Structure-based virtual screening for insect ecdysone receptor ligands using MM/PBSA.

The ecdysone receptor (EcR) is an insect nuclear receptor that is activated by the molting hormone, 20-hydroxyecdysone. Because synthetic EcR ligands disrupt the normal growth of insects, they are attractive candidates for new insecticides. In this study, the Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) method was used to predict the binding activity of EcR ligands. Validity analyses using 40 known EcR ligands showed that the binding activity was satisfactorily predicted when the ligand conformational free energy term was introduced. Subsequently, this MM/PBSA method was applied to structure-based hierarchical virtual screening, and 12 candidate compounds were selected from a database of 3.8 million compounds. Five of these compounds were active in a cell-based competitive binding assay. The most potent compound is a simple proline derivative with low micromolar binding activity, representing a valuable lead compound for further structural optimization.

Classical and three-dimensional QSAR for the inhibition of [3H]ponasterone A binding by diacylhydrazine-type ecdysone agonists to insect Sf-9 cells.

The activity of 52 diacylhydrazine congeners was evaluated by measuring the inhibition of the incorporation of [3H]ponasterone A into intact Sf-9 cells. Eleven compounds were newly synthesized in this study. Results showed that the substitution of the 2-CH3 or 3-OCH3 moiety of methoxyfenozide with other groups or the removal of either group was unfavorable to the activity. The activity was quantitatively analyzed using both classical QSAR (Hansch-Fujita) and three-dimensional QSAR methods (comparative molecular field analysis, CoMFA). Sterically favorable fields were observed at the 3- and 4-positions of the benzene ring opposite from the t-butyl group (B-ring), and a sterically unfavorable field was evidenced at the 2-position. Another sterically unfavorable field developed surrounding the favorable field observed at the 4-position of the B-ring. Electrostatically negative fields were observed near the CO moiety, above the benzene ring, and at the 4-position of the B-ring. The optimum hydrophobicity of compounds in terms of their logP values was calculated to be approximately 4.1. Results of the three dimensional structure-activity relationship analyses were consistent with those obtained from the previously reported classical QSAR for 2-chlorobenzoyl analogs containing various para-substituents. The high activity of potent insecticides such as tebufenozide and chromafenozide were rationalized by CoMFA. Thus, this CoMFA result will be useful in the design of new compounds and in understanding the molecular mechanism of the ligand-receptor interactions.