Interactions between piperonyl butoxide analogues and metabolic enzymes conferring insecticide resistance

Abstract

The insecticide synergist, piperonyl butoxide (PBO), has been used to reduce resistance factors and to characterise metabolic resistance resulting from mixed function oxidases (MFOs). Studies have also shown that PBO can interact with resistance-associated esterases. It is well-documented that the mechanism by which PBO inhibits P450s is the interaction of the methylenedioxyphenyl (MDP) moiety of PBO molecule with the haem moiety of the enzyme. To investigate the interactions between PBO and esterases, a structure activity relationship (SAR) study was carried out using analogues of PBO and E4, a resistanceassociated esterase from the peach-potato aphid Myzus persicae. Results indicate that the polyether and the alkyl chain were fundamentally important in this interaction. Removing one oxygen atom from the MDP moiety of PBO did not affect the binding affinity, but increased affinities resulted from the replacement of the polyether with an alkynyl ether chain or by increasing the length of the alkyl chain. An analogue, EN 16/5-1, that retains the ability to interact with esterases but loses the ability to act on P450s, due to a modification to the MDP moiety, was used in conjunction with PBO to facilitate characterisation of metabolic resistance in M. persicae and pollen beetle Meligethes aeneus. Selected analogues of PBO containing the alkynyl ether side chain exhibited high synergistic effects in vivo and were found to be potent inhibitors of O-deethylation of 7-ethoxycoumarin when tested against pyrethroid resistant M. aeneus. The capability of some of the analogues to act as insecticide synergists was investigated in vivo against two M. persicae clones possessing different metabolic resistance profiles. Finally, the potential of PBO analogues to provide potent and/or specific synergism to overcome insecticide resistance and reduce insecticide titre applied to crops is considered.