Ecdysteroids biological activities

The purpose of this review is to summarise the effects, modes of action, structural diversity and biological activity of ecdysteroids and to show how ecdysteroid QSAR and molecular modelling are being applied in agriculture and medicine. 

The term ecdysteroid was originally defined as "all compounds structurally related to ecdysone" [4], However, Lafont and Horn [5] differentiated between true ecdysteroids and ecdysteroid-related compounds. True ecdysteroids possess a steroid nucleus with an A/B-cis-ring junction and a 14a-hydroxy-7-en-6-one chromophore, irrespective of their biological activity, while ecdysteroid-related compounds do not fulfil all these criteria. 

A similar, but more sensitive, bioassay using larvae of Musca domestica was developed [174-177], This bioassay is still finding application today [140,178], Table (1) summarises the biological activities of ecdysteroids in this bioassay. 

Table 1 Biological activities of ecdysteroids and related compounds in in vivo assays. Data taken from Bergamasco and Horn [171], unless otherwise indicated. The number in brackets after the name of the ecdysteroid refers to the number allocated to it in [171], where the structures for each of these compounds is given.

The evagination of imaginal discs of Dipteran and Lepidopteran insects is a well-characterised ecdysteroid-dependent system, which has been used by several authors to develop bioassays [183-187], However, they have been used to only a limited extent to compare the biological activities of ecdysteroids (Table 3 ). 

The ecdysteroid-responsive Kc permanent cell line was established from disrupted embryos of D. melanogaster [188], Consequently, it is not known what in vivo cell type (if any) they represent. However, the response (aggregation of cells, cessation of division and the formation of axon-like projections) is characteristic and can form the basis of a somewhat time-consuming bioassay [189], which has been used to compare the biological activities of 60 steroids, most of which were inactive. The biological activities of a number of ecdysteroids in this Kc-H cell bioassay are summarised in Table (4). 

Table 5 Biological activities of ecdysteroids in the Drosophila melanogaster Bn bioassay. Activities are presented as the concentration required to half the maximal response (EC5o). Where compounds show no activity at 10 4M, they are described as "inactive". Where the solubility is lower than 10 4M, the activity is given as >[maximal solubility].

After processing a larger group of 7-dey-old pupae the more polar ecdysteroid was isolated and identified as 20,26-dihydro iyecdysone (3). This ecdysteroid was only 1/10 to 1/15 as biologically active as ecdysone or 20-hydroxyecdysone in the house fly assey. The structures and biological activity of the ecdysteroids indicated the sequence of conversion shown in [1]... 

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