Discovery and Development of a Series of Pyrazolo[3,4-d]pyridazinone Compounds as the Novel Covalent Fibroblast Growth Factor Receptor Inhibitors by the Rational Drug Design

Research progress of DDR1 inhibitors in the treatment of multiple human diseases

Discoidin domain receptor 1 (DDR1) is a collagen-activated receptor tyrosine kinase (RTK) and plays pivotal roles in regulating cellular functions such as proliferation, differentiation, invasion, migration, and matrix remodeling. DDR1 is involved in the occurrence and progression of many human diseases, including cancer, fibrosis, and inflammation. Therefore, DDR1 represents a highly promising therapeutic target. Although no selective small-molecule inhibitors have reached clinical trials to date, many molecules have shown therapeutic effects in preclinical studies. For example, BK40143 has demonstrated significant promise in the therapy of neurodegenerative diseases. In this context, our perspective aims to provide an in-depth exploration of DDR1, encompassing its structure characteristics, biological functions, and disease relevance. Furthermore, we emphasize the importance of understanding the structure-activity relationship of DDR1 inhibitors and highlight the unique advantages of dual-target or multitarget inhibitors. We anticipate offering valuable insights into the development of more efficacious DDR1-targeted drugs.

3D-QSAR, docking and molecular dynamics simulations of novel Pyrazolo-pyridazinone derivatives as covalent inhibitors of FGFR1: a scientific approach for possible anticancer agents

Developing highly potent covalent inhibitors of Fibroblast growth factor receptors 1 (FGFR1) has always been a challenging task. In the current study, various computational techniques, such as 3D-QSAR, covalent docking, fingerprinting analysis, MD simulation followed by MMGB/PBSA, and per-residue energy decomposition analysis were used to explore the binding mechanism of pyrazolo[3,4-d]pyridazinone derivatives to FGFR1. The high q2 and r2 values for the CoMFA and CoMSIA models, suggest that the constructed 3D-QSAR models could reliably predict the bioactivities of FGFR1 inhibitors. The structural requirements revealed by the model's contour maps were strategically used to computationally create an in-house library of more than 100 new FGFR1 inhibitors using the R-group exploration technique implemented in the SparkTM software. The compounds from the in-house library were also mapped in the 3D-QSAR model that predicts comparable pIC50 values with the experimental values. A comparison between 3D-QSAR generated contours and molecular docking conformation of ligands was performed to reveal the fundamentals to design potent FGFR1 covalent inhibitors. The estimated binding free energies (MMGB/PBSA) for the selected compounds were in agreement with the experimental value ranking of their binding affinities towards FGFR1. Furthermore, per-residue energy decomposition analysis has identified Arg627 and Glu531 to contribute significantly in improved binding affinity of compound W16. During ADME analysis, the majority of in-house library compounds exhibited pharmacokinetic properties superior to those of experimentally produced compounds. These new compounds may help researchers better understand FGFR1 inhibition and lead to the creation of novel, potent FGFR1 inhibitors.Communicated by Ramaswamy H. Sarma.

Discovery, Optimization, and Evaluation of Novel Pyridin-2(1H)-one Analogues as Potent TRK Inhibitors for Cancer Treatment

Tropomyosin receptor kinase (TRK) fusion, an oncogenic form of kinase with pan-tumor occurrence, is a clinically validated important antitumor target. In this study, we screened our in-house kinase inhibitor library against TRK and identified a promising hit compound 4 with a novel pyridin-2(1H)-one scaffold. Through a combination of structure-based drug design and structure-activity relationship (SAR) study, compound 14q was identified as a potent TRK inhibitor with good kinase selectivity. It also blocked cellular TRK signaling, thereby inhibiting TRK-dependent cell viability. Additionally, 14q displayed acceptable pharmacokinetic properties with 37.8% oral bioavailability in mice. Strong in vivo tumor growth inhibition of 14q was observed in subcutaneous M091 and KM12 tumor xenograft models with TRK fusion, causing significant tumor inhibition or even complete tumor regression.

ZIKV Inhibitors Based on Pyrazolo[3,4-d]pyridazine-7-one Core: Rational Design, In Vitro Evaluation, and Theoretical Studies

The Zika virus (ZIKV) is believed to cause birth defects, and no anti-ZIKV drugs have been approved by medical organizations to date. Starting from antimicrobial lead compounds with a pyrazolo[3,4-d]pyridazine-7-one scaffold, we synthesized 16 derivatives and screened their ability to interfere with ZIKV infection utilizing a cell-based phenotypic assay. Of these, five compounds showed significant inhibition of ZIKV with a selective index value greater than 4.6. In particular, compound 9b showed the best anti-ZIKV activity with a selectivity index of 22.4 (half-maximal effective concentration = 25.6 μM and 50% cytotoxic concentration = 572.4 μM). Through the brine shrimp lethality bioassay, 9b, 10b, 12, 17a, and 19a showed median lethal dose values in a range of 87.2-100.3 μg/mL. Compound 9b was also targeted to the NS2B-NS3 protease of ZIKV using molecular docking protocols, in which it acted as a noncompetitive inhibitor and strongly bound to five key amino acids (His51, Asp75, Ser135, Ala132, Tyr161). Utilizing the pharmacophore model of 9b, the top 20 hits were identified as prospective inhibitors of NS2B-NS3 protease, and six of them were confirmed for their stability with the protease via redocking and molecular dynamics simulations.

KinomeMETA: meta-learning enhanced kinome-wide polypharmacology profiling

Kinase inhibitors are crucial in cancer treatment, but drug resistance and side effects hinder the development of effective drugs. To address these challenges, it is essential to analyze the polypharmacology of kinase inhibitor and identify compound with high selectivity profile. This study presents KinomeMETA, a framework for profiling the activity of small molecule kinase inhibitors across a panel of 661 kinases. By training a meta-learner based on a graph neural network and fine-tuning it to create kinase-specific learners, KinomeMETA outperforms benchmark multi-task models and other kinase profiling models. It provides higher accuracy for understudied kinases with limited known data and broader coverage of kinase types, including important mutant kinases. Case studies on the discovery of new scaffold inhibitors for membrane-associated tyrosine- and threonine-specific cdc2-inhibitory kinase and selective inhibitors for fibroblast growth factor receptors demonstrate the role of KinomeMETA in virtual screening and kinome-wide activity profiling. Overall, KinomeMETA has the potential to accelerate kinase drug discovery by more effectively exploring the kinase polypharmacology landscape.

The Hitchhiker's Guide to Deep Learning Driven Generative Chemistry

This microperspective covers the most recent research outcomes of artificial intelligence (AI) generated molecular structures from the point of view of the medicinal chemist. The main focus is on studies that include synthesis and experimental in vitro validation in biochemical assays of the generated molecular structures, where we analyze the reported structures' relevance in modern medicinal chemistry and their novelty. The authors believe that this review would be appreciated by medicinal chemistry and AI-driven drug design (AIDD) communities and can be adopted as a comprehensive approach for qualifying different research outcomes in AIDD.

Structural Optimization of Fibroblast Growth Factor Receptor Inhibitors for Treating Solid Tumors

Small-molecule fibroblast growth factor receptor (FGFR) inhibitors have emerged as a promising antitumor therapy. Herein, by further optimizing the lead compound 1 under the guidance of molecular docking, we obtained a series of novel covalent FGFR inhibitors. After careful structure-activity relationship analysis, several compounds were identified to exhibit strong FGFR inhibitory activity and relatively better physicochemical and pharmacokinetic properties compared with those of 1. Among them, 2e potently and selectively inhibited the kinase activity of FGFR1-3 wildtype and high-incidence FGFR2-N549H/K-resistant mutant kinase. Furthermore, it suppressed cellular FGFR signaling, exhibiting considerable antiproliferative activity in FGFR-aberrant cancer cell lines. In addition, the oral administration of 2e in the FGFR1-amplified H1581, FGFR2-amplified NCI-H716, and SNU-16 tumor xenograft models demonstrated potent antitumor efficacy, inducing tumor stasis or even tumor regression.

Design and Synthesis of Fibroblast Growth Factor Receptor (FGFR) and Histone Deacetylase (HDAC) Dual Inhibitors for the Treatment of Cancer

The activation of the STAT signal after incubation with the HDAC inhibitor represents a key mechanism causing resistance to HDAC inhibitors in some solid tumor cells, while the FGFR inhibitor could downregulate the level of pSTAT3. Inspired by the therapeutic prospect of FGFR/HDAC dual inhibitors, we designed and synthesized a series of quinoxalinopyrazole hydroxamate derivatives as FGFR/HDAC dual inhibitors. Among them, compound 10e potently inhibited FGFR1-4 and HDAC1/2/6/8 and presented improved antiproliferative effects of tumor cells. Further studies indicated that 10e also downregulated the expression of pSTAT3, potentially overcoming resistance to HDAC inhibitors. What's more, 10e significantly inhibited the tumor growth in HCT116 and SNU-16 xenograft models with favorable pharmacokinetic profiles. Collectively, these results supported that 10e could be a new drug candidate for malignant tumors.

Targeting FGFRs for tumor therapy: current status and novel strategies

The FGF receptors (FGFRs) belong to a family of receptor tyrosine kinases. Abundant evidence shows that FGFRs are closely related to tumor cell invasion and angiogenesis. Hence, targeted modulation of FGFRs has become an effective strategy for cancer treatment. Recently, the development of small-molecule inhibitors targeting FGFRs has been extensively studied, and three inhibitors have been approved for marketing. Based on the clinical problems with the current inhibitors, there is a need to develop novel inhibitors and technologies to address the pitfalls. This review summarizes recent advances in small-molecule inhibitors targeting FGFRs, focusing on structure-activity relationships. Moreover, recent progress of novel technologies are summarized to provide a reference for promoting the application of drugs targeting FGFRs in tumor therapy.

Assessment of the Generalization Abilities of Machine-Learning Scoring Functions for Structure-Based Virtual Screening

In structure-based virtual screening (SBVS), it is critical that scoring functions capture protein-ligand atomic interactions. By focusing on the local domains of ligand binding pockets, a standardized pocket Pfam-based clustering (Pfam-cluster) approach was developed to assess the cross-target generalization ability of machine-learning scoring functions (MLSFs). Subsequently, 12 typical MLSFs were evaluated using random cross-validation (Random-CV), protein sequence similarity-based cross-validation (Seq-CV), and pocket Pfam-based cross-validation (Pfam-CV) methods. Surprisingly, all of the tested models showed decreased performances from Random-CV to Seq-CV to Pfam-CV experiments, not showing satisfactory generalization capacity. Our interpretable analysis suggested that the predictions on novel targets by MLSFs were dependent on buried solvent-accessible surface area (SASA)-related features of complex structures, with greater predicted binding affinities on complexes owning larger protein-ligand interfaces. By combining buried SASA-related features with target-specific patterns that were only shared among structurally similar compounds in the same cluster, the random forest (RF)-Score attained a good performance in the Random-CV test. Based on these findings, we strongly advise assessing the generalization ability of MLSFs with the Pfam-cluster approach and being cautious with the features learned by MLSFs.

Construction of Covalent Bisubstrate Inhibitor of Protein Kinase Reacting with Cysteine Residue at Substrate-Binding Site

Recent clinical success with targeted covalent inhibitors points to new possibilities for development of protein kinase (PK)-targeted drugs by exploiting reactive cysteine residues in and around the ATP-binding site. However, more than 300 human PKs lack cysteine residues in the ATP-binding site. Here, we report the first covalent bisubstrate PK inhibitor whose electrophilic warhead reaches outside the ATP-binding site and reacts with a distant cysteine residue. A series of covalent inhibitors and their reversible counterparts were synthesized and characterized. The most potent reversible inhibitor possessed picomolar affinity and its cysteine-reactive counterpart revealed high value of k_inact/K_I ratio (6.2 × 10⁷ M^-1 s^-1) for the reaction with the catalytic subunit of cAMP-dependent PK (PKAc). Under optimized conditions, fluorescent dye-labeled covalent inhibitors demonstrated PKA-selectivity in the cell lysate and reacted with several proteins inside live cells, including PKAc. The disclosed compounds serve as leads for targeting PKs possessing an analogously positioned cysteine residue.

Signaling Pathway and Small-Molecule Drug Discovery of FGFR: A Comprehensive Review

Targeted therapy is a groundbreaking innovation for cancer treatment. Among the receptor tyrosine kinases, the fibroblast growth factor receptors (FGFRs) garnered substantial attention as promising therapeutic targets due to their fundamental biological functions and frequently observed abnormality in tumors. In the past 2 decades, several generations of FGFR kinase inhibitors have been developed. This review starts by introducing the biological basis of FGF/FGFR signaling. It then gives a detailed description of different types of small-molecule FGFR inhibitors according to modes of action, followed by a systematic overview of small-molecule-based therapies of different modalities. It ends with our perspectives for the development of novel FGFR inhibitors.

4-Aminopyrazolopyrimidine scaffold and its deformation in the design of tyrosine and serine/threonine kinase inhibitors in medicinal chemistry

Deformation of the 4-aminopyrazolopyrimidine scaffold in designing small-molecule inhibitors.

Discovery of Pyrazolo[3,4-d]pyridazinone Derivatives as Selective DDR1 Inhibitors via Deep Learning Based Design, Synthesis, and Biological Evaluation

Alterations of discoidin domain receptor1 (DDR1) may lead to increased production of inflammatory cytokines, making DDR1 an attractive target for inflammatory bowel disease (IBD) therapy. A scaffold-based molecular design workflow was established and performed by integrating a deep generative model, kinase selectivity screening and molecular docking, leading to a novel DDR1 inhibitor compound 2, which showed potent DDR1 inhibition profile (IC₅₀ = 10.6 ± 1.9 nM) and excellent selectivity against a panel of 430 kinases (S (10) = 0.002 at 0.1 μM). Compound 2 potently inhibited the expression of pro-inflammatory cytokines and DDR1 autophosphorylation in cells, and it also demonstrated promising oral therapeutic effect in a dextran sulfate sodium (DSS)-induced mouse colitis model.

Discovery and Optimization of a Novel 2H-Pyrazolo[3,4-d]pyrimidine Derivative as a Potent Irreversible Pan-Fibroblast Growth Factor Receptor Inhibitor

Fibroblast growth factor receptors (FGFRs) have become promising therapeutic targets in various types of cancers. In fact, several selective irreversible inhibitors capable of covalently reacting with the conserved cysteine of FGFRs are currently being evaluated in clinical trials. In this article, we optimized and discovered a novel lead compound 36 with remarkable inhibitory effects against FGFR (1-3), which is a derivative of 2H-pyrazolo[3,4-d]pyrimidine. The irreversible binding to FGFRs was characterized by LC-MS. This compound has been shown to exhibit significant anti-proliferation effects against NCI-H1581 and SNU-16 cancer cell lines both in vitro and in vivo. Compound 36 has also demonstrated a low toxicity profile and adequate pharmacokinetic properties and is currently under validation as a potential drug candidate.

Design, synthesis and biological evaluation of 1H-pyrrolo[2,3-b]pyridine derivatives as potent fibroblast growth factor receptor inhibitors

Abnormal activation of FGFR signaling pathway plays an essential role in various types of tumors. Therefore, targeting FGFRs represents an attractive strategy for cancer therapy. Herein, we report a series of 1H-pyrrolo[2,3-b]pyridine derivatives with potent activities against FGFR1, 2, and 3. Among them, compound 4h exhibited potent FGFR inhibitory activity (FGFR1–4 IC₅₀ values of 7, 9, 25 and 712 nM, respectively). In vitro, 4h inhibited breast cancer 4T1 cell proliferation and induced its apoptosis. In addition, 4h also significantly inhibited the migration and invasion of 4T1 cells. Furthermore, 4h with low molecular weight would be an appealing lead compound which was beneficial to the subsequent optimization. In general, this research has been developing a class of 1H-pyrrolo[2,3-b]pyridine derivatives targeting FGFR with development prospects.

Discovery of a new class of 1H- pyrrorole [2,3-b]pyridine FGFR inhibitors with high ligand efficiency.

Discovery of Novel Benzothiazepinones as Irreversible Covalent Glycogen Synthase Kinase 3β Inhibitors for the Treatment of Acute Promyelocytic Leukemia

Recently, irreversible inhibitors have attracted great interest in antitumors due to their advantages of forming covalent bonds to target proteins. Herein, some benzothiazepinone compounds (BTZs) have been designed and synthesized as novel covalent GSK-3β inhibitors with high selectivity for the kinase panel. The irreversible covalent binding mode was identified by kinetics and mass spectrometry, and the main labeled residue was confirmed to be the unique Cys14 that exists only in GSK-3β. The candidate 4-3 (IC₅₀ = 6.6 μM) showed good proliferation inhibition and apoptosis-inducing ability to leukemia cell lines, low cytotoxicity on normal cell lines, and no hERG inhibition, which hinted the potential efficacy and safety. Furthermore, 4-3 exhibited decent pharmacokinetic properties in vivo and remarkably inhibited tumor growth in the acute promyelocytic leukemia (APL) mouse model. All the results suggest that these newly irreversible BTZ compounds might be useful in the treatment of cancer such as APL.

Design, synthesis and biological evaluation of pyrazolo[3,4-d]pyridazinone derivatives as covalent FGFR inhibitors

Fibroblast growth factor receptors (FGFRs) have emerged as promising targets for anticancer therapy. In this study, we synthesized and evaluated the biological activity of 66 pyrazolo[3,4-d]pyridazinone derivatives. Kinase inhibition, cell proliferation, and whole blood stability assays were used to evaluate their activity on FGFR, allowing us to explore structure−activity relationships and thus to gain understanding of the structural requirements to modulate covalent inhibitors’ selectivity and reactivity. Among them, compound 10h exhibited potent enzymatic activity against FGFR and remarkably inhibited proliferation of various cancer cells associated with FGFR dysregulation, and suppressed FGFR signaling pathway in cancer cells by the immunoblot analysis. Moreover, 10h displayed highly potent antitumor efficacy (TGI = 91.6%, at a dose of 50 mg/kg) in the FGFR1-amplified NCI-H1581 xenograft model.

Drug design targeting active posttranslational modification protein isoforms

Modern drug design aims to discover novel lead compounds with attractable chemical profiles to enable further exploration of the intersection of chemical space and biological space. Identification of small molecules with good ligand efficiency, high activity, and selectivity is crucial toward developing effective and safe drugs. However, the intersection is one of the most challenging tasks in the pharmaceutical industry, as chemical space is almost infinity and continuous, whereas the biological space is very limited and discrete. This bottleneck potentially limits the discovery of molecules with desirable properties for lead optimization. Herein, we present a new direction leveraging posttranslational modification (PTM) protein isoforms target space to inspire drug design termed as "Post-translational Modification Inspired Drug Design (PTMI-DD)." PTMI-DD aims to extend the intersections of chemical space and biological space. We further rationalized and highlighted the importance of PTM protein isoforms and their roles in various diseases and biological functions. We then laid out a few directions to elaborate the PTMI-DD in drug design including discovering covalent binding inhibitors mimicking PTMs, targeting PTM protein isoforms with distinctive binding sites from that of wild-type counterpart, targeting protein-protein interactions involving PTMs, and hijacking protein degeneration by ubiquitination for PTM protein isoforms. These directions will lead to a significant expansion of the biological space and/or increase the tractability of compounds, primarily due to precisely targeting PTM protein isoforms or complexes which are highly relevant to biological functions. Importantly, this new avenue will further enrich the personalized treatment opportunity through precision medicine targeting PTM isoforms.

Azolo[d]pyridazinones in medicinal chemistry

Azolo[d]pyridazinone is a privileged structure and versatile pharmacophore whose derivatives are associated with diverse biological activities, in particular antidiabetic, antiasthmatic, anticancer, analgesic, anti-inflammatory, antithrombotic, antidepressant and antimicrobial activities. The importance of this scaffold against some targets like PDE, COX and DPP-4 has been reviewed in detail previously. In the present review, we have summarized comprehensive information on azolo[d]pyridazinone derivatives investigated by many researchers for their diverse pharmacological activities, structure-activity relationship and molecular modeling studies since 2000. The review may lead scientists in the research fields of organic synthesis, medicinal chemistry and pharmacology to the strategic design and development of azolo[d]pyridazinone-based drug candidates in the future.

Pyrrolo[2,3-b]pyridine-3-one derivatives as novel fibroblast growth factor receptor 4 inhibitors for the treatment of hepatocellular carcinoma

Aberrant signaling of the FGF/FGFR pathway occurs frequently in cancers and is an oncogenic driver in many solid tumors, especially liver cancer. With the resurgence of interest in irreversible inhibitors, efforts have been directed to the discovery of irreversible FGFR4 inhibitors. Currently, several selective irreversible inhibitors containing pyrrolo[2,3-b]pyridine-3-one and pyrrolo[2,3-d]pyrimidin-2-amine skeletons were designed and synthesized as FGFR4 inhibitors. Among the screened compounds, derivative 25 showed excellent enzymatic inhibitory activity (IC₅₀, 51.6 nM) and antiproliferative potency of 0.1397 μM against Hep3B cell lines. Compound 25 exhibited good in vitro human liver microsomal stability with the half-life of 62.0 min, which was more stable than BLU9931 (46.7 min). But the in vivo pharmacokinetic results showed that the oral bioavailability was only 6.65%, which needs to be improved in the next work. These results showed that compound 25 might be an effective lead compound for further investigation to treat the hepatocellular carcinoma.

Pyridazine as a privileged structure: An updated review on anticancer activity of pyridazine containing bioactive molecules

Identification of potent anticancer agents with high selectivity and low toxicity remains on the way to human health. Pyridazine featuring advantageous physicochemical properties and antitumor potential usually is regarded as a central core in numerous anticancer derivatives. There are several approved pyridazine-based drugs in the market and analogues currently going through different clinical phases or registration statuses, suggesting pyridazine as a promising drug-like scaffold. The current review is intended to provide a comprehensive and updated overview of pyridazine derivatives as potential anticancer agents. In particular, we focused on their structure-activity relationship (SAR) studies, design strategies, binding modes and biological activities in the hope of offering novel insights for further rational design of more active and less toxic anticancer drugs.

Fibroblast growth factor receptor inhibitors: patent review (2015-2019)

Introduction: fibroblast growth factor receptors (FGFRs) are a family of tyrosine-kinase receptors whose signaling cascade regulates cellular proliferation, differentiation, and survival. Deregulation of the FGFR pathway is recognized as a driving factor in tumor development. On this basis, FGFR is an attractive target for anti-cancer small-molecule therapeutic agents.Areas covered: This review summarizes patent and literature publications spanning from 2015 to 2019 pertaining to small-molecule FGFR kinase inhibitors.Expert opinion: The first generation of non-covalent FGFR inhibitors is characterized by a broad spectrum of activity and a relatively high toxicity profile. The second generation of FGFR inhibitors shows higher selectivity and a more favorable toxicity profile, but the clinical use appears restricted only to small subsets of cancers strongly dependent on FGFR signaling. Nevertheless, erdafitinib has been approved for the treatment of metastatic urothelial carcinoma, becoming the first marketed selective FGFR inhibitor. The insurgence of mutant kinases, resistant to available therapies, has led to the development of irreversible FGFR inhibitors. The adoption of safer and more selective covalent inhibitors might supersede reversible inhibitors in specific therapeutic areas. Alternative strategies, such as FGF trapping by protein or small-molecule therapeutics, deserve attention and further investigations to unravel their potential.