Safety evaluation of FM101, an A3 adenosine receptor modulator, in rat, for developing as therapeutics of glaucoma and hepatitis

Problems and prospects for finding new pharmacological agents among adenosine receptor agonists, antagonists, or their allosteric modulators for the treatment of cardiovascular diseases

A1-adenosine receptors (A1AR) are widely distributed in the human body and mediate many different effects. They are abundantly present in the cardiovascular system, where they control angiogenesis, vascular tone, heart rate, and conduction. This makes the cardiovascular system A1AR an attractive target for the treatment of cardiovascular diseases (CVD). The review summarizes the literature data on the structure and functioning of A1AR, and analyzes their involvement in the formation of myocardial hypertrophy, ischemia-reperfusion damage, various types of heart rhythm disorders, chronic heart failure, and arterial hypertension. Special attention is paid to the role of some allosteric regulators of A1AR as potential agents for the CVD treatment.

First Potent Macrocyclic A3 Adenosine Receptor Agonists Reveal G-Protein and β-Arrestin2 Signaling Preferences

(N)-Methanocarba adenosine derivatives (A3 adenosine receptor (AR) agonists containing bicyclo[3.1.0]hexane replacing furanose) were chain-extended at N6 and C2 positions with terminal alkenes for ring closure. The resulting macrocycles of 17-20 atoms retained affinity, indicating a spatially proximal orientation of these receptor-bound chains, consistent with molecular modeling of 12. C2-Arylethynyl-linked macrocycle 19 was more A3AR-selective than 2-ether-linked macrocycle 12 (both 5'-methylamides, human (h) A3AR affinities (Ki): 22.1 and 25.8 nM, respectively), with lower mouse A3AR affinities. Functional hA3AR comparison of two sets of open/closed analogues in β-arrestin2 and Gi/o protein assays showed certain signaling preferences divergent from reference agonist Cl-IB-MECA 1. The potencies of 1 at all three Gαi isoforms were slightly less than its hA3AR binding affinity (Ki: 1.4 nM), while the Gαi1 and Gαi2 potencies of macrocycle 12 were roughly an order of magnitude higher than its radioligand binding affinity. Gαi2-coupling was enhanced in macrocycle 12 (EC50 2.56 nM, ∼40% greater maximal efficacy than 1). Di-O-allyl precursor 18 cyclized to form 19, increasing the Gαi1 potency by 7.5-fold. The macrocycles 12 and 19 and their open precursors 11 and 18 potently stimulated β-arrestin2 recruitment, with EC50 values (nM) of 5.17, 4.36, 1.30, and 4.35, respectively, and with nearly 50% greater efficacy compared to 1. This example of macrocyclization altering the coupling pathways of small-molecule (nonpeptide) GPCR agonists is the first for potent and selective macrocyclic AR agonists. These initial macrocyclic derivatives can serve as a guide for the future design of macrocyclic AR agonists displaying unanticipated pharmacology.

Assay-Dependent Inverse Agonism at the A3 Adenosine Receptor: When Neutral Is Not Neutral

The A3 adenosine receptor (A3AR) is implicated in a variety of (patho)physiological conditions. While most research has focused on agonists and antagonists, inverse agonism at A3AR has been scarcely studied. Therefore, this study aimed at exploring inverse agonism, using two previously engineered cell lines (hA3ARLgBiT-SmBiTβarr2 and hA3ARLgBiT-SmBiTminiGαi), both employing the NanoBiT technology. The previously established inverse agonist PSB-10 showed a decrease in basal signal in the β-arrestin 2 (βarr2) but not the miniGαi recruitment assay, indicative of inverse agonism in the former assay. Control experiments confirmed the specificity and reversibility of this observation. Evaluation of a set of presumed neutral antagonists (MRS7907, MRS7799, XAC, and MRS1220) revealed that all displayed concentration-dependent signal decreases when tested in the A3AR-βarr2 recruitment assay, yielding EC50 and Emax values for inverse agonism. Conversely, in the miniGαi recruitment assay, no signal decreases were observed. To assess whether this observation was caused by the inability of the ligands to induce inverse agonism in the G protein pathway, or rather by a limitation inherent to the employed A3AR-miniGαi recruitment assay, a GloSensor cAMP assay was performed. The outcome of the latter also suggests inverse agonism by the presumed neutral antagonists in this latter assay. These findings emphasize the importance of prior characterization of ligands in the relevant test system. Moreover, it showed the suitability of the NanoBiT βarr2 recruitment and the GloSensor cAMP assays to capture inverse agonism at the A3AR, as opposed to the NanoBiT miniGαi recruitment assay.

Species dependence of A3 adenosine receptor pharmacology and function

Efforts to fully understand pharmacological differences between G protein-coupled receptor (GPCR) species homologues are generally not pursued in detail during the drug development process. To date, many GPCRs that have been successfully targeted are relatively well-conserved across species in amino acid sequence and display minimal variability of biological effects. However, the A3 adenosine receptor (AR), an exciting drug target for a multitude of diseases associated with tissue injury, ischemia, and inflammation, displays as little as 70% sequence identity among mammalian species (e.g., rodent vs. primate) commonly used in drug development. Consequently, the pharmacological properties of synthetic A3AR ligands vary widely, not only in binding affinity, selectivity, and signaling efficacy, but to the extent that some function as agonists in some species and antagonists in others. Numerous heterocyclic antagonists that have nM affinity at the human A3AR are inactive or weakly active at the rat and mouse A3ARs. Positive allosteric modulators, including the imidazo [4,5-c]quinolin-4-amine derivative LUF6000, are only active at human and some larger animal species that have been evaluated (rabbit and dog), but not rodents. A3AR agonists evoke systemic degranulation of rodent, but not human mast cells. The rat A3AR undergoes desensitization faster than the human A3AR, but the human homologue can be completely re-sensitized and recycled back to the cell surface. Thus, comprehensive pharmacological evaluation and awareness of potential A3AR species differences are critical in studies to further understand the basic biological functions of this unique AR subtype. Recombinant A3ARs from eight different species have been pharmacologically characterized thus far. In this review, we describe in detail current knowledge of species differences in genetic identity, G protein-coupling, receptor regulation, and both orthosteric and allosteric A3AR pharmacology.

Molecular Simulations and Drug Discovery of Adenosine Receptors

G protein-coupled receptors (GPCRs) represent the largest family of human membrane proteins. Four subtypes of adenosine receptors (ARs), the A1AR, A2AAR, A2BAR and A3AR, each with a unique pharmacological profile and distribution within the tissues in the human body, mediate many physiological functions and serve as critical drug targets for treating numerous human diseases including cancer, neuropathic pain, cardiac ischemia, stroke and diabetes. The A1AR and A3AR preferentially couple to the Gi/o proteins, while the A2AAR and A2BAR prefer coupling to the Gs proteins. Adenosine receptors were the first subclass of GPCRs that had experimental structures determined in complex with distinct G proteins. Here, we will review recent studies in molecular simulations and computer-aided drug discovery of the adenosine receptors and also highlight their future research opportunities.

Exploring Non-orthosteric Interactions with a Series of Potent and Selective A3 Antagonists

A library of potent and highly A₃AR selective pyrimidine-based compounds was designed to explore non-orthosteric interactions within this receptor. Starting from a prototypical orthosteric A₃AR antagonist (ISVY130), the structure-based design explored functionalized residues at the exocyclic amide L1 region and aimed to provide additional interactions outside the A₃AR orthosteric site. The novel ligands were assembled through an efficient and succinct synthetic approach, resulting in compounds that retain the A₃AR potent and selective profile while improving the solubility of the original scaffold. The experimentally demonstrated tolerability of the L1 region to structural functionalization was further assessed by molecular dynamics simulations, giving hints of the non-orthosteric interactions explored by these series. The results pave the way to explore newly functionalized A₃AR ligands, including covalent drugs and molecular probes for diagnostic and delivery purposes.

Glaucoma Clinical Research: Trends in Treatment Strategies and Drug Development

Purpose: To investigate the trends and progresses in glaucoma research by searching two major clinical trial registries; clinicaltrials.gov, and Australianclinicaltrials.gov.au. Methods: All clinical trials with glaucoma covered by Clinicaltrials.gov, and Australianclinicaltrials.gov.au starting the study before 1 January 2021 were included. Trials evaluating glaucoma treatment were separated from non-treatment trials and divided into three major categories: "laser treatment," "surgical treatment," and "medical treatment." In the category of "medical treatment," new compounds and their individual targets were identified and subcategorized according to treatment strategy; intraocular pressure (IOP)-lowering, neuroprotective or vascular. The phase transition success rates were calculated. Results: One-thousand five hundred and thirty-seven trials were identified. Sixty-three percent (n = 971) evaluated glaucoma treatment, of which medical treatment accounted for the largest proportion (53%). The majority of medical trials evaluated IOP-lowering compounds, while trials with neuroprotective or vascular compounds accounted for only 5 and 3%, respectively. Eighty-eight new compounds were identified. Phase I, II, and III transition success rates were 63, 26, and 47%, respectively. Conclusion: The number of clinical trials in glaucoma research has increased significantly over the last 30 years. Among the most recently evaluated compounds, all three main treatment strategies were represented, but clinical trials in neuroprotection and vascular modalities are still sparse. In addition to traditional medicines, dietary supplements and growth factors are assessed for a potential anti-glaucomatous effect. Phase II and III success rates were below previously reported success rates for all diseases and ophthalmology in general. A stricter phenotyping of patients can improve the success rates in glaucoma and ophthalmological research and gain a better understanding of responders and non-responders.

The Latest Drugs in Development That Reduce Intraocular Pressure in Ocular Hypertension and Glaucoma

Glaucoma causes irreversible vision loss, with elevated intraocular pressure (IOP) being the only known modifiable risk factor. There are a variety of medical and interventional options for lowering IOP; however, despite these treatments, glaucoma continues to be a leading cause of visual impairment. Further research continues to strive for treatment options with improved side effect profiles, additional IOP-lowering effects, and ease of use. This review provides a brief summary of current IOP-lowering therapies and then outlines pipeline ocular hypotensive agents, their mechanisms of action, benefits, and side effect profiles. Advancements are seen within currently used eye drop classes such as prostaglandin analogues, Rho kinase inhibitors and nitric oxide donors, whilst there are also new drug classes, such as tyrosine protein kinase activators. Most developing drugs are topical drop formulations, with a number already having entered Phase III trials. Alternative drug delivery methods are also in development and will be briefly discussed. Pharmacological and drug delivery developments continue to provide glaucoma patients and clinicians with new options and the promise of better outcomes, particularly in terms of improved tolerance and reduced frequency of dosing.