Highly Selective and Potent Ectonucleotide Pyrophosphatase-1 (NPP1) Inhibitors Based on Uridine 5'-Pα,α-Dithiophosphate Analogues

Ectonucleotidase inhibitors: targeting signaling pathways for therapeutic advancement-an in-depth review

Ectonucleotidase inhibitors are a family of pharmacological drugs that, by selectively targeting ectonucleotidases, are essential in altering purinergic signaling pathways. The hydrolysis of extracellular nucleotides and nucleosides is carried out by these enzymes, which include ectonucleoside triphosphate diphosphohydrolases (NTPDases) and ecto-5'-nucleotidase (CD73). Ectonucleotidase inhibitors can prevent the conversion of ATP and ADP into adenosine by blocking these enzymes and reduce extracellular adenosine. These molecules are essential for purinergic signaling, which is associated with a variability of physiological and pathological processes. By modifying extracellular nucleotide metabolism and improving purinergic signaling regulation, ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) inhibitors have the potential to improve cancer treatment, inflammatory management, and immune response modulation. Purinergic signaling is affected by CD73 inhibitors because they prevent AMP from being converted to adenosine. These inhibitors are useful in cancer therapy and immunotherapy because they may improve chemotherapy effectiveness and alter immune responses. Purinergic signaling is controlled by NTPDase inhibitors, which specifically target enzymes involved in extracellular nucleotide breakdown. These inhibitors show promise in reducing immunological responses, thrombosis, and inflammation, perhaps assisting in the treatment of cardiovascular and autoimmune illnesses. Alkaline phosphatase (ALP) inhibitors alter the function of enzymes involved in dephosphorylation reactions, which has an impact on a variety of biological processes. By altering the body's phosphate levels, these inhibitors may be used to treat diseases including hyperphosphatemia and certain bone problems. This article provides a guide for researchers and clinicians looking to leverage the remedial capability of ectonucleotidase inhibitors in a variety of illness scenarios by illuminating their processes, advantages, and difficulties.

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

Insight into small-molecule inhibitors targeting extracellular nucleotide pyrophosphatase/phosphodiesterase1 for potential multiple human diseases

Extracellular nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) has been identified as a type II transmembrane glycoprotein. It plays a crucial role in various biological processes, such as bone mineralization, cancer cell proliferation, and immune regulation. Consequently, ENPP1 has garnered attention as a promising target for pharmacological interventions. Despite its potential, the development of clinical-stage ENPP1 inhibitors for solid tumors, diabetes, and silent rickets remains limited. However, there are encouraging findings from preclinical trials involving small molecules exhibiting favorable therapeutic effects and safety profiles. This perspective aims to shed light on the structural properties, biological functions and the relationship between ENPP1 and diseases. Additionally, it focuses on the structure-activity relationship of ENPP1 inhibitors, with the intention of guiding the future development of new and effective ENPP1 inhibitors.

Discovery of 3,4-dihydropyrimido[4,5-d]pyrimidin-2(1H)-one and 3,4-dihydropyrido[2,3-d]pyrimidin-2(1H)-one derivatives as novel ENPP1 inhibitors

Ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) negatively regulates the anti-cancer Stimulator of Interferon Genes (STING) pathway. We discovered that 3,4-dihydropyrimido[4,5-d]pyrimidin-2(1H)-one and 3,4-dihydropyrido[2,3-d]pyrimidin-2(1H)-one derivatives possessed inhibitory activities on ENPP1. A structure-activity relationship (SAR) study led to the identification of 46 and 23 as potent ENPP1 inhibitors. Also, compounds 46 and 23 possessed high microsomal stabilities in human, rat, and mouse liver microsome. Additionally, CYPs (1A2, 2C9, 2C19, 2D6, and 3A4) were not inhibited by 46 and 23. Molecular dynamics simulations provided an insight of binding modes between ENPP1 and compounds (46 and 23).

Nucleotide pyrophosphatase/phosphodiesterases (NPPs) including NPP1 and NPP2/ ATX as important drug targets: A patent review (2015-2020)

INTRODUCTION

Nucleoside triphosphate diphosphohydrolases (NTPDases), alkaline phosphatases (APs), and ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs) are nucleotidases found on the cell surface. It is a promising therapeutic target for a range of disorders, including fibrosis, tumour metastasis, pruritus, inflammation, multiple sclerosis, and autoimmune diseases. As a result, therapeutic intervention including selective inhibitors of NPPs is required.

AREA COVERED

Many chemical substances, including pyrazole, pyridine and bicyclic compounds have demonstrated promising inhibitory potential for ecto-nucleotide pyrophosphatase/phosphodiesterases. The chemistry and clinical applications of NPPs inhibitors patented between 2015 and 2020 are discussed in this review.

EXPERT OPINION

: In recent years, there has been a lot of effort put into finding effective and selective inhibitors of NPPs. Despite the fact that a variety of synthetic inhibitors have been created, only a few investigations on their in vivo activity have been published. In addition to IOA-289 which has passed Phase Ia clinical trials; potent ATX inhibitor compounds such as BLD-0409, IPF and BBT-877 have been placed in phase I clinical studies. Some of the most promising ATX inhibitors in recent years are closely related analogs of previously known inhibitors, such as PF-8380. Knowledge of the structure activity relationship of such promising inhibitors can potentially translate into the discovery of more potent and effective inhibitors of NPP with a variety of structural characteristics and favourable therapeutic activities.

Accelerating the End-to-end Production of Cyclic Phosphate Monomers with Modular Flow Chemistry

Biocompatibility, tunable degradability, broad functionalities of polyphosphoesters and their potential for biomedical applications stimulated a renewed interest from the Chemistry, Medicinal Chemistry and Polymer Sciences. Commercial applications of polyphosphoesters as...

Therapeutic Interventions Targeting Innate Immune Receptors: A Balancing Act

The innate immune system is an organism's first line of defense against an onslaught of internal and external threats. The downstream adaptive immune system has been a popular target for therapeutic intervention, while there is a relative paucity of therapeutics targeting the innate immune system. However, the innate immune system plays a critical role in many human diseases, such as microbial infection, cancer, and autoimmunity, highlighting the need for ongoing therapeutic research. In this review, we discuss the major innate immune pathways and detail the molecular strategies underpinning successful therapeutics targeting each pathway as well as previous and ongoing efforts. We will also discuss any recent discoveries that could inform the development of novel therapeutic strategies. As our understanding of the innate immune system continues to develop, we envision that therapies harnessing the power of the innate immune system will become the mainstay of treatment for a wide variety of human diseases.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Recent progress in non-native nucleic acid modifications

While Nature harnesses RNA and DNA to store, read and write genetic information, the inherent programmability, synthetic accessibility and wide functionality of these nucleic acids make them attractive tools for use in a vast array of applications.

Structure-Aided Development of Small-Molecule Inhibitors of ENPP1, the Extracellular Phosphodiesterase of the Immunotransmitter cGAMP

Cancer cells initiate an innate immune response by synthesizing and exporting the small-molecule immunotransmitter cGAMP, which activates the anti-cancer Stimulator of Interferon Genes (STING) pathway in the host. An extracellular enzyme, ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1), hydrolyzes cGAMP and negatively regulates this anti-cancer immune response. Small-molecule ENPP1 inhibitors are much needed as tools to study the basic biology of extracellular cGAMP and as investigational cancer immunotherapy drugs. Here, we surveyed structure-activity relationships around a series of cell-impermeable and thus extracellular-targeting phosphonate inhibitors of ENPP1. In addition, we solved the crystal structure of an exemplary phosphonate inhibitor to elucidate the interactions that drive potency. This study yielded several best-in-class inhibitors with Ki < 2 nM and excellent physicochemical and pharmacokinetic properties. Finally, we demonstrate that an ENPP1 inhibitor delays tumor growth in a breast cancer mouse model. Together, we have developed ENPP1 inhibitors that are excellent tool compounds and potential therapeutics.

History of ectonucleotidases and their role in purinergic signaling

Ectonucleotidases are key for purinergic signaling. They control the duration of activity of purinergic receptor agonists. At the same time, they produce hydrolysis products as additional ligands of purinergic receptors. Due to the considerable diversity of enzymes, purinergic receptor ligands and purinergic receptors, deciphering the impact of extracellular purinergic receptor control has become a challenge. The first group of enzymes described were the alkaline phosphatases - at the time not as nucleotide-metabolizing but as nonspecific phosphatases. Enzymes now referred to as nucleoside triphosphate diphosphohydrolases and ecto-5'-nucleotidase were the first and only nucleotide-specific ectonucleotidases identified. And they were the first group of enzymes related to purinergic signaling. Additional research brought to light a surprising number of ectoenzymes with broad substrate specificity, which can also hydrolyze nucleotides. This short overview traces the development of the field and briefly highlights important results and benefits for therapies of human diseases achieved within nearly a century of investigations.

The P2Y6 receptor signals through Gαq /Ca2+ /PKCα and Gα13 /ROCK pathways to drive the formation of membrane protrusions and dictate cell migration

Cell migration is a ubiquitous process necessary to maintain and restore tissue functions. However, in cancer, cell migration leads to metastasis development and thus worsens the prognosis. Although the mechanism of cell migration is well understood, the identification of new targets modulating cell migration and deciphering their signaling events could lead to new therapies to restore tissue functions in diseases, such as inflammatory bowel disease, or to block metastatic development in different forms of cancer. Previous research has identified the G-protein-coupled P2Y₆ receptor as an innovative target that could dictate cell migration under normal and pathological conditions. Surprisingly, there is little information on the cellular events triggered by activated P2Y₆ during cell migration. Here, we demonstrated that P2Y₆ activation stimulated A549 human lung cancer cells and Caco-2 colorectal cancer cell migration. Activated P2Y₆ increased the number of filopodia and focal adhesions; two migratory structures required for cell migration. The generation of these structures involved Gα_q /calcium/protein kinases C (PKC) and Gα₁₃ /RHO-associated protein kinase-dependent pathways that dictate the formation of the migratory structures. These pathways led to the stabilization of the actin cytoskeleton through a PKC-dependent phosphorylation of cofilin. These results support the idea that the P2Y₆ receptor represents a target of interest to modulate cell migration and revealed an intricate dialogue between two Gα-protein signaling pathways.

Opportunities for Small Molecules in Cancer Immunotherapy

Cancer immunotherapy has proven remarkably successful through instigation of systemic antitumor T cell responses. Despite this achievement, further advancements are needed to expand the scope of susceptible cancer types and overcome variation in treatment outcomes between patients. Small-molecule drugs targeting defined pathways and/or cells capable of immune modulation are expected to substantially improve efficacy of cancer immunotherapy. Small-molecule drugs possess unique properties compatible with systemic administration and amenable to both extracellular and intracellular targets. These compounds can modify molecular pathways to overcome immune tolerance and suppression towards effective antitumor responses. Here, we provide an overview of how such effects might be achieved by combining immunotherapy with conventional and/or new small-molecule chemotherapeutics.

Adenine-(methoxy)-ethoxy-Pα,α-dithio-triphosphate inhibits pathologic calcium pyrophosphate deposition in osteoarthritic human chondrocytes

Nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) inhibitors have been suggested as a potential treatment for calcium pyrophosphate dihydrate (CPPD) deposition disease. Here, we targeted the development of improved NPP1 inhibitors based on acyclic mimics of Pα,α-phosphorodithioate-substituted adenine nucleotides, 7-10. The latter were obtained in a facile two-step synthesis from adenine-(methoxy)ethanol. Among analogs 7-10, adenine-(methoxy)ethoxy-Pα,α-dithio-triphosphate, 8, was the most potent NPP1 inhibitor both with purified enzyme (IC50 0.645 μM) and in osteoarthritic human chondrocytes (IC50 0.033 μM). Furthermore, it efficaciously (10-fold vs. control) inhibited ATP-induced CPPD in human articular chondrocytes. Importantly, 8 was a highly selective NPP1 inhibitor which showed only minor inhibition of NPP3, CD39 and CD73, and did not inhibit TNAP (tissue nonspecific alkaline phosphatase) activity in human chondrocytes. Furthermore, 8 did not activate P2Y1,2,6 receptors. Analog 8 was not toxic to cultured chondrocytes at 100 μM. Therefore, 8 may be suitable for further development as a drug candidate for the treatment of CPPD arthritis and other NPP1-related diseases.

Structure-activity relationship study of NPP1 inhibitors based on uracil-N1-(methoxy)ethyl-β-phosphate scaffold

Overexpression of ecto-nucleotide pyrophosphatase-1 (NPP1) is associated with diseases such as calcium pyrophosphate dihydrate deposition disease, calcific aortic valve disease, and type 2 diabetes. In this context, NPP1 inhibitors are potential drug candidates for the treatment of these diseases. The present study focuses on the analysis of the structure-activity relationship of NPP1 inhibitors based on acyclic uracil-nucleotides. For this purpose, we synthesized acyclic uridine-monophosphate analogs, 10-11, uridine-diphosphate analogs, 12-14, and uridine-P_α,_α-dithio-triphosphate analogs, 15-17. We evaluated their inhibitory activity and selectivity towards NPP1, -3, NTPDase1, -2, -3, and -8, and P2Y_2,4,6 receptors. Analogs 16 and 17 were the most selective and potent NPP1 inhibitors (Ki 0.94 and 0.73 μM, respectively) among the tested molecules. Analogs 10-17 had only minute effect on uracil-nucleotide responding P2Y_2,4,6 receptors. Analog 17 (100 μM) displayed 96% inhibition of NPPase activity in osteoarthritic human chondrocytes. Analogs 14-17 displayed weak inhibitory effect on alkaline phosphatase activity at equimolar concentrations in human chondrocytes. All tested analogs showed no toxicity at human chondrocytes. We concluded that ribose-ring to chain transformation, as well as the type of the nucleobase, are parameters of minor significance to NPP1 inhibition, whereas the major parameter is P_α-dithio-substitution. In addition, the length of the phosphate chain also significantly affects inhibition. Overall, the experimental results were well reproduced by molecular docking. A correlation was observed between the activities of the compounds and the number of H-bonds and salt bridges formed between the inhibitors and NPP1 binding site residues. Uracil-N1-(methoxy)ethyl-β-P_α,α-dithio, P_β,γ-methylene tri-phosphate, 17, was identified as the most potent, selective, and non-toxic NPP1 inhibitor among the tested analogs, and may be used as a lead structure for further drug development.