Modular Assembly of Allosteric MEK Inhibitor Structural Elements Unravels Potency and Feedback-Modulation Handles.

Having recently identified a so-far unexplored area adjacent to the known binding site of allosteric mitogen-activated protein kinase kinase (MEK) inhibitors, we now report an extension of these studies by combining our new side chains with different MEK inhibitor cores in a modular manner. Replacement of the amide headgroup with inverse sulfonamides resulted in the identification of new MEK inhibitors with at least 10-fold higher cellular potency against K-Ras-mutated tumor cells. A selected inhibitor from this new series retained the favorable pharmacokinetic profile of its predecessor in rodent and non-rodent species and displayed significant in vivo efficacy at once-daily oral doses of 0.25-1 mg kg(-1) in a K-Ras-mutated xenograft model. The brain penetration potential of this analogue was significantly attenuated relative to PD325901. In a second series, the central fluorophenyl core was replaced by a pyridine moiety which gave rise to a similar boost in cellular potency. Most notably, analogues from this second series do not show MEK feedback phosphorylation in K-Ras-mutated A549 cells. Our results complement recent reports on the structural intricacies of MEK-Raf feedback interactions.