Beyond the Rule of 5: Impact of PEGylation with Various Polymer Sizes on Pharmacokinetic Properties, Structure-Properties Relationships of mPEGylated Small Agonists of TGR5 Receptor

Update on the development of TGR5 agonists for human diseases

The G protein-coupled bile acid receptor 1 (GPBAR1) or TGR5 is widely distributed across organs, including the small intestine, stomach, liver, spleen, and gallbladder. Many studies have established strong correlations between TGR5 and glucose homeostasis, energy metabolism, immune-inflammatory responses, and gastrointestinal functions. These results indicate that TGR5 has a significant impact on the progression of tumor development and metabolic disorders such as diabetes mellitus and obesity. Targeting TGR5 represents an encouraging therapeutic approach for treating associated human ailments. Notably, the GLP-1 receptor has shown exceptional efficacy in clinical settings for diabetes management and weight loss promotion. Currently, numerous TGR5 agonists have been identified through natural product-based approaches and virtual screening methods, with some successfully progressing to clinical trials. This review summarizes the intricate relationships between TGR5 and various diseases emphasizing recent advancements in research on TGR5 agonists, including their structural characteristics, design tactics, and biological activities. We anticipate that this meticulous review could facilitate the expedited discovery and optimization of novel TGR5 agonists.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Discovery of betulinic acid derivatives as gut-restricted TGR5 agonists: Balancing the potency and physicochemical properties

The pleiotropic effects of TGR5 make it an appealing target for intervention of metabolic and inflammatory disorders, but systemic activation of TGR5 faces challenges of on-target side effects, especially gallbladder filling. Gut-restricted agonists were proved to be sufficient to circumvent these side effects, but extremely low systemic exposure may not be effective in activating TGR5 since it is located on the basolateral membrane. Herein, to balance potency and physicochemical properties, a series of gut-restricted TGR5 agonists with diversified kinetophores had been designed and synthesized. Compound 22-Na exhibited significant antidiabetic effect, and showed favorable gallbladder safety after 7 days of oral administration in humanized TGR5H88Y mice, confirming that gut-restricted agonism of TGR5 is a viable strategy to alleviate systemic target-related effects.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

The Effect of PEGylation on Drugs' Pharmacokinetic Parameters; from Absorption to Excretion

Until the drugs enter humans life, they may face problems in transportation, drug delivery, and metabolism. These problems can cause reducing drug's therapeutic effect and even increase its side effects. Together, these cases can reduce the patient's compliance with the treatment and complicate the treatment process. Much work has been done to solve or at least reduce these problems. For example, using different forms of a single drug molecule (like Citalopram and Escitalopram); slight changes in the drug's molecule like Meperidine and α-Prodine, and using carriers (like Tigerase®). PEGylation is a recently presented method that can use for many targets. Poly Ethylene Glycol or PEG is a polymer that can attach to drugs by using different methods and resulting sustained release, controlled metabolism, targeted delivery, and other cases. Although they will not necessarily lead to an increase in the effect of the drug, they will lead to the improvement of the treatment process in certain ways. In this article, the team of authors has tried to collect and carefully review the best cases based on the PEGylation of drugs that can help the readers of this article.

Discovery, Structure-Activity Relationships, and In Vivo Activity of Dihydropyridone Agonists of the Bile Acid Receptor TGR5

A novel series of potent agonists of the bile acid receptor TGR5 bearing a dihydropyridone scaffold was developed from a high-throughput screen. Starting from a micromolar hit compound, we implemented an extensive structure-activity-relationship (SAR) study with the synthesis and biological evaluation of 83 analogues. The project culminated with the identification of the potent nanomolar TGR5 agonist 77A. We report the GLP-1 secretagogue effect of our lead compound ex vivo in mouse colonoids and in vivo. In addition, to identify specific features favorable for TGR5 activation, we generated and optimized a three-dimensional quantitative SAR model that contributed to our understanding of our activity profile and could guide further development of this dihydropyridone series.

Design and exploration of gut-restricted bifunctional molecule with TGR5 agonistic and DPP4 inhibitory effects for treating ulcerative colitis

Ulcerative colitis (UC) is a gastrointestinal disease with complex etiology, and the shortage of the treatment further intensifies the need to discover new therapies based on novel mechanisms and strategies. TGR5 and DPP4 are beneficial to treat UC through multiple mechanisms, notably increasing GLP-2 levels by promoting secretion and inhibiting degradation respectively. However, some unwanted systemic effects caused by systemic exposure hinder development, especially the gallbladder-filling effects. Herein, we firstly reported a series of high-potency gut-restricted TGR5-DPP4 bifunctional molecules by gut-restriction and multitarget strategies to utilize the positive impacts of TGR5 and DPP4 on UC and avoid unwanted systemic effects. In particularly, racemic compound 15, a high-potency TGR5-DPP4 bifunctional molecule, showed favorable intestinal distribution, preferable efficacy in mice colitis model and good gallbladder safety. Therefore, the feasibility of gut-restricted TGR5-DPP4 bifunctional molecule was confirmed for the treatment UC, providing a new insight into the development of anti-UC drugs.

Single Stabilizing Point Mutation Enables High-Resolution Co-Crystal Structures of the Adenosine A2A Receptor with Preladenant Conjugates

The G protein-coupled adenosine A_2A receptor (A_2A AR) is an important new (potential) drug target in immuno-oncology, and for neurodegenerative diseases. Preladenant and its derivatives belong to the most potent A_2A AR antagonists displaying exceptional selectivity. While crystal structures of the human A_2A AR have been solved, mostly using the A_2A -StaR2 protein that bears 9 point mutations, co-crystallization with Preladenant derivatives has so far been elusive. We developed a new A_2A AR construct harboring a single point mutation (S91^3.39 K) which renders it extremely thermostable. This allowed the co-crystallization of two novel Preladenant derivatives, the polyethylene glycol-conjugated (PEGylated) PSB-2113, and the fluorophore-labeled PSB-2115. The obtained crystal structures (2.25 Å and 2.6 Å resolution) provide explanations for the high potency and selectivity of Preladenant derivatives. They represent the first crystal structures of a GPCR in complex with PEG- and fluorophore-conjugated ligands. The applied strategy is predicted to be applicable to further class A GPCRs.

Molecular Design in Practice: A Review of Selected Projects in a French Research Institute That Illustrates the Link between Chemical Biology and Medicinal Chemistry

Chemical biology and drug discovery are two scientific activities that pursue different goals but complement each other. The former is an interventional science that aims at understanding living systems through the modulation of its molecular components with compounds designed for this purpose. The latter is the art of designing drug candidates, i.e., molecules that act on selected molecular components of human beings and display, as a candidate treatment, the best reachable risk benefit ratio. In chemical biology, the compound is the means to understand biology, whereas in drug discovery, the compound is the goal. The toolbox they share includes biological and chemical analytic technologies, cell and whole-body imaging, and exploring the chemical space through state-of-the-art design and synthesis tools. In this article, we examine several tools shared by drug discovery and chemical biology through selected examples taken from research projects conducted in our institute in the last decade. These examples illustrate the design of chemical probes and tools to identify and validate new targets, to quantify target engagement in vitro and in vivo, to discover hits and to optimize pharmacokinetic properties with the control of compound concentration both spatially and temporally in the various biophases of a biological system.

Identification of Betulinic Acid Derivatives as Potent TGR5 Agonists with Antidiabetic Effects via Humanized TGR5H88Y Mutant Mice

Takeda G protein-coupled receptor 5 (TGR5) is a promising target for treating metabolic syndrome and inflammatory diseases. Herein, we identified a new series of betulinic acid derivatives as potent TGR5 agonists, which show remarkable activity on human (h) and canine (c) TGR5 but exhibit unpromising activity on murine (m) TGR5. Species difference was also observed with many other reported TGR5 agonists. Therefore, we screened 29 amino acids which were conserved in hTGR5 and cTGR5 but different in mTGR5 and found a key amino acid, H88 in mTGR5 (Y89 in hTGR5), which contributed to the species difference. With the CRISPR/Cas9 system, the mTGR5H88Y mutation was introduced into mice, and the optimized compound 11d-Na displayed a significant glucose-lowering effect and stimulated GLP-1 and insulin secretion in TGR5H88Y mice but not in wild-type animals. Taken together, our study provides a useful tool to bridge the gap of species difference and discovers a potent TGR5 agonist for further investigation.