F. Christopher Zusi

BMS-345541 Is a Highly Selective Inhibitor of IκB Kinase That Binds at an Allosteric Site of the Enzyme and Blocks NF-κB-dependent Transcription in Mice

The signal-inducible phosphorylation of serines 32 and 36 of IκBα is critical in regulating the subsequent ubiquitination and proteolysis of IκBα, which then releases NF-κB to promote gene transcription. The multisubunit IκB kinase responsible for this phosphorylation contains two catalytic subunits, termed IκB kinase (IKK)-1 and IKK-2. BMS-345541 (4(2′-aminoethyl)amino-1,8-dimethylimidazo(1,2-a)quinoxaline) was identified as a selective inhibitor of the catalytic subunits of IKK (IKK-2 IC50 = 0.3 μm, IKK-1 IC50 = 4 μm). The compound failed to inhibit a panel of 15 other kinases and selectively inhibited the stimulated phosphorylation of IκBα in cells (IC50 = 4 μm) while failing to affect c-Jun and STAT3 phosphorylation, as well as mitogen-activated protein kinase-activated protein kinase 2 activation in cells. Consistent with the role of IKK/NF-κB in the regulation of cytokine transcription, BMS-345541 inhibited lipopolysaccharide-stimulated tumor necrosis factor α, interleukin-1β, interleukin-8, and interleukin-6 in THP-1 cells with IC50 values in the 1- to 5-μmrange. Although a Dixon plot of the inhibition of IKK-2 by BMS-345541 showed a non-linear relationship indicating non-Michaelis-Menten kinetic binding, the use of multiple inhibition analyses indicated that BMS-345541 binds in a mutually exclusive manner with respect to a peptide inhibitor corresponding to amino acids 26–42 of IκBα with Ser-32 and Ser-36 changed to aspartates and in a non-mutually exclusive manner with respect to ADP. The opposite results were obtained when studying the binding to IKK-1. A binding model is proposed in which BMS-345541 binds to similar allosteric sites on IKK-1 and IKK-2, which then affects the active sites of the subunits differently. BMS-345541 was also shown to have excellent pharmacokinetics in mice, and peroral administration showed the compound to dose-dependently inhibit the production of serum tumor necrosis factor α following intraperitoneal challenge with lipopolysaccharide. Thus, the compound is effective against NF-κB activation in mice and represents an important tool for investigating the role of IKK in disease models.

Rational design of RAR-selective ligands revealed by RARβ crystal stucture

The crystal structure of the ligand‐binding domain of RARβ, a suspect tumour suppressor, reveals important features that distinguish it from the two other RAR isotypes. The most striking difference is an extra cavity allowing RARβ to bind more bulky agonists. Accordingly, we identified a ligand that shows RARβ selectivity with a 100‐fold higher affinity to RARβ than to α or γ isotypes. The structural differences between the three RAR ligand‐binding pockets revealed a rationale explaining how a single retinoid can be at the same time an RARα, γ antagonist and an RARβ agonist. In addition, we demonstrate how to generate an RARβ antagonist by gradually modifying the bulkiness of a single substitution. Together, our results provide structural guidelines for the synthesis of RARβ‐selective agonists and antagonists, allowing for the first time to address pharmacologically the tumour suppressor role of RARβ in vitro and in animal models.

Selective retinoids and rexinoids in cancer therapy and chemoprevention

Natural and synthetic retinoids are effective inhibitors of tumor cell growth in vitro and in vivo. However, the toxicity of natural derivatives of vitamin A limits their therapeutic use. Recently, synthetic compounds selective for the different retinoid receptor isotypes have been generated that circumvent pan-retinoid toxicity. The tumor-suppressive activity of selective retinoid and/or rexinoid ligands has been established preclinically, and emerging clinical trials are supportive of the chemotherapeutic and chemopreventive potential of these compounds in multiple oncology indications, with reduced toxicity. Moreover, the combination of retinoids and/or rexinoids with chemotherapeutic agents for the synergistic modulation of specific pathways could also be of benefit in cancer therapy.

Synthesis and SAR of indole-and 7-azaindole-1,3-dicarboxamide hydroxyethylamine inhibitors of BACE-1.

Heterocyclic replacement of the isophthalamide phenyl ring in hydroxyethylamine (HEA) BACE-1 inhibitors was explored. A variety of indole-1,3-dicarboxamide HEAs exhibited potent BACE-1 enzyme inhibition, but displayed poor cellular activity. Improvements in cellular activity and aspartic protease selectivity were observed for 7-azaindole-1,3-dicarboxamide HEAs. A methylprolinol-bearing derivative (10n) demonstrated robust reductions in rat plasma Aβ levels, but did not lower rat brain Aβ due to poor central exposure. The same analog exhibited a high efflux ratio in a bidirectional Caco-2 assay and was likely a substrate of the efflux transporter P-glycoprotein. X-ray crystal structures are reported for two indole HEAs in complex with BACE-1.

Discovery of a novel series of quinolone α7 nicotinic acetylcholine receptor agonists

High throughput screening led to the identification of a novel series of quinolone α7 nicotinic acetylcholine receptor (nAChR) agonists. Optimization of an HTS hit (1) led to 4-phenyl-1-(quinuclidin-3-ylmethyl)quinolin-2(1H)-one, which was found to be potent and selective. Poor brain penetrance in this series was attributed to transporter-mediated efflux, which was in turn due to high pKa. A novel 4-fluoroquinuclidine significantly lowered the pKa of the quinuclidine moiety, reducing efflux as measured by a Caco-2 assay.

Evaluation of retinoids as therapeutic agents in dermatology.

Evaluation of 13-cis-12-substituted analogues of retinoic acid in a series of dermatologic screens has revealed that structural modifications can lead to selectivity and specificity. An analogue, 11-cis,13-cis-12-hydroxymethylretinoic acid, δ-lactone, has been found to have good activity and to be devoid of topical and systemic toxicity.

Competitive, Reversible Inhibition of Cytosolic Phospholipase A2 at the Lipid-Water Interface by Choline Derivatives That Partially Partition into the Phospholipid Bilayer

Cytosolic phospholipase A2 (cPLA2) catalyzes the selective release of arachidonic acid from the sn-2 position of phospholipids and is believed to play a key cellular role in the generation of arachidonic acid. When assaying the human recombinant cPLA2 using membranes isolated from [3H]arachidonate-labeled U937 cells as substrate, 2-(2′-benzyl-4-chlorophenoxy)ethyl-dimethyl-n-octadecyl-ammonium chloride (compound 1) was found to inhibit the enzyme in a dose-dependent manner (IC50 = 5 μm). It was over 70 times more selective for the cPLA2 as compared with the human nonpancreatic secreted phospholipase A2, and it did not inhibit other phospholipases. Additionally, it inhibited arachidonate production inN-formyl-methionyl-leucyl-phenylalanine-stimulated U937 cells. To further characterize the mechanism of inhibition, an assay in which the enzyme is bound to vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphomethanol containing 6–10 mol % of 1-palmitoyl-2-[1-14C]arachidonoyl-sn-glycero-3-phosphocholine was employed. With this substrate system, the dose-dependent inhibition could be defined by kinetic equations describing competitive inhibition at the lipid-water interface. The apparent equilibrium dissociation constant for the inhibitor bound to the enzyme at the interface (K I *app) was determined to be 0.097 ± 0.032 mol % versus an apparent dissociation constant for the arachidonate-containing phospholipid of 0.3 ± 0.1 mol %. Thus, compound 1 represents a novel structural class of inhibitor of cPLA2 that partitions into the phospholipid bilayer and competes with the phospholipid substrate for the active site. Shorter n-alkyl-chained (C-4, C-6, C-8) derivatives of compound 1 were shown to have even smallerK I *app values. However, these short-chained analogs were less potent in terms of bulk inhibitor concentration needed for inhibition when using the [3H]arachidonate-labeled U937 membranes as substrate. This discrepancy was reconciled by showing that these shorter-chained analogs did not partition into the [3H]arachidonate-labeled U937 membranes as effectively as compound 1. The implications for in vivo efficacy that result from these findings are discussed.

BMS-933043, a Selective α7 nAChR Partial Agonist for the Treatment of Cognitive Deficits Associated with Schizophrenia

The therapeutic treatment of negative symptoms and cognitive dysfunction associated with schizophrenia is a significant unmet medical need. Preclinical literature indicates that α7 neuronal nicotinic acetylcholine (nACh) receptor agonists may provide an effective approach to treating cognitive dysfunction in schizophrenia. We report herein the discovery and evaluation of 1c (BMS-933043), a novel and potent α7 nACh receptor partial agonist with high selectivity against other nicotinic acetylcholine receptor subtypes (>100-fold) and the 5-HT3A receptor (>300-fold). In vivo activity was demonstrated in a preclinical model of cognitive impairment, mouse novel object recognition. BMS-933043 has completed Phase I clinical trials.

Triazolopyridine ethers as potent, orally active mGlu2 positive allosteric modulators for treating schizophrenia

Triazolopyridine ethers with mGlu2 positive allosteric modulator (PAM) activity are disclosed. The synthesis, in vitro activity, and metabolic stability data for a series of analogs is provided. The effort resulted in the discovery of a potent, selective, and brain penetrant lead molecule BMT-133218 ((+)-7m). After oral administration at 10mg/kg, BMT-133218 demonstrated full reversal of PCP-stimulated locomotor activity and prevented MK-801-induced working memory deficits in separate mouse models. Also, reversal of impairments in executive function were observed in rat set-shifting studies at 3 and 10mg/kg (p.o.). Extensive plasma protein binding as the result of high lipophilicity likely limited activity at lower doses. Optimized triazolopyridine ethers offer utility as mGlu2 PAMs for the treatment of schizophrenia and merit further preclinical investigation.

IKK-2/NF-κB-DEPENDENT TRANSCRIPTION

Inhibitors of IKK-2, which inhibit signaling in the NF-κB pathway (initiated by TNF-a binding to its receptor), represent potential new drug candidates, as shown by the biology/biochemistry of the target and the in vivo activity of inhibitors in a variety of disease-relevant models. In this chapter, the roles of NF-κB and IKK-2 in various disease processes are reviewed, followed by a discussion of the enzymology of IKK-2 and the data supporting its role. A summary of literature reports concerning BMS-345541, an IKK-2 inhibitor with activity in multiple disease models, follows, along with briefer reports on the published activity of other IKK-2 inhibitors. Next, a general discussion of the possible consequences of inhibiting this enzyme is given, followed by some general conclusions and outlook for clinical success.