Diagnosis of Intoxication by the Organophosphate VX: Comparison Between an Electrochemical Sensor and Ellman´s Photometric Method

Simple Chemical and Cholinesterase Methods for the Detection of Nerve Agents Using Optical Evaluation

The extreme toxicity of nerve agents and the broad spectrum of their physical and chemical properties, enabling the use of these agents in a variety of tactical situations, is a continuing challenge in maintaining the knowledge and capability to detect them, as well as in finding new effective methods. Despite significant advances in the instrumentation of the analysis of nerve agents, relatively simple methods based on the evaluation of colour signals (absorption and fluorescence), in particular those using the cholinesterase reaction, continue to be of importance. This review provides a brief presentation of the current status of these simple methods, with an emphasis on military applications, and illustrates the high interest of the professional community in their further development. At the same time, it also contains some peculiarities (high reliability and durability, resistance to extreme climatic conditions, work in deployed means of protection, low purchase prices, economic availability especially in a state of war, etc.) that the authors believe research and development of simple methods and means for the detection of nerve agents should respect.

Computational design of a sensitive, selective phase-changing sensor protein for the VX nerve agent

The VX nerve agent is one of the deadliest chemical warfare agents. Specific, sensitive, real-time detection methods for this neurotoxin have not been reported. The creation of proteins that use biological recognition to fulfill these requirements using directed evolution or library screening methods has been hampered because its toxicity makes laboratory experimentation extraordinarily expensive. A pair of VX-binding proteins were designed using a supercharged scaffold that couples a large-scale phase change from unstructured to folded upon ligand binding, enabling fully internal binding sites that present the maximum surface area possible for high affinity and specificity in target recognition. Binding site residues were chosen using a new distributed evolutionary algorithm implementation in protCAD. Both designs detect VX at parts per billion concentrations with high specificity. Computational design of fully buried molecular recognition sites, in combination with supercharged phase-changing chassis proteins, enables the ready development of a new generation of small-molecule biosensors.

EGFR and COX-2 Dual Inhibitor: The Design, Synthesis, and Biological Evaluation of Novel Chalcones

For most researchers, discovering new anticancer drugs to avoid the adverse effects of current ones, to improve therapeutic benefits and to reduce resistance is essential. Because the COX-2 enzyme plays an important role in various types of cancer leading to malignancy enhancement, inhibition of apoptosis, and tumor-cell metastasis, an indispensable objective is to design new scaffolds or drugs that possess combined action or dual effect, such as kinase and COX-2 inhibition. The start compounds A1 to A6 were prepared through the diazo coupling of 3-aminoacetophenone with a corresponding phenol and then condensed with two new chalcone series, C7–18. The newly synthesized compounds were assessed against both COX-2 and epidermal growth factor receptor (EGFR) for their inhibitory effect. All novel compounds were screened for cytotoxicity against five cancer cell lines. Compounds C9 and G10 exhibited potent EGFR inhibition with IC₅₀ values of 0.8 and 1.1 µM, respectively. Additionally, they also displayed great COX-2 inhibition with IC₅₀ values of 1.27 and 1.88 µM, respectively. Furthermore, the target compounds were assessed for their cytotoxicity against pancreatic ductal cancer (Panc-1), lung cancer (H-460), human colon cancer (HT-29), human malignant melanoma (A375) and pancreatic cancer (PaCa-2) cell lines. Interestingly, compounds C10 and G12 exhibited the strongest cytotoxic effect against PaCa-2 with average IC₅₀ values of 0.9 and 0.8 µM, respectively. To understand the possible binding modes of the compounds under investigation with the receptor cites of EGFR and COX-2, a virtual docking study was conducted.

Novel Phenolic Compounds as Potential Dual EGFR and COX-2 Inhibitors: Design, Semisynthesis, in vitro Biological Evaluation and in silico Insights

Introduction

Epidermal growth factor receptor (EGFR) inhibition is an imperative therapeutic approach targeting various types of cancer including colorectal, lung, breast, and pancreatic cancer types. Moreover, cyclooxygenase-2 (COX-2) is frequently overexpressed in different types of cancers and has a role in the promotion of malignancy, apoptosis inhibition, and metastasis of tumor cells. Combination therapy has been emerged to improve the therapeutic benefit against cancer and curb intrinsic and acquired resistance.

Methods

Three semi-synthetic series of compounds (C1-4, P1-4, and G1-4) were prepared and evaluated biologically as potential dual epidermal growth factor receptor (EGFR) and COX-2 inhibitors. The main phenolic constituents of Amaranthus spinosus L. (p-coumaric, caffeic and gallic) acids have been isolated and subsequently subjected to diazo coupling with various amines to get novel three chemical scaffolds with potential anticancer activities.

Results

Compounds C4 and G4 showed superior inhibitory activity against EGFR (IC₅₀: 0.9 and 0.5 µM, respectively) and displayed good COX-2 inhibition (IC₅₀: 4.35 and 2.47 µM, respectively). Moreover, the final compounds were further evaluated for their cytotoxic activity against human colon cancer (HT-29), pancreatic cancer (PaCa-2), human malignant melanoma (A375), lung cancer (H-460), and pancreatic ductal cancer (Panc-1) cell lines. Interestingly, compounds C4 and G4 exhibited the highest cytotoxic activity with average IC₅₀ values of 1.5 µM and 2.8 µM against H-460 and Panc-1, respectively. The virtual docking study was conducted to gain proper understandings of the plausible-binding modes of target compounds within EGFR and COX-2 binding sites.

Discussion

The NMR of prepared compounds showed characteristic peaks that confirmed the structure of the target compounds. The synthesized benzoxazolyl scaffold containing compounds showed inhibitory activities for both COXs and EGFR which are consistent with the virtual docking study.

Cholinesterases and Engineered Mutants for the Detection of Organophosphorus Pesticide Residues

Nowadays, pesticide residues constitute an increasing public health concern. Cholinesterases, acetylcholinesterase, and butyrylcholinesterase, are reported to be involved in detoxification processes owing to their capability of scavenging organophosphates and carbamates. Thus, these enzymes are targeted for the discovery of sensors aiming at detecting pesticide residues. In recent years, cholinesterase-based biosensors have attracted more and more attention in the detection of pesticides. Herein, this review describes the recent progress on the engineering of cholinesterases and the development of the corresponding sensors that could be used for the detection of organophosphorus pesticide residues.

Oximes: inhibitors of human recombinant acetylcholinesterase. A structure-activity relationship (SAR) study

Acetylcholinesterase (AChE) reactivators were developed for the treatment of organophosphate intoxication. Standard care involves the use of anticonvulsants (e.g., diazepam), parasympatolytics (e.g., atropine) and oximes that restore AChE activity. However, oximes also bind to the active site of AChE, simultaneously acting as reversible inhibitors. The goal of the present study is to determine how oxime structure influences the inhibition of human recombinant AChE (hrAChE). Therefore, 24 structurally different oximes were tested and the results compared to the previous eel AChE (EeAChE) experiments. Structural factors that were tested included the number of pyridinium rings, the length and structural features of the linker, and the number and position of the oxime group on the pyridinium ring.

Assessment of acetylcholinesterase activity using indoxylacetate and comparison with the standard Ellman's method

Assay of acetylcholinesterase (AChE) activity plays an important role in diagnostic, detection of pesticides and nerve agents, in vitro characterization of toxins and drugs including potential treatments for Alzheimer’s disease. These experiments were done in order to determine whether indoxylacetate could be an adequate chromogenic reactant for AChE assay evaluation. Moreover, the results were compared to the standard Ellman’s method. We calculated Michaelis constant Km (2.06 × 10⁻⁴ mol/L for acetylthiocholine and 3.21 × 10⁻³ mol/L for indoxylacetate) maximum reaction velocity V_max (4.97 × 10⁻⁷ kat for acetylcholine and 7.71 × 10⁻⁸ kat for indoxylacetate) for electric eel AChE. In a second part, inhibition values were plotted for paraoxon, and reactivation efficacy was measured for some standard oxime reactivators: obidoxime, pralidoxime (2-PAM) and HI-6. Though indoxylacetate is split with lower turnover rate, this compound appears as a very attractive reactant since it does not show any chemical reactivity with oxime antidots and thiol used for the Ellman’s method. Thus it can be advantageously used for accurate measurement of AChE activity. Suitability of assay for butyrylcholinesterase activity assessment is also discussed.

Preparation and in vitro screening of symmetrical bis-isoquinolinium cholinesterase inhibitors bearing various connecting linkage--implications for early Myasthenia gravis treatment

Inhibitors of acetylcholinesterase are compounds widely used in the treatment of various diseases, such as Alzheimer's disease, glaucoma and Myasthenia gravis (MG). Compounds used in the therapy of MG posses a positive charge in the molecule to ensure peripheral effect of action and minimal blood-brain barrier penetration. The most prescribed carbamate inhibitors are however known for many severe side effects related to the carbamylation of AChE. This paper describes preparation and in vitro evaluation of 20 newly prepared bis-isoquinolinium inhibitors of potential concern for MG. The newly prepared compounds were evaluated in vitro on human recombinant AChE and human plasmatic butyrylcholinesterase (BChE). Their inhibitory ability was expressed as IC50 and compared to chosen standards ambenonium dichloride, edrophonium chloride, BW284c51 and ethopropazine hydrochloride. Three novel compounds presented promising inhibition (in nM range) of both enzymes in vitro better or similar to edrophonium and BW284c51, but worse to ambenonium. The novel inhibitors did not present higher selectivity toward AChE or BChE. The kinetic assay confirmed non-competitive inhibition of hAChE by two selected promising novel compounds. Two newly prepared compounds were also chosen for docking studies that confirmed apparent π-π or π-cationic interactions aside the cholinesterases catalytic sites. The SAR findings were discussed.

Preparation, in vitro screening and molecular modelling of symmetrical 4-tert-butylpyridinium cholinesterase inhibitors--analogues of SAD-128

Carbamate inhibitors (e.g., pyridostimine bromide) are used as a pre-exposure treatment for the prevention of organophosphorus poisoning. They work by blocking acetylcholinesterase's (AChE) native function and thus protect AChE against irreversible inhibition by organophosphorus compounds. However, carbamate inhibitors are known for many undesirable side-effects related to the carbamylation of AChE. In this Letter, 19 analogues of SAD-128 were prepared and evaluated as cholinesterase inhibitors. The screening results showed promising inhibitory ability of four compounds better to used standards (pralidoxime, obidoxime, BW284c51, ethopropazine, SAD-128). Four most promising compounds were selected for further molecular docking studies. The SAR was stated from obtained data. The former receptor studies were reported and discussed. The further in vivo studies were recommended in the view of OP pre-exposure treatment.

Preparation and in vitro screening of symmetrical bispyridinium cholinesterase inhibitors bearing different connecting linkage-initial study for Myasthenia gravis implications

Reversible inhibitors (e.g., pyridostigmine bromide, neostigmine bromide) of carbamate origin are used in the early treatment of Myasthenia gravis (MG) to block acetylcholinesterase (AChE) native function and conserve efficient amount of acetylcholine for decreasing number of nicotinic receptors. Carbamate inhibitors are known for many undesirable side effects related to the reversible inhibition of AChE. In contrast, this paper describes 20 newly prepared bispyridinium inhibitors of potential concern for MG. Although some compounds from this series have been known before, they were not assayed for cholinesterase inhibition yet. The newly prepared compounds were evaluated in vitro on human erythrocyte AChE and human plasmatic butyrylcholinesterase (BChE). Their inhibitory ability was expressed as IC(50) and compared to standard carbamate drugs. Three compounds presented promising inhibition (in muM range) of both enzymes in vitro similar to the used standards. The novel inhibitors did not present selectivity between AChE and BChE. Two newly prepared compounds were chosen for docking studies and confirmed apparent pi-pi or pi-cationic interactions aside enzyme's catalytic sites. The kinetics assay confirmed non-competitive inhibition of AChE by two best newly prepared compounds.

Variation of cholinesterase-based biosensor sensitivity to inhibition by organophosphate due to ionizing radiation

A cholinesterase based biosensor was constructed in order to assess the effects of ionizing radiation on exposed AChE. Although the primary objective of the experiment was to investigate the effect of ionizing radiation on the activity of the biosensor, no changes in cholinesterase activity were observed. Current provided by oxidation of thiocholine previously created from acetylthiocholine by enzyme catalyzed reaction was in a range 395-455 nA. No significant influence of radiation on AChE activity was found, despite the current variation. However, a surprising phenomenon was observed when a model organophosphate paraoxon was assayed. Irradiated biosensors seem to be more susceptible to the inhibitory effects of paraoxon. Control biosensors provided a 94 ± 5 nA current after exposure to 1 ppm paraoxon. The biosensors irradiated by a 5 kGy radiation dose and exposed to paraoxon provided a current of 49 ± 6 nA. Irradiation by doses ranging from 5 mGy to 100 kGy were investigated and the mentioned effect was confirmed at doses above 50 Gy. After the first promising experiments, biosensors irradiated by 5 kGy were used for calibration on paraoxon and compared with the control biosensors. Limits of detection 2.5 and 3.8 ppb were achieved for irradiated and non-irradiated biosensors respectively. The overall impact of this effect is discussed.

Evaluation of cholinesterase activities during in vivo intoxication using an electrochemical sensor strip - correlation with intoxication symptoms

Cholinesterase activity in blood of laboratory rats was monitored. Rats were intoxicated with paraoxon at dosis of 0 - 65 - 125 - 170 - 250 - 500 nmol. The 250 nmol dose was found to be the LD(50). An electrochemical sensor was found useful to provide information about cholinesterase activity. The decrease of cholinesterase activity was correlated to intoxication symptoms and mortality level. It was found that the symptoms of intoxication are not observed while at least 50% of cholinesterase activity in blood remains. The minimal cholinesterase activity essential to survival is around 10%, when compared with the initial state. No changes in levels of low moleculary weight antioxidants were observed.