Protein tyrosine kinase inhibitors as anticancer agents

Recent advances in nitrogen-containing heterocyclic compounds as receptor tyrosine kinase inhibitors for the treatment of cancer: Biological activity and structural activity relationship

Erratic cell proliferation is the initial symptom of cancer, which can eventually metastasize to other organs. Before cancer becomes metastatic, its spread is triggered by pro-angiogenic factors including vascular endothelial growth factor receptor (VEGFR), epidermal growth factor receptor (EGFR), Platelet-derived growth factor receptor (PDGFR), fibroblast growth factor receptor (FGFR) and Platelet Factor (PF4), all of which are part of receptor tyrosine kinase (RTK) family. Receptor tyrosine kinases (RTKs) are cell-surface proteins and aresignaling enzymes that transfer ATP-phosphate to tyrosine residue substrates. Important biological processes like proliferation, differentiation, motility, and cell-cycle regulation are all possessedby these proteins. Unusual RTK expression is typically associated with cell growth abnormalities, which is linked to tumor acquisition, angiogenesis, and cancer progression. In addition to the already available medications, numerous other heterocyclic are being studied for their potential action against a variety of cancers. In the fight against cancer, in particular, these heterocycles have been used for their dynamic core scaffold and their inherent adaptability. In this review article, we have compiled last five years research work including nitrogen containing heterocycles that have targeted RTK. Herein, the SAR and activity of various compounds containing diverse heterocyclic (pyrimidine, indole, pyridine, pyrazole, benzimidazole, and pyrrole) scaffolds are discussed, and they may prove useful in the future for designing new leads against RTKs. Our focus in this manuscript is to comprehensively review the latest research on the biological activity and structural activity relationship of nitrogen compounds as RTK inhibitors. We believe that this may be an important contribution to the field, as it can help guide future research efforts and facilitate the development of more effective cancer therapies.

Design, Synthesis, Biological Evaluation, and Molecular Dynamics Studies of Novel Lapatinib Derivatives

Co-expression of the epidermal growth factor receptor (EGFR, also known as ErbB1) and human epidermal growth factor receptor 2 (HER2) has been identified as a diagnostic or prognostic sign in various tumors. Despite the fact that lapatinib (EGFR/HER2 dual inhibitor) has shown to be successful, many patients do not respond to it or develop resistance for a variety of reasons that are still unclear. As a result, new approaches and inhibitory small molecules are still needed for EGFR/HER2 inhibition. Herein, novel lapatinib derivatives possessing 4-anilinoquinazoline and imidazole scaffolds (6a-l) were developed and screened as EGFR/HER2 dual inhibitors. In vitro and in silico investigations revealed that compound 6j has a high affinity for the ATP-binding regions of EGFR and HER2. All of the designed candidates were predicted to not penetrate the BBB, raising the expectation for the absence of CNS side effects. At 10 µM, derivatives possessing 3-chloro-4-(pyridin-2-ylmethoxy)aniline moiety (6i-l) demonstrated outstanding ranges of percentage inhibition against EGFR (97.65-99.03%) and HER2 (87.16-96.73%). Compound 6j showed nanomolar IC₅₀ values over both kinases (1.8 nM over EGFR and 87.8 nM over HER2). Over EGFR, compound 6j was found to be 50-fold more potent than staurosporine and 6-fold more potent than lapatinib. A kinase selectivity panel of compound 6j showed poor to weak inhibitory activity over CDK2/cyclin A, c-MET, FGFR1, KDR/VEGFR2, and P38a/MAPK14, respectively. Structure-activity relationship (SAR) that were obtained with different substitutions were justified. Additionally, molecular docking and molecular dynamics studies revealed insights into the binding mode of the target compounds. Thus, compound 6j was identified as a highly effective and dual EGFR/HER2 inhibitor worthy of further investigation.

Rational design-aided discovery of novel 1,2,4-oxadiazole derivatives as potential EGFR inhibitors

A molecular dynamics-based sampling of epidermal growth factor receptor tyrosine kinase (EGFR-TK) was carried out to search for energetically more stable protein, which was then used for molecular docking of a series of 1,2,4-oxadiazole derivatives previously reported from our laboratory. A total of 14 compounds were docked, where compounds 6a and 6b showed better binding to EGFR in silico. Further, physicochemical properties of all the compounds were calculated, which suggested that all the molecules obeyed Lipinski's rule of 5 and had favorable polar surface area and CaCO2 permeability along with the low potential for HERG inhibition. All the compounds were then screened for their ability to produce cytotoxicity in four different cell lines overexpressing EGFR (A549, HCT-116, HEPG2, MCF-7) and one EGFR negative cancer cell line (SW620); at three concentrations: 10, 1, and 0.1 µM. None of the compounds showed activity against SW620, which suggested that the compounds show cytotoxicity through inhibition of EGFR. Compounds that showed promise in this 3-concentration screen were further subjected to multiple dose-response curves to identify the IC₅₀ values for the shortlisted eight compounds. It was encouraging to see 6a and 6b showing the best IC₅₀ values against almost all the cell-lines which further suggests that our design protocol can be applied to optimize this lead (which are currently in the low micromolar range) to design the homologous compounds to achieve the desired potency in the nanomolar range and also to achieve selectivity across a range of kinases.

Diosgenin-conjugated PCL–MPEG polymeric nanoparticles for the co-delivery of anticancer drugs: design, optimization, in vitro drug release and evaluation of anticancer activity

In this study, a polymeric nanoparticle-mediated dual anti-cancer drug delivery system was designed and developed.

In vitro apoptosis-inducing effect and gene expression profiles of mixed ligand Cu(ii) complexes derived from 4-acyl pyrazolones on human lung cancer cells

Mixed-ligand Cu(ii) complexes of 4-acylpyrazolone ligands and poly pyridyls were synthesized, characterized and their anticancer activity was evaluated against A549 lung carcinoma cell lines.

Synthesis of 4-(thiazol-2-ylamino)-benzenesulfonamides with carbonic anhydrase I, II and IX inhibitory activity and cytotoxic effects against breast cancer cell lines

A series of 4-(thiazol-2-ylamino)-benzenesulfonamides was synthesized and screened for their carbonic anhydrase (CA, EC 4.2.1.1) inhibitory and cytotoxic activity on human breast cancer cell line MCF-7. Human (h) CA isoforms I, II and IX were included in the study. The new sulfonamides showed excellent inhibition of all three isoforms, with KIs in the range of 0.84-702nM against hCA I, of 0.41-288nM against hCA II and of 5.6-29.2 against the tumor-associated hCA IX, a validated anti-tumor target, with a sulfonamide (SLC-0111) in Phase I clinical trials for the treatment of hypoxic, metastatic solid tumors overexpressing CA IX. The new compounds showed micromolar inhibition of growth efficacy against breast cancer MCF-7 cell lines.

Targeting EGFR/HER2 tyrosine kinases with a new potent series of 6-substituted 4-anilinoquinazoline hybrids: Design, synthesis, kinase assay, cell-based assay, and molecular docking

Coexpression of EGFR and HER2 has been found in many tumors such as breast, ovarian, colon and prostate cancers, with poor prognosis of the patients. Herein, our team has designed and synthesized new eighteen compounds with 6-substituted 4-anilinoquinazoline core to selectively inhibit EGFR/HER2 tyrosine kinases. Twelve compounds (8a-8d, 9a, 9c, 9d, 10a, 10c, 11b, 14, and 15) showed nanomolar range of IC50 values on EGFR and/or HER2 kinases. Accordingly, a detailed structure activity relationship (SAR) was established. A molecular docking study demonstrated the favorable binding modes of 8d, 9b, 9d and 10d at the ATP active site of both kinases. A kinase selectivity profile performed for compound 8d showed great selectivity for EGFR and HER2. In addition, 8d, 9c, and 9d exerted selective promising cytotoxic activity over BT-474 cell line with IC50 values of 2.70, 1.82 and 1.95 μM, respectively. From these results, we report analogs 8d, 9c, and 9d as promising candidates for the discovery of well-balanced compounds in terms of the kinase inhibitory potency and antiproliferative activity.

Polypharmacology of sulfonamides: pazopanib, a multitargeted receptor tyrosine kinase inhibitor in clinical use, potently inhibits several mammalian carbonic anhydrases

Pazopanib, a new, multi-targeted tyrosine kinase inhibitor (TKI) used clinically for the treatment of several types of tumors, incorporates a primary sulfonamide moiety normally associated with the inhibition of the metallo enzyme carbonic anhydrase (CA, EC 4.2.1.1). Here we show that pazopanib and related sulfonamides such as indisulam, acetazolamide or ureido-substituted peptidomimetic benzenesulfonamides are low nanomolar inhibitors of many of the fifteen human isoforms hCA I-XIV. These data indicate that in addition to the TK inhibitory action, pazopanib may exert antitumor/antimetastatic effects also due to the potent inhibition of the tumor-associated, hypoxia-inducible enzymes CA IX and XII.

Molecular modeling studies of vascular endothelial growth factor receptor tyrosine kinase inhibitors using QSAR and docking

The vascular endothelial growth factor (VEGF) and its receptor tyrosine kinases VEGFR-2 or kinase insert domain receptor (KDR) are attractive targets for the development of novel anticancer agents. In the present work, comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were performed on a series of selective inhibitors of KDR. Docking studies were performed to explore the binding mode between all of the inhibitors and the KDR and produce the bioactive conformation of each compound in the whole dataset. Two conformer-based alignment strategies were employed to construct reliable 3D-QSAR models. The docked conformer-based alignment strategy gave the best 3D-QSAR models. The best CoMFA and CoMSIA models gave a cross-validated coefficient q(2) of 0.546 and 0.715, non-cross-validated r(2) values of 0.936 and 0.961, predicted r(2) values of 0.673 and 0.797, respectively. The information obtained from molecular modeling studies were very helpful to design some novel selective inhibitors of KDR with desired activity.

Discovery of brivanib alaninate ((S)-((R)-1-(4-(4-fluoro-2-methyl-1H-indol-5-yloxy)-5-methylpyrrolo[2,1-f][1,2,4]triazin-6-yloxy)propan-2-yl)2-aminopropanoate), a novel prodrug of dual vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 kinase inhibitor (BMS-540215)

A series of amino acid ester prodrugs of the dual VEGFR-2/FGFR-1 kinase inhibitor 1 (BMS-540215) was prepared in an effort to improve the aqueous solubility and oral bioavailability of the parent compound. These prodrugs were evaluated for their ability to liberate parent drug 1 in in vitro and in vivo systems. The l-alanine prodrug 8 (also known as brivanib alaninate/BMS-582664) was selected as a development candidate and is presently in phase II clinical trials.

2D Autocorrelation, CoMFA, and CoMSIA modeling of protein tyrosine kinases' inhibition by substituted pyrido[2,3-d]pyrimidine derivatives

2D Autocorrelation, comparative molecular field analysis (CoMFA), and comparative molecular similarity indices analysis (CoMSIA) were undertaken for a series of substituted pyrido[2,3-d]pyrimidine derivatives to correlate platelet-derived growth factor receptor (PDGFR), fibroblast growth factor receptor (FGFR), and c-Src tyrosine kinases' inhibition with 2D and 3D structural properties of 22 known compounds. QSAR models with considerable internal as well as external predictive ability were obtained. The relevant 2D autocorrelation descriptors for modeling each protein tyrosine kinase (PTK) inhibitory activity were selected by genetic algorithm (GA) and multiple linear regression (MLR) approach. The 2D autocorrelation space brings different descriptors for each PTK inhibition and suggests the atomic properties relevant for the inhibitors to interact with each PTK active site. CoMFA and CoMSIA were developed with a focus on interpretative ability using coefficient contour maps. CoMSIA produced significantly better results for all correlations. The results indicate a strong correlation between the inhibitory activity of the modeled compounds and the hydrophobic and H-bond donor fields around them.

Therapeutic potential of sulfamides as enzyme inhibitors

Sulfamide, a quite simple molecule incorporating the sulfonamide functionality, widely used by medicinal chemists for the design of a host of biologically active derivatives with pharmacological applications, may give rise to at least five types of derivatives, by substituting one to four hydrogen atoms present in it, which show specific biological activities. Recently, some of these compounds started to be exploited for the design of many types of therapeutic agents. Among the enzymes for which sulfamide-based inhibitors were designed, are the carbonic anhydrases (CAs), a large number of proteases belonging to the aspartic protease (HIV-1 protease, gamma-secretase), serine protease (elastase, chymase, tryptase, and thrombin among others), and metalloprotease (carboxypeptidase A (CPA) and matrix metalloproteinases (MMP)) families. Some steroid sulfatase (STS) and protein tyrosine phosphatase inhibitors belonging to the sulfamide class of derivatives have also been reported. In all these compounds, many of which show low nanomolar affinity for the target enzymes for which they have been designed, the free or substituted sulfamide moiety plays important roles for the binding of the inhibitor to the active site cavity, either by directly coordinating to a metal ion found in some metalloenzymes (CAs, CPA, STS), usually by means of one of the nitrogen atoms present in the sulfamide motif, or as in the case of the cyclic sulfamides acting as HIV protease inhibitors, interacting with the catalytically critical aspartic acid residues of the active site by means of an oxygen atom belonging to the HN-SO2-NH motif, which substitutes a catalytically essential water molecule. In other cases, the sulfamide moiety is important for inducing desired physico-chemical properties to the drug-like compounds incorporating it, such as enhanced water solubility, better bioavailability, etc., because of the intrinsic properties of this highly polarized moiety when attached to an organic scaffold. This interesting motif is thus of great value for the design of pharmacological agents with a lot of applications.

Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC50 = 4 nmol/L) but has much less activity (IC50s > 1 micromol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC50 = 2, 4, and 7 nmol/L for PDGFR-beta, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC50 = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED50 = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED50 = 1.5-5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC50 corrected for plasma protein binding = 0.08 microg/mL, >or=7 hours) than with plasma area under the curve or Cmax. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer.

Design, synthesis and antitumor evaluation of a new series of N-substituted-thiourea derivatives

AIM

To design and synthesize a novel class of protein tyrosine kinase inhibitors, featuring the N-(2-oxo-1,2-dihydroquinolin-3-yl-methyl)-thiourea framework.

METHODS

First, compounds 1 and 2 were identified using the virtual screening approach in conjunction with binding assay based on surface plasmon resonance. Subsequently, 3 regions of compounds 1 and 2 were selected for chemical modification. All compounds were characterized potent inhibitory activities toward the human lung adenocarcinoma cell line SPAC1.

RESULTS

Forty new compounds (1-2, 3a-g, 4a-w, and 5a-l) were designed, synthesized and bioassayed. Six compounds (1, 3e, 4l, 4w, 5a, and 5b) were found to show promising inhibitory activity against the SPAC1 tumor cell line. The inhibitory activity of compound 5a increases approximately 10 times more than that of the original compound 1.

CONCLUSION

This study provides a promising new template with potential antitumor activity.

Alkynyl pyrimidines as dual EGFR/ErbB2 kinase inhibitors

Anilinoalkynylpyrimidines were prepared and evaluated as dual EGFR/ErbB2 kinase inhibitors. A preference was found for substituted phenyl and heteroaromatic rings attached to the alkyne. In addition, the presence of a potential hydrogen bond donor appended to this ring was favored. Selected molecules in the series demonstrated some activity against human tumor cell lines.

Synthesis and antitumor evaluation of novel 5-substituted-4-hydroxy-8-nitroquinazolines as EGFR signaling-targeted inhibitors

The synthesis and biological activity of a series of novel 5-substituted-4-hydroxy-8-nitroquinazolines that may function as inhibitors of EGFR- and/or ErbB-2-related oncogenic signaling are described. These compounds were prepared by S(N)Ar reaction of 5-chloro-4-hydroxy-8-nitroquinazoline with alkyl or aryl amines, or alkyl alcohol as nucleophiles. Although the enzyme assay showed a weak inhibition effect against both EGFR and ErbB-2 tyrosine kinases, the cell-based antitumor activity turned out promising. Compounds having 5-anilino substituent exhibit high potency with 5-(4-methoxy)anilino-4-hydroxy-8-nitroquinazoline (1h) being the best dual EGFR/ErbB-2 inhibitors, which effectively inhibited the growth of both EGFR (MDA-MB-468, IC(50)<0.01microM) and ErbB-2 (SK-BR-3, IC(50)=13microM) overexpressing human tumor cell lines in vitro. More interestingly, the variation of the substituent(s) at the 3- and/or 4-position of the 5-anilino portion was found to modulate the selectivity and potency dramatically. However, compounds having an alkylamino or alkyloxy group at the 5-position of 4-hydroxy-8-nitroquinazolines are essentially inactive. These results are consistent with molecular modeling observations. This study was the first attempt to identify new structural types of dual EGFR/ErbB-2-related signaling inhibitors by incorporation of the anilino group at the 5-position of 4-hydroxy-8-nitroquinazolines' core structure, providing promising new templates for further development of potent inhibitors targeting both EGFR and ErbB-2 tyrosine kinases.

Optimization of 6,7-disubstituted-4-(arylamino)quinoline-3-carbonitriles as orally active, irreversible inhibitors of human epidermal growth factor receptor-2 kinase activity

A series of new 6,7-disubstituted-4-(arylamino)quinoline-3-carbonitrile derivatives that function as irreversible inhibitors of human epidermal growth factor receptor-2 (HER-2) and epidermal growth factor receptor (EGFR) kinases have been prepared. These compounds demonstrated enhanced activities for inhibiting HER-2 kinase and the growth of HER-2 positive cells compared to our EGFR kinase inhibitor 86 (EKB-569). Three synthetic routes were used to prepare these compounds. They were prepared mostly by acylation of 6-amino-4-(arylamino)quinoline-3-carbonitriles with unsaturated acid chlorides or by amination of 4-chloro-6-(crotonamido)quinoline-3-carbonitriles with monocyclic or bicyclic anilines. The third route was developed to prepare a key intermediate, 6-acetamido-4-chloroquinoline-3-carbonitrile, that involved a safer cyclization step. We show that attaching a large lipophilic group at the para position of the 4-(arylamino) ring results in improved potency for inhibiting HER-2 kinase. We also show the importance of a basic dialkylamino group at the end of the Michael acceptor for activity, due to intramolecular catalysis of the Michael addition. This, along with improved water solubility, resulted in compounds with enhanced biological properties. We present molecular modeling results consistent with the proposed mechanism of inhibition. Binding studies of one compound, 25o (C-14 radiolabeled), showed that it binds irreversibly to HER-2 protein in BT474 cells. Furthermore, it demonstrated excellent oral activity, especially in HER-2 overexpressing xenografts. Compound 25o (HKI-272) was selected for further studies and is currently in phase I clinical trials for the treatment of cancer.