Identification of coumarin derivatives as a novel class of allosteric MEK1 inhibitors

Abstract—A homogenous TR-FRET-based in vitro coupling assay for the MAP3Ks–MEK1–ERK2 kinase cascade was establishedand was used to screen for inhibitors of the ERK/MAPK pathway. A series of coumarin derivatives were identified from the screen.These compounds potently inhibit the activation of the unactivated human MEK1 by upstream MAP3Ks (including BRAF andCOT), but do not inhibit the activity of the activated MEK1. In addition, the potency of these compounds in inhibiting MEK1 acti-vation is not affected by varying the ATP concentration, suggesting that these inhibitors are not competitive with ATP. As expected,the coumarin compounds potently inhibit LPS-induced TNFa production and ERK phosphorylation in THP-1 cells, with the mostpotent compound having an IC 50 of 90 nM. Molecular modeling studies suggest that these coumarins bind to an allosteric site in theinactive conformation of MEK1. This site has been shown to be utilized by the biarylamine series of MEK inhibitors such asPD318088. Very interestingly, the identified coumarin derivatives are almost identical to a series of inhibitors recently reported thatblock LPS-induced TNFa production. Our findings have therefore raised the possibility that other naturally occurring or syntheticcoumarins with anti-cancer and anti-inflammatory activities might exert their biological function through the inhibition of MEK1. 2005 Elsevier Ltd. All rights reserved.