Novel prostaglandin receptor modulators: a patent review (2002 – 2012) – part I: non-EP receptor modulators

Discovery of MK-8318, a Potent and Selective CRTh2 Receptor Antagonist for the Treatment of Asthma

A novel series of tricyclic tetrahydroquinolines were identified as potent and selective CRTh2 receptor antagonists. The agonism and antagonism switch was achieved through structure-based drug design (SBDD) using a CRTh2 receptor homologue model. The challenge of very low exposures in pharmacokinetic studies was overcome by exhaustive medicinal chemistry lead optimization through focused SAR studies on the tricyclic core. Further optimization resulted in the identification of the preclinical candidate 4-(cyclopropyl((3aS,9R,9aR)-7-fluoro-4-(4-(trifluoromethoxy)benzoyl)-2,3,3a,4,9,9a-hexahydro-1H-cyclopenta[b]quinolin-9-yl)amino)-4-oxobutanoic acid (15c, MK-8318) with potent and selective CRTh2 antagonist activity and a favorable PK profile suitable for once daily oral dosing for potential treatment of asthma.

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Opportunities and Challenges for Fatty Acid Mimetics in Drug Discovery

Fatty acids beyond their role as an endogenous energy source and storage are increasingly considered as signaling molecules regulating various physiological effects in metabolism and inflammation. Accordingly, the molecular targets involved in formation and physiological activities of fatty acids hold significant therapeutic potential. A number of these fatty acid targets are addressed by some of the oldest and most widely used drugs such as cyclooxygenase inhibiting NSAIDs, whereas others remain unexploited. Compounds orthosterically binding to proteins that endogenously bind fatty acids are considered as fatty acid mimetics. On the basis of their structural resemblance, fatty acid mimetics constitute a family of bioactive compounds showing specific binding thermodynamics and following similar pharmacokinetic mechanisms. This perspective systematically evaluates targets for fatty acid mimetics, investigates their common structural characteristics, and highlights demands in their discovery and design. In summary, fatty acid mimetics share particularly favorable characteristics justifying the conclusion that their therapeutic potential vastly outweighs the challenges in their design.

Pirinixic acids: flexible fatty acid mimetics with various biological activities

Pirinixic acid is a typical fatty acid mimetic and was developed as synthetic antihyperlipidemic agent. While its target remained unknown in the early development, it has later been characterized as dual PPARα/γ agonist. Based on this activity, pirinixic acid has served as a lead compound for several structure–activity relationship (SAR) studies addressing diverse targets for lipid mimetics. Many structural variants of pirinixic acid descendants have been developed and thereby potent agents on metabolic, inflammatory and neuroprotective targets were discovered of which some have proven in vivo efficacy. This article reviews pirinixic acid descendants along with their in vitro-pharmacological profiles, summarizes their in vivo data and finally gives a future perspective for this valuable class of fatty acid mimetics.

Solving time-dependent CYP3A4 inhibition for a series of indole-phenylacetic acid dual antagonists of the PGD(2) receptors CRTH2 and DP

Based on their structural similarity to previously described compound AMG 009, indole-phenyl acetic acids were proposed to be potent dual inhibitors of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2 or DP2) and prostanoid D receptor (DP or DP1). This series was equipotent to AMG 009 in binding assays against both receptors but exhibited decreased serum shift. We discovered early in the optimization of these indole-phenylacetic acid compounds that they demonstrated CYP3A4 time-dependent inhibition (TDI). Hypothesizing that the source of TDI was the indole core we modified the 1,2,3-substitution to eventually afford a highly potent modulator of CRTH2 and DP which did not exhibit TDI.

Update on the status of DP2 receptor antagonists; from proof of concept through clinical failures to promising new drugs

INTRODUCTION

The identification of PGD2 as the cognate ligand for the DP2 (formerly CRTH2) receptor and the apparent role of that receptor in allergic disease has led to considerable interest in the development of DP2 receptor antagonists for the treatment of asthma. Around 20 DP2 receptor antagonists have progressed into development.

AREAS COVERED

The DP2 antagonists in clinical development and those whose development has been discontinued are discussed in detail. This article highlights the former and examines the available clinical data in respect of both groups of antagonists. It draws upon data that are available from clinical trial registries as well as data that have been presented.

EXPERT OPINION

The unpromising clinical outcomes obtained with setipiprant, vidupiprant and AZD-1981, and the reason why development of OC-459 appears stalled, are all considered. An assessment of the nine DP2 antagonists currently in clinical development highlights the apparent advantages of ADC-3680 and MK-1029. The scope for licensing opportunities in this field is also highlighted.