Inhibition of prenylated KRAS in a lipid environment.

RAS mutations lead to a constitutively active oncogenic protein that signals through multiple effector pathways. In this chemical biology study, we describe a novel coupled biochemical assay that measures activation of the effector BRAF by prenylated KRASG12V in a lipid-dependent manner. Using this assay, we discovered compounds that block biochemical and cellular functions of KRASG12V with low single-digit micromolar potency. We characterized the structural basis for inhibition using NMR methods and showed that the compounds stabilized the inactive conformation of KRASG12V. Determination of the biophysical affinity of binding using biolayer interferometry demonstrated that the potency of inhibition matches the affinity of binding only when KRAS is in its native state, namely post-translationally modified and in a lipid environment. The assays we describe here provide a first-time alignment across biochemical, biophysical, and cellular KRAS assays through incorporation of key physiological factors regulating RAS biology, namely a negatively charged lipid environment and prenylation, into the in vitro assays. These assays and the ligands we discovered are valuable tools for further study of KRAS inhibition and drug discovery.

Crystal structures of novel non-peptidic, non-zinc chelating inhibitors bound to MMP-12.

Human macrophage elastase (MMP-12) plays an important role in inflammatory processes and has been implicated in diseases such as emphysema and chronic obstructive pulmonary disease (COPD). It is therefore an attractive target for therapeutic agents. As part of a structure-based drug design programme to find new inhibitors of MMP-12, the crystal structures of the MMP-12 catalytic domain (residues 106-268) complexed to three different non-peptidic small molecule inhibitors have been determined. The structures reveal that all three ligands bind in the S1' pocket but show varying degrees of interaction with the Zn atom. The structures of the complexes with inhibitors CP-271485 and PF-00356231 reveal that their central morpholinone and thiophene rings, respectively, sit over the Zn atom at a distance of approximately 5A, locating the inhibitors halfway down the S1' pocket. In both of these structures, an acetohydroxamate anion, an artefact of the crystallisation solution, chelates the zinc atom. By contrast, the acetohydroxamate anion is displaced by the ligand in the structure of MMP-12 complexed to PD-0359601 (Bayer), a potent zinc chelating N-substituted biaryl butyric acid, used as a reference compound for crystallisation. Although a racemate was used for the crystallisation, the S enantiomer only is bound in the crystal. Important hydrophobic interactions between the inhibitors and residues from the S1' pocket are observed in all of the structures. The relative selectivity displayed by these ligands for MMP-12 over other MMP family members is discussed.