Electrophysiological Recording of The Central Nervous System Activity of Third-Instar <em> Drosophila Melanogaster </em>

The majority of the currently available insecticides target the nervous system and genetic mutations of invertebrate neural proteins oftentimes yield ...

Virginia Tech

Malaria is a devastating disease in sub-Saharan Africa, and current vector control measures are threatened by emerging resistance mechanisms. With the goal of developing new, selective, resistance-breaking insecticides we explored α-fluorinated methyl ketones as reversible covalent inhibitors of Anopheles gambiae acetylcholinesterase (AgAChE). Trifluoromethyl ketones 5 demonstrated remarkable volatility in microtiter plate assays, but 5c,e-h exhibited potent (1-100 nM) inhibition of wild type (WT) AgAChE and weak inhibition of resistant mutant G119S mutant AgAChE. Fluoromethyl ketones 10c-i exhibited submicromolar to micromolar inhibition of WT AgAChE, but again only weakly inhibited G119S AgAChE. Interestingly, difluoromethyl ketone inhibitors 9c and 9g had single digit nanomolar inhibition of WT AgAChE, and 9g had excellent potency against G119S AgAChE. Approach to steady-state inhibition was quite slow, but after 23 h incubation an IC50 value of 25.1 ± 1.2 nM was measured. We attribute the slow, tight-binding G119S AgAChE inhibition of 9g to a balance of steric size and electrophilicity. However, toxicities of 5g, 9g, and 10g to adult A. gambiae in tarsal contact, fumigation, and injection assays were lower than expected based on WT AgAChE inhibition potency and volatility. Potential toxicity-limiting factors are discussed.

Difluoromethyl ketones: Potent inhibitors of wild type and carbamate-insensitive G119S mutant Anopheles gambiae acetylcholinesterase.

Widespread pyrethroid resistance has caused an urgent need to develop new insecticides for control of the malaria mosquito, Anopheles gambiae. Insecticide discovery efforts were directed towards the construction of bivalent inhibitors that occupy both the peripheral and catalytic sites of the mosquito acetylcholinesterase (AChE). It was hypothesized that this approach would yield a selective, high potency inhibitor that would also circumvent known catalytic site mutations (e.g. G119S) causing target site resistance. Accordingly, a series of bivalent phthalimide-pyrazole carbamates were prepared having an alkyl chain linker of varying length, along with other modifications. The most active compound was (1-(3-(1,3-dioxoisoindolin-2-yl)propyl)-1H-pyrazol-4-yl methylcarbamate, 8a), which has a chain length of three carbons, good mosquito anticholinesterase activity, and ca. 5-fold selectivity compared to human AChE. Moreover, this compound was toxic to mosquitoes by topical application (LD = 63 ng/female) with only 6-fold cross resistance in the Akron strain of Anopheles gambiae that showed 50- to 60-fold resistance to conventional carbamate insecticides. However, contact lethality in the WHO paper assay was disappointing. The implications of these results for design of new mosquitocides are discussed.

Bivalent Carbamates as Novel Control Agents of the Malaria Mosquito, Anopheles gambiae.

New public health insecticides are urgently required to prevent the spread of vector-borne disease. With the goal of identifying new K-channel-directed mosquitocides, analogs of the RH-5849 family of diacyl t-butylhydrazines were synthesized and tested for topical toxicity against adult Anopheles gambiae, the African vector of malaria. In total, 80N'-monoacyl and N, N'-diacyl derivatives of benzyl- and arylhydrazines were prepared. Three compounds (2bo, 2kb, 3ab) were identified that were more toxic than RH-5849 and RH-1266. The potencies of these compounds to block K currents in An. gambiae and human Kv2.1 channels were assessed to address their possible mechanism of mosquitocidal action. Selectivity for inhibition of An. gambiae Kv2.1 vs human Kv2.1 did not exceed 3-fold. Furthermore, no correlation was seen between the potency of insecticidal action and K channel blocking potency. These observations, combined with the minimal knockdown seen with 2bo near its LD value, suggests a mode of action outside of the nervous system.

N'-mono- and N, N'-diacyl derivatives of benzyl and arylhydrazines as contact insecticides against adult Anopheles gambiae.

Mosquito-borne diseases account for the deaths of approximately 700,000 people annually throughout the world, with many more succumbing to the debilitating side effects associated with these etiologic disease agents. This is exacerbated in many countries where the lack of mosquito control and resources to prevent and treat mosquito-borne disease coincide. As populations of mosquito species grow more resistant to currently utilized control chemistries, the need for new and effective chemical means for vector control is more important than ever. Previous work revealed that plant essential oils enhance the toxicity of permethrin against multiple mosquito species that are of particular importance to public health. In this study, we screened permethrin and deltamethrin in combination with plant essential oils against a pyrethroid-susceptible and a pyrethroid-resistant strain of both  and . A number of plant essential oils significantly enhanced the toxicity of pyrethroids equal to or better than piperonyl butoxide, a commonly used synthetic synergist, in all strains tested. Significant synergism of pyrethroids was also observed for specific combinations of plant essential oils and pyrethroids. Moreover, plant essential oils significantly inhibited both cytochrome P450 and glutathione -transferase activities, suggesting that the inhibition of detoxification contributes to the enhancement or synergism of plant essential oils for pyrethroids. This study highlights the potential of using diverse plant oils as insecticide additives to augment the efficacy of insecticidal formulations.

Plant Essential Oils Enhance Diverse Pyrethroids against Multiple Strains of Mosquitoes and Inhibit Detoxification Enzyme Processes.

 Giles (Diptera: Culicidae) is the most prolific malaria vector in sub-Saharan Africa, where widespread insecticide resistance has been reported.  laboratory strains are commonly used to study the basic biology of this important mosquito vector, and also in new insecticide discovery programs, where insecticide-susceptible and -resistant strains are often used to screen new molecules for potency and cross-resistance, respectively. This study investigated the toxicity of permethrin, a Type-I pyrethroid insecticide, and etofenprox, a non-ester containing pyrethroid insecticide, against  at three life stages. This characterization was performed with susceptible (G3; MRA-112) and resistant (A; MRA-1280)  strains; the A strain is known to contain the L1014F mutation in the voltage-sensitive sodium channel. Surprisingly, etofenprox displays a lower level of resistance than permethrin against all stages of mosquitoes, except in a headless larval paralysis assay designed to minimize penetration factors. In first-instar  larvae, permethrin had significant resistance, determined by the resistance ratio (RR = 5), but etofenprox was not significantly different (RR = 3.4) from the wild-type strain. Fourth-instar larvae displayed the highest level of resistance for permethrin (RR = 108) and etofenprox (RR = 35). Permethrin (PC = 2 ppb) and etofenprox (PC = 9 ppb) resulted in headless larval paralysis (5-h), but resistance, albeit lower, was still present for permethrin (RR = 5) and etofenprox (RR = 6.9). In adult female mosquitoes, permethrin displayed higher resistance (RR = 14) compared to etofenprox (RR = 4.3). The level of etofenprox resistance was different from that previously reported for a similar Akron  laboratory strain (MRA-913). The chemical synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) were able to synergize permethrin, but not etofenprox in the resistant strain (A). In conclusion, multiple mechanisms are likely involved in pyrethroid resistance, but resistance profiles are dependent upon selection. Etofenprox is an effective insecticide against  in the lab but will likely suffer from resistance in the field.

Aaron D. Gross

Department of Entomology

Virginia Tech

Electrophysiological Recording of The Central Nervous System Activity of Third-Instar Drosophila Melanogaster

Aaron D. Gross

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Entomology

Virginia Tech

Electrophysiological Recording of The Central Nervous System Activity of Third-Instar Drosophila Melanogaster

Department of Entomology