Pyrimidinone nicotinamide mimetics as selective tankyrase and wnt pathway inhibitors suitable for in vivo pharmacology

Pyrrole-containing hybrids as potential anticancer agents: An insight into current developments and structure-activity relationships

Cancer poses a significant threat to human health. Therefore, it is urgent to develop potent anti-cancer drugs with excellent inhibitory activity and no toxic side effects. Pyrrole and its derivatives are privileged heterocyclic compounds with significant diverse pharmacological effects. These compounds can target various aspects of cancer cells and have been applied in clinical settings or are undergoing clinical trials. As a result, pyrrole has emerged as a promising drug scaffold and has been further probed to get novel entities for the treatment of cancer. This article reviews recent research progress on anti-cancer drugs containing pyrrole. It focuses on the mechanism of action, biological activity, and structure-activity relationships of pyrrole derivatives, aiming to assist in designing and synthesizing innovative pyrrole-based anti-cancer compounds.

Phytochemical profiling, in vitro biological activities, and in silico (molecular docking and absorption, distribution, metabolism, excretion, toxicity) studies of Polygonum cognatum Meissn

Polygonum cognatum Meissn, a perennial herbaceous belonging to the Polygonaceae family, is an aromatic plant. High-performance liquid chromatography/diode array detector method was developed and validated for the phytochemical analysis of the plant. Also, various methods were used to investigate the antioxidant, antimicrobial, and cytotoxic activities of the methanolic extracts. Antioxidant activities were researched by 2,2'-diphenyl-1-picrylhydrazyl and cupric reducing antioxidant capacity methods. Among the tested standard microbial strains, Candida albicans was found to be more sensitive with a 24.60 ± 0.55 mm inhibition zone according to the diffusion tests. In the microdilution tests, the minimum inhibitory concentration and minimum bactericidal/fungicidal concentration values were 4.75 and ≥ 4.75 mg/mL, respectively, for all tested pathogens. Human colon carcinoma cells were used to investigate cytotoxicity by using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide analysis (IC50  = 2891 μg/mL for Plant A, IC50  = 3291 μg/mL for Plant B). Molecular docking and absorption, distribution, metabolism, excretion, and toxicity analysis were used to explain inhibition mechanisms of major phenolic compounds of plants against Tankyrase 1, Tankyrase 2 enzymes, and deoxyribonucleic acid gyrase subunit B and found compatible with experimental results.

An Evolutionary Perspective on the Origin, Conservation and Binding Partner Acquisition of Tankyrases

Tankyrases are poly-ADP-ribosyltransferases that regulate many crucial and diverse cellular processes in humans such as Wnt signaling, telomere homeostasis, mitotic spindle formation and glucose metabolism. While tankyrases are present in most animals, functional differences across species may exist. In this work, we confirm the widespread distribution of tankyrases throughout the branches of multicellular animal life and identify the single-celled choanoflagellates as earliest origin of tankyrases. We further show that the sequences and structural aspects of TNKSs are well-conserved even between distantly related species. We also experimentally characterized an anciently diverged tankyrase homolog from the sponge Amphimedon queenslandica and show that the basic functional aspects, such as poly-ADP-ribosylation activity and interaction with the canonical tankyrase binding peptide motif, are conserved. Conversely, the presence of tankyrase binding motifs in orthologs of confirmed interaction partners varies greatly between species, indicating that tankyrases may have different sets of interaction partners depending on the animal lineage. Overall, our analysis suggests a remarkable degree of conservation for tankyrases, and that their regulatory functions in cells have likely changed considerably throughout evolution.

Studies on Anemone nemorosa L. extracts; polyphenols profile, antioxidant activity, and effects on Caco-2 cells by in vitro and in silico studies

In this study, two polar extracts (aqueous and ethanolic) from the aerial part of Anemone nemorosa L. (dried plant) were assessed to reveal their polyphenols profile, antioxidant activity, cytotoxic, and antiproliferative activity on Caco-2 (ATCC-HTB-37) cell line. In silico studies on two key compounds, protoanemonin and anemonin, on four molecular targets – cyclooxygenase-1 and cyclooxygenase-2, and human tankyrase 1 and human tankyrase 2 in relation to human colon cancer cell development have also been achieved. The results are as follows: caffeic acid esters and quercetin glycosides, including (iso)rhamnetin derivates, are the major polyphenol compounds in wood anemone polar extracts; the two polar extracts indicated very strong antioxidant activity in the interval from 0.1 to 5 µg [GAE] per 1 mL sample (IC50 < 0.290 µg GAE/mL), and in vitro studies on Caco-2 cells have revealed their simultaneous stimulatory and protective activity exactly in the concentration area with the strongest antioxidant activity. In silico studies have revealed moderate inhibitory activity of the two key compounds, anemonin and protoanemonin, on the four molecular targets studied; it was concluded having particular benefits of the wood anemone polar extracts in managing postoperative intestinal recovery, and generally in regenerative medicine.

The Tankyrase Inhibitor OM-153 Demonstrates Antitumor Efficacy and a Therapeutic Window in Mouse Models

The catalytic enzymes tankyrase 1 and 2 (TNKS1/2) alter protein turnover by poly-ADP-ribosylating target proteins, which earmark them for degradation by the ubiquitin-proteasomal system. Prominent targets of the catalytic activity of TNKS1/2 include AXIN proteins, resulting in TNKS1/2 being attractive biotargets for addressing of oncogenic WNT/β-catenin signaling. Although several potent small molecules have been developed to inhibit TNKS1/2, there are currently no TNKS1/2 inhibitors available in clinical practice. The development of tankyrase inhibitors has mainly been disadvantaged by concerns over biotarget-dependent intestinal toxicity and a deficient therapeutic window. Here we show that the novel, potent, and selective 1,2,4-triazole-based TNKS1/2 inhibitor OM-153 reduces WNT/β-catenin signaling and tumor progression in COLO 320DM colon carcinoma xenografts upon oral administration of 0.33-10 mg/kg twice daily. In addition, OM-153 potentiates anti-programmed cell death protein 1 (anti-PD-1) immune checkpoint inhibition and antitumor effect in a B16-F10 mouse melanoma model. A 28-day repeated dose mouse toxicity study documents body weight loss, intestinal damage, and tubular damage in the kidney after oral-twice daily administration of 100 mg/kg. In contrast, mice treated oral-twice daily with 10 mg/kg show an intact intestinal architecture and no atypical histopathologic changes in other organs. In addition, clinical biochemistry and hematologic analyses do not identify changes indicating substantial toxicity. The results demonstrate OM-153-mediated antitumor effects and a therapeutic window in a colon carcinoma mouse model ranging from 0.33 to at least 10 mg/kg, and provide a framework for using OM-153 for further preclinical evaluations.

Significance

This study uncovers the effectiveness and therapeutic window for a novel tankyrase inhibitor in mouse tumor models.

Small-Molecule Inhibitors of Tankyrases as Prospective Therapeutics for Cancer

Tankyrases are multifunctional poly(adenosine diphosphate-ribose) polymerases that regulate diverse biological processes including telomere maintenance and cellular signaling. These processes are often implicated in a number of human diseases, with cancer being the most prevalent example. Accordingly, tankyrase inhibitors have gained increasing attention as potential therapeutics. Since the discovery of XAV939 and IWR-1 as the first tankyrase inhibitors over two decades ago, tankyrase-targeted drug discovery has made significant progress. This review starts with an introduction of tankyrases, with emphasis placed on their cancer-related functions. Small-molecule inhibitors of tankyrases are subsequently delineated based on their distinct modes of binding to the enzymes. In addition to inhibitors that compete with oxidized nicotinamide adenine dinucleotide (NAD⁺) for binding to the catalytic domain of tankyrases, non-NAD⁺-competitive inhibitors are detailed. This is followed by a description of three clinically trialled tankyrase inhibitors. To conclude, some of challenges and prospects in developing tankyrase-targeted cancer therapies are discussed.

Pyrrolotriazinone as an Underexplored Scaffold in Drug Discovery

Heterocyclic amino derivatives have been extensively synthesized and validated as potent bioactive compounds, and nowadays, numerous marketed drugs share these scaffolds, from very simple structures (monoamino, monocyclic compounds) to much more complex molecules (polycyclic derivatives with two or more nitrogen atoms within the (fused) rings). In a constant quest for new chemical entities in drug discovery, a few novel heterocycles have emerged in recent years as promising building blocks for the obtainment of bioactive modulators. In this context, pyrrolotriazinones have attracted attention, and some show promising biological activities. Here, we offer an extensive review of pyrrolo[2,1-f][1,2,4]triazin-4(1H)-one and pyrrolo[1,2-d][1,2,4]triazin-4(3H)-one, describing their biological properties en route to drug discovery.

Pyrrolo[2,1-f][1,2,4]triazine: a promising fused heterocycle to target kinases in cancer therapy

Cancer is the second leading cause of death worldwide responsible for about 10 million deaths per year. To date several approaches have been developed to treat this deadly disease including surgery, chemotherapy, radiation therapy, hormonal therapy, targeted therapy, and synthetic lethality. The targeted therapy refers to targeting only specific proteins or enzymes that are dysregulated in cancer rather than killing all rapidly dividing cells, has gained much attention in the recent past. Kinase inhibition is one of the most successful approaches in targeted therapy. As of 30 March 2021, FDA has approved 65 small molecule protein kinase inhibitors and most of them are for cancer therapy. Interestingly, several kinase inhibitors contain one or more fused heterocycles as part of their structures. Pyrrolo[2,1-f][1,2,4]triazine is one the most interesting fused heterocycle that is an integral part of several kinase inhibitors and nucleoside drugs viz. avapritinib and remdesivir. This review articles focus on the recent advances made in the development of kinase inhibitors containing pyrrolo[2,1-f][1,2,4]triazine scaffold.

Discovery of 5-{4-[(7-Ethyl-6-oxo-5,6-dihydro-1,5-naphthyridin-3-yl)methyl]piperazin-1-yl}-N-methylpyridine-2-carboxamide (AZD5305): A PARP1-DNA Trapper with High Selectivity for PARP1 over PARP2 and Other PARPs

Poly-ADP-ribose-polymerase (PARP) inhibitors have achieved regulatory approval in oncology for homologous recombination repair deficient tumors including BRCA mutation. However, some have failed in combination with first-line chemotherapies, usually due to overlapping hematological toxicities. Currently approved PARP inhibitors lack selectivity for PARP1 over PARP2 and some other 16 PARP family members, and we hypothesized that this could contribute to toxicity. Recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for driving efficacy in a BRCA mutant background. Herein, we describe the structure- and property-based design of 25 (AZD5305), a potent and selective PARP1 inhibitor and PARP1-DNA trapper with excellent in vivo efficacy in a BRCA mutant HBCx-17 PDX model. Compound 25 is highly selective for PARP1 over other PARP family members, with good secondary pharmacology and physicochemical properties and excellent pharmacokinetics in preclinical species, with reduced effects on human bone marrow progenitor cells in vitro.

Identification of response signatures for tankyrase inhibitor treatment in tumor cell lines

Small-molecule tankyrase 1 and tankyrase 2 (TNKS1/2) inhibitors are effective antitumor agents in selected tumor cell lines and mouse models. Here, we characterized the response signatures and the in-depth mechanisms for the antiproliferative effect of tankyrase inhibition (TNKSi). The TNKS1/2-specific inhibitor G007-LK was used to screen 537 human tumor cell lines and a panel of particularly TNKSi-sensitive tumor cell lines was identified. Transcriptome, proteome, and bioinformatic analyses revealed the overall TNKSi-induced response signatures in the selected panel. TNKSi-mediated inhibition of wingless-type mammary tumor virus integration site/β-catenin, yes-associated protein 1 (YAP), and phosphatidylinositol-4,5-bisphosphate 3-kinase/AKT signaling was validated and correlated with lost expression of the key oncogene MYC and impaired cell growth. Moreover, we show that TNKSi induces accumulation of TNKS1/2-containing β-catenin degradasomes functioning as core complexes interacting with YAP and angiomotin proteins during attenuation of YAP signaling. These findings provide a contextual and mechanistic framework for using TNKSi in anticancer treatment that warrants further comprehensive preclinical and clinical evaluations.

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TNKSi-responding tumor cell lines were identified

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TNKSi targets WNT/β-catenin, YAP, and PI3K/AKT signaling

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Reduced MYC expression leads to impaired tumor cell growth

Characterization of GECPAR, a noncoding RNA that regulates the transcriptional program of diffuse large B-cell lymphoma

Enhancers are regulatory regions of DNA, which play a key role in cell-type specific differentiation and development. Most active enhancers are transcribed into enhancer RNA (eRNA) that can regulate transcription of target genes by means of in cis as well as in trans action. eRNA stabilize contacts between distal genomic regions and mediate the interaction of DNA with master transcription factors. Here, we characterized an enhancer eRNA, GECPAR (germinal center proliferative adapter RNA), which is specifically transcribed in normal and neoplastic germinal center B cells from the super-enhancer of POU2AF1, a key regulatory gene of the germinal center reaction. Using diffuse large B-cell lymphoma cell line models, we demonstrated the tumor suppressor activity of GECPAR, which is mediated via its transcriptional regulation of proliferation and differentiation genes, particularly MYC and the Wnt pathway.

Small-Molecule Inhibitors Targeting the Canonical WNT Signaling Pathway for the Treatment of Cancer

Canonical WNT signaling is an important developmental pathway that has attracted increased attention for anticancer drug discovery. From the production and secretion of WNT ligands, their binding to membrane receptors, and the β-catenin destruction complex to the expansive β-catenin transcriptional complex, multiple components have been investigated as drug targets to modulate WNT signaling. Significant progress in developing WNT inhibitors such as porcupine inhibitors, tankyrase inhibitors, β-catenin/coactivators, protein-protein interaction inhibitors, casein kinase modulators, DVL inhibitors, and dCTPP1 inhibitors has been made, with several candidates (e.g., LGK-974, PRI-724, and ETC-159) in human clinical trials. Herein we summarize recent progress in the drug discovery and development of small-molecule inhibitors targeting the canonical WNT pathway, focusing on their specific target proteins, in vitro and in vivo activities, physicochemical properties, and therapeutic potential. The relevant opportunities and challenges toward maintaining the balance between efficacy and toxicity in effectively targeting this pathway are also highlighted.

Bioinformatic Analysis of the Nicotinamide Binding Site in Poly(ADP-Ribose) Polymerase Family Proteins

Simple Summary

The PARP family consists of 17 proteins, and some of them are responsible for cancer cells’ viability. Much attention is therefore given to the search for chemical compounds with the ability to suppress distinct PARP family members (for example, PARP-5a and 5b). Here, we present the results of a family-wide bioinformatic analysis of an important functional region in the PARP structure and describe factors that can guide the design of highly selective compounds.

Abstract

The PARP family consists of 17 members with diverse functions, including those related to cancer cells’ viability. Several PARP inhibitors are of great interest as innovative anticancer drugs, but they have low selectivity towards distinct PARP family members and exert serious adverse effects. We describe a family-wide study of the nicotinamide (NA) binding site, an important functional region in the PARP structure, using comparative bioinformatic analysis and molecular modeling. Mutations in the NA site and D-loop mobility around the NA site were identified as factors that can guide the design of selective PARP inhibitors. Our findings are of particular importance for the development of novel tankyrase (PARPs 5a and 5b) inhibitors for cancer therapy.

Engineering mono- and multi-valent inhibitors on a modular scaffold

Here we exploit the simple, ultra-stable, modular architecture of consensus-designed tetratricopeptide repeat proteins (CTPRs) to create a platform capable of displaying both single as well as multiple functions and with diverse programmable geometrical arrangements by grafting non-helical short linear binding motifs (SLiMs) onto the loops between adjacent repeats. As proof of concept, we built synthetic CTPRs to bind and inhibit the human tankyrase proteins (hTNKS), which play a key role in Wnt signaling and are upregulated in cancer. A series of mono-valent and multi-valent hTNKS binders was assembled. To fully exploit the modular scaffold and to further diversify the multi-valent geometry, we engineered the binding modules with two different formats, one monomeric and the other trimeric. We show that the designed proteins are stable, correctly folded and capable of binding to and inhibiting the cellular activity of hTNKS leading to downregulation of the Wnt pathway. Multivalency in both the CTPR protein arrays and the hTNKS target results in the formation of large macromolecular assemblies, which can be visualized both in vitro and in the cell. When delivered into the cell by nanoparticle encapsulation, the multivalent CTPR proteins displayed exceptional activity. They are able to inhibit Wnt signaling where small molecule inhibitors have failed to date. Our results point to the tremendous potential of the CTPR platform to exploit a range of SLiMs and assemble synthetic binding molecules with built-in multivalent capabilities and precise, pre-programmed geometries.

Dissecting the molecular determinants of clinical PARP1 inhibitor selectivity for tankyrase1

Poly-ADP-ribosyltransferases play a critical role in DNA repair and cell death, and poly(ADP-ribosyl) polymerase 1 (PARP1) is a particularly important therapeutic target for the treatment of breast cancer because of its synthetic lethal relationship with breast cancer susceptibility proteins 1 and 2. Numerous PARP1 inhibitors have been developed, and their efficacy in cancer treatment is attributed to both the inhibition of enzymatic activity and their ability to trap PARP1 on to the damaged DNA, which is cytotoxic. Of the clinical PARP inhibitors, talazoparib is the most effective at trapping PARP1 on damaged DNA. Biochemically, talazoparib is also suspected to be a potent inhibitor of PARP5a/b (tankyrase1/2 [TNKS1/2]), which is an important regulator of Wnt/β-catenin pathway. Here we show using competition experiments in cell lysate that, at a clinically relevant concentration, talazoparib can potentially bind and engage TNKS1. Using surface plasmon resonance, we measured the dissociation constants of talazoparib, olaparib, niraparib, and veliparib for their interaction with PARP1 and TNKS1. The results show that talazoparib has strong affinity for PARP1 as well as uniquely strong affinity for TNKS1. Finally, we used crystallography and hydrogen deuterium exchange mass spectroscopy to dissect the molecular mechanism of differential selectivity of these PARP1 inhibitors. From these data, we conclude that subtle differences between the ligand-binding sites of PARP1 and TNKS1, differences in the electrostatic nature of the ligands, protein dynamics, and ligand conformational energetics contribute to the different pharmacology of these PARP1 inhibitors. These results will help in the design of drugs to treat Wnt/β-catenin pathway-related cancers, such as colorectal cancers.

Rational Design of Cell-Active Inhibitors of PARP10

Poly-ADP-ribose polymerases (PARPs 1-16) have emerged as major regulators of diverse cellular processes. PARPs can be subclassified based on their ability to catalyze poly-ADP-ribosylation (PARylation) or mono-ADP-ribosylation (MARylation). While much is known about the cellular roles of PARPs that catalyze PARylation (e.g., PARP1), the function of PARPs that catalyze MARylation (e.g., PARP10) is substantially less understood. This is due in large part to the lack of small-molecule inhibitors that are selective for individual PARP family members that catalyze MARylation. Herein, we describe the rational design and synthesis of selective inhibitors of PARP10. Using structure-based design, we targeted a hydrophobic subpocket within the nicotinamide-binding site of PARP10. We synthesized a series of small molecules based on a 3,4-dihydroisoquinolin-1(2H)-one (dq, 1) scaffold that contain various substituents at the C-5 and C-6 positions designed to exploit this hydrophobic subpocket. We found a dq analogue (22) that contains a methyl group at the C-5 position and a substituted pyridine at the C-6 position that exhibits >10-fold selectivity for PARP10 over a large subset of other PARP family members. The results of this study will serve as a platform for future small-molecule probe development for PARP10 and other PARP family members that catalyze MARylation.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

A Potent and Selective PARP11 Inhibitor Suggests Coupling between Cellular Localization and Catalytic Activity

Poly-ADP-ribose polymerases (PARPs1-16) play pivotal roles in diverse cellular processes. PARPs that catalyze poly-ADP-ribosylation (PARylation) are the best characterized PARP family members because of the availability of potent and selective inhibitors for these PARPs. There has been comparatively little success in developing selective small-molecule inhibitors of PARPs that catalyze mono-ADP-ribosylation (MARylation), limiting our understanding of the cellular role of MARylation. Here we describe the structure-guided design of inhibitors of PARPs that catalyze MARylation. The most selective analog, ITK7, potently inhibits the MARylation activity of PARP11, a nuclear envelope-localized PARP. ITK7 is greater than 200-fold selective over other PARP family members. Using live-cell imaging, we show that ITK7 causes PARP11 to dissociate from the nuclear envelope. These results suggest that the cellular localization of PARP11 is regulated by its catalytic activity.

Lowering Lipophilicity by Adding Carbon: One-Carbon Bridges of Morpholines and Piperazines

In this article, we report our investigation of a phenomenon by which bridging morpholines across the ring with one-carbon tethers leads to a counterintuitive reduction in lipophilicity. This effect was also found to occur in piperazines and piperidines and lowered the measured log D_7.4 of the bridged molecules by as much as -0.8 relative to their unbridged counterparts. As lowering lipophilicity without introducing additional heteroatoms can be desirable, we believe this potentially provides a useful tactic to improve the drug-like properties of molecules containing morpholine-, piperazine-, and piperidine-like motifs.

2-Phenylquinazolinones as dual-activity tankyrase-kinase inhibitors

Tankyrases (TNKSs) are enzymes specialized in catalyzing poly-ADP-ribosylation of target proteins. Several studies have validated TNKSs as anti-cancer drug targets due to their regulatory role in Wnt/β-catenin pathway. Recently a lot of effort has been put into developing more potent and selective TNKS inhibitors and optimizing them towards anti-cancer agents. We noticed that some 2-phenylquinazolinones (2-PQs) reported as CDK9 inhibitors were similar to previously published TNKS inhibitors. In this study, we profiled this series of 2-PQs against TNKS and selected kinases that are involved in the Wnt/β-catenin pathway. We found that they were much more potent TNKS inhibitors than they were CDK9/kinase inhibitors. We evaluated the compound selectivity to tankyrases over the ARTD enzyme family and solved co-crystal structures of the compounds with TNKS2. Comparative structure-based studies of the catalytic domain of TNKS2 with selected CDK9 inhibitors and docking studies of the inhibitors with two kinases (CDK9 and Akt) revealed important structural features, which could explain the selectivity of the compounds towards either tankyrases or kinases. We also discovered a compound, which was able to inhibit tankyrases, CDK9 and Akt kinases with equal µM potency.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

The novel tankyrase inhibitor (AZ1366) enhances irinotecan activity in tumors that exhibit elevated tankyrase and irinotecan resistance

BACKGROUND

Dysregulation of the canonical Wnt signaling pathway has been implicated in colorectal cancer (CRC) development as well as incipient stages of malignant transformation. In this study, we investigated the antitumor effects of AZ1366 (a novel tankyrase inhibitor) as a single agent and in combination with irinotecan in our patient derived CRC explant xenograft models.

RESULTS

Six out of 18 CRC explants displayed a significant growth reduction to AZ1366. There was one CRC explant (CRC040) that reached the threshold of sensitivity (TGII ≤ 20%) in this study. In addition, the combination of AZ1366 + irinotecan demonstrated efficacy in 4 out of 18 CRC explants. Treatment effects on the WNT pathway revealed that tankyrase inhibition was ineffective at reducing WNT dependent signaling. However, the anti-tumor effects observed in this study were likely a result of alternative tankyrase effects whereby tankyrase inhibition reduced NuMA levels.

MATERIALS AND METHODS

Eighteen CRC explants were treated with AZ1366 single agent or in combination for 28 days and treatment responses were assessed. Pharmacokinetic (AZ1366 drug concentrations) and pharmacodynamic effects (Axin2 levels) were investigated over 48 hours. Immunohistochemistry of nuclear β-catenin levels as well as western blot was employed to examine the treatment effects on the WNT pathway as well as NuMA.

CONCLUSIONS

Combination AZ1366 and irinotecan achieved greater anti-tumor effects compared to monotherapy. Activity was limited to CRC explants that displayed irinotecan resistance and increased protein levels of tankyrase and NuMA.

Regulation of Wnt/β-catenin signalling by tankyrase-dependent poly(ADP-ribosyl)ation and scaffolding

The Wnt/β-catenin signalling pathway is pivotal for stem cell function and the control of cellular differentiation, both during embryonic development and tissue homeostasis in adults. Its activity is carefully controlled through the concerted interactions of concentration-limited pathway components and a wide range of post-translational modifications, including phosphorylation, ubiquitylation, sumoylation, poly(ADP-ribosyl)ation (PARylation) and acetylation. Regulation of Wnt/β-catenin signalling by PARylation was discovered relatively recently. The PARP tankyrase PARylates AXIN1/2, an essential central scaffolding protein in the β-catenin destruction complex, and targets it for degradation, thereby fine-tuning the responsiveness of cells to the Wnt signal. The past few years have not only seen much progress in our understanding of the molecular mechanisms by which PARylation controls the pathway but also witnessed the successful development of tankyrase inhibitors as tool compounds and promising agents for the therapy of Wnt-dependent dysfunctions, including colorectal cancer. Recent work has hinted at more complex roles of tankyrase in Wnt/β-catenin signalling as well as challenges and opportunities in the development of tankyrase inhibitors. Here we review some of the latest advances in our understanding of tankyrase function in the pathway and efforts to modulate tankyrase activity to re-tune Wnt/β-catenin signalling in colorectal cancer cells.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

Mouse Red Blood Cell-Mediated Rare Xenobiotic Phosphorylation of a Drug Molecule Not Intended to Be a Kinase Substrate

Phosphorylation of xenobiotics is rare, probably owing to a strong evolutionary pressure against it. This rarity may have attracted more attention recently as a result of intentionally designed kinase-substrate analogs that depend on kinase-catalyzed activation to form phosphorylated active drugs. We report a rare phosphorylated metabolite observed unexpectedly in mouse plasma samples after an oral dose of a Tankyrase inhibitor that was not intended to be a kinase substrate, i.e., (S)-2-(4-(6-(3,4-dimethylpiperazin-1-yl)-4-methylpyridin-3-yl)phenyl)-8-(hydroxymethyl)quinazolin-4(3H)-one (AZ2381). The phosphorylated metabolite was not generated in mouse hepatocytes. In vitro experiments showed that the phosphorylation of AZ2381 occurred in mouse whole blood with heparin as anticoagulant but not in mouse plasma. The phosphorylated metabolite was also produced in rat, dog, and human blood, albeit at lower yields than in mouse. Divalent metal ions are required for the phosphorylation since the reaction is inhibited by the metal chelator EDTA. Further investigations with different cellular fractions of mouse blood revealed that the phosphorylation of AZ2381 was mediated by erythrocytes but did not occur with leukocytes. The levels of ¹⁸O incorporation into the phosphorylated metabolite when inorganic ¹⁸O₄-phosphate and γ-¹⁸O₄-ATP were added to the mouse blood incubations separately suggested that the phosphoryl transfer was from inorganic phosphate rather than ATP. It remains unclear which enzyme present in red blood cells is responsible for this rare phosphorylation.

Targeting Wnt-driven cancers: Discovery of novel tankyrase inhibitors

Recent years have seen substantially heightened interest in the discovery of tankyrase inhibitors (TNKSi) as new promising anticancer agents. In this framework, the aim of this review article is focused on the description of potent TNKSi also endowed with disruptor activity toward the Wnt/β-catenin signaling pathway. Beginning with an overview of the most characterized TNKSi deriving from several drug design approaches and classifying them on the basis of the molecular interactions with the target, we discuss only those ones acting against Wnt cancer cell lines. In addition, comprehensive structure property relationships (SPR) emerging from the hit evolution processes and preclinical results are provided. We then review the most promising TNKSi hitherto reported in literature, acting in vivo models of Wnt-driven cancers. Some outlooks on current issues and future directions in this field are also discussed.

Pyrrolo[2,1-f][1,2,4]triazines: From C-nucleosides to kinases and back again, the remarkable journey of a versatile nitrogen heterocycle

Pyrrolo[2,1-f][1,2,4]triazine, a unique NN bond-containing heterocycle with a bridgehead nitrogen, was first synthesized in the late 1970s but did not find utility until more than a decade later in the early 1990s when it was incorporated into C-nucleosides as a novel purine-like mimetic. This heterocycle remained at the fringes of medicinal chemistry until a confluence of events spurred by the explosion of the kinase inhibitor field in the early 2000s and the pressing need for novel, druggable scaffolds to occupy that exciting space led to numerous applications against diverse therapeutic targets. This digest will explore the history of this scaffold and the importance of chemistry in propelling drug discovery. The varied uses of this scaffold will be detailed as it progressed from C-nucleosides, to kinase inhibitors, to recognition as a "privileged" template, and finally reemergence in the C-nucleoside field.

Niclosamide-conjugated polypeptide nanoparticles inhibit Wnt signaling and colon cancer growth

Abnormal Wnt activity is a major mechanism responsible for many diseases, including cancer. Previously, we reported that the anthelmintic drug Niclosamide (NIC) inhibits Wnt/β-catenin signaling and suppresses colon cancer cell growth. Although the pharmacokinetic properties of NIC are appropriate for use as an anthelmintic agent, its low solubility, low bioavailability and low systemic exposure limit its usefulness in treating systemic diseases. To overcome these limitations, we conjugated NIC to recombinant chimeric polypeptides (CPs), and the CP-NIC conjugate spontaneously self-assembled into sub-100 nm near-monodisperse nanoparticles. CP-NIC nanoparticles delivered intravenously act as a pro-drug of NIC to dramatically increase exposure of NIC compared to dosing with free NIC. CP-NIC improved anti-tumor activity compared to NIC in a xenograft model of human colon cancer. Because NIC has multiple biological activities, CP-NIC could be used for treatment of multiple diseases, including cancer, bacterial and viral infection, type II diabetes, NASH and NAFLD.

Targeting Tankyrase to Fight WNT-dependent Tumours

Aberrant WNT signalling activity is linked to various diseases due to the WNT dependency of fundamental processes during development and in adult tissue homeostasis. Mutations in components of the multi-protein β-catenin destruction complex promote excessive amounts of the main transcriptional activator β-catenin and are particularly common in colorectal cancer (CRC). The tankyrase enzymes were recently implicated as negative regulators of destruction complex activity by mediating degradation of the scaffolding protein AXIN. Indeed, tankyrase inhibitors (TNKSi) have emerged as promising therapeutics by restoring functional signal-limiting destruction complexes in CRCs. Furthermore, as TNKSi-induced destruction complexes (so-called degradasomes) can be visualized by microscopy, they have served as a valuable experimental model system to address unresolved aspects regarding the structure, function and composition of the β-catenin destruction complex. This MiniReview provides an overview of the current knowledge on the regulatory mechanisms and interactions that govern the β-catenin destruction complex activity. It further highlights the potential of TNKSi as anticancer drugs and as a novel research tool to dissect the WNT signalling pathway.

Macrocyclized Extended Peptides: Inhibiting the Substrate-Recognition Domain of Tankyrase

We report a double-click macrocyclization approach for the design of constrained peptide inhibitors having non-helical or extended conformations. Our targets are the tankyrase proteins (TNKS), poly(ADP-ribose) polymerases (PARP) that regulate Wnt signaling by targeting Axin for degradation. TNKS are deregulated in many different cancer types, and inhibition of TNKS therefore represents an attractive therapeutic strategy. However, clinical development of TNKS-specific PARP catalytic inhibitors is challenging due to off-target effects and cellular toxicity. We instead targeted the substrate-recognition domain of TNKS, as it is unique among PARP family members. We employed a two-component strategy, allowing peptide and linker to be separately engineered and then assembled in a combinatorial fashion via click chemistry. Using the consensus substrate-peptide sequence as a starting point, we optimized the length and rigidity of the linker and its position along the peptide. Optimization was further guided by high-resolution crystal structures of two of the macrocyclized peptides in complex with TNKS. This approach led to macrocyclized peptides with submicromolar affinities for TNKS and high proteolytic stability that are able to disrupt the interaction between TNKS and Axin substrate and to inhibit Wnt signaling in a dose-dependent manner. The peptides therefore represent a promising starting point for a new class of substrate-competitive inhibitors of TNKS with potential for suppressing Wnt signaling in cancer. Moreover, by demonstrating the application of the double-click macrocyclization approach to non-helical, extended, or irregularly structured peptides, we greatly extend its potential and scope, especially given the frequency with which such motifs mediate protein-protein interactions.

Structural Basis for Potency and Promiscuity in Poly(ADP-ribose) Polymerase (PARP) and Tankyrase Inhibitors

Selective inhibitors could help unveil the mechanisms by which inhibition of poly(ADP-ribose) polymerases (PARPs) elicits clinical benefits in cancer therapy. We profiled 10 clinical PARP inhibitors and commonly used research tools for their inhibition of multiple PARP enzymes. We also determined crystal structures of these compounds bound to PARP1 or PARP2. Veliparib and niraparib are selective inhibitors of PARP1 and PARP2; olaparib, rucaparib, and talazoparib are more potent inhibitors of PARP1 but are less selective. PJ34 and UPF1069 are broad PARP inhibitors; PJ34 inserts a flexible moiety into hydrophobic subpockets in various ADP-ribosyltransferases. XAV939 is a promiscuous tankyrase inhibitor and a potent inhibitor of PARP1 in vitro and in cells, whereas IWR1 and AZ-6102 are tankyrase selective. Our biochemical and structural analysis of PARP inhibitor potencies establishes a molecular basis for either selectivity or promiscuity and provides a benchmark for experimental design in assessment of PARP inhibitor effects.

Synthesis of pyrrolo[2,1-f][1,2,4]triazin-4(3H)-ones: Rearrangement of pyrrolo[1,2-d][1,3,4]oxadiazines and regioselective intramolecular cyclization of 1,2-biscarbamoyl-substituted 1H-pyrroles

Pyrrolo[2,1-f][1,2,4]triazin-4(3H)-ones 12 have been easily prepared via nucleophile-induced rearrangement of pyrrolooxadiazines 11 and regioselective intramolecular cyclization of 1,2-biscarbamoyl-substituted 1H-pyrroles 10. In this work, we demonstrated that the described synthetic approaches can be considered to be more facile and practical than previously reported procedures.

AZ1366: An Inhibitor of Tankyrase and the Canonical Wnt Pathway that Limits the Persistence of Non-Small Cell Lung Cancer Cells Following EGFR Inhibition

Purpose: The emergence of EGFR inhibitors such as gefitinib, erlotinib, and osimertinib has provided novel treatment opportunities in EGFR-driven non-small cell lung cancer (NSCLC). However, most patients with EGFR-driven cancers treated with these inhibitors eventually relapse. Recent efforts have identified the canonical Wnt pathway as a mechanism of protection from EGFR inhibition and that inhibiting tankyrase, a key player in this pathway, is a potential therapeutic strategy for the treatment of EGFR-driven tumors.Experimental Design: We performed a preclinical evaluation of tankyrase inhibitor AZ1366 in combination with multiple EGFR-inhibitors across NSCLC lines, characterizing its antitumor activity, impingement on canonical Wnt signaling, and effects on gene expression. We performed pharmacokinetic and pharmacodynamic profiling of AZ1366 in mice and evaluated its therapeutic activity in an orthotopic NSCLC model.Results: In combination with EGFR inhibitors, AZ1366 synergistically suppressed proliferation of multiple NSCLC lines and amplified global transcriptional changes brought about by EGFR inhibition. Its ability to work synergistically with EGFR inhibition coincided with its ability to modulate the canonical Wnt pathway. Pharmacokinetic and pharmacodynamic profiling of AZ1366-treated orthotopic tumors demonstrated clinically relevant serum drug levels and intratumoral target inhibition. Finally, coadministration of an EGFR inhibitor and AZ1366 provided better tumor control and improved survival for Wnt-responsive lung cancers in an orthotopic mouse model.Conclusions: Tankyrase inhibition is a potent route of tumor control in EGFR-dependent NSCLC with confirmed dependence on canonical Wnt signaling. These data strongly support further evaluation of tankyrase inhibition as a cotreatment strategy with EGFR inhibition in an identifiable subset of EGFR-driven NSCLC. Clin Cancer Res; 23(6); 1531-41. ©2016 AACR.

Potent and Selective CK2 Kinase Inhibitors with Effects on Wnt Pathway Signaling in Vivo

The Wnt pathway is an evolutionarily conserved and tightly regulated signaling network with important roles in embryonic development and adult tissue regeneration. Impaired Wnt pathway regulation, arising from mutations in Wnt signaling components, such as Axin, APC, and β-catenin, results in uncontrolled cell growth and triggers oncogenesis. To explore the reported link between CK2 kinase activity and Wnt pathway signaling, we sought to identify a potent, selective inhibitor of CK2 suitable for proof of concept studies in vivo. Starting from a pyrazolo[1,5-a]pyrimidine lead (2), we identified compound 7h, a potent CK2 inhibitor with picomolar affinity that is highly selectivity against other kinase family enzymes and inhibits Wnt pathway signaling (IC50 = 50 nM) in DLD-1 cells. In addition, compound 7h has physicochemical properties that are suitable for formulation as an intravenous solution, has demonstrated good pharmacokinetics in preclinical species, and exhibits a high level of activity as a monotherapy in HCT-116 and SW-620 xenografts.

Small-molecule inhibitors of Wnt signaling pathway: towards novel anticancer therapeutics

BACKGROUND

The Wnt signaling pathway involves secreted glycoproteins that bind to the Frizzled family receptors to activate intracellular signal transduction events that regulate cell proliferation, apoptosis, cell migration and many critical aspects of developmental biology.

DISCUSSION

Aberrant Wnt signaling underlies a wide range of pathologies in humans including tumor initiation, tumor growth, cell senescence, cell death, differentiation and metastasis. The inhibition of Wnt signaling offers a novel approach for anticancer therapeutics.

CONCLUSION

Focusing on recent developments, we reviewed the small-molecule inhibitors targeting various components of Wnt signaling pathways and the progress from the discovery of lead compounds to highly potent inhibitors with significant therapeutic potential.

Fragment-Based Drug Design of Novel Pyranopyridones as Cell Active and Orally Bioavailable Tankyrase Inhibitors

Tankyrase activity has been linked to the regulation of intracellular axin levels, which have been shown to be crucial for the Wnt pathway. Deregulated Wnt signaling is important for the genesis of many diseases including cancer. We describe herein the discovery and development of a new series of tankyrase inhibitors. These pyranopyridones are highly active in various cell-based assays. A fragment/structure based optimization strategy led to a compound with good pharmacokinetic properties that is suitable for in vivo studies and further development.