Chalcones inhibit firefly bioluminescence dependent on A and B-ring substitution pattern - a structure-activity study combined with molecular docking.

Chalcones represent a privileged scaffold in medicinal chemistry, with pyranochalcones, featuring an additional chromane-like ring, identified as neurogenic and neuroprotective. Reporter gene assays, often used to study these and other effects, can produce false positives due to firefly luciferase stabilisation by inhibitors. The present study demonstrates that pyranochalcones inhibit firefly luciferase activity, with inhibition levels ranging from none to 100% and IC₅₀ values of 7.82 µM to 92.99 µM. Furthermore, molecular docking offers potential structure-based explanations for the observed selectivity of compounds towards firefly luciferase inhibition. Even slight modifications in the molecular structure lead to significant changes in luciferase inhibition, underscoring the importance of these findings for understanding structure-activity relationships in reporter gene assays. Accordingly, caution is advised when using reporter gene assays based on firefly luciferase and pyranochalcones, as the IC₅₀ values are within the range of concentrations commonly used in both in vivo and in vitro assays.