Ecdysteroids potency

Figure 10 Pharmacophore hypothesis for ecdysteroid potency in the Drosophila melanogaster Bn bioassay (redrawn from [28]).

Table 2 Potencies of ecdysteroids in in vivo assays based on the induction of pup(ari)ation in ligated last-instar larvae of Dermestes vulpinus, Galleria mellonella and Sarcophaga bullata. Data are taken from Slama et al. [31] and are expressed as ED50 values (pg/g). n.d. not determined.

The early literature on ecdysteroid structure-activity studies has been reviewed [120,150,171], The various bioassays employed vary in their complexity of performance and interpretation. A number of factors can affect the potency of a test compound to a greater or lesser extent depending on the assay system penetration, metabolism, excretion rate, sequestration and target site activity. In vivo assays will give a measure of all of these acting in concert, but not allow the individual contributions to be identified. On the other hand, cell-free receptor assays probably give a direct measure of target activity, but may bear little resemblance to the in vivo situation. 

The ecdysteroid antagonists identified to date are all of rather low potency This may be a consequence of them all being plant natural products, which the plant is able to produce in high concentrations at low cost to itself [231],... 

Table 7 Relative potencies of known ecdysteroid antagonists in the Drosophila melanogaster Bn bioassay. EC50 values were determined in the presence of 5 x 10 8M 20-hydroxyecdysone. Only compounds for which it was possible to determine distinct EC50 values are included.

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