The Activity of Analogs of the Natural Product Dillapiol and Sessamol as Detoxification Enzyme Inhibitors and Insecticide Synergists

Title: The Activity of Analogs of the Natural Product Dillapiol and Sessamol as Detoxification Enzyme Inhibitors and Insecticide Synergists
Authors: Liu, Su Qi
Date: 2015
Abstract: In the present thesis, analogs of the plant derived compound, dillapiol, were investigated for their potential as cytochrome P450 inhibitors and insecticide synergists. Dillapiol was chosen as a lead compound because it has a methylenedioxyphenyl (MDP) functionality that serves as a cytochrome P450 inhibitor and reported insecticide synergist activity comparable to the commercially used piperonyl butoxide (PBO). Initially a set of fifty two dillapiol analogs was investigated for inhibition of cytochrome P450 using cloned Human CYP3A4, a highly standardized preparation that allowed accurate determination of structure activity relationships. A qualitative analysis revealed that analogs with a large acyl group attached via ester bonds had higher in vitroCYP3A4 inhibitory activity. However, a Gaussian Quantitative Structure Activity Relationship model also showed the importance of hydrophobic interactions and predicted new structures with higher P4503A4 inhibition. Subsequently selected analogs were investigated as potential pyrethrum synergists in insecticide susceptible (SS-CPB) and resistant (RS-CPB) Colorado potato beetle (Leptinotarsadecemlineata Say) (Coleoptera: Chrysomelidae) as well as the European corn borer (ECB, Ostrinia nubilalis Hübner). Using discriminating dose and full concentration bioassays, the synergistic activity of selected analogs was studied. Ether analogs demonstrated stronger synergistic activity than ester analogs for both insect species. All tested compounds displayed higher synergistic activity by ingestion than topical administration, and each analog type (ester and ether) had one compound with a synergism ratio greater than 20. Both compounds successfully restored the insecticide susceptibility within RS-CPB resistant strain larvae to pyrethrum. In greenhouse and field trials, pyrethrum extract combined with dillapiol was effective against SS-CPB, and the pyrethrum + dillapiol formulation demonstrated efficacy at least 10 times higher than that of pyrethrum alone. This suggested the feasibility of dillapiol as a novel PBO replacement for organic farming. The intrinsic toxicity of the most active analogs compared to dillapiol or PBO were determined by growth inhibition bioassay with ECB larvae which were administrated a synergist treated diet. In several growth parameters of ECB evaluated, PBO was found to have the strongest intrinsic toxicity, followed by the ester analog. Dillapiol showed the least toxicity among four tested compounds, while the ether analog, which was the best pyrethrum synergist against both oligophagous CPB and polyphagous ECB, had a similar safety level compared todillapiol.T o explore the underlying mechanism of the synergists, the impact of selected compounds on three major detoxification enzymes, monooxygenase P450, Gluthatione S-transferases (GST) and esterases of both insect species were evaluated. All selected analogs effectively inhibited in vitro and in vivoP450 monooxygenases activity for both oligophagous CPB and polyphagous ECB. The best pyrethrum synergist also displayed significantly greater P450 inhibitory activity than PBO which was eleven times more effective than PBO as an inhibitor of ECB in vitroP450 activity. The inhibition assay with either CPB or ECB GSTs respectively produced the surprising result that the best pyrethrum synergist exhibited a 180-fold or 575-fold lower IC50than the standard inhibitor of GST. To our knowledge, this is the first report of MDP related compounds showing significant GST inhibitory activity. A pilot study of insect dysregulation induced by synergists was conducted with Ultra Performance Liquid Chromotagraphy (UPLC)-Quadrupole Time of Flight Mass Spectrometry (QTOF/MS). It was found to be a suitable technique to study the metabolites changes induced by selected analogs for the two insect species. The application of UPLC-QTOF/MS produced high-resolution metabolites profiles which guarantees the success of the dynamic metabolism research of selected insects in the future.
CollectionThèses, 2011 - // Theses, 2011 -