Cell-Based Screening Identifies Neoblechnum brasiliense Extract as a Potent Antagonist of the Ecdysteroid Receptor in Dipteran Cells

The ecdysteroid receptor (EcR) plays a crucial role in insect development and metamorphosis, making it a promising target for the design of novel biorational compounds. This study investigated the cytotoxicity, as well as the EcR agonist and antagonist activities, of three synthetic molecules analogous to tebufenozide and extracts from nine plant species using the dipteran S2 cell line which originates from the insect model of the fruit fly Drosophila melanogaster. Cytotoxicity assays were performed to determine appropriate concentrations of the synthetic molecules and plant extracts for cell transfection. EcR agonist and antagonist activities were evaluated using 20-hydroxyecdysone (20E) as the control hormone. The synthetic molecules analogous to tebufenozide did not activate EcR in S2 cells. In contrast, the plant extract of Neoblechnum brasiliense, commonly known as Brazilian dwarf tree fern, exhibited significant antagonistic activity at 100 µM, reducing receptor activity by 92%, likely due to its phytosteroid content, and without inducing cytotoxic effects. These findings demonstrate that certain plant extracts, particularly N. brasiliense, act as effective EcR antagonists and may represent promising natural leads for the development of environmentally compatible biorational compounds to control economically important dipteran pests, such as fruit flies and mosquitoes.