Design, synthesis and structure–activity relationships of novel 4-phenoxyquinoline derivatives containing pyridazinone moiety as potential antitumor agents

The development of pyridazinone-based andrographolide derivatives as anti-cancer agents with the ability of inhibiting the TFAP4/Wnt/β-catenin signaling pathway

Emerging evidence indicated that natural andrographolide and its derived compounds could exert anti-cancer effects on a broad range of cancer cells by several mechanisms of actions. However, the potent andrographolide derivatives with novel structures are needed and the comprehensive understanding of the underlying mechanisms of actions are still lacking. In this work, we reported the pyridazinone-based anti-cancer andrographolide derivative A61, which is superior to the widely-used anti-cancer drug 5-FU (around 5-fold more potent), it showed high potency to inhibit the growth and migration of a panel of cancer cells, in which the gastric cancer cells exhibited the highest drug sensitivity. Preliminary anti-cancer mechanistic studies indicated that A61 exerted its anti-gastric cancer effect by inducing cell apoptosis through intrinsic mitochondria-mediated pathways and arresting cell circle at S phase. Further exploration at the molecular level indicated that compound A61 may inhibit the transcriptional activity and nuclear localization of TFAP4 in gastric cancer cells by inhibiting the TFAP4/Wnt/β-catenin signaling pathway. For the first time, the TFAP4/Wnt/β-catenin signaling pathway was found to be responsible for the anti-cancer activity of andrographolide derivative. In addition, A61 was demonstrated to have significantly increased bioavailability in rats compared with andrographolide. This work provides pertinent information for the understanding of the anti-cancer mechanism by this class of compounds.

Design, synthesis, and biological evaluation of 4-(2-fluorophenoxy)pyridine derivatives as novel FLT3-ITD inhibitors

FMS-like tyrosine kinase 3 (FLT3) is an ideal drug target for the treatment of acute myeloid leukemia (AML). Although several FLT3 inhibitors have been approved or evaluated in clinical trials, selectivity over c-Kit kinase and FLT3 WT remains a major challenge. Herein, we report a series of 4-(2-fluorophenoxy)pyridine derivatives with potent inhibitory activities against FLT3 internal tandem duplication (FLT3-ITD). The representative compound 13v inhibited FLT3-ITD kinase and isogenic BaF3-FLT3-ITD cells with nanomolar IC50 values and achieved selectivity over c-Kit (>53-fold) and FLT WT (19-fold) in transformed BaF3 cells. In addition, compound 13v displayed excellent selectivity against FLT3-ITD driven AML cells compared to other leukemia cells, solid tumors, and normal peripheral blood mononuclear cells. Mechanistic studies revealed that 13v disrupted FLT3 signal transduction and induced G0/G1 cell cycle arrest and apoptosis. Moreover, it also showed good developmental profiles in ADME assays. In in vivo studies, 13v demonstrated desirable pharmacokinetic (PK) profiles and sufficient tumor growth inhibition in a MOLM-13 xenograft model. Taken together, 13v may represent a starting point for the development of improved FLT3-ITD inhibitors.

Design, Synthesis, and Herbicidal Activity of Biaryl-Pyridazinone/Phthalimide Derivatives as Novel Protoporphyrinogen Oxidase Inhibitors

In this study, a series of biaryl-pyridazinone/phthalimide derivatives were designed and synthesized as novel protoporphyrinogen IX oxidase (PPO) inhibitors. Herbicidal activity and crop safety assessments revealed that some compounds exhibited excellent herbicidal activity and crop safety profiles. For instance, at 37.5 g ai/ha, compound 7m inhibited Amaranthus retroflexus (AR), Abutilon theophrasti (AT), Medicago sativa (MS), Echinochloa crus-galli (EC), and Digitaria sanguinalis (DS) with 90% to 100% efficacy, comparable to the commercial herbicide saflufenacil (SAF). Compound 7m still showed effective weed control against the test broadleaf weeds at a lower dose of 9.375 g ai/ha. Additionally, 7m demonstrated excellent safety for wheat and corn at dosages up to 150 g ai/ha. In vitro experiments revealed that the representative compounds exhibited significant inhibitory activity against Arabidopsis thaliana PPO (AtPPO). Molecular docking of Nicotiana tabacum PPO (NtPPO) and 7m showed significant hydrogen bonding, π-π stacking, and π-alkyl interactions between 7m and residues, such as Cys-177, Thr-176, Arg-98, Phe-392, and Leu-372. Furthermore, 7m caused a notable reduction in chlorophyll (Chl) content in weeds. 7m is a promising candidate for the development of novel herbicides.

An Overview of Pyridazinone Analogs: Chemical and Pharmacological Potential

Pyridazinones are classical molecules that occupy an important place in heterocyclic chemistry, and since their discovery, they have been widely developed. The introduction of new functional groups into pyridazinone structures has enabled the synthesis of a large diversity of compounds. The pharmacological and agrochemical importance of pyridazinone derivatives has aroused the interest of chemists and directed their research toward the synthesis of new compounds with the aim of improving their biological effectiveness. In this review, we have compiled and discussed the different synthetic routes, reactivity, and pharmacological and agrochemical applications of the pyridazinone ring.

Discovery of LAH-1 as potent c-Met inhibitor for the treatment of non-small cell lung cancer

ABSTRCTDysregulated HGF/c-Met pathway has been implicated in multiple human cancers and has become an attractive target for cancer intervention. Herein, we report the discovery of N-(3-fluoro-4-((2-(3-hydroxyazetidine-1-carboxamido)pyridin-4-yl)oxy)phenyl)-1-(4-fluorophenyl)-4-methyl-6-oxo-1,6-dihydropyridazine-3-carboxamide (LAH-1), which demonstrated nanomolar MET kinase activity as well as desirable antiproliferative activity, especially against EBC-1 cells. Mechanism studies confirmed the effects of LAH-1 on modulation of HGF/c-Met pathway, induction of cell apoptosis, inhibition on colony formation as well as cell migration and invasion. In addition, LAH-1 also showed desirable in vitro ADME properties as well as acceptable in vivo PK parameters. The design, synthesis, and characterisation of LAH-1 are described herein.

Mono- and Difluoromethylation of 3(2H)-Pyridazinones

A method for direct N-monofluoromethylation of pyridazinones with S-monofluoromethyl-S-phenyl-2,3,4,5-tetramethylphenylsulfonium triflate is disclosed. A method for the N- and O-difluoromethylated pyridazinones with TMSCF2Br as the only promising difluorocarbene precursor is also reported. Substrates with various relevant functional groups, including analogues of Lynparza, are tolerated under both methods.

Design and biological evaluation of 3-substituted quinazoline-2,4(1H,3H)-dione derivatives as dual c-Met/VEGFR-2-TK inhibitors

The dual c-Met/vascular endothelial growth factor receptor 2 (VEGFR-2) TK inhibition is a good strategy to overcome therapeutic resistance to small molecules VEGFR-2 inhibitors. In this study, we designed 3-substituted quinazoline-2,4(1H,3H)-dione derivatives as dual c-Met/VEGFR-2 TK inhibitors. We introduced new synthetic methods for reported derivatives of 3-substituted quinazoline-2,4(1H,3H)-dione 2a-g, in addition to the preparation of some new derivatives namely, 3 and 4a-j. Three compounds namely, 2c, 4b, and 4e showed substantial amount of inhibition for both c-Met and VEGFR-2 TK (IC₅₀ range 0.052-0.084 µM). Both compounds 4b, 4e showed HB with highly conserved residue Asp1222 in the HB region of c-Met TK. For VEGFR-2 TK, compound 4b showed HB with a highly conserved residue Asp1046 in the HB region. Compound 4e showed HB with Glu885 and Asp1046. Moreover, in silico prediction of pharmacokinetic and physicochemical parameters of target compounds was carried out using SwissADME website. The quinazoline-2,4(1H,3H)-dione derivatives are promising antiproliferative candidates that require further optimisation.HighlightsNew 3-substituted quinazoline-2,4(1H,3H)-dione derivatives were synthesised and characterised.Compounds 4b and 4e showed higher cytotoxic activity than cabozantinib against HCT-116 colorectal cell lines.Both compounds 4b and 4e showed less toxicity to WI38 normal cell line compared to HCT 116 colon cancer cell line.Compound 4b was superior to cabozantinib in VEGFR-2 inhibition while compound 2c was equipotent to cabozantinib.Compounds 4b and 4e showed remarkable c-Met inhibitory activity.Compounds 4b and 4e arrested cell cycle and induced significant levels of apoptosis.In silico ADME prediction revealed high oral bioavailability and enhanced water solubility of target compounds as compared to cabozantinib.Target compounds interacted with both c-Met and VEGFR-2 active site in similar way to cabozantinib.

SABRE hyperpolarized anticancer agents for use in 1 H MRI

Purpose

Enabling drug tracking (distribution/specific pathways) with magnetic resonance spectroscopy requires manipulation (via hyperpolarization) of spin state populations and targets with sufficiently long magnetic lifetimes to give the largest possible window of observation. Here, we demonstrate how the proton resonances of a group of thienopyridazines (with known anticancer properties), can be amplified using the para‐hydrogen (p‐H₂) based signal amplification by reversible exchange (SABRE) hyperpolarization technique.

Methods

Thienopyridazine isomers, including a ²H version, were synthesized in house. Iridium‐based catalysts dissolved in a methanol‐d₄ solvent facilitated polarization transfer from p‐H₂ gas to the target thienopyridazines. Subsequent SABRE ¹H responses of hyperpolarized thienopyridazines were completed (400 MHz NMR). Pseudo‐singlet state approaches were deployed to extend magnetic state lifetimes. Proof of principle spectral‐spatial images were acquired across a range of field strengths (7T‐9.4T MRI).

Results

¹H‐NMR signal enhancements of −10,130‐fold at 9.4T (~33% polarization) were achieved on thieno[2,3‐d]pyridazine (T[2,3‐d]P), using SABRE under optimal mixing/field transfer conditions. ¹H T₁ lifetimes for the thienopyridazines were ~18‐50 s. Long‐lived state approaches extended the magnetic lifetime of target proton sites in T[2,3‐d]P from an average of 25‐40 seconds. Enhanced in vitro imaging (spatial and chemical shift based) of target T[2,3‐d]P was demonstrated.

Conclusion

Here, we demonstrate the power of SABRE to deliver a fast and cost‐effective route to hyperpolarization of important chemical motifs of anticancer agents. The SABRE approach outlined here lays the foundations for realizing continuous flow, hyperpolarized tracking of drug delivery/pathways.

Design, synthesis and anti-tumor evaluation of 1,2,4-triazol-3-one derivatives and pyridazinone derivatives as novel CXCR2 antagonists

Chemokine receptor 2 (CXCR2) is the receptor of glutamic acid-leucine-arginine sequence-contained chemokines CXCs (ELR⁺ CXCs). In recent years, CXCR2-target treatment strategy has come a long way in cancer therapy. CXCR2 antagonists could block CXCLs/CXCR2 axis, and are widely used in regulating immune cell migration, tumor metastasis, apoptosis and angiogenesis. Herein, two series of new CXCR2 small-molecule inhibitors, including 1,2,4-triazol-3-one derivatives 1-11 and pyridazinone derivatives 12-22 were designed and synthesized based on the proof-to-concept. The pyridazinone derivative 18 exhibited good CXCR2 antagonistic activity (69.4 ± 10.5 %Inh at 10 μM) and demonstrated its significant anticancer metastasis activity in MDA-MB-231 cells and remarkable anti-angiogenesis activity in HUVECs. Furthermore, noteworthy was that 18 exhibited an obvious synergistic effect with Sorafenib in anti-proliferation assay in MDA-MB-231 cells. Moreover, 18 showed a distinct reduction of the phosphorylation levels of both PI3K and AKT proteins in MDA-MB-231 cells, and also affected the expression levels of other PI3K/AKT signaling pathway-associated proteins. The molecular docking studies of 18 with CXCR2 also verified the rationality of our design strategy. All of these results revealed pyridazinone derivative 18 as a promising CXCR2 antagonist for future cancer therapy.

Design, synthesis and biological evaluation of novel N-[4-(2-fluorophenoxy)pyridin-2-yl]cyclopropanecarboxamide derivatives as potential c-Met kinase inhibitors

Three series of novel 4-phenoxypyridine derivatives containing 4-methyl-6-oxo-1,6-dihydropyridazine- 3-carboxamide, 5-methyl-4-oxo-1,4-dihydropyridazine-3-carboxamide and 4-methyl-3,5-dioxo-2,3,4,5- tetrahydro-1,2,4-triazine-6-carboxamide moieties were synthesized and evaluated for their in vitro inhibitory activitives against c-Met kinase and cytotoxic activitives against A549, H460, HT-29 cancer cell lines. The results indicated that most of the compounds showed moderate to good antitumor activitives. The most promising compound 26a (with c-Met IC₅₀ value of 0.016 μM) showed remarkable cytotoxicity against A549, H460, and HT-29 cell lines with IC₅₀ values of 1.59 μM, 0.72 μM and 0.56 μM, respectively. Their preliminary structure-activity relationships (SARs) studies indicate that 4-methyl-3,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carboxamide was more preferred as linker part, and electron-withdrawing groups on the terminal phenyl rings are beneficial for improving the antitumor activitives. Furthermore, the colony formation, acridine orange/ethidium bromide (AO/EB) staining, apoptosis, and wound-healing assay of 26a were performed on HT-29 and/or A549 cell lines.

Design, synthesis, and biological evaluation of 4-((6,7-dimethoxyquinoline-4-yl)oxy)aniline derivatives as FLT3 inhibitors for the treatment of acute myeloid leukemia

FMS-like tyrosine kinase 3 (FLT3) was an important therapeutic target in acute myeloid leukemia (AML). We synthesized two series of 4-((6,7-dimethoxyquinoline-4-yl)oxy)aniline derivatives possessing the semicarbazide moiety and 2,2,2-trifluoro-N,N'-dimethylacetamide moiety as the linker. The cell proliferation assay in vitro against HL-60 and MV4-11 cell lines demonstrated that most series I compounds containing semicarbazide moiety had more potent than Cabozantinib. Furthermore, the enzyme assay showed that compound 12c and 12g were potent FLT3 inhibitors with IC₅₀ values of 312 nM and 384 nM, respectively. Following that, molecular docking analysis was also performed to determine possible binding mode between FLT3 and the target compound.

A new pyridazinone exhibits potent cytotoxicity on human cancer cells via apoptosis and poly-ubiquitinated protein accumulation

In the last 15 years, pyridazinone derivatives have acquired extensive attention due to their widespread biological activities and pharmacological applications. Pyridazinones are well known for their anti-microbial, anti-viral, anti-inflammatory, anti-cancer, and cardiovascular activities, among others. In this study, we evaluated the anti-cancer activity of a new pyridazinone derivative and propose it as a potential anti-neoplastic agent in acute promyelocytic leukemia cells. Pyr-1 cytotoxicity was assessed on several human cancer and two non-cancerous cell lines by the DNS assay. Pyr-1 demonstrated potent cytotoxicity against 22 human cancer cell lines, exhibiting the most favorable selective cytotoxicity on leukemia (CEM and HL-60), breast (MDA-MB-231 and MDA-MB-468), and lung (A-549) cancer cell lines, when compared with non-cancerous breast epithelial MCF-10A cells. Analyses of apoptosis/necrosis pathways, reactive oxygen species (ROS) production, mitochondria health, caspase-3 activation, and cell cycle profile were performed via flow cytometry. Both hmox-1 RNA and protein expression levels were evaluated by quantitative real-time PCR and Western blotting assays, respectively. Pyr-1 induced apoptosis in acute promyelocytic leukemia cells as confirmed by phosphatidylserine externalization, mitochondrial depolarization, caspase-3 activation, DNA fragmentation, and disrupted cell cycle progression. Additionally, it was determined that Pyr-1 generates oxidative and proteotoxic stress by provoking the accumulation of ROS, resulting in the overexpression of the stress-related hmox-1 mRNA transcripts and protein and a marked increase in poly-ubiquitinated proteins. Our data demonstrate that Pyr-1 induces cell death via the intrinsic apoptosis pathway by accumulating ROS and by impairing proteasome activity.

Efficient 1,3,4-Thiadiazole-4,5-dihydropyridazin-3(2H)-ones as Antimicrobial Agents

A set of novel series of 1,3,4-thiadiazolyl-sulfanyl-4,5-dihydropyridazin-3(2H)-ones with anticipated antimicrobial activity has been synthesized. The synthetic protocol of the targeted compounds was accomplished by treating β-aroylacrylic acid 1 with 5-amino-1,3,4-thiadiazole-2-thiol (2) to afford the thia-Michael adduct 3. Afterwards, the obtained thia-Michael adduct 3 was cyclized to 4,5-dihydropyridazin-3(2H)-ones 4a-d and the non-cyclized product hydrazone 5 by using different hydrazines. Moreover, adduct 3 was reacted with esters like diethyl malonate and ethyl acetoacetate affording 1,3,4-thiadiazolobutanamides 6a, b. Furthermore, the concurrent reaction of later butamides 6a, b with the hydrazine derivatives furnished thiadiazolopyridazin-3(2H)-ones 7a-d, 8, and butanoic acid 9.

A new compound of thiophenylated pyridazinone IMB5043 showing potent antitumor efficacy through ATM-Chk2 pathway

Through cell-based screening models, we have identified a new compound IMB5043, a thiophenylated pyridazinone, which exerted cytotoxicity against cancer cells. In the present study, we evaluated its antitumor efficacy and the possible mechanism. By MTT assay, IMB5043 inhibited the proliferation of various human cancer cells lines, especially hepatocarcinoma SMMC-7721 cells. IMB5043 blocked cell cycle with G2/M arrest, induced cell apoptosis, and inhibited the migration and invasion of SMMC-7721 cells. As verified by comet assay and γ-H2AX foci formation, IMB5043 caused DNA damage and activated ATM, Chk2 and p53 through phosphorylation. As shown by Gene microarray analysis, the differentially expressed genes in SMMC-7721 cells treated with IMB5043 were highly related to cell death and apoptosis. IMB5043 suppressed the growth of hepatocarcinoma SMMC-7721 xenograft in athymic mice. By histopathological examination, no lesions were found in bone marrow and various organs of the treated mice. Our findings reveal that IMB5043 as an active compound consisting of both pyridazinone and thiophene moieties exerts antitumor efficacy through activation of ATM-Chk2 pathway. IMB5043 may serve as a promising leading compound for the development of antitumor drugs.

Development of efficient docking strategies and structure-activity relationship study of the c-Met type II inhibitors

c-Met is a transmembrane receptor tyrosine kinase and an important therapeutic target for anticancer drugs. In the present study, we systematically investigated the influence of a range of parameters on the correlation between experimental and calculated binding free energies of type II c-Met inhibitors. We especially focused on evaluating the impact of different force fields, binding energy calculation methods, docking protocols, conformation sampling strategies, and conformations of the binding site captured in several crystallographic structures. Our results suggest that the force fields, the protein flexibility, and the selected conformation of the binding site substantially influence the correlation coefficient, while the sampling strategies and ensemble docking only mildly affect the prediction accuracy. Structure-activity relationship study suggests that the structural determinants to the high binding affinity of the type II inhibitors originate from its overall linear shape, hydrophobicity, and two conserved hydrogen bonds. Results from this study will form the basis for establishing an efficient computational docking approach for c-Met type II inhibitors design.

Synthesis of Some New Pyridazine Derivatives for Anti-HAV Evaluation

4-(2-(4-Halophenyl)hydrazinyl)-6-phenylpyridazin-3(2H)-ones 1a,b were prepared and treated with phosphorus oxychloride, phosphorus pentasulphide and ethyl chloroformate to give the corresponding chloropyridazine, pyridazinethione, oxazolopyridazine derivatives 2–4, respectively. Compound 2 reacted with hydrazine hydrate to afford hydrazinylpyridazine 7. The reaction of 4-(2-(4-chlorophenyl)hydrazinyl)-3-hydrazinyl-6-phenylpyridazine (7) with acetic anhydride, p-chlorobenzaldehyde and carbon disulphide gave the corresponding pyridazinotriazine derivatives 8–10. On the other hand, 5-(4-chlorophenylamino)-7-(3,5-dimethoxybenzylidene)-3-phenyl-5H-pyridazino[3,4-b][1,4]thiazin-6(7H)-one (11) was prepared directly from the reaction of compound 3 with chloroacetic acid in presence of p-chlorobenzaldehyde. Compound 11 reacted with nitrogen nucleophiles (hydroxylamine hydrochloride, hydrazine hydrate) and active methylene group-containing reagents (malononitrile, ethyl cyanoacetate) to afford the corresponding fused compounds 12–15, respectively. Pharmacological screening for antiviral activity against hepatitis A virus (HAV) was performed for the new compounds. 4-(4-Chlorophenylamino)-6-phenyl-1,2-dihydropyridazino[4,3-e][1,2,4]triazine-3(4H)-thione (10) showed the highest effect against HAV.

Ligand cluster-based protein network and ePlatton, a multi-target ligand finder

BACKGROUND

Small molecules are information carriers that make cells aware of external changes and couple internal metabolic and signalling pathway systems with each other. In some specific physiological status, natural or artificial molecules are used to interact with selective biological targets to activate or inhibit their functions to achieve expected biological and physiological output. Millions of years of evolution have optimized biological processes and pathways and now the endocrine and immune system cannot work properly without some key small molecules. In the past thousands of years, the human race has managed to find many medicines against diseases by trail-and-error experience. In the recent decades, with the deepening understanding of life and the progress of molecular biology, researchers spare no effort to design molecules targeting one or two key enzymes and receptors related to corresponding diseases. But recent studies in pharmacogenomics have shown that polypharmacology may be necessary for the effects of drugs, which challenge the paradigm, 'one drug, one target, one disease'. Nowadays, cheminformatics and structural biology can help us reasonably take advantage of the polypharmacology to design next-generation promiscuous drugs and drug combination therapies.

RESULTS

234,591 protein-ligand interactions were extracted from ChEMBL. By the 2D structure similarity, 13,769 ligand emerged from 156,151 distinct ligands which were recognized by 1477 proteins. Ligand cluster- and sequence-based protein networks (LCBN, SBN) were constructed, compared and analysed. For assisting compound designing, exploring polypharmacology and finding possible drug combination, we integrated the pathway, disease, drug adverse reaction and the relationship of targets and ligand clusters into the web platform, ePlatton, which is available at http://www.megabionet.org/eplatton.

CONCLUSIONS

Although there were some disagreements between the LCBN and SBN, communities in both networks were largely the same with normalized mutual information at 0.9. The study of target and ligand cluster promiscuity underlying the LCBN showed that light ligand clusters were more promiscuous than the heavy one and that highly connected nodes tended to be protein kinases and involved in phosphorylation. ePlatton considerably reduced the redundancy of the ligand set of targets and made it easy to deduce the possible relationship between compounds and targets, pathways and side effects. ePlatton behaved reliably in validation experiments and also fast in virtual screening and information retrieval.Graphical abstractCluster exemplars and ePlatton's mechanism.

Synthesis and bioevaluation of 2-phenyl-5-methyl-2H-1,2,3-triazole-4-carboxylic acid/carbohydrazide derivatives as potent xanthine oxidase inhibitors

A series of 2-phenyl-5-methyl-2H-1,2,3-triazole-4-carboxylic acids/carbohydrazides as analogues of febuxostat were synthesized and evaluated for their in vitro xanthine oxidase (XO) inhibitory activity.

An efficient injectable formulation with block copolymer micelles for hydrophobic antitumor candidate-pyridazinone derivatives

Aim: To make delivery improvements via delivery systems for 6-(4-morpholino-3-(trifluoromethyl)phenyl)pyridazin-3(2H)-one (DZO) – a model compound of hydrophobic antitumor candidate pyridazinone derivatives. Materials & methods: Methoxy poly(ethylene glycol)-poly(d,l-lactide) (MPEG-PDLLA) micelle was employed as a vector, and DZO was encapsulated in. The DZO-loaded micelles were characterized in detail and its cytotoxicity, maximum tolerated dose (MTD) and pharmacokinetic experiments were done. In vivo anticancer activity was studied through a subcutaneous 4T1 tumor model. Results: Compared with free DZO, the DZO-loaded micelles possessed a sustained release property, an improved MTD, better pharmacokinetic parameters and an enhanced antitumor activity for subcutaneous 4T1 model in vivo. Conclusion: An effective injectable delivery system for DZO was developed successfully.

Design and biological evaluation of novel 4-(2-fluorophenoxy)quinoline derivatives bearing an imidazolone moiety as c-Met kinase inhibitors

A series of 4-(2-fluorophenoxy)quinoline derivatives containing an imidazolone moiety were designed, synthesized and evaluated for their in vitro biological activities against c-Met kinase and four cancer cell lines (A549, H460, HT-29 and MKN-45). Most compounds showed moderate to excellent activities in enzyme and cellular assays. The most promising analog, 58 (c-Met IC50=1.42 nM), displayed 2.1-, 8.6-fold increase against H460, and MKN-45 cell lines, respectively, compared with foretinib. An analysis of structure-activity relationships revealed that an ortho substituted phenyl ring as well as an N-unsubstituted imidazolone linker is favorable for antitumor activity.