Many drug candidates fail in clinical trials due to a lack of efficacy from limited target engagement or an insufficient therapeutic index. Minimizing off-target effects while retaining the desired pharmacodynamic (PD) response can be achieved by reduced exposure for drugs that display kinetic selectivity in which the drug:target complex has a longer half-life than off-target:drug complexes. However, while slow-binding inhibition kinetics are a key feature of many marketed drugs1,2, prospective tools that integrate drug-target residence time into predictions of drug efficacy are lacking, hindering the integration of drug-target kinetics into the drug discovery cascade. Here we describe a mechanistic PD model that includes drug-target kinetic parameters including the on- and off-rates for the formation and breakdown of the drug-target complex. We demonstrate the utility of this model by using it to predict dose response curves for inhibitors of the LpxC enzyme from Pseudomonas aeruginosa in an animal model of infection.

Aberrant activation of signaling through the RAS-RAF-MEK-ERK (MAPK) pathway is implicated in numerous cancers, making it an attractive therapeutic target. Although BRAF and MEK-targeted combination therapy has demonstrated significant benefit beyond single-agent options, the majority of patients develop resistance and disease progression after approximately 12 months. Reactivation of ERK signaling is a common driver of resistance in this setting. Here we report the discovery of BVD-523 (ulixertinib), a novel, reversible, ATP-competitive ERK1/2 inhibitor with high potency and ERK1/2 selectivity. In vitro BVD-523 treatment resulted in reduced proliferation and enhanced caspase activity in sensitive cells. Interestingly, BVD-523 inhibited phosphorylation of target substrates despite increased phosphorylation of ERK1/2. In in vivo xenograft studies, BVD-523 showed dose-dependent growth inhibition and tumor regression. BVD-523 yielded synergistic antiproliferative effects in a BRAF V600E -mutant melanoma cell line xenograft model when used in combination with BRAF inhibition. Antitumor activity was also demonstrated in in vitro and in vivo models of acquired resistance to singleagent and combination BRAF/MEK-targeted therapy. On the basis of these promising results, these studies demonstrate BVD-523 holds promise as a treatment for ERK-dependent cancers, including those whose tumors have acquired resistance to other treatments targeting upstream nodes of the MAPK pathway. Assessment of BVD-523 in clinical trials is underway

The Ras/Raf/MEK/ERK signal transduction, an oncogenic pathway implicated in a variety of human cancers, is a key target in anticancer drug design. A novel series of pyrimidylpyrrole ERK inhibitors has been identified. Discovery of a conformational change for lead compound 2, when bound to ERK2 relative to antitarget GSK3, enabled structure-guided selectivity optimization, which led to the discovery of 11e, a potent, selective, and orally bioavailable inhibitor of ERK.

The Ras/Raf/MEK/ERK signal transduction is a key oncogenic pathway implicated in a variety of human cancers. We have identified a novel series of pyrazolylpyrroles as inhibitors of ERK. Aided by the discovery of two distinct binding modes for the pyrazolylpyrrole scaffold, structure-guided optimization culminated in the discovery of 6p, a potent and selective inhibitor of ERK.

Studies are reported on two different types of activated ketones as inhibitors of two important intracellular phospholipase A 2 s (PLA 2 ): the group IV 85 kDa Ca 2+ -dependent phospholipase A 2 (cPLA 2 ) and the P388D 1 Ca 2+independent phospholipase A 2 (iPLA 2 ). In a mixed micelle assay, we observed that the reaction progress curve of cPLA 2 in the presence of a trifluoromethyl ketone (TFMK) is linear at pH 7.4, while at pH 9.0 it is nonlinear and slows with time. An investigation of this discrepancy demonstrated that the TFMKs are slow, tight-binding inhibitors of the cPLA 2 at both pH's, that the rate of dissociation of the enzyme-inhibitor complex is the same at both pH's, but that the rate of association of enzyme and inhibitor is slower at pH 7.4 than at pH 9.0. A novel group of activated ketone inhibitors has been synthesized that contain a fatty acyl tricarbonyl. These compounds also inhibit the cPLA 2 in the mixed micelle assay. The inhibition of cPLA 2 by the tricarbonyls is readily reversible upon dilution and does not involve slow binding. For both types of inhibitor, no preference for fatty acid chain was observed as the palmityl analogs inhibited as well as the arachidonoyl analogs, despite the fact that the cPLA 2 shows a strong preference for arachidonoyl-containing phospholipid substrates over palmitoyl-containing substrates. With the iPLA 2 , the inhibition by TFMKs is reversible and does not involve slow or tight binding. The tricarbonyls also inhibited the iPLA 2 , but were less potent than the TFMKs. Unlike the cPLA 2 , the iPLA 2 does exhibit a fatty acid preference as the palmityl analogs of both compounds inhibit better than the arachidonoyl analogs. The palmityl TFMK displayed a 10-fold lower IC 50 at pH 9.0 than at pH 7.5, whereas the potency of the tricarbonyl was unchanged in this range. Thus, the TFMKs inhibit both the cPLA 2 and the iPLA 2 , but the mechanism of inhibition of the two enzymes appears to be quite different. The tricarbonyls also inhibited both enzymes, but in both cases in a reversible manner and as such appear to be poorer inhibitors than the TFMKs.Ketones with enhanced electrophilic reactivity (hydrateforming ketones), such as trifluoromethyl ketones (TFMKs), R-diketones, R-keto esters, and R,β-dioxo esters or vicinal tricarbonyls, 1,2 are a well-established class of inhibitors for proteases, lipases, and other serine esterases. This type of inhibitor has now been used to study phospholipase A 2 s (PLA 2 ), a class of esterases which carry out a reaction similar to that of lipases. Of particular interest are two intracellular PLA 2 s, the Group IV, 85 kDa, Ca 2+ -dependent PLA 2 (cPLA 2 ) 3-5 and the murine P388D 1 80 kDa, Ca 2+ -independent PLA 2 (iPLA 2 ). 6 The mechanisms of action of these two PLA 2 s are not well established, although the cPLA 2 reaction is believed to proceed through an acyl-enzyme intermediate. 7,8 Sharp