Certain withanolides from Iochroma gesnerioides antagonize ecdysteroid action in a Drosophila melanogaster cell line

Sixteen withanolides isolated from Iochroma gesnerioides (Kunth) Miers (Solanaceae) have been assessed for their activities as ecdysteroid agonists and antagonists. None of the compounds showed any agonistic activity, but several showed significant antagonistic activity. With a 20‐hydroxyecdysone concentration of 5 times 10 −8 M, the ED 50 values for 2,3‐dihydro‐3ξ‐methoxywithaferin A, 2,3‐dihydro‐3ξ‐methoxywithacnistine, 2,3‐dihydro‐3ξ‐methoxyiochromolide and 2,3‐dihydro‐3ξ‐hydroxyξwithacnistine are 3.5 times 10 −5 M, 1 times 10 −5 M, 5 times 10 −6 M and 2.5 times 10 −6 M, respectively.