Discovery of Trifluorobutene Amide Derivatives as Potential Nematicides: Design, Synthesis, Nematicidal Activity Evaluation, SAR, and Mode of Action Study

Plant-parasitic nematodes are one of the major threats to crop protection. However, only limited nematicides are currently available and are confronted with a growing resistance problem, which necessitates the development of novel nematicides. In this study, a series of trifluorobutene amide derivatives was synthesized through the strategy of amide bond reversal, and their nematicidal activity against Meloidogyne incognita was evaluated. The bioassay showed that compounds C2, C10, and C18 and some analogues thereof exhibited good nematicidal activity. Among them, the derivatives of compound C2 containing a benzene ring [C26 (R = 2-CH3) and C33 (R = 2-Cl)] exhibited excellent bioactivity against M. incognita in vitro. The LC50/72h values reached 14.13 and 14.71 mg·L-1, respectively. Moreover, analogues of compounds C10 and C18 containing a thiophene ring [C43 (R = 5-CH3), C44 (R = 4-CH3), and C50 (R = 5-Cl)] exhibited significant bioactivity against M. incognita in vivo with inhibition rates of 68.8, 65.5, and 69.8% at 2.5 mg·L-1 in a matrix, respectively. Meanwhile, C44 and C50 also showed excellent control effects against M. incognita in both cups and microplots. The structure-activity relationship (SAR) of synthesized compounds was discussed in detail. Comparative molecular field analysis (CoMFA) was also conducted to develop the SAR profile. The preliminary mode of action investigation showed that compound C33 exhibited strong inhibition on egg hatching, motility, feeding behavior, and growth of Caenorhabditis elegans. At the same time, the impact of active compounds on biochemical indicators related to oxidative stress showed that compound C33 influenced the production of ROS (reactive oxygen species), and the accumulation of lipofuscin and lipids on C. elegans.

Increased Cell Proliferation as a Key Event in Chemical Carcinogenesis: Application in an Integrated Approach for the Testing and Assessment of Non-Genotoxic Carcinogenesis

In contrast to genotoxic carcinogens, there are currently no internationally agreed upon regulatory tools for identifying non-genotoxic carcinogens of human relevance. The rodent cancer bioassay is only used in certain regulatory sectors and is criticized for its limited predictive power for human cancer risk. Cancer is due to genetic errors occurring in single cells. The risk of cancer is higher when there is an increase in the number of errors per replication (genotoxic agents) or in the number of replications (cell proliferation-inducing agents). The default regulatory approach for genotoxic agents whereby no threshold is set is reasonably conservative. However, non-genotoxic carcinogens cannot be regulated in the same way since increased cell proliferation has a clear threshold. An integrated approach for the testing and assessment (IATA) of non-genotoxic carcinogens is under development at the OECD, considering learnings from the regulatory assessment of data-rich substances such as agrochemicals. The aim is to achieve an endorsed IATA that predicts human cancer better than the rodent cancer bioassay, using methodologies that equally or better protect human health and are superior from the view of animal welfare/efficiency. This paper describes the technical opportunities available to assess cell proliferation as the central gateway of an IATA for non-genotoxic carcinogenicity.

Evaluation of the human hazard of the liver and lung tumors in mice treated with permethrin based on mode of action

The non-genotoxic synthetic pyrethroid insecticide permethrin produced hepatocellular adenomas and bronchiolo-alveolar adenomas in female CD-1 mice, but not in male CD-1 mice or in female or male Wistar rats. Studies were performed to evaluate possible modes of action (MOAs) for permethrin-induced female CD-1 mouse liver and lung tumor formation. The MOA for liver tumor formation by permethrin involves activation of the peroxisome proliferator-activated receptor alpha (PPARα), increased hepatocellular proliferation, development of altered hepatic foci, and ultimately liver tumors. This MOA is similar to that established for other PPARα activators and is considered to be qualitatively not plausible for humans. The MOA for lung tumor formation by permethrin involves interaction with Club cells, followed by a mitogenic effect resulting in Club cell proliferation, with prolonged administration producing Club cell hyperplasia and subsequently formation of bronchiolo-alveolar adenomas. Although the possibility that permethrin exposure may potentially result in enhancement of Club cell proliferation in humans cannot be completely excluded, there is sufficient information on differences in basic lung anatomy, physiology, metabolism, and biologic behavior of tumors in the general literature to conclude that humans are quantitatively less sensitive to agents that increase Club cell proliferation and lead to tumor formation in mice. The evidence strongly indicates that Club cell mitogens are not likely to lead to increased susceptibility to lung tumor development in humans. Overall, based on MOA evaluation it is concluded that permethrin does not pose a tumorigenic hazard for humans, this conclusion being supported by negative data from permethrin epidemiological studies.

S-Glycosylation of Fluensulfone in Tomatoes: An Important Way of Fluensulfone Metabolism

Fluensulfone (FSF) becomes increasingly popular because of its nonfumigation application method. However, studies on the metabolic mechanism of FSF in plants are lacking. Here, tomato seedling was cultivated in hydroponic media to investigate the connection among FSF's metabolism in tomato, the regulation of tomato endogenous glycosides, and the elimination of hydrogen peroxide in tomato cells. The accumulation of FSF was only detected in the lower stems of tomatoes; FSF was mainly metabolized into S-glycosylated conjugates in the roots, and the roots were the tissues with the highest metabolite content; and no FSF and metabolites were detected in the upper leaves. In response to FSF stress (2 mg/L for 7 d), the content of sugar and glycosides in the stems of tomato seedlings significantly increased. The amount of some compounds on the pathway related to glucose was affected by FSF. The three precursor compounds (homomethioine, isoleucine, and l-tyrosine) in the pathway of glucosinolate biosynthesis increased significantly under the stress of FSF, which indicates that FSF may compete with them for UGT74B1. Besides, FSF-induced flavonoid glycosides may play a role in the process of removing hydrogen peroxide. This research provides inspiration for the fate of many xenobiotics containing sulfonyl groups in plants.

Club Cells Are the Primary Target for Permethrin-Induced Mouse Lung Tumor Formation

Permethrin has been shown to increase lung adenomas in female CD-1 mice, but not in male mice or Wistar rats. The proposed mode of action (MOA) for permethrin-induced female mouse lung tumor formation involves morphological changes in Club cells; increased Club cell proliferation; increased Club cell hyperplasia, and lung tumor formation. In this study, the treatment of female CD-1 mice with tumorigenic doses (2500 and 5000 ppm) of permethrin, but not with a nontumorigenic dose (20 ppm), for 14 and/or 28 days increased Club cell replicative DNA synthesis. Global gene expression analysis of female mouse lung samples demonstrated that permethrin treatment up-regulated 3 genes associated with cell proliferation, namely aldehyde dehydrogenase 3a1 (Aldh3a1), oxidative stress-induced growth inhibitor 1, and thioredoxin reductase 1. Treatment with 2500 and 5000 ppm, but not 20 ppm, permethrin for 7 days produced significant increases in mRNA levels of these 3 genes. Immunohistochemical analysis demonstrated that Club cell secretory protein, CYP2F2, and ALDH3A1 colocalized in Club cells; confirmed by flow cytometry analysis of lung cells employing KI67 as a cell proliferation marker. Overall, the present data extend the proposed MOA by demonstrating that Club cells are the primary initial target of permethrin administration in female mouse lungs. As humans are quantitatively much less sensitive to agents that increase Club cell proliferation and lung tumor formation in mice, it is most likely that permethrin could not produce lung tumors in humans. This conclusion is supported by available negative epidemiological data from several studies.

Small Airway Susceptibility to Chemical and Particle Injury

Small airways (SA) in humans are commonly defined as those conducting airways <2 mm in diameter. They are susceptible to particle- and chemical-induced injury and play a major role in the development of airway disease such as COPD and asthma. Susceptibility to injury can be attributed in part to structural features including airflow dynamics and tissue architecture, but recent evidence may indicate a more prominent role for cellular composition in directing toxicological responses. Animal studies support the hypothesis that inherent cellular differences across the tracheobronchial tree, including metabolic CYP450 expression in the distal conducting airways, can influence SA susceptibility to injury. Currently, there is insufficient information in humans to make similar conclusions, prompting further necessary work in this area. An understanding of why the SA are more susceptible to certain chemical and particle exposures than other airway regions is fundamental to our ability to identify hazardous materials, their properties, and accompanying exposure scenarios that compromise lung function. It is also important for the ability to develop appropriate models for toxicity testing. Moreover, it is central to our understanding of SA disease aetiology and how interventional strategies for treatment may be developed. In this review, we will document the structural and cellular airway regional differences that are likely to influence airway susceptibility to injury, including the role of secretory club cells. We will also describe recent advances in single-cell sequencing of human airways, which have provided unprecedented details of cell phenotype, likely to impact airway chemical and particle injury.

Relevance of mouse lung tumors to human risk assessment

Mouse lung is a common site for chemical tumorigenicity, but the relevance to human risk remains debated. Long-term bioassays need to be assessed for appropriateness of the dose, neither exceeding Maximum Tolerated Dose (MTD) nor Kinetically based Maximum Dose (KMD). An example of the KMD issue is 1,3-dichloropropene (1,3-D), which only produced an increased incidence of lung tumors at a dose exceeding the KMD. In addition, since mouse lung tumors are common (>1% incidence), the appropriate statistical significance is p < .01. Numerous differences exist for mouse lung and tumors compared to humans, including anatomy, respiratory rate, metabolism, tumor histogenesis, and metastatic frequency. The recent demonstration of the critical role of mouse lung specific Cyp2 F2 metabolism in mouse lung carcinogenicity including styrene or fluensulfone indicates that this tumor response is not qualitatively or quantitatively relevant to humans. For non-DNA reactive and non-mutagenic carcinogens, the mode of action involves direct mitogenicity such as for isoniazid, styrene, fluensulfone, permethrin or cytotoxicity with regeneration such as for naphthalene. However, the possibility of mixed mitogenic and cytotoxic modes of action cannot always be excluded. The numerous differences between mouse and human, combined with epidemiologic evidence of no increased cancer risk for several of these chemicals make the relevance of mouse lung tumors for human cancer risk dubious.

Cell proliferation analysis is a reliable predictor of lack of carcinogenicity: Case study using the pyrethroid imiprothrin on lung tumorigenesis in mice

In the mouse carcinogenicity study, an apparent increase in lung adenocarcinoma was observed in male mice at 7000 ppm. Based on the overall evaluation of toxicology, oncology, pathology and statistics, we concluded that the apparent increase in lung tumors is not relevant for evaluation of carcinogenicity of imiprothrin (Regul Toxicol Pharmacol, 105, 1-14, 2019). To investigate whether imiprothrin has any mitogenic effect on mouse Club cells, the present study examined its effects on replicative DNA synthesis of Club cells and lung histopathology in male mice treated with imiprothrin for 7 days at 3500 and 7000 ppm in the diet. Isoniazid, a known mouse lung mitogen and tumor inducer, was also examined at 1000 ppm in the diet as a positive control of Club cell mitogenesis and morphological changes. Neither imiprothrin nor isoniazid caused any necrotic changes in lung by light or electron microscopy. There were no increases observed in the bromodeoxyuridine (BrdU) labeling index in the imiprothrin groups, while there was a statistically significant increase in the BrdU labeling index in the isoniazid group. These findings demonstrate that imiprothrin does not induce mouse Club cell proliferation or morphologic changes, supporting our previous conclusion described above. Thus, imiprothrin should not be classified as a carcinogen. Furthermore, this study indicates that short-term studies focusing on cell proliferation can be reliable for predicting a lack of carcinogenic potential of test chemicals.

Development of a Novel AOP for Cyp2F2-Mediated Lung Cancer in Mice

Traditional methods for carcinogenicity testing rely heavily on the rodent bioassay as the standard for identification of tumorigenic risk. As such, identification of species-specific outcomes and/or metabolism are a frequent argument for regulatory exemption. One example is the association of tumor formation in the mouse lung after exposure to Cyp2F2 ligands. The adverse outcome pathway (AOP) framework offers a theoretical platform to address issues of species specificity that is consistent, transparent, and capable of integrating data from new approach methodologies as well as traditional data streams. A central premise of the AOP concept is that pathway progression from the molecular initiating event (MIE) implies a definable “response-response” (R-R) relationship between each key event (KE) that drives the pathway towards a specific adverse outcome (AO). This article describes an AOP for lung cancer in the mouse from an MIE of Cyp2F2-specific reactive metabolite formation, advancing through KE that include protein and/or nucleic acid adducts, diminished Club Cell 10 kDa (CC10) protein expression, hyperplasia of CC10 deficient Club cells, and culminating in the AO of mixed-cell tumor formation in the distal airways. This tumor formation is independent of route of exposure and our AOP construct is based on overlapping mechanistic events for naphthalene, styrene, ethyl benzene, isoniazid, and fluensulfone in the mouse. This AOP is intended to accelerate the explication of an apparent mouse-specific outcome and serve as a starting point for a quantitative analysis of mouse-human differences in susceptibility to the tumorigenic effects of Cyp2F2 ligands.

Scientific support for preparing an EU position in the 50th Session of the Codex Committee on Pesticide Residues (CCPR)

In accordance with Article 43 of Regulation (EC) 396/2005, EFSA received a request from the European Commission to provide support for the preparation of the EU position for 50th session of the Codex Committee on Pesticide Residues (CCPR). In 2017, Joint FAO/WHO Meeting on Pesticide Residues (JMPR) evaluated 15 active substances regarding the setting of toxicological reference values to be used in consumer risk assessment (bicyclopyrone, chlormequat, cyclaniliprole, fenazaquin, fenpropimorph, fenpyrazamine, fenpyroximate, fosetyl Al, isoprothiolane, natamycin, oxamyl, phosphonic acid, propylene oxide, thiophanate-methyl, triflumezopyrim) and 36 substances for deriving maximum residue limit (MRL) proposals (acetamiprid, azoxystrobin, bicyclopyrone, captan, chlormequat, cyclaniliprole, cyprodinil, 2,4-D, difenoconazole, fenazaquin, fenpropimorph, fenpyrazamine, fenpyroximate, flonicamid, fluensulfone, fluopyram, flupyradifurone, fosetyl Al, imazamox, imazapyr, imidacloprid, isoprothiolane, isopyrazam, natamycin, oxamyl, phosphonic acid, picoxystrobin, propiconazole, propylene oxide, prothioconazole, quinclorac, saflufenacil, spinetoram, tebuconazole, trifloxystrobin, triflumezopyrim); EFSA prepared comments on the Codex MRL proposals and the proposed toxicological reference values. In addition, EFSA provided the views on follow-up assessments of JMPR on pesticides where specific concerns were raised in the previous CCPR meetings. The current report should serve as the basis for deriving the EU position for the CCPR meeting, relevant findings are summarised in this report.