Handbook of experimental pharmacology最新文献

This chapter considers biased signaling as a natural function of G protein-coupled receptors (GPCRs) in the form of probe dependence. Thus, any ligand that changes the conformation of the receptor (agonist, antagonist, or allosteric modulator) has the potential to change the natural signaling of the receptor through unequal conformational alterations in the receptor structure. This gives an added dimension to agonist selectivity beyond extracellular recognition, namely the ability of agonists to emphasize certain signaling pathways in the cell at the expense of others. Given this, selectivity is discussed in terms of varying intrinsic efficacy and selective stabilization of receptor states with methods to detect and measure these effects. Last, the translation of in vitro to complex in vivo systems will be considered.

Allosteric modulation of G protein-coupled receptors (GPCRs) is emerging as a powerful approach in drug discovery, offering enhanced subtype selectivity and the ability to bias signaling toward therapeutically preferred pathways, thereby reducing off-target effects. While most approved GPCR drugs act via the orthosteric site, this approach often lacks subtype specificity and induces pleiotropic signaling that can compromise therapeutic efficacy. Orthosteric biased ligands have provided proof of concept for functional selectivity, yet their development has been limited by site homology and challenges in fine-tuning pathway specificity. In contrast, allosteric modulators (AMs) bind to spatially and structurally distinct, less conserved sites located across extracellular, transmembrane, and intracellular receptor domains. By stabilizing discrete receptor conformations, AMs can fine-tune transducer engagement and preferentially direct signaling toward either G protein or β-arrestin (βarr) pathway. Recent structural and biophysical studies have provided insights into how diverse AMs lock GPCRs in specific conformations and modulate signaling across receptor families. Taken together, these findings reflect a shift in GPCR pharmacology, driven by the convergence of biased signaling and allosteric modulation. Biased allosteric modulators (BAMs) represent a promising class of ligands that bind at allosteric sites and selectively tune signaling pathways by biasing orthosteric ligand-induced responses. This review outlines the principles of biased signaling and allosteric modulation and highlights strategies for designing BAMs for GPCRs. Identifying BAMs could revolutionize GPCR drug discovery by enabling pathway-specific precision therapeutics with improved efficacy and fewer side effects.

G protein-coupled receptors (GPCRs) are key mediators of cellular signaling, participating in various physiological and pathological processes. Emerging evidence reveals that GPCRs can form functional heterodimers, wherein two distinct receptor subtypes interact mutually to generate unique signaling complexes. GPCR heterodimers play a crucial role in modulating cellular responses and are involved in biased signaling, a phenomenon where receptor activation preferentially triggers specific intracellular pathways (e.g., G protein vs. β-arrestin pathways). In this review, we will explore the molecular mechanisms underlying GPCR heterodimerization and the modulation of biased signaling in heterodimers. We first discuss the assembly and activation mechanisms based on heterodimerization in Class C GPCRs. Furthermore, we explore the impact of receptor dimerization on downstream biased signaling and the physiological relevance of these heterodimers. Next, we also summarize three criteria and essential technologies for identifying potential heterodimers. Lastly, we address the challenges and future directions in the study of GPCR heterodimers, particularly for drug discovery, highlighting their potential in designing novel therapeutics with enhanced specificity and reduced side effects.

Selectivity of a drug for a desired response as compared to undesirable responses (side effect) is a key goal of drug development. Early concepts to achieve such selectivity were based on selectivity for a molecular target as compared to others, pharmacokinetic factors to achieve high concentrations in the target tissue as compared to low concentrations in others, differential efficacy in the target vs. others tissues, and leveraging the concept of cell type and tissue differences in expression levels of receptors and their related signaling molecules, which can be further complicated by alterations of such ratios in disease. Biased agonism occurs when one response is activated preferentially over another after accounting for the above other factors. Thus, assessment of ligand bias is not always easy. β-Adrenoceptors have played a relevant role in our understanding of the phenomenon of biased agonism. Several clinically used β-adrenoceptor ligands were proposed to exhibit biased agonism, but the findings often are inconclusive, at least partly based on the overall complexity of assessment of biased signaling. These complexities also make it challenging to determine the desired biased profile of a ligand at the start of a drug research and development project, particularly for innovative applications. Thus, biased agonism has potential to contribute to functional target selectivity, but its prospective use remains challenging.

G protein-coupled receptors (GPCRs) represent the largest family of cell surface receptors. They orchestrate various signaling pathways, playing a central role in regulating various physiological and pathophysiological processes. Dysregulation of GPCR signaling has been intricately linked to cancer pathogenesis, including tumor growth, angiogenesis, metastasis, and immune modulation. Biased GPCR signaling occurs when a ligand preferentially activates one signaling pathway over another, leading to distinct cellular outcomes. In cancer, biased GPCR signaling represents a complex, dynamic phenomenon, significantly influencing cancer development, progression, and treatment resistance. This chapter reviews recent advances in our understanding of GPCR biased signaling in various aspects of cancer biology and explores its therapeutic potential. Given the fragmented nature of existing evidence, we integrate available literature with findings from our own proteomics studies on GPCR and β-arrestin function to provide a preliminary framework for understanding β-arrestin-mediated signaling in cancer. While this overview may capture only a limited snapshot of the broader landscape, it provides a valuable foundation for generating new hypotheses and guiding future research and drug discovery efforts in oncology.

GPCRs are known for their versatile signaling roles at the plasma membrane; however, recent studies have revealed that these receptors also function within various intracellular compartments, such as endosomes, the Golgi apparatus, and the endoplasmic reticulum. This spatially distinct signaling, termed location bias, allows GPCRs to initiate unique signaling cascades and influence cellular processes-including cAMP production, calcium mobilization, and protein phosphorylation-in a compartment-specific manner. By mapping the impact of GPCR signaling from these subcellular locations, this chapter emphasizes the mechanisms underlying signaling from intracellular receptor pools in diversifying receptor functionality. Such mechanistic insights into location-biased signaling open up novel therapeutic strategies aimed at targeting GPCRs within specific organelles, promising new levels of precision in therapeutic modulation and potential improvements in treatment efficacy and specificity.

G protein-coupled receptors (GPCRs), the largest family of membrane receptors in humans, primarily regulate diverse physiological and pathological processes through G protein- and arrestin-mediated signaling pathways, making them important drug targets. Notably, arrestins not only mediate GPCR desensitization and internalization but also regulate G protein-independent signal transduction. However, the mechanisms underlying arrestin-mediated biased signaling remain incompletely understood, posing significant challenges for developing targeted GPCR drugs with signaling bias. To address this knowledge gap, researchers have conducted systematic investigations and proposed innovative models, including the flute model, the polyproline sorting dock model, and the time order effects of GPCR phospho-barcodes to elucidate the dynamic processes driving biased signaling in arrestin activations. These key findings not only refine the theoretical framework of GPCR phosphorylation in biased signaling but also provide a solid foundation for developing biased drugs targeting the GPCR-arrestin pathway, offering new opportunities for precision therapeutics in diverse diseases.

Platelets are central mediators of haemostasis, responding rapidly to vascular injury through tightly regulated activation and inhibitory mechanisms. This response is mediated by a range of agonists, membrane receptors, and associated signalling pathways, enabling platelets to respond rapidly and specifically to stimuli. This chapter outlines the processes of platelet activation following vascular damage, highlighting the roles of collagen, von Willebrand factor, and secondary agonists such as ADP, thromboxane A₂, and thrombin, alongside endothelial-derived inhibitory signals that restrain excessive activation. It focuses on tyrosine kinase-linked receptors, detailing immunoreceptor tyrosine-based activatory (ITAM and hemITAM) and inhibitory (ITIM/ITSM) pathways, with emphasis on key kinases including Src family kinases, Syk, and Tec family members, and receptors such as GPVI, FcγRIIA, CLEC-2, PECAM-1, and G6b-B. Adhesion receptors, particularly integrins αIIbβ3 and α2β1 and the GPIb- IX-V complex, are examined with respect to inside-out and outside-in signalling and mechanotransduction. Finally, the G-protein-coupled receptors that amplify or inhibit platelet responses are discussed, including PARs, purinergic receptors, thromboxane, and prostaglandin receptors, along with emerging concepts in the regulation of platelets by GPCRs and in therapeutic targeting. The activatory and inhibitory pathways outlined here work together to maintain a balance between haemostasis and thrombosis. This enables a rapid and coordinated platelet response to vascular damage while preventing inappropriate and excessive activation. This maintains vascular integrity while preventing excessive bleeding and pathological thrombosis.

Hydrogen sulfide (H₂S) is an important gasotransmitter with multiple roles and is involved in several pathophysiological processes, including atherosclerosis and associated cardiometabolic comorbidities. This chapter examines the molecular mechanisms by which H₂S can influence the development and progression of atherosclerosis, including its effects on vascular tone, angiogenesis, oxidative stress, and inflammation, which can also affect atherosclerotic plaque stability. Moreover, we describe how H₂S affects the outcomes of cardiometabolic comorbidities associated with atherosclerosis, such as diabetes, hypertension, cardiac ischemia-reperfusion injury (IRI), stroke, metabolic-associated fatty liver disease (MAFLD), and kidney disease. Finally, we discuss how H₂S levels could potentially serve as biomarkers and the potential of increasing H₂S levels (both donors and metabolic pathway modulators) as promising therapeutic agents for improving vascular function, reducing plaque formation, and mitigating cardiovascular disease risk.

This chapter provides a comprehensive overview of direct oral anticoagulants (DOACs), focusing on their mechanisms of action, clinical utility, and practical considerations in anticoagulation management. DOACs have revolutionised anticoagulation by selectively targeting thrombin and activated factor X (FXa), offering improved safety, predictable pharmacokinetics, and reduced need for monitoring. The chapter covers their indications, contraindications, dosing, perioperative management, reversal, and use in special populations, including those with renal or hepatic impairment, cancer-associated thrombosis, and extreme body weights. It provides clinicians with practical guidance for the effective application of DOACs in various clinical settings.