Eryn L. Werry, Tristan A. Reekie, Michael Kassiou

Oxytocin and oxytocin receptors are synthesized in the periphery where paracrine/autocrine actions have been described alongside endocrine actions effected by central release of oxytocin from the posterior pituitary. In the female reproductive system, classical actions of uterine contraction and milk ejection from mammary glands are accompanied by actions in the ovaries where roles in steroidogenesis, follicle recruitment and ovulation have been described. Steroidogenesis, contractile activity, and gamete health are similarly affected by oxytocin in the male reproductive tract. In the cardiovascular system, a local oxytocinergic system appears to play an important cardio-protective role. This role is likely associated with emerging evidence that peripheral oxytocin is an important hormone in the endocrinology of glucose homeostasis due to its actions in adipose, the pancreas, and the largely ignored oxytocinergic systems of the adrenal glands and liver. Gene polymorphisms are shown to be associated with a number of reported traits, not least factors associated with metabolic syndrome.

Timothy B Callis, Taylor R Garrett, Andrew P Montgomery, Jonathan J Danon, Michael Kassiou

The concept of bioisosterism and the implementation of bioisosteric replacement is fundamental to medicinal chemistry. The exploration of bioisosteres is often used to probe key structural features of candidate pharmacophores and enhance pharmacokinetic properties. As the understanding of bioisosterism has evolved, capabilities to undertake more ambitious bioisosteric replacements have emerged. Scaffold hopping is a broadly used term in the literature referring to a variety of different bioisosteric replacement strategies, ranging from simple heterocyclic replacements to topological structural overhauls. In this work, we have highlighted recent applications of scaffold hopping in the central nervous system drug discovery space. While we have highlighted the benefits of using scaffold hopping approaches in central nervous system drug discovery, these are also widely applicable to other medicinal chemistry fields.

Elijah Genetzakis, Jayson Gilchrist, Michael Kassiou, Gemma A. Figtree

The purinoceptor 7 receptor (P2X7R) plays an important role in promoting inflammation in response to accumulating damage-associated molecular patterns (DAMPs) released from stressed or apoptotic cells and has been connected to various pathological conditions. The initial investment by large pharmaceutical companies such as AstraZeneca and Pfizer led to the development of several classes of P2X7R antagonists for the treatment of rheumatoid arthritis and Crohn’s disease. While these compounds showed early promise as therapeutic agents and were found to potently inhibit adenosine triphosphate (ATP)-induced release of interleukin 1 beta (IL-1β) in patient-derived monocytes primed with lipopolysaccharide (LPS), they failed to elicit a therapeutic benefit in phase II clinical trials. Within the last 10 years, a wealth of strong preclinical and clinical evidence has implicated IL-1β as an aggressor in the development and progression of cardiovascular diseases, a cytokine modulated by the P2X7R. On account of the immune-mediated events that regulate atherosclerosis, antagonism of the P2X7R has been proposed as a therapeutic strategy due to the unique functionality of the receptor as an instigator of sterile inflammation. Here, we review the success and failures in P2X7R drug development to evaluate the major barriers to successful clinical translation of P2X7R antagonists. These avenues should be addressed by researchers and pharmaceutical companies to ensure future clinical success in the treatment of CAD.

Eryn L. Werry, Fiona M. Bright & Michael Kassiou 

Neuroinflammation is a hallmark feature across the spectrum of neurodegenerative disorders. Central to neuroinflammation is the activation of microglia and astrocytes. Activated microglia, and perhaps astrocytes, display an upregulation of TSPO in neuroinflammation and in neurodegenerative disease models, based on culture and animal studies. This indicates TSPO may be a biomarker for neuroinflammation, however, clinical use of TSPO-targeting positron emission tomography to monitor neuroinflammation in neurodegenerative disorders has been hindered by the presence of a TSPO polymorphism (A147T). TSPO ligands bind with lower affinity to A147T TSPO, restricting the clinical utility of this approach. This chapter reviews the ongoing efforts to produce ligands that bind highly to A147T TSPO. It also explores the question of how to interpret the TSPO PET signal, by examining which microglial phenotypes upregulate TSPO in neuroinflammation, and what other brain cell types might contribute to the TSPO PET signal.

Alexandra Maximova, Eryn L. Werry, Michael Kassiou 

Amyotrophic lateral sclerosis (ALS) is a progressive motor neurodegenerative disease that currently has no cure and has few effective treatments. On a cellular level, ALS manifests through significant changes in the proper function of astrocytes, microglia, motor neurons, and other central nervous system (CNS) cells, leading to excess neuroinflammation and neurodegeneration. Damage to the upper and lower motor neurons results in neural and muscular dysfunction, leading to death most often due to respiratory paralysis. A new therapeutic strategy is targeting glial cells affected by senescence, which contribute to motor neuron degeneration. Whilst this new therapeutic approach holds much promise, it is yet to be trialled in ALS-relevant preclinical models and needs to be designed carefully to ensure selectivity. This review summarizes the pathways involved in ALS-related senescence, as well as known senolytic agents and their mechanisms of action, all of which may inform strategies for ALS-focused drug discovery efforts.

Ben B. Ma, Andrew P. Montgomery, Biling Chen, Michael Kassiou, Jonathan J. Danon

The purinergic 2Y type 12 receptor (P2Y12R) is a well-known biological target for anti-thrombotic drugs due to its role in platelet aggregation and blood clotting. While the importance of the P2Y12R in the periphery has been known for decades, much less is known about its expression and roles in the central nervous system (CNS), where it is expressed exclusively on microglia – the first responders to brain insults and neurodegeneration. Several seminal studies have shown that P2Y12 is a robust, translatable biomarker for anti-inflammatory and neuroprotective microglial phenotypes in models of degenerative diseases such as multiple sclerosis and Alzheimer’s disease. An enduring problem for studying this receptor in vivo, however, is the lack of selective, high-affinity small molecule ligands that can bypass the blood–brain barrier and accumulate in the CNS. In this Digest, we discuss previous attempts by researchers to target the P2Y12R in the CNS and opine on strategies that may be employed to design and assess the suitability of novel P2Y12 ligands for this purpose going forward.

Annukka Kallinen and Michael Kassiou

This review outlines small molecule radiotracers developed for positron emission tomography (PET) imaging of proteinopathies, neurodegenerative diseases characterised by accumulation of malformed proteins, over the last two decades with the focus on radioligands that have progressed to clinical studies. Introduction provides a short summary of proteinopathy targets used for PET imaging, including vastly studied proteins Aβ and tau and emerging α-synuclein. In the main section, clinically relevant Aβ and tau radioligand classes and their properties are discussed, including an overview of lead compounds and radioligand candidates studied as α-synuclein imaging agents in the early discovery and preclinical development phase. Lastly, the specific challenges and future directions in proteinopathy radioligand development are summarized.

Alexander Jackson, Eryn L. Werry, James O'Brien-Brown, PaolomSchiavini, Shane Wilkinson, Erick C.N. Wong, André D.J. McKenzie, Alexandra Maximova, Michael Kassiou

Antagonists of the P2X7 receptor (P2X7R) have the potential to treat diseases where neuroinflammation is present such as depression, chronic pain and Alzheimer's disease. We recently developed a structural hybrid (C1; 1-((adamantan-1-yl)methyl)-2-cyano-3-(quinolin-5-yl)guanidine) of a purported competitive P2X7R antagonist (C2; 2-cyano-1-((1S)-1-phenylethyl)-3-(quinolin-5-yl)guanidine) and a likely negative allosteric modulator (NAM) of the P2X7R (C3; N-((adamantan-1-yl)methyl)-2-chloro-5-methoxybenzamide). Here we aimed to pharmacologically characterize C1, to gain insights into how select structural components impact antagonist interaction with the P2X7R. A second aim was to examine the role of the peptide LL-37, an apparent activator of the P2X7R, and compare the ability of multiple P2X7R antagonists to block its effects. Compounds 1, 2 and 3 were characterised using washout, Schild and receptor protection studies, all using dye uptake assays in HEK293 cells expressing the P2X7R. LL-37 was examined in the same HEK293 cells and THP-1 monocytes. Compounds 2 and 3 acted as a BzATP-competitive antagonist and NAM of the P2X7R respectively. Compound 1 was a slowly reversible NAM of the P2X7R suggesting the incorporation of an appropriately positioned adamantane promotes binding to the allosteric site of the P2X7R. LL-37 was shown to potentiate the ability of ATP to induce dye uptake at low concentrations (1–3 μg mL-1) or induce dye uptake alone at higher concentrations (10–20 μg mL-1). None of the P2X7R antagonists studied were able to block LL-37-induced dye uptake bringing in to question the ability of current P2X7R antagonists to inhibit the inflammatory action of LL-37 in vivo.

Prita R. Asih, Anne Poljak, Michael Kassiou, Yazi D. Ke, Lars M. Ittner

The translocator protein (TSPO) has been implicated in mitochondrial transmembrane cholesterol transport, brain inflammation, and other mitochondrial functions. It is upregulated in glial cells during neuroinflammation in Alzheimer’s disease. High affinity TSPO imaging radioligands are utilized to visualize neuroinflammation. However, this is hampered by the common A147T polymorphism which compromises ligand binding. Furthermore, this polymorphism has been linked to increased risk of neuropsychiatric disorders, and possibly reduces TSPO protein stability. Here, we used immunoprecipitation coupled to mass-spectrometry (IP-MS) to establish a mitochondrial protein binding profile of wild-type (WT) TSPO and the A147T polymorphism variant. Using mitochondria from human glial cells expressing either WT or A147T TSPO, we identified 30 WT TSPO binding partners, yet only 23 for A147T TSPO. Confirming that A147T polymorphism of the TSPO might confer loss of function, we found that one of the identified interactors of WT TSPO, 14-3-3 theta (YWHAQ), a protein involved in regulating mitochondrial membrane proteins, interacts much less with A147T TSPO. Our data presents a network of mitochondrial interactions of TSPO and its A147T polymorphism variant in human glial cells and indicate functional relevance of A147T in mitochondrial protein networks.