Editors' ChoiceMalaria and Dengue

Using Genomics to Get Rid of Pests

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Science Translational Medicine  15 Feb 2012:
Vol. 4, Issue 121, pp. 121ec26
DOI: 10.1126/scitranslmed.3003838

Because a vaccine for many arthropod-borne diseases such as malaria and dengue is not currently available, a multidisciplinary approach to vector control with a focus on the interface between the mosquito and human habitat is important in lessening the human burden of disease. In this regard, vector control efforts focused on the eradication of standing water in combination with the use of insecticide-impregnated bed nets have been successful, albeit limited, stopgaps. However, vector resistance to insecticides and the limited number of novel compounds in development that are both environmentally sound and not toxic to humans remains a concern. Now, Meyer and colleagues demonstrate a genome-to-lead approach in the characterization of new dopaminergic targets in the mosquito A. aegypti, the vector for dengue and yellow fever, while providing an innovative approach for screening new compounds for other vector-borne diseases.

G protein–coupled receptors (GPCRs), a family of molecules involved in multiple systems including neurotransmission and vision, have been tapped as a new insecticide target. In the mosquito, a GPCR acts as a dopamine receptor in the salivary gland and may affect vector transmission during blood feeding. To study a novel dopaminergic target for mosquito control, Meyer and colleagues first identified gene sequences for dopamine receptors (Aadop1 and Aadop2) from an open source platform, VectorBase. To evaluate gene expression of these regions, RNA was extracted from the eggs, larvae, and pupae of the mosquitoes and amplified by using reverse transcription polymerase chain reaction. With the mRNA sequences that encode the dopamine receptors in hand, the investigators predicted the protein sequences and structures and thus defined the familial relationship between AaDOP1 and AaDOP2 and other amine receptors. This analysis provided evidence for conserved regions as well as other unique areas that may be targeted by novel insecticides.

To assign function to AaDOP1 and AaDOP2, their encoding genes were expressed in human embryonic kidney 293 cells. The investigators focused on the Aadop2 gene for the antagonist screen because it was not stimulated by sister biogenic amines (norepinephrine and epinephrine) and had a strong dopamine response with low constitutive activity. Using a chemical library derived from the Library of Pharmacologically Active Compounds (LOPAC1280), Meyer and colleages evaluated various substances that inhibited dopamine by at least 81%. Fifty-one antagonists were defined that ranged in function from pure dopamine antagonists to compounds that affected the cell cycle and apoptosis. Because of the concern about possible cross-reactivity with the human dopamine receptor, compounds designated as hits underwent a second set of experiments to assess cross-toxicity. Interestingly, when compared with the human dopamine receptor, AaDOP2 displayed different binding properties for several of the compounds identified in the screen. Two of the compounds, amitriptyline and doxepin, exhibited unique pharmacology when compared with the human dopamine receptor and, when studied in larval experiments, demonstrated killing at effective drug concentrations.

The last insecticide was developed nearly 30 years ago, and as such, there is evolutionary pressure to develop new, safe alternatives. The genome-to-lead approach defined here offers a strategic genomic approach toward high-throughput screening for new compounds or, as shown in this study, old compounds with a new use.

J. M. Meyer et al., A “genome-to-lead” approach for insecticide discovery: Pharmacological characterization and screening of Aedes aegypti D1-like dopamine receptors. PLoS Negl. Trop. Dis. 6, e1478 (2012). [Abstract]

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