A photoaffinity, non-steroidal, ecdysone agonist, bisacylhydrazine compound, RH-131039: Characterization of binding and functional activity

In this paper we describe the synthesis, ligand-binding and functional activity characteristics of the photoaffinity, non-steroidal, ecdysone agonist, bisacylhydrazine compound, 3-benzoyl-benzoic acid N-tert-butyl-N′-(2-ethyl-3-methoxy-benzoyl)-hydrazide (RH-131039). Tritiated RH-131039 is the first non-steroidal photoaffinity compound that was shown to bind specifically to ecdysone receptors (EcRs) from insects belonging to the orders Diptera and Lepidoptera. The spruce budworm (Choristoneura fumiferana) ecdysone receptor (CfEcR) bound with high affinity (K_d=2.23±0.27 nM) to this compound. When irradiated with UV light (λ=350 nm) under equilibrium ligand-binding conditions, RH-131039 attached specifically and covalently to the CfEcR ligand-binding domain (LBD). RH-131039 also bound to cloned ecdysone receptor proteins from three dipteran insects, Drosophila melanogaster, Aedes aegypti and Chironomous tentans. This paper also describes and invokes caution in interpretation of ligand-binding results obtained using crude cellular extracts containing target receptors, as illustrated with the use of Drosophila Kc cells that have functional EcR and L57 cells (derivatives of Kc cells in which EcR-B isoforms have been knocked out by "parahomologous" recombination). Tritiated RH-131039 is a useful tool to dissect ligand-binding and functional differences for EcRs from different arthropod species.