Discovery of potent, balanced and orally active dual NK1/NK3 receptor ligands

The Neurokinins: Peptidomimetic Ligand Design and Therapeutic Applications

The neurokinins are indisputably essential neurotransmitters in numerous pathoand physiological events. Being widely distributed in the Central Nervous System (CNS) and peripheral tissues, their discovery rapidly promoted them to drugs targets. As a necessity for molecular tools to understand the biological role of this class, endogenous peptides and their receptors prompted the scientific community to design ligands displaying either agonist and antagonist activity at the three main neurokinin receptors, called NK1, NK2 and NK3. Several strategies were implemented for this purpose. With a preference to small non-peptidic ligands, many research groups invested efforts in synthesizing and evaluating a wide range of scaffolds, but only the NK1 antagonist Aprepitant (EMENDT) and its prodrug Fosaprepitant (IVEMENDT) have been approved by the Food Drug Administration (FDA) for the treatment of Chemotherapy-Induced and Post-Operative Nausea and Vomiting (CINV and PONV, respectively). While non-peptidic drugs showed limitations, especially in side effect control, peptidic and pseudopeptidic compounds progressively regained attention. Various strategies were implemented to modulate affinity, selectivity and activity of the newly designed ligands. Replacement of canonical amino acids, incorporation of conformational constraints, and fusion with non-peptidic moieties gave rise to families of ligands displaying individual or dual NK1, NK2 and NK3 antagonism, that ultimately were combined with non-neurokinin ligands (such as opioids) to target enhanced biological impact.

Design, Synthesis, and Optimization of Balanced Dual NK1/NK3 Receptor Antagonists

In connection with a program directed at potent and balanced dual NK1/NK3 receptor ligands, a focused exploration of an original class of peptidomimetic derivatives was performed. The rational design and molecular hybridization of a novel phenylalanine core series was achieved to maximize the in vitro affinity and antagonism at both human NK1 and NK3 receptors. This study led to the identification of a new potent dual NK1/NK3 antagonist with pK i values of 8.6 and 8.1, respectively.

Progress in the development of neurokinin 3 modulators for the treatment of schizophrenia: molecule development and clinical progress

The neuropeptide NK3 receptor is expressed almost exclusively within the mammalian nervous system and its localization is commensurate with a role in modulating central monoaminergic neurotransmission. Following on from our previous work we review the rationale for NK3 receptor antagonists as wide spectrum antipsychotics and the recent scientific and patent literature that has highlighted new chemical strategies to identify selective NK3 and dual activity NK1/3 receptor ligands for the putative treatment of schizophrenia. We discuss the emerging structural biology and its use in the design of molecules with increased structural diversity and predictable receptor pharmacology. Particular attention is paid to the progress in improving ligand drug-like properties. The status of imaging and the development of translational technologies in the neurokinin field are also discussed. Finally, we summarize the available clinical information on the compounds that have progressed into psychiatric patient populations and evaluate the potential therapeutic utility of NK3 receptor targeted ligands.

Design and synthesis of potential dual NK(1)/NK(3) receptor antagonists

The tachykinin NK1 and NK3 receptors are a novel drug target for schizophrenia in order to treat not only the positive and cognitive symptoms, but also the associated co-morbid depression and sleep disturbances associated with the disease. A novel class of peptidomimetic derivatives based on a versatile phenylglycine central core was synthesized and tested in vitro as dual NK1/NK3 receptor antagonists. From this series emerged compounds with good NK1 receptor affinity, although only modest dual NK1/NK3 receptor affinity was observed with one of these analogs.

Characterization of RO4583298 as a novel potent, dual antagonist with in vivo activity at tachykinin NK₁ and NK₃ receptors

BACKGROUND AND PURPOSE

Clinical results of osanetant and talnetant (selective-NK₃ antagonists) indicate that blocking the NK₃ receptor could be beneficial for the treatment of schizophrenia. The objective of this study was to characterize the in vitro and in vivo properties of a novel dual NK₁/NK₃ antagonist, RO4583298 (2-phenyl-N-(pyridin-3-yl)-N-methylisobutyramide derivative).

EXPERIMENTAL APPROACH

RO4583298 in vitro pharmacology was investigated using radioligand binding ([³H]-SP, [³H]-osanetant, [³H]-senktide), [³H]-inositol-phosphate accumulation Schild analysis (SP- or [MePhe⁷]-NKB-induced) and electrophysiological studies in guinea-pig substantia nigra pars compacta (SNpc). The in vivo activity of RO4583298 was assessed using reversal of GR73632-induced foot tapping in gerbils (GFT; NK₁) and senktide-induced tail whips in mice (MTW; NK₃).

KEY RESULTS

RO4583298 has a high-affinity for NK₁ (human and gerbil) and NK₃ (human, cynomolgus monkey, gerbil and guinea-pig) receptors and behaves as a pseudo-irreversible antagonist. Unusually it binds with high-affinity to mouse and rat NK₃, yet with a partial non-competitive mode of antagonism. In guinea-pig SNpc, RO4583298 inhibited the senktide-induced potentiation of spontaneous activity of dopaminergic neurones with an apparent non-competitive mechanism of action. RO4583298 (p.o.) robustly blocked the GFT response, and inhibited the MTW.

CONCLUSIONS AND IMPLICATIONS

RO4583298 is a high-affinity, non-competitive, long-acting in vivo NK₁/NK₃ antagonist; hence providing a useful in vitro and in vivo pharmacological tool to investigate the roles of NK₁ and NK₃ receptors in psychiatric disorders.

Tachykinin neurokinin 3 receptor antagonists: a patent review (2005 - 2010)

INTRODUCTION

The neurokinin 3 (NK(3)) receptor is a GPCR that has been shown to modulate monoaminergic systems within regions of the brain implicated in schizophrenia. Preclinical and Phase II clinical results of osanetant and talnetant in schizophrenic patients have indicated that NK(3) antagonists may provide significant improvement of the positive symptoms and cognitive impairment associated with this disorder. Recent findings have also indicated that neurokinin B (NKB)-NK(3) signaling plays a key role in the hypothalamic regulation of reproduction in humans.

AREAS COVERED

This review article discusses the latest medicinal chemistry strategies used to derive novel NK(3) receptor antagonists which have been patented during the period 2005 - 2010.

EXPERT OPINION

Since the report of a beneficial effect of osanetant in schizophrenic patients, major pharmaceutical companies have been involved in this field, leading to a very large number of patent applications disclosed. Nevertheless, only three NK(3) selective antagonists entered into Phase II, but were then terminated for various reasons. Currently, the main challenge to move forward a selective NK(3) antagonist into the clinic would be to define a safety margin between the desired therapeutic effect and the effect on testosterone levels. The involvement of NKB-NK(3) signaling in reproduction in humans may also lead to new exciting indications, such as treatment for sex steroid-sensitive cancers of breast and prostate.