Insights into the synergistic mechanism of target resistance: A case study of N. lugens RDL-GABA receptors and fipronil

Novel Insecticidal Benzo[4,5]imidazo[1,2-b]pyrazole Derivatives Idenatified Through Ring-Closure Scaffold Hopping on Fipronil

A series of innovative benzo[4,5]imidazo[1,2-b]pyrazole scaffold containing compounds were rationally designed through a ring-closure scaffold hopping strategy and synthetized with an intermediate derivatization approach. Physicochemical properties analysis indicated the potential pesticide-likeness of the target compounds. The optimal target compound A14 showed relatively good insecticidal activity against P. xylostella, with an LC50 value of 37.58 mg/L, and demonstrated lower acute fish toxicity compared to fipronil. Docking binding mode analysis demonstrated that compound A14 bound to GABAR through a H-bond between the amide group and the residue of 6'Thr. The differences in binding modes between benzo[4,5]imidazo[1,2-b]pyrazole target compounds and fipronil may be a key factor for the reduced insecticidal activities. The elucidated binding mode and SAR profile lay a foundation for the further structural optimization of insecticidal benzo[4,5]imidazo[1,2-b]pyrazole derivatives.

Synthesis and biological evaluation of rationally designed pyrazoles as insecticidal agents

The current research focused on the synthesis of two series of pyrazole derivatives and evaluation of their insecticidal effectiveness. In the first series, seven pyrazole Schiff bases 3a-g were successfully synthesized with yields (79-95%) by condensing phenylfuran-2-carbaldehyde with substituted pyrazole rings. In the second series, eleven amino acid-pyrazole conjugates 6a-k were synthesized utilizing acetic acid, sulfuric acid, morpholine, and EDC. HCl achieving yields of 59% to 94%. The synthesized compounds were assessed for their chemotherapeutic efficacy against locusts and termites by calculating LC50 values, thereby determining their potential as anti-termite and anti-locust agents. Among the eighteen synthesized pyrazole compounds, the Schiff base pyrazole molecules 3f (LC50 = 0.001 μg/mL) and 3d (LC50 = 0.006 μg/mL) demonstrated excellent anti-termite activity compared to the reference drug fipronil (LC50 = 0.038 μg/mL). Pyrazole derivative 6 h with LC50 = 47.68 μg/mL exhibited superior anti-locust activity than the reference drug fipronil (LC50 = 63.09 μg/mL). Additionally, compound 3b, containing NO2 functionality at the meta position, exhibited notable and significant anti-locust activity with an LC50 values of 100.00 μg/mL. However, the highest mortality was caused by the glycine conjugate of fipronil 6 h of the 2nd series with an LC50 value of 47.68 μg/mL, which also proved to be a potent anti-locust agent. This study explores the efficacy of biologically active pyrazole structures as potential insecticidal agents through a combination of virtual molecular docking analysis and biological experimental investigations. The results demonstrate a strong correlation between the computational predictions and experimental outcomes, suggesting that the pyrazole derivatives exhibit significant insecticidal properties. The findings highlight the potential of these compounds in the development of innovative insecticides, paving the way for future research in pest control strategies.

Functional validation of A2'N mutation of the RDL GABA receptor against fipronil via molecular modeling and genome engineering in drosophila

BACKGROUND

Insect RDL (resistant to dieldrin) receptors are essential pentameric ligand-gated chloride channels that mediate the neuroinhibitory effect of GABA, the chief inhibitory neurotransmitter in the central nervous system. These receptors serve as primary targets for various insecticides, including noncompetitive antagonists (NCAs) such as cyclodiene organochlorines and phenylpyrazoles, as well as allosteric modulators like meta-diamides and isoxazolines. This study focuses on a newly discovered A2'N mutation within the RDL receptors, identified in fipronil-resistant planthoppers. Despite in vitro electrophysiological studies have proposed its role in conferring target-site resistance, in vivo genetic functional validation of this mutation remains unexplored.

RESULTS

Our research employed toxicity bioassays, assessing various Rdl genotypes against a spectrum of insecticides, including fipronil, α-endosulfan, broflanilide, and isocycloseram. Results revealed distinct resistance profiles for A2'N and A2'S mutants, indicating different binding interactions of RDL receptors with NCAs. Significantly, the A2'N heterozygote showed substantial resistance to fipronil, despite its homozygous lethality. Molecular modeling and docking simulations further supported these findings, highlighting unique binding poses for fipronil and α-endosulfan.

CONCLUSION

This study confirmed that A2'N mutation of the RDL GABA receptor confer high resistance to fipronil in vivo. The observed resistance in A2'N mutants is likely attributable to a steric hindrance mechanism, wherein the introduction of larger side chains hampers fipronil binding, even in a heterozygous state. © 2023 Society of Chemical Industry.

Immunoassays and Emerging Analytical Techniques of Fipronil and its Metabolites for Food Safety: A Review

Fipronil, classified as a phenylpyrazole insecticide, is utilized to control agricultural, public health, and veterinary pests. Notably, its unique ecological fate involves degradation to toxic metabolites, which poses the risk of contamination in water and foodstuffs and potential human exposure through the food chain. In response to these concerns, there is a pressing need to develop analytical methodologies for detecting fipronil and its metabolites. This review provides a concise overview of the mode of action, metabolism, and toxicology of fipronil. Additionally, various detection strategies, encompassing antibody-based immunoassays and emerging analytical techniques, such as fluorescence assays based on aptamer/molecularly imprinted polymer/fluorescent probes, electrochemical sensors, and Raman spectroscopy, are thoroughly reviewed and discussed. The focus extends to detecting fipronil and its metabolites in crops, fruits, vegetables, animal-derived foods, water, and bodily fluids. This comprehensive exploration contributes valuable insights into the field, aiming to foster the development and innovation of more sensitive, rapid, and applicable analytical methods.

4-oxo-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine derivatives: design, synthesis, insecticidal assay and binding mode studies

A series of 4-oxo-4,5,6,7-tetrahydro-1 H -pyrazolo[3,4- d ]pyrimidine derivatives were designed and synthesized based on the fipronil low energy conformation by scaffold hopping strategy. Physicochemical properties calculation, insecticidal activities evaluation and binding mode studies were also performed. As a result, the insecticidal activities of the target compounds were lower than that of fipronil. The differences in binding mode between these compounds and fipronil may be the major reason for reduced insecticidal activities.

Insect RDL Receptor Models for Virtual Screening: Impact of the Template Conformational State in Pentameric Ligand-Gated Ion Channels

The RDL receptor is one of the most relevant protein targets for insecticide molecules. It belongs to the pentameric ligand-gated ion channel (pLGIC) family. Given that the experimental structures of pLGICs are difficult to obtain, homology modeling has been extensively used for these proteins, particularly for the RDL receptor. However, no detailed assessments of the usefulness of homology models for virtual screening (VS) have been carried out for pLGICs. The aim of this study was to evaluate which are the determinant factors for a good VS performance using RDL homology models, specially analyzing the impact of the template conformational state. Fifteen RDL homology models were obtained based on different pLGIC templates representing the closed, open, and desensitized states. A retrospective VS process was performed on each model, and their performance in the prioritization of active ligands was assessed. In addition, the three best-performing models among each of the conformations were subjected to molecular dynamics simulations (MDS) in complex with a representative active ligand. The models showed variations in their VS performance parameters that were related to the structural properties of the binding site. VS performance tended to improve in more constricted binding cavities. The best performance was obtained with a model based on a template in the closed conformation. MDS confirmed that the closed model was the one that best represented the interactions with an active ligand. These results imply that different templates should be evaluated and the structural variations between their channel conformational states should be specially examined, providing guidelines for the application of homology modeling for VS in other proteins of the pLGIC family.