Structure-based, multi-targeted drug discovery approach to eicosanoid inhibition: Dual inhibitors of mPGES-1 and 5-lipoxygenase activating protein (FLAP).

BACKGROUND: Due to the importance of both prostaglandins (PGs) and leukotrienes (LTs) as pro-inflammatory mediators, and the potential for eicosanoid shunting in the presence of pathway target inhibitors, we have investigated an approach to inhibiting the formation of both PGs and LTs as part of a multi-targeted drug discovery effort. METHODS: We generated ligand-protein X-ray crystal structures of known inhibitors of microsomal prostaglandin E2 synthase-1 (mPGES-1) and the 5-Lipoxygenase Activating Protein (FLAP), with their respective proteins, to understand the overlapping pharmacophores. We subsequently used molecular modeling and structure-based drug design (SBDD) to identify hybrid structures intended to inhibit both targets. RESULTS: This work enabled the preparation of compounds 4 and 5, which showed potent in vitro inhibition of both targets. SIGNIFICANCE: Our findings enhance the structural understanding of mPGES-1 and FLAP's unique ligand binding pockets and should accelerate the discovery of additional dual inhibitors for these two important integral membrane protein drug targets.

Identification and Mitigation of Reactive Metabolites of 2-Aminoimidazole-Containing Microsomal Prostaglandin E Synthase-1 Inhibitors Terminated Due to Clinical Drug-Induced Liver Injury.

Two 2-aminoimidazole-based inhibitors, LY3031207 (1) and LY3023703 (2), of the microsomal prostaglandin E synthase-1 (mPGES-1) enzyme were found to cause drug-induced liver injury (DILI) in humans. We studied imidazole ring substitutions to successfully mitigate reactive metabolite (RM) formation. These studies support the conclusion that RM formation may play a role in the observations of DILI and the consideration of 2-aminoimidazoles as structure alerts, due to the high likelihood of bioactivation to generate RMs.

Discovery and characterization of [(cyclopentyl)ethyl]benzoic acid inhibitors of microsomal prostaglandin E synthase-1.

We describe a novel class of acidic mPGES-1 inhibitors with nanomolar enzymatic and human whole blood (HWB) potency. Rational design in conjunction with structure-based design led initially to the identification of anthranilic acid 5, an mPGES-1 inhibitor with micromolar HWB potency. Structural modifications of 5 improved HWB potency by over 1000×, reduced CYP2C9 single point inhibition, and improved rat clearance, which led to the selection of [(cyclopentyl)ethyl]benzoic acid compound 16 for clinical studies. Compound 16 showed an IC80 of 24nM for inhibition of PGE2 formation in vitro in LPS-stimulated HWB. A single oral dose resulted in plasma concentrations of 16 that exceeded its HWB IC80 in both rat (5mg/kg) and dog (3mg/kg) for over twelve hours.

Novel Autotaxin Inhibitors for the Treatment of Osteoarthritis Pain: Lead Optimization via Structure-Based Drug Design.

In an effort to develop a novel therapeutic agent aimed at addressing the unmet need of patients with osteoarthritis pain, we set out to develop an inhibitor for autotaxin with excellent potency and physical properties to allow for the clinical investigation of autotaxin-induced nociceptive and neuropathic pain. An initial hit identification campaign led to an aminopyrimidine series with an autotaxin IC50 of 500 nM. X-ray crystallography enabled the optimization to a lead compound that demonstrated favorable potency (IC50 = 2 nM), PK properties, and a robust PK/PD relationship.

Characterization of 3,3-dimethyl substituted N-aryl piperidines as potent microsomal prostaglandin E synthase-1 inhibitors.

Here we report on novel, potent 3,3-dimethyl substituted N-aryl piperidine inhibitors of microsomal prostaglandin E synthases-1(mPGES-1). Example 14 potently inhibited PGE2 synthesis in an ex vivo human whole blood (HWB) assay with an IC50 of 7nM. In addition, 14 had no activity in human COX-1 or COX-2 assays at 30µM, and failed to inhibit human mPGES-2 at 62.5µM in a microsomal prep assay. These data are consistent with selective mPGES-1-mediated reduction of PGE2. In dog, 14 had oral bioavailability (74%), clearance (3.62mL/(min*kg)) and volume of distribution (Vd,ss=1.6L/kg) values within our target ranges. For these reasons, 14 was selected for further study.

Identification of potent and selective retinoic acid receptor gamma (RARγ) antagonists for the treatment of osteoarthritis pain using structure based drug design.

A series of triaryl pyrazoles were identified as potent pan antagonists for the retinoic acid receptors (RARs) α, ß and γ. X-ray crystallography and structure-based drug design were used to improve selectivity for RARγ by targeting residue differences in the ligand binding pockets of these receptors. This resulted in the discovery of novel antagonists which maintained RARγ potency but were greater than 500-fold selective versus RARα and RARß. The potent and selective RARγ antagonist LY2955303 demonstrated good pharmacokinetic properties and was efficacious in the MIA model of osteoarthritis-like joint pain. This compound demonstrated an improved margin to RARα-mediated adverse effects.

Identification and Characterization of Novel Microsomal Prostaglandin E Synthase-1 Inhibitors for Analgesia.

Prostaglandin (PG) E2 plays a critical role in eliciting inflammation. Nonsteroidal anti-inflammatory drugs and selective inhibitors of cyclooxygenase, which block PGE2 production, have been used as key agents in treating inflammation and pain associated with arthritis and other conditions. However, these agents have significant side effects such as gastrointestinal bleeding and myocardial infarction, since they also block the production of prostanoids that are critical for other normal physiologic functions. Microsomal prostaglandin E2 synthase-1 is a membrane-bound terminal enzyme in the prostanoid pathway, which acts downstream of cyclooxygenase 2 and is responsible for PGE2 production during inflammation. Thus, inhibition of this enzyme would be expected to block PGE2 production without inhibiting other prostanoids and would provide analgesic efficacy without the side effects. In this report, we describe novel microsomal prostaglandin E2 synthase-1 inhibitors that are potent in blocking PGE2 production and are efficacious in a guinea pig monoiodoacetate model of arthralgia. These molecules may be useful in treating the signs and symptoms associated with arthritis.

Discovery and Characterization of 2-Acylaminoimidazole Microsomal Prostaglandin E Synthase-1 Inhibitors.

As part of a program aimed at the discovery of antinociceptive therapy for inflammatory conditions, a screening hit was found to inhibit microsomal prostaglandin E synthase-1 (mPGES-1) with an IC50 of 17.4 µM. Structural information was used to improve enzyme potency by over 1000-fold. Addition of an appropriate substituent alleviated time-dependent cytochrome P450 3A4 (CYP3A4) inhibition. Further structure-activity relationship (SAR) studies led to 8, which had desirable potency (IC50 = 12 nM in an ex vivo human whole blood (HWB) assay) and absorption, distribution, metabolism, and excretion (ADME) properties. Studies on the formulation of 8 identified 8·H3PO4 as suitable for clinical development. Omission of a lipophilic portion of the compound led to 26, a readily orally bioavailable inhibitor with potency in HWB comparable to celecoxib. Furthermore, 26 was selective for mPGES-1 inhibition versus other mechanisms in the prostanoid pathway. These factors led to the selection of 26 as a second clinical candidate.

Novel 3-aryl indoles as progesterone receptor antagonists for uterine fibroids.

We report the synthesis and characterization of novel 3-aryl indoles as potent and efficacious progesterone receptor (PR) antagonists with potential for the treatment of uterine fibroids. These compounds demonstrated excellent selectivity over other steroid nuclear hormone receptors such as the mineralocorticoid receptor (MR). They were prepared from 2-bromo-6-nitro indole in four to six steps using a Suzuki cross-coupling as the key step. Compound 8f was orally active in the complement 3 model of progesterone antagonism in the rat uterus and demonstrated partial antagonism in the McPhail model of progesterone activity.