Anthranilic acid amides: a novel class of antiangiogenic VEGF receptor kinase inhibitors

Heterogeneity in VEGF Receptor-2 Mobility and Organization on the Endothelial Cell Surface Leads to Diverse Models of Activation by VEGF

The dynamic nanoscale organization of cell surface receptors plays an important role in signaling. We determine this organization and its relation to activation of VEGF receptor-2 (VEGFR-2), a critical receptor tyrosine kinase in endothelial cells (ECs), by combining single-molecule imaging of endogenous VEGFR-2 in live ECs with multiscale computational analysis. We find that surface VEGFR-2 can be mobile or exhibit restricted mobility and be monomeric or non-monomeric, with a complex interplay between the two. This basal heterogeneity results in heterogeneity in the sequence of steps leading to VEGFR-2 activation by VEGF. Specifically, we find that VEGF can bind to monomeric and non-monomeric VEGFR-2 and that, when binding to monomeric VEGFR-2, its effect on dimerization depends on the mobility of VEGFR-2. Our study highlights the dynamic and heterogeneous nature of cell surface receptor organization and the need for multiscale, single-molecule-based analysis to determine its relationship to receptor activation and signaling.

da Rocha-Azevedo et al. show that VEGFR-2 exhibits mobility and interaction heterogeneity on the endothelial cell surface. The sequence of steps leading to VEGFR-2 activation by VEGF depends on the basal state of VEGFR-2. Thus, there is not one model but multiple co-existing models of VEGFR-2 activation by VEGF.

Synthesis and evaluation of novel radioiodinated anthranilate derivatives for in vivo imaging of vascular endothelial growth factor receptor with single-photon emission computed tomography

OBJECTIVE

Angiogenesis facilitates tumor survival and promotes malignancy. The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) tyrosine kinase (TK) signaling pathway is a key factor mediating angiogenesis, suggesting that this pathway may be a target for diagnosis and therapy. In this study, we aimed to develop small molecule radioiodinated probes applicable for in vivo VEGFR imaging considering the versatility and usefulness of single-photon emission computed tomography (SPECT).

METHODS

We designed and synthesized four radioiodinated anthranilate compounds (6a-d) based on the structure of an anticancer drug targeting VEGFR-TK. The inhibitory potencies of corresponding cold compounds 4a-d and in vitro stability of compounds 6a-d were assessed by cellular proliferation inhibition assays and radio thin-layer chromatography after incubation in neutral solution. In vivo biodistributions were evaluated by determining radioactivity in tissues of interest after intravenous injection of test compounds in tumor-bearing mice. In vitro and in vivo blocking experiments using a selective VEGFR-TK inhibitor and SPECT/computed tomography (CT) imaging were performed in tumor-bearing mice.

RESULTS

The radioiodinated compounds 6a-d were obtained with more than 68.0% radiochemical yield and more than 95% radiochemical purity. Because compounds 4a-d showed high inhibitory potencies and compounds 6c and 6d showed high in vitro stability, 6c ([¹²⁵I]m-NPAM) and 6d ([¹²⁵I]p-NPAM) were further evaluated. Analysis of the in vivo biodistribution revealed a tumor to blood radioactivity ratio of greater than 4 at 24 h after [¹²⁵I]p-NPAM administration. Accumulation of radioactivity in cultured tumor cells and tumor xenografts after [¹²⁵I]p-NPAM administration was significantly blocked by inhibitor pretreatment. Tumors were clearly imaged at 24 h after [¹²⁵I]p-NPAM injection with SPECT/CT in comparison to that in inhibitor-pretreated tumor-bearing mice.

CONCLUSION

[¹²⁵I]p-NPAM may have potential applications as a lead compound for future development of a clinically usable VEGFR imaging probe for SPECT.

Platelet releasate promotes skeletal myogenesis by increasing muscle stem cell commitment to differentiation and accelerates muscle regeneration following acute injury

AIM

The use of platelets as biomaterials has gained intense research interest. However, the mechanisms regarding platelet-mediated skeletal myogenesis remain to be established. The aim of this study was to determine the role of platelet releasate in skeletal myogenesis and muscle stem cell fate in vitro and ex vivo respectively.

METHODS

We analysed the effect of platelet releasate on proliferation and differentiation of C2C12 myoblasts by means of cell proliferation assays, immunohistochemistry, gene expression and cell bioenergetics. We expanded in vitro findings on single muscle fibres by determining the effect of platelet releasate on murine skeletal muscle stem cells using protein expression profiles for key myogenic regulatory factors.

RESULTS

TRAP6 and collagen used for releasate preparation had a more pronounced effect on myoblast proliferation vs thrombin and sonicated platelets (P < 0.05). In addition, platelet concentration positively correlated with myoblast proliferation. Platelet releasate increased myoblast and muscle stem cell proliferation in a dose-dependent manner, which was mitigated by VEGFR and PDGFR inhibition. Inhibition of VEGFR and PDGFR ablated MyoD expression on proliferating muscle stem cells, compromising their commitment to differentiation in muscle fibres (P < 0.001). Platelet releasate was detrimental to myoblast fusion and affected differentiation of myoblasts in a temporal manner. Most importantly, we show that platelet releasate promotes skeletal myogenesis through the PDGF/VEGF-Cyclin D1-MyoD-Scrib-Myogenin axis and accelerates skeletal muscle regeneration after acute injury.

CONCLUSION

This study provides novel mechanistic insights on the role of platelet releasate in skeletal myogenesis and set the physiological basis for exploiting platelets as biomaterials in regenerative medicine.

Phenyl and Diaryl Ureas with Thiazolo[5,4-d]pyrimidine Scaffold as Angiogenesis Inhibitors: Design, Synthesis and Biological Evaluation

Angiogenesis is crucial for tumor growth and inhibition of angiogenesis has been regarded as a promising approach for cancer therapy. Vascular endothelial growth factor receptor-2 (VEGFR-2) is an important factor in angiogenesis. In this work, a novel series of thiazolo[5,4-d]pyrimidine derivatives inhibiting angiogenesis were rationally designed and synthesized. Their inhibitory activities against human umbilical vein endothelial cells (HUVEC) were investigated in vitro. 1-(4-Fluorophenyl)-3-{4-[(5-methyl-2-phenyl[1,3]thiazolo[5,4-d]pyrimidin-7-yl)amino]phenyl}urea (19b) and 1-(3-Fluorophenyl)-3-{4-[(5-methyl-2-phenyl[1,3]thiazolo[5,4-d]pyrimidin-7-yl)amino]phenyl}urea (19g) exhibited the most potent inhibitory effect on HUVEC proliferation (IC₅₀ =12.8 and 5.3 μm, respectively). Compound 19g could inhibit the migration of human umbilical vein endothelial cells. These results support the further investigation of these compounds as potent anticancer agents.

Pyrimidinylacetamide-based 2-pyridylureas as Angiogenesis Inhibitors: Design, Synthesis and Biological Evaluation

BACKGROUND

VEGFR-2 inhibitors have been widely used in the treatment of cancer. In our continued efforts to search for potent and novel VEGFR-2 inhibitors as antitumor agents, we have identified a series of ureas and amides bearing a oxazolopyrimidine scaffold.

AIM OF THE STUDY

To discover more potent VEGFR-2 inhibitors with stronger binding affinity and better physical and chemical properties.

METHODS

23 pyrimidinylacetamide-based ureas were designed and synthesized. Replacement of oxazolopyrimidine with a pyrimidinylacetamide generated a series of novel VEGFR-2 inhibitors.

RESULTS AND CONCLUSIONS

In HUVEC inhibition assay, the most potent compound (compound 16) possessed an IC₅₀ value of 0.43 μM. Compound 16 also inhibited the migration and capillary like tube formation of HUVECs with inhibition rate at 22% (1 μM) and 17.5% (0.8 μM) respectively. These results support the further investigation of compound 16 as a potential anti-cancer agent.

Synthesis and biological evaluation of novel oxazolo[5,4-d]pyrimidines as potent VEGFR-2 inhibitors

Tumor angiogenesis is mediated by vascular endothelial growth factor receptor (VEGFR) and other protein kinases. Inhibition of these kinases presents an attractive approach for developing anticancer therapeutics. In this work, a series of 2,5,7-trisubstituted oxazolo[5,4-d]pyrimidines were synthesized, and their inhibitory activities were investigated against VEGFR-2 and human umbilical vein endothelial cells (HUVEC) in vitro. Compound 9n exhibited the most potent inhibitory activity with IC50 values of 0.33 and 0.29 μM for VEGFR-2 kinase and HUVEC, respectively. A further kinase selectivity assay revealed that these compounds exhibit good VEGFR and moderate EGFR inhibitory activities. Docking analysis suggested a common mode of interaction at the ATP-binding site of VEGFR-2.

Palladium-catalyzed enolate arylation as a key C-C bond-forming reaction for the synthesis of isoquinolines

The palladium-catalyzed coupling of an enolate with an ortho-functionalized aryl halide (an α-arylation) furnishes a protected 1,5-dicarbonyl moiety that can be cyclized to an isoquinoline with a source of ammonia. This fully regioselective synthetic route tolerates a wide range of substituents, including those that give rise to the traditionally difficult to access electron-deficient isoquinoline skeletons. These two synthetic operations can be combined to give a three-component, one-pot isoquinoline synthesis. Alternatively, cyclization of the intermediates with hydroxylamine hydrochloride engenders direct access to isoquinoline N-oxides; and cyclization with methylamine, gives isoquinolinium salts. Significant diversity is available in the substituents at the C4 position in four-component, one-pot couplings, by either trapping the in situ intermediate after α-arylation with carbon or heteroatom-based electrophiles, or by performing an α,α-heterodiarylation to install aryl groups at this position. The α-arylation of nitrile and ester enolates gives access to 3-amino and 3-hydroxyisoquinolines and the α-arylation of tert-butyl cyanoacetate followed by electrophile trapping, decarboxylation and cyclization, C4-functionalized 3-aminoisoquinolines. An oxime directing group can be used to direct a C-H functionalization/bromination, which allows monofunctionalized rather than difunctionalized aryl precursors to be brought through this synthetic route.

In vitro cytotoxic and in silico activity of piperine isolated from Piper nigrum fruits Linn

Background

Piper nigrum [Piperaceae], commonly known as black pepper is used as medicine fairly throughout the greater part of India and as a spice globally.

Purpose

To isolate piperine and evaluate in vitro cytotoxic [antiproliferative] activity and in silico method.

Methods

Piperine was isolated from the fruits of P.nigrum. Piperine was characterized by UV,IR, ¹H-NMR, ¹³C-NMR and Mass spectrum. Standardization of piperine was done also by HPTLC fingerprinting. In vitro cytotoxic activity was done using HeLa cell lines by MTT assay at different concentrations ranging from 20 to 100 μg/ml in triplicate and in silico docking studies using enzyme EGFR tyrosine kinase.

Results

Fingerprinting of isolated piperine were done by HPTLC method. The IC₅₀ value was found to be 61.94 ± 0.054 μg/ml in in vitro cytotoxic activity in HeLa Cell lines. Piperine was subjected to molecular docking studies for the inhibition of the enzyme EGFR tyrosine kinase, which is one of the targets for inhibition of cancer cells. It has shown −7.6 kJ mol⁻¹ binding and 7.06 kJ mol⁻¹ docking energy with two hydrogen bonds.

Conclusion

piperine has shown to possess in vitro cytotoxic activity and in silico studies.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for anticancer hybrids

A Hybrid drug which comprises the incorporation of two drug pharmacophores in one single molecule are basically designed to interact with multiple targets or to amplify its effect through action on another bio target as one single molecule or to counterbalance the known side effects associated with the other hybrid part(.) The present review article offers a detailed account of the design strategies employed for the synthesis of anticancer agents via molecular hybridization techniques. Over the years, the researchers have employed this technique to discover some promising chemical architectures displaying significant anticancer profiles. Molecular hybridization as a tool has been particularly utilized for targeting tubulin protein as exemplified through the number of research papers. The microtubule inhibitors such as taxol, colchicine, chalcones, combretasatin, phenstatins and vinca alkaloids have been utilized as one of the functionality of the hybrids and promising results have been obtained in most of the cases with some of the tubulin based hybrids exhibiting anticancer activity at nanomolar level. Linkage with steroids as biological carrier vector for anticancer drugs and the inclusion of pyrrolo [2,1-c] [1,4]benzodiazepines (PBDs), a family of DNA interactive antitumor antibiotics derived from Streptomyces species in hybrid structure based drug design has also emerged as a potential strategy. Various heteroaryl based hybrids in particular isatin and coumarins have also been designed and reported to posses' remarkable inhibitory potential. Apart from presenting the design strategies, the article also highlights the structure activity relationship along with mechanistic insights revealed during the biological evaluation of the hybrids.

Trapping of naive lymphocytes triggers rapid growth and remodeling of the fibroblast network in reactive murine lymph nodes

Adaptive immunity is initiated in T-cell zones of secondary lymphoid organs. These zones are organized in a rigid 3D network of fibroblastic reticular cells (FRCs) that are a rich cytokine source. In response to lymph-borne antigens, draining lymph nodes (LNs) expand several folds in size, but the fate and role of the FRC network during immune response is not fully understood. Here we show that T-cell responses are accompanied by the rapid activation and growth of FRCs, leading to an expanded but similarly organized network of T-zone FRCs that maintains its vital function for lymphocyte trafficking and survival. In addition, new FRC-rich environments were observed in the expanded medullary cords. FRCs are activated within hours after the onset of inflammation in the periphery. Surprisingly, FRC expansion depends mainly on trapping of naïve lymphocytes that is induced by both migratory and resident dendritic cells. Inflammatory signals are not required as homeostatic T-cell proliferation was sufficient to trigger FRC expansion. Activated lymphocytes are also dispensable for this process, but can enhance the later growth phase. Thus, this study documents the surprising plasticity as well as the complex regulation of FRC networks allowing the rapid LN hyperplasia that is critical for mounting efficient adaptive immunity.

Aberrant, ectopic expression of VEGF and VEGF receptors 1 and 2 in malignant colonic epithelial cells. Implications for these cells growth via an autocrine mechanism

Vascular endothelial growth factor A (referred to as VEGF) is implicated in colon cancer growth. Currently, the main accepted mechanism by which VEGF promotes colon cancer growth is via the stimulation of angiogenesis, which was originally postulated by late Judah Folkman. However, the cellular source of VEGF in colon cancer tissue; and, the expression of VEGF and its receptors VEGF-R1 and VEGF-R2 in colon cancer cells are not fully known and are subjects of controversy.

MATERIAL AND METHODS

We examined and quantified expression of VEGF, VEGF-R1 and VEGF-R2 in three different human colonic tissue arrays containing sections of adenocarcinoma (n=43) and normal mucosa (n = 41). In human colon cancer cell lines HCT116 and HT29 and normal colon cell lines NCM356 and NCM460, we examined expression of VEGF, VEGF-R1 and VEGF-R2 mRNA and protein, VEGF production and secretion into the culture medium; and, the effect of a potent, selective inhibitor of VEGF receptors, AL-993, on cell proliferation.

RESULTS

Human colorectal cancer specimens had strong expression of VEGF in cancer cells and also expressed VEGF-R1 and VEGF-R2.In vitro studies showed that human colon cancer cell lines, HCT116 and HT29, but not normal colonic cell lines, express VEGF, VEGF-R1 and VEGF-R2 and secrete VEGF into the medium up to a concentration 2000 pg/ml within 48 h. Furthermore, we showed that inhibition of VEGF receptors using a specific VEGF-R inhibitor significantly reduced proliferation (by >50%) of cultured colon cancer cell lines.

CONCLUSIONS

Our findings support the contention that VEGF generated by colon cancer cells stimulates their growth directly through an autocrine mechanism that is independent of its primary function in the induction of angiogenesis.

N2-Trimethylacetyl substituted and unsubstituted-N4-phenylsubstituted-6-(2-pyridin-2-ylethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines: design, cellular receptor tyrosine kinase inhibitory activities and in vivo evaluation as antiangiogenic, antimetastatic and antitumor agents

Six novel N(4)-phenylsubstituted-6-(2-pyridin-2-ylethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines and their N(2)-trimethylacetyl substituted analogs were synthesized as receptor tyrosine kinase (RTK) inhibitors. A microwave-mediated Sonogashira reaction was used as a key step for the synthesis of these compounds. Biological evaluation, in whole cell assays, showed that some analogs had remarkable inhibitory activity against a variety of RTKs and in particular cytotoxic activity against A431 tumor cells in culture. The inhibitory data against RTKs in this study demonstrated that variation of the 4-anilino substituents of these analogs dictates both potency and specificity of inhibitory activity against various RTKs. The study also supported the hypothesis that interaction of substituents on the 2-amino group with hydrophobic site-II provides an increase in potency. Compound 8 of this series was selected for evaluation in vivo in a B16-F10 syngeneic mouse tumor model and exhibited significant reduction in tumor growth rate, in tumor vascular density and in metastases to the lung compared to the control.

Anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates as p53 activators in cervical cancer cells

A library of new anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates were designed, synthesized, and evaluated for their anticancer activity in cervical cancer cells such as HeLa and SiHa that possess low levels of p53. All 24 conjugates showed antiproliferative activity, while some of them exhibit significant cytotoxicity. In assays related to cell-cycle distribution, these conjugates induced G(2) /M arrest in HeLa cells and G(1) cell-cycle arrest in SiHa cells. Immunocytochemistry assays revealed that these compounds cause nuclear translocation of p53, thereby indicating the activation of p53. In cervical cancer cells, the p53 protein is degraded by E6 oncoprotein. Immunoblot and RT-PCR analyses proved the presence of mitochondria-mediated apoptosis with involvement p53 target genes such as BAX, Bcl2, and p21 (CDKI). Moreover, these compounds increased the phosphorylated forms of p53 and provide signals for apoptosis induction. Interestingly, one of the conjugates, (2-phenyl-7-(3,4,5-trimethoxyphenyl)pyrazolo[1,5-a]pyrimidin-5-yl)(4-(2-(thiophen-2-ylmethylamino)benzoyl)piperazin-1-yl)methanone, is the most promising candidate in this series and has the potential to be taken up for further detailed studies.

Notch-dependent VEGFR3 upregulation allows angiogenesis without VEGF-VEGFR2 signalling

Developing tissues and growing tumours produce vascular endothelial growth factors (VEGFs), leading to the activation of the corresponding receptors in endothelial cells. The resultant angiogenic expansion of the local vasculature can promote physiological and pathological growth processes. Previous work has uncovered that the VEGF and Notch pathways are tightly linked. Signalling triggered by VEGF-A (also known as VEGF) has been shown to induce expression of the Notch ligand DLL4 in angiogenic vessels and, most prominently, in the tip of endothelial sprouts. DLL4 activates Notch in adjacent cells, which suppresses the expression of VEGF receptors and thereby restrains endothelial sprouting and proliferation. Here we show, by using inducible loss-of-function genetics in combination with inhibitors in vivo, that DLL4 protein expression in retinal tip cells is only weakly modulated by VEGFR2 signalling. Surprisingly, Notch inhibition also had no significant impact on VEGFR2 expression and induced deregulated endothelial sprouting and proliferation even in the absence of VEGFR2, which is the most important VEGF-A receptor and is considered to be indispensable for these processes. By contrast, VEGFR3, the main receptor for VEGF-C, was strongly modulated by Notch. VEGFR3 kinase-activity inhibitors but not ligand-blocking antibodies suppressed the sprouting of endothelial cells that had low Notch signalling activity. Our results establish that VEGFR2 and VEGFR3 are regulated in a highly differential manner by Notch. We propose that successful anti-angiogenic targeting of these receptors and their ligands will strongly depend on the status of endothelial Notch signalling.

N⁴-Aryl-6-substitutedphenylmethyl-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines as receptor tyrosine kinase inhibitors

Six novel N(4)-substitutedphenyl-6-substitutedphenylmethyl-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines were synthesized as multiple receptor tyrosine kinase (RTK) inhibitors and antitumor agents. An improvement in the inhibitory potency against epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor 1 (VEGFR-1) and vascular endothelial growth factor receptor 2 (VEGFR-2) assays and in the A431 cellular proliferation assay was observed for compounds 8-13 over the previously reported 5-7. Three compounds (8, 9 and 13) demonstrated potent, multiple RTK inhibition and were more potent or equipotent compared to the lead compounds 5 and 7 and the standard compounds. Compounds 10 and 12 showed potent inhibition of VEGFR-2 over EGFR, platelet-derived growth factor receptor-β (PDGFR-β) and VEGFR-1. The results indicate that the RTK inhibitory profile could be modulated with slight variations to the N(4)-aryl-6-substitutedphenylmethyl-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamino scaffold.

Anthranilic acid-based inhibitors of phosphodiesterase: design, synthesis, and bioactive evaluation

Our previous studies identified two 2-benzoylaminobenzoate derivatives 1, which potently inhibited superoxide (O(2)˙(-)) generation induced by formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) in human neutrophils. In an attempt to improve their activities, a series of anthranilic acid derivatives were synthesized and their anti-inflammatory effects and underlying mechanisms were investigated in human neutrophils. Of these, compounds 17, 18, 46, 49, and 50 showed the most potent inhibitory effect on FMLP-induced release of O(2)˙(-) in human neutrophils with IC(50) values of 0.20, 0.16, 0.15, 0.06, and 0.29 μM, respectively. SAR analysis showed that the activities of most compounds were dependent on the ester chain length in the A ring. Conversely, a change in the linker between the A and B ring from amide to sulfonamide or N-methyl amide, as well as exchanges in the benzene rings (A or B rings) by isosteric replacements were unfavorable. Further studies indicated that inhibition of O(2)˙(-) production in human neutrophils by these anthranilic acids was associated with an elevation in cellular cAMP levels through the selective inhibition of phosphodiesterase 4. Compound 49 could be approved as a lead for the development of new drugs in the treatment of neutrophilic inflammatory diseases.

KDR inhibitor with the intramolecular non-bonded interaction: conformation-activity relationships of novel indole-3-carboxamide derivatives

We previously reported that compound 1, having a similar conformation to PTK787 (2) by forming a pseudo ring structure with an intramolecular non-bonded S-O interaction, exhibited a potent inhibitory activity against VEGFR2 tyrosine kinase (KDR). Applying the ideas of pseudo ring formations, we have designed three types of novel indole carboxamide derivatives 5-7 with an intramolecular hydrogen bonding or non-bonded S-O interaction. We describe the design and synthesis of 5-7, and also discuss the relationships of their KDR inhibitory activity and conformations that were stabilized by their intramolecular non-bonded interactions.

Oxidative stress induces angiogenesis by activating TLR2 with novel endogenous ligands

Reciprocity of inflammation, oxidative stress and neovascularization is emerging as an important mechanism underlying numerous processes from tissue healing and remodelling to cancer progression. Whereas the mechanism of hypoxia-driven angiogenesis is well understood, the link between inflammation-induced oxidation and de novo blood vessel growth remains obscure. Here we show that the end products of lipid oxidation, ω-(2-carboxyethyl)pyrrole (CEP) and other related pyrroles, are generated during inflammation and wound healing and accumulate at high levels in ageing tissues in mice and in highly vascularized tumours in both murine and human melanoma. The molecular patterns of carboxyalkylpyrroles are recognized by Toll-like receptor 2 (TLR2), but not TLR4 or scavenger receptors on endothelial cells, leading to an angiogenic response that is independent of vascular endothelial growth factor. CEP promoted angiogenesis in hindlimb ischaemia and wound healing models through MyD88-dependent TLR2 signalling. Neutralization of endogenous carboxyalkylpyrroles impaired wound healing and tissue revascularization and diminished tumour angiogenesis. Both TLR2 and MyD88 are required for CEP-induced stimulation of Rac1 and endothelial migration. Taken together, these findings establish a new function of TLR2 as a sensor of oxidation-associated molecular patterns, providing a key link connecting inflammation, oxidative stress, innate immunity and angiogenesis.

Design, synthesis, and biological evaluation of dibromotyrosine analogues inspired by marine natural products as inhibitors of human prostate cancer proliferation, invasion, and migration

Bioactive secondary metabolites originating from dibromotyrosine are common in marine sponges, such as sponges of the Aplysina species. Verongiaquinol (1), 3,5-dibromo-1-hydroxy-4-oxocyclohexa-2,5-diene-1-acetamide, and aeroplysinin-1 are examples of such bioactive metabolites. Previous studies have shown the potent antimicrobial as well as cytotoxic properties of verongiaquinol and the anti-angiogenic activity of aeroplysinin-1. The work presented herein shows the design and synthesis of dibromotyrosine-inspired phenolic ester and ether analogues with anti-angiogenic, anti-proliferative and anti-migratory properties and negligible cytotoxicity. Several analogues were synthesized based on docking experiments in the ATP binding site of VEGFR2 and their anti-angiogenic potential and ability to inhibit angiogenesis and prostate cancer proliferation, migration and invasion were evaluated using the chick chorioallantoic membrane (CAM) assay, MTT, wound-healing, and Cultrex® BME cell invasion assay models, respectively. Analogues with high docking scores showed promising anti-angiogenic activity in the CAM assay. In general, ester analogues (5, 6, and 8-10) proved to be of higher anti-migratory activity whereas ether analogues (11-14) showed better anti-proliferative activity. These results demonstrate the potential of dibromotyrosines as promising inhibitory scaffolds for the control of metastatic prostate cancer proliferation and migration.

Suppression of hypoxia-induced HIF-1alpha accumulation by VEGFR inhibitors: Different profiles of AAL993 versus SU5416 and KRN633

The hypoxia-inducible factor (HIF) is a heterodimeric basic helix-loop-helix transcriptional factor and the activated HIF plays pivotal roles in various pathological conditions, including inflammation and cancer. HIF-1alpha overexpression has been observed in many common human cancers, including brain, breast, colon, lung, ovary, and prostate, and HIF-mediated genes, such as vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS), and insulin-like growth factor (IGF)-1, are associated with tumor angiogenesis, metastasis, and invasion. Therefore, the pro-oncogenic protein HIF is a novel target of cancer therapy. We examined the effects of VEGFR inhibitors, AAL993, SU5416, and KRN633, on suppression of HIF-1alpha accumulation under the hypoxic condition. We found that VEGFR tyrosine kinase inhibitors, AAL993, SU5416, and KRN633, possess dual functions: inhibition of VEGFR signaling and HIF-1alpha expression under the hypoxic condition. The detailed mechanistic study indicated that SU5416 and KRN633 suppressed HIF-1alpha expression through inhibition of both Akt and ERK phosphorylation signaling pathways, whereas AAL993 suppressed HIF-1alpha expression through ERK inhibition without affecting Akt phosphorylation.

Synthesis and biological activity of N(4)-phenylsubstituted-6-(2,4-dichloro phenylmethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines as vascular endothelial growth factor receptor-2 inhibitors and antiangiogenic and antitumor agents

A series of eight N(4)-phenylsubstituted-6-(2,4-dichlorophenylmethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines 8-15 were synthesized as vascular endothelial growth factor receptor-2 (VEGFR-2) inhibitors with varied substitutions in the phenyl ring of the 4-anilino moiety. In addition, five N(4)-phenylsubstituted-6-phenylmethylsubstituted-7H-pyrrolo[2,3-d]pyrimidin-4-amines 16-20 were synthesized to evaluate the importance of the 2-NH(2) moiety for multiple receptor tyrosine kinase (RTK) inhibition. Cyclocondensation of alpha-halomethylbenzylketones with 2,6-diamino-4-hydroxypyrimidine afforded 2-amino-6-(2,4-dichlorophenylmethyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one, 23 and reaction of alpha-bromomethylbenzylketones with ethylamidinoacetate followed by cyclocondensation with formamide afforded the 6-phenylmethylsubstituted-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-ones, 40-42, respectively. Chlorination of the 4-position and displacement with appropriate anilines afforded the target compounds 8-20. Compounds 8, 10 and 14 were potent VEGFR-2 inhibitors and were 100-fold, 40-fold and 8-fold more potent than the standard semaxanib, respectively. Previously synthesized multiple RTK inhibitor, 5 and the VEGFR-2 inhibitor 8 from this study, were chosen for further evaluation in a mouse orthotopic model of melanoma and showed significant inhibition of tumor growth, angiogenesis and metastasis.

An overview of small-molecule inhibitors of VEGFR signaling

VEGFR inhibitors are in broad use for the treatment of metastatic renal-cell carcinoma, gastrointestinal stromal tumors and hepatocellular carcinoma and in development in a number of other oncology indications, including colorectal cancer, non-small-cell lung cancer, pancreatic cancer, thyroid malignancies, ovarian cancer, breast cancer and sarcomas. This Review outlines the structure-activity relationships of the 44 VEGFR inhibitors currently in development. An overview of the pharmacokinetic profile of each molecule and its stage in development is provided. Phase III clinical trials being conducted for licensing of these agents for specific indications and phase III developmental efficacy trials are described in detailed tables that include the disease studied, trial design including combination therapy, study end points, and projected or final accrual. The relative frequency of on-target and off-target adverse events observed in 3,060 patients is described for a subset of agents in development in clinical trials sponsored by the National Cancer Institute. No interagent comparisons were undertaken and no data from pharmaceutical pharmacovigilance databases were used. The on-target effects seem to be mechanistically based and predicted by VEGFR inhibition. Small-molecule inhibitors of angiogenesis are active in a wide variety of malignancies and fill a unique niche for cancer therapeutics.

Topological polar surface area: a useful descriptor in 2D-QSAR

Topological polar surface area (TPSA), which makes use of functional group contributions based on a large database of structures, is a convenient measure of the polar surface area that avoids the need to calculate ligand 3D structure or to decide which is the relevant biological conformation or conformations. We demonstrate the utility of TPSA in 2D-QSAR for 14 sets of diverse pharmacological activity data. Even though a large pool of reports showing the importance of the classic 2D descriptors such as calculated logP (ClogP) and calculated molar refractivity (CMR) exists in the 2D-QSAR literature, this is the first report to demonstrate the value of TPSA as a relevant descriptor applicable to a large, structurally and pharmacologically diverse set of classes of compounds. We also address the limitations of applicability of this descriptor for 2D-QSAR analysis. We observed a negative correlation of TPSA with activity data for anticancer alkaloids, MT1 and MT2 agonists, MAO-B and tumor necrosis factor-alpha inhibitors and a positive correlation with inhibitory activity data for telomerase, PDE-5, GSK-3, DNA-PK, aromatase, malaria, trypanosomatids and CB2 agonists.

3,4-Disubstituted isothiazoles: novel potent inhibitors of VEGF receptors 1 and 2

Novel derivatives of isothiazoles are described as potent ATP-competitive inhibitors of vascular endothelial growth factor receptors I and II (VEGFR-1/2). A number of compounds exhibited VEGFR-2 inhibitory activity comparable to that of Vatalanib in both HTRF enzymatic and cellular assays. Several derivatives featuring bulky meta-substituents in the amide portion of the molecule displayed 4- to 8-fold specificity for VEGFR-2 versus VEGFR-1. Active molecules also showed high intrinsic permeability (> 30 x 10(-5) cm/min) across Caco-2 cell monolayer.

Vascular endothelial growth factor receptor-1 contributes to resistance to anti-epidermal growth factor receptor drugs in human cancer cells

PURPOSE

The resistance to selective EGFR inhibitors involves the activation of alternative signaling pathways, and Akt activation and VEGF induction have been described in EGFR inhibitor-resistant tumors. Combined inhibition of EGFR and other signaling proteins has become a successful therapeutic approach, stimulating the search for further determinants of resistance as basis for novel therapeutic strategies.

EXPERIMENTAL DESIGN

We established human cancer cell lines with various degrees of EGFR expression and sensitivity to EGFR inhibitors and analyzed signal transducers under the control of EGFR-dependent and EGFR-independent pathways.

RESULTS

Multitargeted inhibitor vandetanib (ZD6474) inhibited the growth and the phosphorylation of Akt and its effector p70S6 kinase in both wild-type and EGFR inhibitor-resistant human colon, prostate, and breast cancer cells. We found that the resistant cell lines exhibit, as common feature, VEGFR-1/Flt-1 overexpression, increased secretion of VEGF and placental growth factor, and augmented migration capabilities and that vandetanib is able to antagonize them. Accordingly, a new kinase assay revealed that in addition to VEGF receptor (VEGFR)-2, RET, and EGFR, vandetanib efficiently inhibits also VEGFR-1. The contribution of VEGFR-1 to the resistant phenotype was further supported by the demonstration that VEGFR-1 silencing in resistant cells restored sensitivity to anti-EGFR drugs and impaired migration capabilities, whereas exogenous VEGFR-1 overexpression in wild-type cells conferred resistance to these agents.

CONCLUSIONS

This study shows that VEGFR-1 contributes to anti-EGFR drug resistance in different human cancer cells. Moreover, vandetanib inhibits VEGFR-1 activation, cell proliferation, and migration, suggesting its potential utility in patients resistant to EGFR inhibitors.

Synthesis and evaluation of heteroaryl-ketone derivatives as a novel class of VEGFR-2 inhibitors

We have discovered novel inhibitors of VEGFR-2 kinase with low nanomolar potency in both enzymatic and cell-based assays. Active series are heteroaryl-ketone compounds containing a central aromatic ring with either an indazolyl or indolyl keto group in the ortho orientation to the benzylic amine group (Fig. 1). The best compounds were demonstrated to be inactive against a small select panel of tyrosine and serine/threonine kinases with the exception of VEGFR-1 kinase, a close family member. In addition, the lead candidate 8 displayed acceptable exposure levels when administered orally to mice.

2,4-Dichloro-N-cyclo-hexyl-benzamide

In the title mol­ecule, C₁₃H₁₅Cl₂NO, the cyclohexane ring adopts a chair conformation. The aromatic ring plane is oriented with respect to the N/O/C plane at a dihedral angle of 51.88 (7)°. In the crystal structure, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into infinite chains along the [010] direction.

N-(2-Methoxyphenyl)-2-nitrobenzamide

Geometric parameters of the title compound, C₁₄H₁₂N₂O₄, are in the usual ranges. The dihedral angle between the two aromatic rings is 28.9 (1)°. The nitro group is twisted by 40.2 (1)° out of the plane of the aromatic ring to which it is attached. The crystal structure is stabilized by an N—H⋯O hydrogen bond.

N-(2-Methyl-phen-yl)-2-nitro-benzamide

In the title compound, C₁₄H₁₂N₂O₃, the dihedral angle between the two aromatic rings is 41.48 (5)°. The nitro group is twisted by 24.7 (3)° out of the plane of the aromatic ring to which it is attached. The mol­ecules are connected by N—H⋯O hydrogen bonds into chains running along the a axis.

1H-1,2,4-triazol-3-yl-anilines: novel potent inhibitors of vascular endothelial growth factor receptors 1 and 2

Novel derivatives of 1,2,4-triazoles are described as potent ATP-competitive inhibitors of vascular endothelial growth factor receptors I and II (VEGFR-1/2). A number of compounds display VEGFR-2 inhibitory activity comparable to that of Vatalanib and Vandetanib in both homogenous time-resolved fluorescence enzymatic and cellular assays. Several active molecules feature high intrinsic permeability (>30 x 10(-5) cm/min) across Caco-2 cell monolayer.