Identification and Characterization of Novel Juvenile Hormone-related Insect Growth Regulators

Abstract

Mosquitoes are medically important insect pests that transmit various diseases when they feed on humans. The Asian tiger mosquito, Aedes albopictus Skuse (Diptera: Culicidae), is one of the most invasive vectors of various diseases including dengue fever, chikungunya, and zika virus. Chemical insecticides have been commonly used to control mosquitoes. However, due to their toxicity to environments and development of insect resistance, sustained use of chemical insecticides are limited. Insect growth regulators (IGRs) could become an effective alternative to control mosquitoes and other vector transmitting diseases because they are specific to target insects and relatively low toxic to environment. However, recent studies, mosquitoes and other pests also have developed resistance to certain IGR insecticides. Hence, there is an urgent need to develop novel IGR insecticides. In this study, the yeast two-hybrid β-galactosidase assays using the yeast cells transformed with the genes of JH receptor and its partner, Met-FISC of A. aegypti were performed to identify novel juvenile hormone (JH)-related IGR compounds. Among the 2,349 chemical compounds, one JH agonist (JHA) candidate and 17 JH antagonist (JHAN) candidates were screened out and loreclezole hydrochloride and penfluridol were selected based on their high levels of JHA and JHAN activity and insecticidal activity against 3rd instar of A. albopictus larvae, respectively. Loreclezole hydrochloride and penfluridol are well known as anticonvulsant and neuroleptic dug, respectively. However, these compounds showed not only high levels of JH-related IGR activity, but also high levels of insecticidal activity against 3rd instar of A. albopictus larvae compared to those of pyriproxyfen. To find more effective compounds with JH-related IGRs activity for control of mosquitoes, loreclezole hydrochloride and its derivatives were synthesized. Among these derivatives, K21877 demonstrated high level of JHAN activity. Although both loreclezole hydrochloride and K21877 have similar structures, one compound simulated the binding of A. aegypti Met-FISC while the other interfered with the pyriproxyfen-mediated binding of A. aegypti Met-FISC. Both of the JHA and JHAN showed much higher larvicidal activities than that of currently used JHA insecticide, pyriproxyfen. There also showed high embryonic lethality and toxicity against A. albopictus adults, which were due to the modulation of JH-regulated physiological functions such as expression of JH-responsive genes and follicle development. To investigate the transcriptional responses of the A. albopictus treated with loreclezole hydrochloride and K21877, comprehensive transcriptome sequencing was performed and analyzed. These results suggested that JH-interaction of Met could regulate the expression of genes that are related to metabolic process, nucleotide binding process, and translation pathway and loreclezole hydrochloride and K21877 could modulate the JH-regulated gene expression.