Mode Of Action Classes Research Articles

Grouping of chemicals into mode of action classes by automated effect pattern analysis using the zebrafish embryo toxicity test

A central element of high throughput screens for chemical effect assessment using zebrafish is the assessment and quantification of phenotypic changes. By application of an automated and more unbiased analysis of these changes using image analysis, patterns of phenotypes may be associated with the mode of action (MoA) of the exposure chemical. The aim of our study was to explore to what extent compounds can be grouped according to their anticipated toxicological or pharmacological mode of action using an automated quantitative multi-endpoint zebrafish test. Chemical-response signatures for 30 endpoints, covering phenotypic and functional features, were generated for 25 chemicals assigned to 8 broad MoA classes. Unsupervised clustering of the profiling data demonstrated that chemicals were partially grouped by their main MoA. Analysis with a supervised clustering technique such as a partial least squares discriminant analysis (PLS-DA) allowed to identify markers with a strong potential to discriminate between MoAs such as mandibular arch malformation observed for compounds interfering with retinoic acid signaling. The capacity for discriminating MoAs was also benchmarked to an available battery of in vitro toxicity data obtained from ToxCast library indicating a partially similar performance. Further, we discussed to which extent the collected dataset indicated indeed differences for compounds with presumably similar MoA or whether other factors such as toxicokinetic differences could have an important impact on the determined response patterns.

Machine-learning assisted antibiotic detection and categorization using a bacterial sensor array

With the extensive global use of antibiotics, the problems associated with environmental and food antibiotic residues have significantly increased, necessitating new methods for rapid detection and categorization of compounds with antibiotic activity. In an answer to this need, we report a new platform, bacterial array solid-phase assay (BacSPA), based on monitoring the responses of 15 stress-responsive Escherichia coli sensor strains. These bioreporters, genetically modified by fusing bioluminescence (luxCDABE) reporter genes upstream of stress-induced gene promoters, were inoculated on solidified agar slabs individually mixed with 11 different antibiotics, belonging to 7 mode of action classes. The antibiotic-induced bioluminescence by the different strains generated a distinct response pattern for each antibiotic class. This luminescence pattern was monitored by time-lapse photography, and a machine learning algorithm, Multiclass Decision Forest, was applied to train categorization models that either identified the compound or categorized its class. The best model displayed a 65% accuracy for compound identification and 90% for class classification, within three hours of exposing the sensor array to the tested compound. The method also effectively categorized antibiotics at different concentrations: the trained model categorized eight antibiotics at concentrations ranging from 125 ppb to 1000 ppb, with accuracies mostly higher than 70%. The method was further successfully applied for categorizing antibiotics not included in the training. With a more extensive future database, encompassing a broader range of existing antibiotics, this method may be turned into a powerful tool for detecting and categorizing both known and new antibiotic residues in food or environmental samples.

A four-year survey on insecticide resistance and likelihood of chemical control failure for tomato leaf miner Tuta absoluta in the European/Asian region

Tuta absoluta is an invasive destructive pest that is currently posing a major threat for tomato production worldwide. Insecticides are a key component of typical pest management schemes. Resistance to diamides, the most recently introduced class of insecticides, was recently reported in Italy. Monitoring of insecticide efficacy is the basic tool for proactive evidence-based resistance management. Here, we report the findings of a 4-year survey performed at the Euro-Asian region. A total of 35 populations were collected between 2012 and 2016 from Greece, Italy, Spain, Israel and UK. The response of these populations was evaluated through laboratory bioassays with the main insecticides used for T. absoluta control: chlorantraniliprole, indoxacarb, emamectin benzoate and spinosad. Analysis of the results indicated six cases of low/moderate resistance to the emamectin benzoate (resistance ratio (RR) > 15-fold), a single case of resistance to spinosad (RR: 33-fold) and five cases of resistance to indoxacarb (RR: 13- to 91-fold). Likelihood of control failure was detected for indoxacarb, but reports of poor field performance were absent. Resistance to chlorantraniliprole, after 2015, was widespread in Italy and Greece with high RR (>64-fold) and significant likelihood of control failure in most cases. Chlorantraniliprole resistance was also detected in Israel (RR: 22,573-fold) but not in Spain and UK (RR < twofold). The absence of diamide resistance in tomato leaf miner populations in Spain is most likely linked to a recently established integrated pest management program including non-chemical measures and the rotational use of insecticides of different mode of action classes.

Evaluation of Commercial Agrochemicals as New Tools for Malaria Vector Control.

Malaria is a vector-borne and life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. The vector control insecticide market represents a small fraction of the crop protection market and is estimated to be valued at up to $500 million at the active ingredient level. Insecticide resistance towards the current WHOPES-approved products urgently requires the development of new tools to protect communities against the transmission of malaria. The evaluation of commercial products for malaria vector control is a viable and cost effective strategy to identify new malaria vector control products. Several examples of such spin-offs from crop protection insecticides are already evidencing the success of this strategy, namely pirimiphos-methyl for indoor residual sprays and spinosad, diflubenzuron, novaluron, and pyriproxifen for mosquito larvae control, a supplementary technology for control of malaria vectors. In our study the adulticidal activities of 81 insecticides representing 23 insecticidal modes of action classes, 34 fungicides from 6 fungicidal mode of action classes and 15 herbicides from 2 herbicidal modes of action classes were tested in a newly developed screening system. WHOPES approved insecticides for malaria vector control consistently caused 80-100% mortality of adult Anopheles stephensi at application rates between 0.2 and 20 mg active ingradient (AI) litre-1. Chlorfenapyr, fipronil, carbosulfan and endosulfan showed the expected good activity. Four new insecticides and three fungicides with promising activity against adult mosquitoes were identified, namely the insecticides acetamiprid, thiamethoxam, thiocyclam and metaflumizone and the fungicides diflumetorin, picoxystrobin, and fluazinam. Some of these compounds certainly deserve to be further evaluated for malaria vector control. This is the first report describing good activity of commercial fungicides against malaria vectors.

Proposal for a unified nomenclature for target-site mutations associated with resistance to fungicides.

Evolved resistance to fungicides is a major problem limiting our ability to control agricultural, medical and veterinary pathogens and is frequently associated with substitutions in the amino acid sequence of the target protein. The convention for describing amino acid substitutions is to cite the wild‐type amino acid, the codon number and the new amino acid, using the one‐letter amino acid code. It has frequently been observed that orthologous amino acid mutations have been selected in different species by fungicides from the same mode of action class, but the amino acids have different numbers. These differences in numbering arise from the different lengths of the proteins in each species. The purpose of the present paper is to propose a system for unifying the labelling of amino acids in fungicide target proteins. To do this we have produced alignments between fungicide target proteins of relevant species fitted to a well‐studied ‘archetype’ species. Orthologous amino acids in all species are then assigned numerical ‘labels’ based on the position of the amino acid in the archetype protein. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Resistance Management for San Jose Scale (Hemiptera: Diaspididae).

The San Jose scale Diaspidiotus perniciosus Comstock is one of the most important pests of deciduous fruit trees. The major cause of recent outbreaks in apple orchards is thought to be the development of insecticide resistance, specifically organophosphates. The first report was given in North America, and now, in Chile. In the present study, San Jose scale populations collected from two central regions of Chile were checked for their susceptibility to different mode of action insecticides in order to establish alternatives to manage this pest. No evidence of cross resistance between organophosphates insecticides and acetamiprid, buprofezin, pyriproxyfen, spirotetramat, sulfoxaflor, or thiacloprid was found. Baselines of LC50-LC95 for different life stages of San Jose scale are given, as reference to future studies of resistance monitoring. The systemic activity of acetamiprid, spirotetramat, and thiacloprid was higher than the contact residue effect of these compounds. For sulfoxaflor, both values were similar. Program treatments including one or more of these compounds are compared in efficacy and impact on resistance ratio values. In order to preserve new insecticides as an important tool to control San Jose scale, resistance management programs should be implemented, considering insecticide mode of action classes alternated or mixed.

Development of risk-based nanomaterial groups for occupational exposure control.

Given the almost limitless variety of nanomaterials, it will be virtually impossible to assess the possible occupational health hazard of each nanomaterial individually. The development of science-based hazard and risk categories for nanomaterials is needed for decision-making about exposure control practices in the workplace. A possible strategy would be to select representative (benchmark) materials from various mode of action (MOA) classes, evaluate the hazard and develop risk estimates, and then apply a systematic comparison of new nanomaterials with the benchmark materials in the same MOA class. Poorly soluble particles are used here as an example to illustrate quantitative risk assessment methods for possible benchmark particles and occupational exposure control groups, given mode of action and relative toxicity. Linking such benchmark particles to specific exposure control bands would facilitate the translation of health hazard and quantitative risk information to the development of effective exposure control practices in the workplace. A key challenge is obtaining sufficient dose-response data, based on standard testing, to systematically evaluate the nanomaterials' physical-chemical factors influencing their biological activity. Categorization processes involve both science-based analyses and default assumptions in the absence of substance-specific information. Utilizing data and information from related materials may facilitate initial determinations of exposure control systems for nanomaterials.

INTEGRATED APPROACHES TO POSTHARVEST DISEASE MANAGEMENT IN CALIFORNIA CITRUS PACKINGHOUSES

INTEGRATED APPROACHES TO POSTHARVEST DISEASE MANAGEMENT IN CALIFORNIA CITRUS PACKINGHOUSES

Application of a multiple endpoint bacterial reporter assay to evaluate toxicological relevant endpoints of perfluorinated compounds with different functional groups and varying chain length

Perfluorinated compounds are widely distributed in the environment; good knowledge about the toxic mode of action of these compounds can contribute to improved molecular design and risk assessment. The studied compounds were evaluated with a bacterial multiple endpoint reporter assay for responses in four different mode of action classes (oxidative damage, DNA damage, general cell lesions and membrane damage). The results of our study clearly demonstrate that inductions of stress responsive genes occur for the different compounds and confirm some of the known mechanisms of work for well studied compounds like PFOA and PFOS, and in addition provide new information for less studied compounds. Few inductions were observed after exposure to the low carbon number carboxylic acids, PFBtA (CF 3(CF 2) 2C(O)O −), PFPtA (CF 3(CF 2) 3C(O)O −), PFHxA (CF 3(CF 2) 4C(O)O −) and PFHpA (CF 3(CF 2) 5C(O)O −) at equimolar concentrations (0.0156–1 mM). The induction of membrane damage markers ( MicF and OsmY) is prominently present after exposure to PFOS (CF 3(CF 2) 7 SO 3 - ) and even more after exposure to PFNA (CF 3(CF 2) 7C(O)O −). This is the first report describing the mode of action of carboxylic acids with 11 and 12 carbon atoms; they are equally potent inducers relative to PFOS and PFNA. Overall, the effects seen at the level of gene expression were higher for the sulfonic acids than for the carboxylic acids, but the effect of the chain length is more important than the effect of the functional group.

Control of Postharvest Gray Mold of Table Grapes in the San Joaquin Valley of California by Fungicides Applied During the Growing Season

Fungicides applied before harvest were evaluated to control postharvest gray mold of table grapes, caused by Botrytis cinerea. The concentrations of thiophanate methyl (THM), iprodione (IPR), cyprodinil (CYP), pyraclostrobin + boscalid (PS+BO), pyrimethanil (PYR), or fenhexamid (FEN) that inhibited the growth of four isolates sensitive to these fungicides by 50% (EC50) were 12.4, 2.5, 0.61, 0.29/0.57, 0.26, or 0.17 mg liter-1, respectively. THM, IPR, CYP, PS+BO, PYR, or FEN were applied to detached 'Thompson Seedless' berries at the equivalent of the maximum approved rates of 600, 500, 270, 59/116, 370, or 290 mg liter-1, respectively, except PS+BO, which were used at 54.2% of their current registered maximum rates. The berries were inoculated with B. cinerea 48 or 24 h before treatment or 24 or 48 h after treatment. Gray mold 2 weeks after treatment and storage at 15°C was lowest after FEN application, followed by PYR, CYP, IPR, PS+BO, and THM. In commercial vineyards, one application of FEN, PYR, CYP, or PS+BO, all at their current maximum approved rates, 2 weeks before harvest reduced postharvest gray mold by approximately 50%. When fungicides were applied repeatedly after berry set either in mixtures or alternated with fungicides of different mode of action classes, postharvest gray mold was reduced by about 50% using a commercial air-blast sprayer and by 70 to 87% using a hand-held sprayer that was directed into the clusters. The fungicide sensitivity of isolates collected in numerous vineyards indicated those with reduced sensitivity to all of the tested fungicides, except FEN, were common. The efficacy of preharvest fungicide regimes was not sufficient to replace postharvest sulfur dioxide fumigation.

Discriminating Toxicant Classes by Mode of Action - 1. (Eco)toxicity Profiles

Predictive toxicology, particularly quantitative structure-activity relationships (QSARs), require classification of chemicals by mode of action (MOA). MOA is, however, not a constant property of a compound but it varies between species and may change with concentration and duration of exposure. A battery of MOA-specific in-vitro and low-complexity assays, featuring biomolecular targets for major classes of environmental pollutants, provides characteristic responses for (1.) classification of chemicals by MOA, (2.) identification of (eco)toxicity profiles of chemicals, (3.) identification of chemicals with specific MOAs, (4.) indication of most sensitive species, (5.) identification of chemicals that are outliers in QSARs and (6.) selection of appropriate QSARs for predictions. Chemicals covering nine distinct modes of toxic action (non-polar non-specific toxicants (n=14), polar non-specific toxicants (n=18), uncouplers of oxidative phosphorylation (n=25), inhibitors of photosynthesis (n=15), inhibitors of acetylcholinesterase (n=14), inhibitors of respiration (n=3), thiol-alkylating agents (n=9), reactives (irritants) (n=8), estrogen receptor agonists (n=9)) were tested for cytotoxicity in the neutralred assay, oxygen consumption in isolated mitochondria, oxygen production in algae, inhibition of AChE, reaction with GSH and activity in the yeast estrogen receptor assay. Data on in-vivo aquatic toxicity (LC50, EC50) towards fish, daphnids, algae and bacteria were collected from the literature for reasons of comparison and reference scaling. In the MOA-specific in-vitro test battery, most test chemicals are specifically active at low concentrations, though multiple effects do occur. Graphical and statistical evaluation of the individual classes versus MOA 1 (non-polar non-specific toxicants) identifies interactions related to predominant MOA. Discriminant analyses (DA) on subsets of the data revealed correct classifications between 70% (in-vivo data) and >90% (in-vitro data). Functional similarity of chemical substances is defined in terms of their (eco)toxicity profiles. Within each MOA class, the compounds share some properties related to the rate-limiting interactions, e.g., steric fit to the target site and/or reactivity with target biomolecules, revealing a specific pattern (fingerprint) of characteristic effects. The successful discrimination of toxicant classes by MOA is based on comprehensive characterization of test chemicals' properties related to interactions with target sites. The suite of aquatic in-vivo tests using fish, daphnids, algae and bacteria covers most acute effects, whilst long-term (latent) impacts are generally neglected. With the MOA-specific in-vitro test battery such distinctions are futile, because it focuses on isolated targets, i.e. it indicates the possible targets of a chemical regardless of the timescale of effects. The data analysis indicates that the in-vitro battery covers most effects in vivo and moreover provides additional aspects of the compounds' MOA. Translating in-vitro effects to in-vivo toxicity requires combining physiological and chemical knowledge about underlying processes. Comparison of the specific in-vitro effects of a compound with the respective sensitivities of aquatic organisms indicates particularly sensitive species. Classifications of toxicants by MOA based on physicochemical descriptors provides insight to interactions and directs to mechanistic QSARs.

Structure and activity of avermectins and milbemycins in animal health

The avermectins and, to a lesser extent, the milbemycins, have revolutionized antiparasitic and antipest control over the last decade. Both avermectins and milbemycins have macrocyclic lactone structures that are superimposable, they are produced by the same genus of soil dwelling organisms, they have the same mode of action, they exert this action against the same e namatode/acarine/insect spectrum of targets, and they show the same mechanism-based toxicity in mammals. Reports suggesting that milbemycins have a different mode of action from avermectins with implications that there will be no mutual resistance to the groups have been shown to be false. Contributing to the belief that there were differences in mode of action between the two groups are the vague definitions of resistance presently in use which rely on the ability of the parasite to survive treatment at the manufacturer's recommended use level. More appropriately, drug resistance should be defined as ‘a change in gene frequency of a population, produced by drug selection, which renders the minimal, effective dosage previously used to kill a defined portion (e.g. 95%) of the population no longer equally effective’. This type of definition would allow us to detect changes in susceptibility of a population earlier and is essential when comparing different chemicals to determine if there is mutual resistance to them. It is concluded that much effort has been expended by pharmaceutical, government, and academic scientists searching for broad-spectrum second generation avermectin and milbemycin products, but none has exceeded the original avermectin in any fundamental way. The newer avermectin and milbemycin compounds that have appeared claim niches in the market place based on emphasis of certain narrow parts of the overall spectrum. Consequently, there are no second generation avermectins and milbemycins at present and all newer compounds from this mode of action class are viewed as siblings of the first generation.