor Based on Generation 4.0 PAMAM Dendrimers for the Detection of Caffeine

Cytochromes P450 (CYP, P450) are a large family of heme-active-site proteins involved in many catalytic processes, including steroidogenesis. In humans, four primary enzymes are involved in the metabolism of almost all xenobiotics. Among these enzymes, CYP3A4 is responsible for the inactivation of the majority of used drugs which makes this enzyme an interesting target for many fields of research, especially pharmaceutical research. Since the late 1970s, attempts have been made to construct and develop electrochemical sensors for the determination of substrates. This paper is concerned with the establishment of such a CYP3A4-containing biosensor. The sensor was constructed by adsorption of alternating layers of sub-nanometer gold particle-modified PAMAM (poly-amido-amine) dendrimers of generation 4.0, along with the enzyme by a layer-by-layer assembly technique. Atomic force microscopy (AFM), quartz crystal microbalance (QCM), and Fourier-transformed infrared spectroscopy (FTIR) were employed to elucidate the sensor assembly. Additionally, the biosensor was tested by cyclic voltammetry using caffeine as a substrate.

Application of nanodisc technology for direct electrochemical investigation of plant cytochrome P450s and their NADPH P450 oxidoreductase

Direct electrochemistry of cytochrome P450 containing systems has primarily focused on investigating enzymes from microbes and animals for bio-sensing applications. Plant P450s receive electrons from NADPH P450 oxidoreductase (POR) to orchestrate the bio-synthesis of a plethora of commercially valuable compounds. In this report, full length CYP79A1, CYP71E1 and POR of the dhurrin pathway in Sorghum bicolor were reconstituted individually in nanoscale lipid patches, "nanodiscs", and directly immobilized on unmodified gold electrodes. Cyclic voltammograms of CYP79A1 and CYP71E1 revealed reversible redox peaks with average midpoint potentials of 80 ± 5 mV and 72 ± 5 mV vs. Ag/AgCl, respectively. POR yielded two pairs of redox peaks with midpoint potentials of 90 ± 5 mV and -300 ± 10 mV, respectively. The average heterogeneous electron transfer rate constant was calculated to be ~1.5 s(-1). POR was electro-catalytically active while the P450s generated hydrogen peroxide (H2O2). These nanodisc-based investigations lay the prospects and guidelines for construction of a simplified platform to perform mediator-free, direct electrochemistry of non-engineered cytochromes P450 under native-like conditions. It is also a prelude for driving plant P450 systems electronically for simplified and cost-effective screening of potential substrates/inhibitors and fabrication of nano-bioreactors for synthesis of high value natural products.

Toward the development of smart and low cost point-of-care biosensors based on screen printed electrodes

Screen printing technology provides a cheap and easy means to fabricate disposable electrochemical devices in bulk quantities which are used for rapid, low-cost, on-site, real-time and recurrent industrial, pharmaceutical or environmental analyses. Recent developments in micro-fabrication and nano-characterization made it possible to screen print reproducible feature on materials including plastics, ceramics and metals. The processed features forms screen-printed disposable biochip (SPDB) upon the application of suitable bio-chemical recognition receptors following appropriate methods. Adequacy of biological and non-biological materials is the key to successful biochip development. We can further improve recognition ability of SPDBs by adopting new screen printed electrode (SPE) configurations. This review covers screen-printing theory with special emphasis on the technical impacts of SPE architectures, surface treatments, operational stability and signal sensitivity. The application of SPE in different areas has also been summarized. The article aims to highlight the state-of-the-art of SPDB at the laboratory scale to enable us in envisaging the deployment of emerging SPDB technology on the commercial scale.

Cytochromes P450 as promising catalysts for biotechnological application: chances and limitations

Cytochromes P450 (CYPs) belong to the superfamily of heme b containing monooxygenases with currently more than 21,000 members. These enzymes accept a vast range of organic molecules and catalyze diverse reactions. These extraordinary capabilities of CYP systems that are unmet by other enzymes make them attractive for biotechnology. However, the complexity of these systems due to the need of electron transfer from nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) via redox partner proteins for the initial hydroxylation step limits a broader technical implementation of CYP enzymes. There have been several reviews during the past years tackling the potential CYPs for synthetic application. The aim of this review is to give a critical overview about possibilities and chances for application of these interesting catalysts as well as to discuss drawbacks and problems related to their use. Solutions to overcome these limitations will be demonstrated, and several selected examples of successful CYP applications under industrial conditions will be reviewed.

Electrochemical detection of human cytochrome P450 2A6 inhibition: a step toward reducing dependence on smoking

Inhibition of human cytochrome P450 2A6 has been demonstrated to play an important role in nicotine metabolism and consequent smoking habits. Here, the "molecular Lego" approach was used to achieve the first reported electrochemical signal of human CYP2A6 and to improve its catalytic efficiency on electrode surfaces. The enzyme was fused at the genetic level to flavodoxin from Desulfovibrio vulgaris (FLD) to create the chimeric CYP2A6-FLD. Electrochemical characterization by cyclic voltammetry shows clearly defined redox transitions of the haem domain in both CYP2A6 and CYP2A6-FLD. Electrocatalysis experiments using coumarin as substrate followed by fluorimetric quantification of the product were performed with immobilized CYP2A6 and CYP2A6-FLD. Comparison of the kinetic parameters showed that coumarin catalysis was carried out with a higher efficiency by the immobilized CYP2A6-FLD, with a calculated kcat value significantly higher (P < 0.005) than that of CYP2A6, whereas the affinity for the substrate (KM) remained unaltered. The chimeric system was also successfully used to demonstrate the inhibition of the electrochemical activity of the immobilized CYP2A6-FLD, toward both coumarin and nicotine substrates, by tranylcypromine, a potent and selective CYP2A6 inhibitor. This work shows that CYP2A6 turnover efficiency is improved when the protein is linked to the FLD redox module, and this strategy can be utilized for the development of new clinically relevant biotechnological approaches suitable for deciphering the metabolic implications of CYP2A6 polymorphism and for the screening of CYP2A6 substrates and inhibitors.

The use of immobilized cytochrome P4502C9 in PMMA-based plug flow bioreactors for the production of drug metabolites

Cytochrome P450 enzymes play a key role in the metabolism of pharmaceutical agents. To determine metabolite toxicity, it is necessary to obtain P450 metabolites from various pharmaceutical agents. Here, we describe a bioreactor that is made by immobilizing cytochrome P450 2C9 (CYP2C9) to a poly(methyl methacrylate) surface and, as an alternative to traditional chemical synthesis, can be used to biosynthesize P450 metabolites in a plug flow bioreactor. As part of the development of the CYP2C9 bioreactor, we have studied two different methods of attachment: (1) coupling via the N-terminus using N-hydroxysulfosuccinimide 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and (2) using the Ni(II) chelator 1-acetato-4-benzyl-triazacyclononane to coordinate the enzyme to the surface using a C-terminal histidine tag. Additionally, the propensity for metabolite production of the CYP2C9 proof-of-concept bioreactors as a function of enzyme attachment conditions (e.g., time and enzyme concentration) was examined. Our results show that the immobilization of CYP2C9 enzymes to a PMMA surface represents a viable and alternative approach to the preparation of CYP2C9 metabolites for toxicity testing. Furthermore, the basic approach can be adapted to any cytochrome P450 enzyme and in a high-throughput, automated process.

Measurement of electron transfer through cytochrome P450 protein on nanopillars and the effect of bound substrates

Electron transfer in cytochrome P450 enzymes is a fundamental process for activity. It is difficult to measure electron transfer in these enzymes because under the conditions typically used they exist in a variety of states. Using nanotechnology-based techniques, gold conducting nanopillars were constructed in an indexed array. The P450 enzyme CYP2C9 was attached to each of these nanopillars, and conductivity measurements made using conducting probe atomic force microscopy under constant force conditions. The conductivity measurements were made on CYP2C9 alone and with bound substrates, a bound substrate-effector pair, and a bound inhibitor. Fitting of the data with the Poole-Frenkel model indicates a correlation between the barrier height for electron transfer and the ease of CYP2C9-mediated metabolism of the bound substrates, though the spin state of iron is not well correlated. The approach described here should have broad application to the measurement of electron transfer in P450 enzymes and other metalloenzymes.

Optimization of the bacterial cytochrome P450 BM3 system for the production of human drug metabolites

Drug metabolism in human liver is a process involving many different enzymes. Among them, a number of cytochromes P450 isoforms catalyze the oxidation of most of the drugs commercially available. Each P450 isoform acts on more than one drug, and one drug may be oxidized by more than one enzyme. As a result, multiple products may be obtained from the same drug, and as the metabolites can be biologically active and may cause adverse drug reactions (ADRs), the metabolic profile of a new drug has to be known before this can be commercialized. Therefore, the metabolites of a certain drug must be identified, synthesized and tested for toxicity. Their synthesis must be in sufficient quantities to be used for metabolic tests. This review focuses on the progresses done in the field of the optimization of a bacterial self-sufficient and efficient cytochrome P450, P450 BM3 from Bacillus megaterium, used for the production of metabolites of human enzymes. The progress made in the improvement of its catalytic performance towards drugs, the substitution of the costly NADPH cofactor and its immobilization and scale-up of the process for industrial application are reported.

A rapid screening for cytochrome P450 catalysis on new chemical entities: cytochrome P450 BM3 and 1,2,5-oxadiazole derivatives

This work presents the validation of a rapid screening procedure for the catalysis of cytochrome P450 on new chemical entities. The assay is tested on the prototypical, catalytically self-sufficient and soluble cytochrome P450 BM3 from Bacillus megaterium that shares a high degree of homology with mammalian counterparts. The so-called alkali assay developed in our laboratory is validated here also by product formation and molecular modeling on a number of derivatives sharing the molecular scaffold of the 1,2,5-oxadiazole ring, a class of molecules very different from the long-chain fatty acids known to be oxidized by cytochrome P450 BM3. The alkali assay reveals the ability of this cytochrome to oxidize NADPH in the presence of nine out of thirteen 1,2,5-oxadiazole derivatives tested. The enzyme shows high affinity and coupling efficiencies when incubated with four 1,2,5-oxadiazole derivatives. The presence of oxidation products deriving from catalysis was also confirmed by high-performance liquid chromatography (HPLC). Molecular docking suggests that a key factor for the 1,2,5-oxadiazole derivatives to enter the active site and induce catalysis is the presence of the -SO(2) moiety bridging the 1,2,5-oxadiazole and phenyl rings. These data indicate that the alkali assay is able to quickly and cheaply detect the recognition of new substrates by cytochrome P450. The assay is not intended to substitute HPLC-mass spectrometry analysis, but it is a preliminary screening that allows elimination of obvious nonsubstrates from the start.

Microfluidic electrochemical array for detection of reactive metabolites formed by cytochrome P450 enzymes

A novel, simple, rapid microfluidic array using bioelectronically driven cytochrome P450 enzyme catalysis for reactive metabolite screening is reported for the first time. The device incorporates an eight-electrode screen-printed carbon array coated with thin films of DNA, [Ru(bpy)(2)(PVP)(10)](ClO(4)) {RuPVP}, and rat liver microsomes (RLM) as enzyme sources. Catalysis features electron donation to cyt P450 reductase in the RLMs and subsequent cyt P450 reduction while flowing an oxygenated substrate solution past sensor electrodes. Metabolites react with DNA in the film if they are able, and damaged DNA is detected by catalytic square wave voltammetry (SWV) utilizing the RuPVP polymer. The microfluidic device was tested for a set of common pollutants known to form DNA-reactive metabolites. Logarithmic turnover rates based on SWV responses gave excellent correlation with the rodent liver TD(50) toxicity metric, supporting the utility of the device for toxicity screening. The microfluidic array gave much better S/N and reproducibility than single-electrode sensors based on similar principles.

Enzyme-based amperometric platform to determine the polymorphic response in drug metabolism by cytochromes P450

"Personalized medicine" is a new concept in health care, one aspect of which defines the specificity and dosage of drugs according to effectiveness and safety for each patient. Dosage strongly depends from the rate of metabolism which is primarily regulated by the activity of cytochrome P450. In addition to the need for a genetic characterization of the patients, there is also the necessity to determine the drug-clearance properties of the polymorphic P450 enzyme. To address this issue, human P450 2D6 and 2C9 were engineered and covalently linked to an electrode surface allowing fast, accurate, and reliable measurements of the kinetic parameters of these phase-1 drug metabolizing polymorphic enzymes. In particular, the catalytic activity of P450 2C9 on the electrode surface was found to be improved when expressed from a gene-fusion with flavodoxin from Desulfovibrio vulgaris (2C9/FLD). The results are validated using marker drugs for these enzymes, bufuralol for 2D6, and warfarin for 2C9/FLD. The platform is able to measure the same small differences in K(M), and it allows a fast and reproducible mean to generated the product identified by HPLC from which the k(cat) is calculated.