Structure-activity relationships of pyrimidine nucleotides containing a 5'-α,β-methylene diphosphonate at the P2Y6 receptor

Comprehensive insights into potential roles of purinergic P2 receptors on diseases: Signaling pathways involved and potential therapeutics

BACKGROUND

Purinergic P2 receptors, which can be divided into ionotropic P2X receptors and metabotropic P2Y receptors, mediate cellular signal transduction of purine or pyrimidine nucleoside triphosphates and diphosphate. Based on the wide expression of purinergic P2 receptors in tissues and organs, their significance in homeostatic maintenance, metabolism, nociceptive transmission, and other physiological processes is becoming increasingly evident, suggesting that targeting purinergic P2 receptors to regulate biological functions and signal transmission holds significant promise for disease treatment.

AIM OF REVIEW

This review highlights the detailed mechanisms by which purinergic P2 receptors engage in physiological and pathological progress, as well as providing prospective strategies for discovering clinical drug candidates.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The purinergic P2 receptors regulate complex signaling and molecular mechanisms in nervous system, digestive system, immune system and as a result, controlling physical health states and disease progression. There has been a significant rise in research and development focused on purinergic P2 receptors, contributing to an increased number of drug candidates in clinical trials. A few influential pioneers have laid the foundation for advancements in the evaluation, development, and of novel purinergic P2 receptors modulators, including agonists, antagonists, pharmaceutical compositions and combination strategies, despite the different scaffolds of these drug candidates. These advancements hold great potential for improving therapeutic outcomes by specifically targeting purinergic P2 receptors.

Functionalized Congeners of 2H-Chromene P2Y6 Receptor Antagonists

The P2Y6 receptor (P2Y6R), a Gq-coupled receptor, is a potential drug discovery target for various inflammatory and degenerative conditions. Antagonists have been shown to attenuate colitis, acute lung injury, etc. In the search for competitive antagonists, we have investigated the SAR of 3-nitro-2-(trifluoromethyl)-2H-chromene derivatives, although high affinity is lacking. We now reveal that long-chain amino-functionalized congeners display greatly enhanced affinity in the antagonism of UDP-induced Ca2+ mobilization in human (h) P2Y6R-transfected 1321N1 astrocytoma cells. A 6-(Boc-amino-n-heptylethynyl) analogue 30 (MRS4940) had an IC50 of 162 nM, which was a 123-fold greater affinity than the corresponding unprotected primary alkylamine, 107-fold greater than the corresponding pivaloyl derivative 30, and 132-fold selective compared to the P2Y14R. However, similar Boc-amino chains attached at the 8-position produced weak µM affinity. Thus, the P2Y6R affinity depended on the chain length, attachment point, and terminal functionality. Off-target activities, at 45 sites, were tested for acylamino derivatives 20, 24, 26, 30, 31, and 37, which showed multiple interactions, particularly at the biogenic amine receptors. The more potent analogues may be suitable for evaluation in inflammation and cancer models, which will be performed in future studies.

Moving out of CF3 -Land: Synthesis, Receptor Affinity, and in silico Studies of NK1 Receptor Ligands Containing a Pentafluorosulfanyl (SF5 ) Group

The NK1 receptor (NK1R) is a molecular target for both approved and experimental drugs intended for a variety of conditions, including emesis, pain, and cancers. While contemplating modifications to the typical NK1R pharmacophore, we wondered whether the CF3 groups common for many NK1R ligands, could be replaced with some other moiety. Our attention was drawn by the SF5 group, and so we designed, synthesized, and tested ten novel SF5 -containing compounds for NK1R affinity. All analogues exhibit detectable NK1R binding, with the best of them, compound 5 a, (3-bromo-5-(pentafluoro-λ6 -sulfanyl)benzyl acetyl-L-tryptophanate) binding only slightly worse (IC50 =34.3 nM) than the approved NK1R-targeting drug, aprepitant (IC50 =27.7 nM). Molecular docking provided structural explanation of SAR. According to our analysis, the SF5 group in our compounds occupies a position similar to that of one of the CF3 groups of aprepitant as found in the crystal structure. Additionally, we checked whether the docking scoring function or energies derived from Fragment Molecular Orbital quantum chemical calculations may be helpful in explaining and predicting the experimental receptor affinities for our analogues. Both these methods produce moderately good results. Overall, this is the first demonstration of the utility of the SF5 group in the design of NK1R ligands.

Ligand-dependent intracellular trafficking of the G protein-coupled P2Y6 receptor

Endosomal trafficking is intricately linked to G protein-coupled receptors (GPCR) fate and signaling. Extracellular uridine diphosphate (UDP) acts as a signaling molecule by selectively activating the GPCR P2Y₆. Despite the recent interest for this receptor in pathologies, such as gastrointestinal and neurological diseases, there is sparse information on the endosomal trafficking of P2Y₆ receptors in response to its endogenous agonist UDP and synthetic selective agonist 5-iodo-UDP (MRS2693). Confocal microscopy and cell surface ELISA revealed delayed internalization kinetics in response to MRS2693 vs. UDP stimulation in AD293 and HCT116 cells expressing human P2Y₆. Interestingly, UDP induced clathrin-dependent P2Y₆ internalization, whereas receptor stimulation by MRS2693 endocytosis appeared to be associated with a caveolin-dependent mechanism. Internalized P2Y₆ was associated with Rab4, 5, and 7 positive vesicles independent of the agonist. We have measured a higher frequency of receptor expression co-occurrence with Rab11-vesicles, the trans-Golgi network, and lysosomes in response to MRS2693. Interestingly, a higher agonist concentration reversed the delayed P2Y₆ internalization and recycling kinetics in the presence of MRS2693 stimulation without changing its caveolin-dependent internalization. This work showed a ligand-dependent effect affecting the P2Y₆ receptor internalization and endosomal trafficking. These findings could guide the development of bias ligands that could influence P2Y₆ signaling.

Synthesis and pharmacological characterization of multiply substituted 2H-chromene derivatives as P2Y6 receptor antagonists

P2Y6 receptor (P2Y6R) antagonists represent potential drugs for treating cancer, pain, neurodegeneration, asthma, diabetes, colitis and other disorders. However, there are few chemical classes of known competitive antagonists. We recently explored the structure activity relationship (SAR) of 2H-chromene derivatives as P2Y6R antagonists of moderate affinity. New analogues in this series modified at five positions were synthesized and shown to antagonize Ca2+ transients induced by the native agonist UDP in human (h) P2Y6R-expressing (but not turkey P2Y1R-, hP2Y2R- or hP2Y4R-expressing) astrocytoma cells. Alternatives to the reported 2-(trifluoromethyl)- and 3-nitro- substitutions of this scaffold were not identified. However, 6‑fluoro 11 and 6‑chloro 12 analogues displayed enhanced potency compared to other halogens, although still in the 1 - 2 µM range. Similar halogen substitution at 5, 7 or 8 positions reduced affinity. 5- or 8‑Triethylsilylethynyl extension maintained hP2Y6R affinity, with IC50 0.46 µM for 26 (MRS4853). The 6,8‑difluoro analogue 27 (IC50 2.99 µM) lacked off-target activities among 45 sites examined, unlike earlier analogues that bound to biogenic amine receptors. 11 displayed only one weak off-target activity (σ2). Mouse P2Y6R IC50s of 5, 25, 26 and 27 were 4.94, 17.6, 6.15 and 17.8 µM, respectively, but most other analogues had reduced affinity (>20 µM) compared to the hP2Y6R. These analogues are suitable for evaluation in in vivo inflammation and cancer models, which will be performed in the future studies.

Adipocyte purinergic receptors activated by uracil nucleotides as obesity and type 2 diabetes targets

Extracellular uridine nucleotides regulate physiological and pathophysiological metabolic processes through the activation of P2Y₂, P2Y₄, P2Y₆ and P2Y₁₄ purinergic receptors, which play a key role in adipogenesis, glucose uptake, lipolysis and adipokine secretion. Using adipocyte-specific knockout mouse models, it has been demonstrated that lack of the P2Y₆R or P2Y₁₄R can protect against diet-induced obesity and improve whole-body glucose metabolism. The P2Y₂R facilitated adipogenesis and inflammation, and the loss of P2Y₄R or P2Y₁₄R raised the levels of the protective endocrine factor adiponectin. Hence, potent antagonists for these receptors may be tested to identify drug candidates for the treatment of obesity and type 2 diabetes. However, future studies are required to provide insight into purinergic regulation of brown adipocytes and their role in thermogenesis. This review summarizes the current studies on uridine nucleotide-activated P2YRs and their role in adipocyte function, diet-induced obesity and associated metabolic deficits.

Structure-Activity Relationship of 3-Methylcytidine-5'-α,β-methylenediphosphates as CD73 Inhibitors

We recently reported N4-substituted 3-methylcytidine-5'-α,β-methylenediphosphates as CD73 inhibitors, potentially useful in cancer immunotherapy. We now expand the structure-activity relationship of pyrimidine nucleotides as human CD73 inhibitors. 4-Chloro (MRS4598 16; Ki = 0.673 nM) and 4-iodo (MRS4620 18; Ki = 0.436 nM) substitution of the N4-benzyloxy group decreased Ki by ∼20-fold. Primary alkylamine derivatives coupled through a p-amido group with a varying methylene chain length (24 and 25) were functionalized congeners, for subsequent conjugation to carrier or reporter moieties. X-ray structures of hCD73 with two inhibitors indicated a ribose ring conformational adaptation, and the benzyloxyimino group (E configuration) binds to the same region (between the C-terminal and N-terminal domains) as N4-benzyl groups in adenine inhibitors. Molecular dynamics identified stabilizing interactions and predicted conformational diversity. Thus, by N4-benzyloxy substitution, we have greatly enhanced the inhibitory potency and added functionality enabling molecular probes. Their potential as anticancer drugs was confirmed by blocking CD73 activity in tumor tissues in situ.

Purinergic Signaling in Liver Pathophysiology

Extracellular nucleosides and nucleotides activate a group of G protein-coupled receptors (GPCRs) known as purinergic receptors, comprising adenosine and P2Y receptors. Furthermore, purinergic P2X ion channels are activated by ATP. These receptors are expressed in liver resident cells and play a critical role in maintaining liver function. In the normal physiology, these receptors regulate hepatic metabolic processes such as insulin responsiveness, glycogen and lipid metabolism, and bile secretion. In disease states, ATP and other nucleotides serve as danger signals and modulate purinergic responses in the cells. Recent studies have demonstrated that purinergic receptors play a significant role in the development of metabolic syndrome associated non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), fibrosis, hepatocellular carcinoma (HCC) and liver inflammation. In this concise review, we dissect the role of purinergic signaling in different liver resident cells involved in maintaining healthy liver function and in the development of the above-mentioned liver pathologies. Moreover, we discuss potential therapeutic strategies for liver diseases by targeting adenosine, P2Y and P2X receptors.