2,7-naphthyridinone-based MET kinase inhibitors: A promising novel scaffold for antitumor drug development

Design, synthesis, and anti-mycobacterial evaluation of 1,8-naphthyridine-3-carbonitrile analogues

Twenty-eight compounds, viz., 1,8-naphthyridine-3-carbonitrile (ANC and ANA) derivatives, were designed and synthesized through a molecular hybridization approach. The structures of these compounds were analyzed and confirmed using 1H NMR, 13C NMR, LCMS, and elemental analyses. The synthesized compounds were evaluated by in vitro testing for their effectiveness against tuberculosis using the MABA assay, targeting the Mycobacterium tuberculosis H37Rv strain. Their minimum inhibitory concentration (MIC) was determined, showing that the tested compounds' MIC values ranged from 6.25 to ≤50 μg mL-1. Among the derivatives studied, ANA-12 demonstrated prominent anti-tuberculosis activity with a MIC of 6.25 μg mL-1. Compounds ANC-2, ANA-1, ANA 6-8, and ANA-10 displayed moderate to good anti-tuberculosis activity with MIC values of 12.5 μg mL-1. Compounds with MIC ≤ 12.5 μg mL-1 were screened against human embryonic kidney cells to assess their potential cytotoxicity. Interestingly, these compounds showed less toxicity towards normal cells, with a selectivity index value ≥ 11. To further evaluate the binding pattern in the active site of enoyl-ACP reductase (InhA) from Mtb (PDB-4TZK), a molecular docking analysis of compound ANA-12 was performed using the glide module of Schrodinger software. The stability, confirmation, and intermolecular interactions of the cocrystal ligand and the highly active compound ANA-12 on the chosen target protein were investigated through molecular dynamics simulations lasting 100 ns. In silico predictions were utilized to assess the ADMET properties of the final compounds. A suitable single crystal was developed and analyzed for compound ANA-5 to gain a deeper understanding of the compounds' structures.

Design, synthesis and biological evaluation of sulfonylamidines as potent c-Met inhibitors by enhancing hydrophobic interaction

The dysregulation of c-Met kinase has emerged as a significant contributing factor for the occurrence, progression, poor clinical outcomes and drug resistance of various human cancers. In our ongoing pursuit to identify promising c-Met inhibitors as potential antitumor agents, a docking study of the previously reported c-Met inhibitor 7 revealed a large unoccupied hydrophobic pocket, which could present an opportunity for further exploration of structure-activity relationships to improve the binding affinity with the allosteric hydrophobic back pocket of c-Met. Herein we performed structure-activity relationship and molecular modeling studies based on lead compound 7. The collective endeavors culminated in the discovery of compound 21j with superior efficacy to 7 and positive control foretinib by increasing the hydrophobic interaction with the hydrophobic back pocket of c-Met active site.

Recent progress on vascular endothelial growth factor receptor inhibitors with dual targeting capabilities for tumor therapy

Vascular endothelial growth factor receptors (VEGFRs) are a family of receptor protein tyrosine kinases that play an important role in the regulation of tumor-induced angiogenesis. Currently, VEGFR inhibitors have been widely used in the treatment of various tumors. However, current VEGFR inhibitors are limited to a certain extent due to limited clinical efficacy and potential toxicity, which hinder their clinical application. Thus, the development of new strategies to improve the clinical outcomes and minimize the toxic effects of VEGFR inhibitors is required. Given the synergistic effect of VEGFR and other therapies in tumor development and progression, VEGFR dual-target inhibitors are becoming an attractive approach due to their favorable pharmacodynamics, low toxicity, and anti-resistant effects. This perspective provides an overview of the development of VEGFR dual-target inhibitors from multiple aspects, including rational target combinations, drug discovery strategies, structure–activity relationships and future directions.

Palladium-Catalyzed Carbo-Aminative Cyclization of 1,6-Enynes: Access to Napthyridinone Derivatives

1,6-Enynes have recently stimulated enormous attention toward paving the way to unique cascade cyclizations offering complex cyclic motifs from linear substrates. We describe herein a general approach to napthyridinones via the Pd-catalyzed annulation of 1,6-enynes with 2-iodoanilines. This protocol represents a rare carbo-aminative annulative cyclization via the 6-endo-trig mode, subduing the well-documented exo-trig/dig cyclizations. The regioselective aryl palladation of alkyne followed by Heck-type intramolecular coupling before isomerization were key in realizing this cascade.

Enhancement of Antibiotic Activity by 1,8-Naphthyridine Derivatives against Multi-Resistant Bacterial Strains

The search for new antibacterial agents has become urgent due to the exponential growth of bacterial resistance to antibiotics. Nitrogen-containing heterocycles such as 1,8-naphthyridine derivatives have been shown to have excellent antimicrobial properties. Therefore, the purpose of this study was to evaluate the antibacterial and antibiotic-modulating activities of 1,8-naphthyridine derivatives against multi-resistant bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the following compounds: 7-acetamido-1,8-naphthyridin-4(1H)-one and 3-trifluoromethyl-N-(5-chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide. The antibiotic-modulating activity was analyzed using subinhibitory concentrations (MIC/8) of these compounds in combination with norfloxacin, ofloxacin, and lomefloxacin. Multi-resistant strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were used in both tests. Although the compounds had no direct antibacterial activity (MIC ≥ 1.024 µg/mL), they could decrease the MIC of these fluoroquinolones, indicating synergism was obtained from the association of the compounds. These results suggest the existence of a structure-activity relationship in this group of compounds with regard to the modulation of antibiotic activity. Therefore, we conclude that 1,8-naphthyridine derivatives potentiate the activity of fluoroquinolone antibiotics against multi-resistant bacterial strains, and thereby interesting candidates for the development of drugs against bacterial infections caused by multidrug resistant strains.

An updated patent review of small-molecule c-Met kinase inhibitors (2018-present)

INTRODUCTION

c-Met tyrosine kinase receptor is a high-affinity ligand of hepatocyte growth factor (HGF). c-Met is widely expressed in a variety of normal human tissues, but shows abnormally high expression, amplification or mutation in tumour tissues such as lung, gastric and breast cancers. Therefore, the use of c-Met as a target can achieve the inhibition of a series of abnormal physiological processes such as tumourigenesis, development and metastasis. A number of small molecule tyrosine kinase inhibitors targeting c-Met have been successfully marketed.

AREAS COVERED

This article reviews recent advances in patented c-Met small molecule inhibitors and their inhibitory activity against various cancer cells from 2018 to date.

EXPERT OPINION

To date, small molecule inhibitors targeting c-Met have demonstrated impressive therapeutic efficacy in the clinical setting. Most recent patents have focused on addressing the direction of c-Met amplification and overexpression. Despite the great success in the development of selective c-Met inhibitors, the effects of bypass secretion and mutagenesis have led to a need for new c-Met small molecule inhibitors that are safe, efficient, selective and less toxic with novel structures and effective against other targets.

Transforming Type II to Type I c-Met kinase inhibitors via combined scaffold hopping and structure-guided synthesis of new series of 1,3,4-thiadiazolo[2,3-c]-1,2,4-triazin-4-one derivatives

Novel 1,3,4-thiadiazolo[2,3-c]-1,2,4-triazin-4-one derivatives 3a-e, 4a-f and 5a-f were designed as Type I c-Met kinase inhibitors based on scaffold hopping of our previous Type II c-Met kinase lead. Target compounds were then synthesized under the guidance of molecular docking analysis to identify the potential inhibitors that fit the binding pocket of c-Met kinase in the characteristic manner as the reported Type I c-Met kinase inhibitors. All synthesized derivatives were evaluated for their c-Met kinase inhibitory activity at 10 µM concentration, where 3d, 5d and 5f displayed >80% inhibition. Further IC₅₀ investigation of these compounds identified 5d as the most potent c-Met kinase inhibitor with IC₅₀ value of 1.95 µM. Moreover, 5d showed selective antitumor activity against c-Met over-expressing colon HCT-116 and lung A549 adenocarcinoma cells with IC₅₀ values of 6.18 and 10.6 µg/ml, respectively. More significantly, 5d effectively inhibited c-Met phosphorylation in the Western blot experiment. Also, 5d induced cellular apoptosis in HCT-116 cancer cells as well as cell cycle arrest with accumulation of cells in G2/M phase. Finally, kinase selectivity profiling of 5d against nine oncogenic kinases revealed its selectivity to only Tyro3 kinase (% inhibition = 80%, IC₅₀ = 3 µM). All these experimental findings clearly demonstrate that 5d is a potential dual acting inhibitor against c-Met and Tyro3 kinases, standing out as a viable lead that deserves further investigation and development to new generation of antitumor agents.

Pharmacoinformatics and Preclinical Studies of NSC765690 and NSC765599, Potential STAT3/CDK2/4/6 Inhibitors with Antitumor Activities against NCI60 Human Tumor Cell Lines

Signal transducer and activator of transcription 3 (STAT3) is a transcriptional regulator of a number of biological processes including cell differentiation, proliferation, survival, and angiogenesis, while cyclin-dependent kinases (CDKs) are a critical regulator of cell cycle progression. These proteins appear to play central roles in angiogenesis and cell survival and are widely implicated in tumor progression. In this study, we used the well-characterized US National Cancer Institute 60 (NCI60) human tumor cell lines to screen the in vitro anti-cancer activities of our novel small molecule derivatives (NSC765690 and NSC765599) of salicylanilide. Furthermore, we used the DTP-COMPARE algorithm and in silico drug target prediction to identify the potential molecular targets, and finally, we used molecular docking to assess the interaction between the compounds and prominent potential targets. We found that NSC765690 and NSC765599 exhibited an anti-proliferative effect against the 60 panels of NCI human cancer cell lines, and dose-dependent cytotoxic preference for NSCLC, melanoma, renal, and breast cancer cell lines. Protein–ligand interactions studies revealed that NSC765690 and NSC765599 were favored ligands for STAT3/CDK2/4/6. Moreover, cyclization of the salicylanilide core scaffold of NSC765690 mediated its higher anti-cancer activities and had greater potential to interact with STAT3/CDK2/4/6 than did NSC765599 with an open-ring structure. NSC765690 and NSC765599 met the required safety and criteria of a good drug candidate, and are thus worthy of further in-vitro and in-vivo investigations in tumor-bearing mice to assess their full therapeutic efficacy.

Structure-activity relationship study of novel quinazoline-based 1,6-naphthyridinones as MET inhibitors with potent antitumor efficacy

As a privileged scaffold, the quinazoline ring is widely used in the development of EGFR inhibitors, while few quinazoline-based MET inhibitors are reported. In our ongoing efforts to develop new MET-targeted anticancer drug candidates, a series of quinazoline-based 1,6-naphthyridinone derivatives were designed, synthesized, and evaluated for their biological activities. The preliminary SARs studies indicate that the quinazoline scaffold was also acceptable for the block A of class II MET inhibitors. The further pharmacokinetic studies led to the identification of the most promising compound 22a with favorable in vitro potency (MET, IC₅₀ = 9.0 nM), human microsomal metabolic stability (t_1/2 = 621.2 min) and oral bioavailability (F = 42%). Moreover, 22a displayed good in vivo antitumor efficacy (IR of 81% in 75 mg/kg) in MET-positive human glioblastoma U-87 MG xenograft model. These positive results indicated that 22a is a potential new MET-targeted antitumor drug lead, which is worthy of further development.

Ultrasonically Assisted N-Cyanoacylation and Synthesis of Alkyl(4-(3-cyano-4,6-dimethyl-2-oxopyridin-1(2H)-yl)benzoyl)amino Acid Ester Derivatives

This work represents the use of N-3-(3,5-dimethyl-1H-pyrazol-1-yl)-3-oxopropanenitrile as a cyanoacetylating agent for the synthesis of cyanoacetamide benzoic acid and benzophenone derivatives by two different methods, namely, conventional heating and ultrasonication. The cyanoacetamide derivatives were subjected to cyclization to produce N-substituted 2-pyridone derivatives under conventional heating and by an ultrasonic method as well. The ultrasonic method afforded the products in less reaction time with high yields and purities compared to the conventional method, as observed from their spectral data. N-(4-Carboxy phenyl)-4,6-dimethyl-3-cyano-2-pyridone was coupled with different amino acid esters by the OxymaPure/DIC methodology under traditional and ultrasonic conditions. Again, ultrasonication assisted the coupling step and afforded the products with higher yields and purities compared to the traditional method. Fourier transform infrared spectroscopy, NMR (¹H and ¹³C), elemental analysis, and LC-MS were used to determine the structures of all compounds. Finally, a feature of this protocol is exploring the utilization of ultrasonication as an eco-friendly alternative conventional heating method for N-cyanoacylation and synthesis of N-substituted pyridinone derivatives and as a coupling method for the formation of an amide bond, which might be of interest for many researchers.

Grignard Reagent Utilization Enables a Practical and Scalable Construction of 3-Substituted 5-Chloro-1,6-naphthyridin-4-one Derivatives

A robust, practical, and scalable approach for the construction of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 via the addition of Grignard reagents to 4-amino-2-chloronicotinonitrile (15) was developed. Starting with various Grignard reagents, a wide range of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 were conveniently synthesized in moderate-to-good yields through addition–acidolysis–cyclocondensation. In addition, the robustness and applicability of this synthetic route was proven on a 100 g scale, which would enable convenient sample preparation in the preclinical development of 1,6-naphthyridin-4-one-based MET-targeting antitumor drug candidates.

Efficient Arylation of 2,7-Naphthyridin-1(2H)-one with Diaryliodonium Salts and Discovery of a New Selective MET/AXL Kinase Inhibitor

New 8-chloro-2-phenyl-2,7-naphthyridin-1(2H)-one building blocks bearing diverse substitutes on the 2-phenyl group were synthesized via an efficient diaryliodonium salt-based N-arylation strategy with the advantage of mild conditions, short reaction times, and high yields. A small combinatorial library of 8-amino substituted 2-phenyl-2,7-naphthyridin-1(2H)-one was further conveniently constructed based on the above chlorinated naphthyridinones and substituted aniline. Preliminary biochemical screening resulted in the discovery of the new 2,7-naphthyridone-based MET/AXL kinase inhibitors. More importantly, 17c (IC_50,MET of 13.8 nM) or 17e (IC_50,AXl of 17.2 nM) and 17i (IC_50,AXl of 31.8 nM) can efficient selectively inhibit MET or AXL kinase, respectively, while commercial cabozantinib showed no selectivity. The further exploration of the 8-substituted 2-phenyl-2,7-naphthyridin-1(2H)-one combinatorial library would significantly accelerate the discovery of more potent and selective inhibitors against diverse kinases.

Research Progress of Small Molecule VEGFR/c-Met Inhibitors as Anticancer Agents (2016-Present)

Vascular endothelial growth factor receptor 2 (VEGFR-2) binds to VEGFR-A, VEGFR-C and VEGFR-D and participates in the formation of tumor blood vessels, mediates the proliferation of endothelial cells, enhances microvascular permeability, and blocks apoptosis. Blocking or downregulating the signal transduction of VEGFR is the main way to discover new drugs for many human angiogenesis-dependent malignancies. Mesenchymal epithelial transfer factor tyrosine kinase (c-Met) is a high affinity receptor for hepatocyte growth factor (HGF). Abnormal c-Met signaling plays an important role in the formation, invasion and metastasis of human tumors. Therefore, the HGF/c-Met signaling pathway has become a significant target for cancer treatment. Related studies have shown that the conduction of the VEGFR and c-Met signaling pathways has a synergistic effect in inducing angiogenesis and inhibiting tumor growth. In recent years, multi-target small molecule inhibitors have become a research hotspot, among which the research of VEGFR and c-Met dual-target small molecule inhibitors has become more and more extensive. In this review, we comprehensively summarize the chemical structures and biological characteristics of novel VEGFR/c-Met dual-target small-molecule inhibitors in the past five years.

Design, synthesis and biological evaluation of novel N-sulfonylamidine-based derivatives as c-Met inhibitors via Cu-catalyzed three-component reaction

In our continuing efforts to develop novel c-Met inhibitors as potential anticancer candidates, a series of new N-sulfonylamidine derivatives were designed, synthesized via Cu-catalyzed multicomponent reaction (MCR) as the key step, and evaluated for their in vitro biological activities against c-Met kinase and four cancer cell lines (A549, HT-29, MKN-45 and MDA-MB-231). Most of the target compounds showed moderate to significant potency at both the enzyme-based and cell-based assay and possessed selectivity for A549 and HT-29 cancer cell lines. The preliminary SAR studies demonstrated that compound 26af (c-Met IC₅₀ = 2.89 nM) was the most promising compound compared with the positive foretinib, which exhibited the remarkable antiproliferative activities, with IC₅₀ values ranging from 0.28 to 0.72 μM. Mechanistic studies of 26af showed the anticancer activity was closely related to the blocking phosphorylation of c-Met, leading to cell cycle arresting at G2/M phase and apoptosis of A549 cells by a concentration-dependent manner. The promising compound 26af was further identified as a relatively selective inhibitor of c-Met kinase, which also possessed an acceptable safety profile and favorable pharmacokinetic properties in BALB/c mouse. The favorable drug-likeness of 26af suggested that N-sulfonylamidines may be used as a promising scaffold for antitumor drug development. Additionally, the docking study and molecular dynamics simulations of 26af revealed a common mode of interaction with the binding site of c-Met. These positive results indicated that compound 26af is a potential anti-cancer candidate for clinical trials, and deserves further development as a selective c-Met inhibitor.

Discovery of N-substituted-3-phenyl-1,6-naphthyridinone derivatives bearing quinoline moiety as selective type II c-Met kinase inhibitors against VEGFR-2

New N-substituted-3-phenyl-1,6-naphthyridinone derivatives are designed and synthesized, based on structural modification of our previously reported compound 3. Extensive enzyme-based SAR studies and PK evaluation led to the discovery of compound 4r, with comparable c-Met potency to that of Cabozantinib and high VEGFR-2 selectivity, while Cabozantinib displayed no VEGFR-2 selectivity. More importantly, at oral doses of 45 mg/kg (Q.D.), compound 4r exhibits significant tumor growth inhibition (93%) in a U-87MG human gliobastoma xenograft model. The promising selectivity against VEGFR-2 and excellent tumor growth inhibition of compound 4r suggest that it could be used as a new lead molecule for further discovery of selective type II c-Met inhibitors.

Discovery of 1,6-naphthyridinone-based MET kinase inhibitor bearing quinoline moiety as promising antitumor drug candidate

A series of 1,6-naphthyridinone-based MET kinase inhibitors bearing quinoline moiety in block A were designed and synthesized based on the structures of Cabozantinib and our reported compound IV. Extensive SAR and DMPK studies led to the identification of 20j, a potent and orally bioavailable MET kinase inhibitor with favorable kinase selectivity. More importantly, 20j exhibited statistically significant tumor growth inhibition (Tumor growth inhibition/TGI of 131%, 4/6 partial regression/PR) in the U-87 MG xeograft model, which is superior to that of Cabozantinib (TGI of 97%, 2/6 PR), and significantly better than that of compound IV (TGI of 15%, 0/6 PR) at the same dose (12.5 mg/kg). Combined with favorable in vitro potency, kinase selectivity, pharmacokinetic profile and in vivo efficacy, the promising antitumor drug candidate 20j has subsequently advanced into preclinical research.

Discovery of 8-Amino-Substituted 2-Phenyl-2,7-Naphthyridinone Derivatives as New c-Kit/VEGFR-2 Kinase Inhibitors

The 2,7-naphthyridone scaffold has been proposed as a novel lead structure of MET inhibitors by our group. To broaden the application of this new scaffold, a series of 8-amino-substituted 2-phenyl-2,7-naphthyridin-1(2H)-one derivatives were designed and synthesized. Preliminary biological screening resulted in the discovery of a new lead of c-Kit and VEGFR-2 kinase inhibitors. Compound 9k exhibited excellent c-Kit inhibitory activity, with an IC₅₀ value of 8.5 nM, i.e., it is 38.8-fold more potent than compound 3 (IC₅₀ of 329.6 nM). Moreover, the compounds 10l and 10r exhibited good VEGFR-2 inhibitory activity, with IC₅₀ values of 56.5 and 31.7 nM, respectively, i.e., they are 5.0–8.8-fold more potent than compound 3 (IC₅₀ of 279.9 nM). Molecular docking experiments provided further insight into the binding interactions of the new lead compounds with c-Kit and VEGFR-2 kinase. In this study, an 8-amino-substituted 2-phenyl-2,7-naphthyridin-1(2H)-one scaffold was identified as the new lead structure of c-Kit and VEGFR-2 kinase inhibitors.