Location: Animal Production and Protection
Project Number: 0208-32000-001-074-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Feb 17, 2015
End Date: Feb 16, 2020
Objective:
Investigate and optimize the mosquitocidal/acaricidal activity of: chloride channel blockers (Objective 1), resistance-circumventing carbamates (Objective 2), and neonicotinoids (Objective 3).
Approach:
1. Acquire novel molecules for the screening components of the project. Clearly, a novel active insecticide requires a novel chemical structure, which is critical for IP generation, and involvement of the private sector in bringing discoveries to the soldier in the field. The synthetic chemistry portion of the project will generate analogs of uniquely active isoxazolines or neonicotinoids. Acquisition of new compounds for this project urgently requires a dedicated organic synthesis effort.
2. Identify possible mode(s) of action. Confirmatory experiments on the appropriate mosquito (Aedes aegypti) targets will validate the hypotheses about how isoxazolines (block the GABA receptor) and neonicotinoids (activate/block the nAchR) work. Appropriate electrophysiological and biochemical studies to define cellular site and mode of action of these carbamates will be performed.
3. Define potency on target systems, in vitro. Once the primary mode of action is established, relevant in vitro screens will be developed. These screens will provide the kind of pharmacodynamic data (direct action on the target receptor without the confounding variables of penetration, metabolism, etc.) required to guide synthetic chemistry. Our goal is to produce a compound with high activity against the mosquito target, and low activity against the human homolog, if it exists. This parameter will be defined by the Selectivity Ratio (SR), which is human IC50 or EC50 / mosquito IC50 or EC50.
4. Characterize in vivo activity and identify compounds with contact toxicity to adult female mosquitoes, including resistant strains. We need to confirm that potency observed, in vitro, is expressed as mosquito killing or incapacitation effect, in vivo. The compound must have the proper pharmacokinetic profile in order to penetrate into the mosquito and reach the target site, factors that are absent in the in vitro screens. Studies will include surface contact, topical, and, if necessary, injection treatments to identify effective routes of exposure. Insects will initially be observed for rapid knockdown, which usually reflects a rapid action on nerve or muscle. Synergists (piperonyl butoxide, triphenylphosphate, and diethyl maleate) will be used to assess sensitivity to oxidation, esteratic cleavage, and glutathione-S-transferase activity, respectively. Compounds requiring injection for activity will be rejected. Other studies under this objective will include the use of oils or other adjuvants to increase contact activity, especially for the neonicotinoids, which are too polar to work by contact. Toxicity will be defined by LD50 or LC50 values and will use propoxur as a standard.
5. Confirm low mammalian lethality of possible field candidates. This Activity is significant to assess the acute lethality of compounds meeting the performance objectives for field. These studies will estimate the level of acute whole animal toxicity of our compounds, important information for prospective licensees (multinational chemical companies), who will be decide if properties of a molecule will justify investment to carry out registration toxicology studies.
