Small molecule inhibitors of tumor-promoted angiogenesis, including protein tyrosine kinase inhibitors

Impact of sorafenib on epidural fibrosis: An immunohistochemical study

AIM

To determine if sorafenib, an antineoplastic agent, could prevent the development of spinal epidural fibrosis (EF).

METHODS

The study used CD105 and osteopontin antibodies in an immunohistochemical approach to quantify EF that occurred as a consequence of laminectomy in rats. Wistar albino rats (n = 16) were divided into two groups: control (L1-2 level laminectomy only) and sorafenib treatment (L1-2 level laminectomy + topical sorafenib). The animals were euthanatized after 6 wk, and the EF tissues were examined for histopathological changes after immunohistochemical staining. The EF grades were assigned to the tissues, and the treatment and control groups were compared.

RESULTS

The EF thickness, inflammatory cell density, and arachnoid adherences determined by light microscopy were significantly higher in the control group compared to the sorafenib-treated group. Based on fibrosis scores, the extent of EF in the treatment group was significantly lower than in the controls. Immunohistochemical staining for CD105 to identify microvessels revealed that the EF grades based on vessel count were significantly lower in the treatment group. Staining for osteopontin did not show any significant differences between the groups in terms of the extent of EF. The staging of EF based on vascular counts observed after immunohistochemical staining for CD105, but not for osteopontin, was compatible with conventional staging methods. Neither toxic effects on tissues nor systemic side effects were observed with the use of sorafenib.

CONCLUSION

Local administration of sorafenib significantly reduced post-laminectomy EF. Decreased neovascularization in spinal tissue may be due to the sorafenib-induced inhibition of vascular endothelial growth factor.

Angiogenesis and its therapeutic opportunities

Angiogenesis plays critical roles in human physiology that range from reproduction and fetal growth to wound healing and tissue repair. The sophisticated multistep process is tightly regulated in a spatial and temporal manner by "on-off switch signals" between angiogenic factors, extracellular matrix components, and endothelial cells. Uncontrolled angiogenesis may lead to several angiogenic disorders, including vascular insufficiency (myocardial or critical limb ischemia) and vascular overgrowth (hemangiomas, vascularized tumors, and retinopathies). Thus, numerous therapeutic opportunities can be envisaged through the successful understanding and subsequent manipulation of angiogenesis. Here, we review the clinical implications of angiogenesis and discuss pro- and antiangiogenic agents that offer potential therapy for cancer and other angiogenic diseases.

Evaluation of Indole Esters As Inhibitors of p60c-Src Receptor Tyrosine Kinase and Investigation of the Inhibition Using Receptor Docking Studies

Several indole esters were tested as inhibitors of tyrosine kinase p60(c-Src). Compound (4) was found fairly active against the enzyme with IC50 = 1.34 microM. DOCK methodology was used to asses our inhibitors for their inhibitory potency against tyrosine kinase. The docking results showed that compounds (4), (25) and (26) were bound to the active site of the enzyme Lys 295 of p60(c-Src) tyrosine kinase. Both activity and docking studies showed a parallel result, with compound (4) having a better interaction with the enzyme active site and also greater activity than the other compounds, indicating a potential role as new lead inhibitor.

Synthesis and activity of novel 5-substituted pyrrolo[2,3-d]pyrimidine analogues as pp60(c-Src) tyrosine kinase inhibitors

Therapy with receptor tyrosine kinase inhibitors provides an improved treatment option in a number of diseases such as cancer, myocardial infection, osteoporosis, stroke, and neurodegeneration. We have designed, synthesized, and evaluated a series of novel 2-amino-5-[(benzyl)imino]methyl-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidine-4-one 7a and 2-amino-5-[(substituted-benzyl)imino]methyl-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidine-4-one 7b-e derivatives as potential tyrosine kinase inhibitors. These compounds were synthesized by condensation reaction using 2-tritylamino-4-oxo-4,7-dihydro-3H-pyrrolo[2,3-d]pyrimidine-5-carbaldehyde 5 and appropriate benzylamines followed by detritylation. Compounds were evaluated for their inhibitory activity toward tyrosine phosphorylation for the pp60c-Src tyrosine kinase. Compounds 7a, 7d, and 7e demonstrated potent inhibitory activities against pp60c-Src tyrosine kinase with IC50 values of 13.9, 34.5, and 78.4 microM, respectively. Dihalogenated compounds 7d and 7e have 3 to 7-times lower IC50 values than that of the parent compound 7a.

Suppression of angiogenesis and tumor growth by orally active deoxycholic acid-heparin conjugate

Heparin, a potent inhibitor of blood coagulation, exhibits antitumoral action in tumor progression such as in angiogenesis and metastasis but is not orally absorbed in the body, making it an attractive candidate as an oral drug for antiangiogenic cancer therapy. We generated LHD or orally active heparin using low molecular weight heparin (LMWH) and deoxycholic acid that is effectively absorbed in the gastrointestinal tract. Using the in vitro endothelial tubular formation and chicken chorioallantoic membrane angiogenesis assay, we found that antiangiogenic activity of this LHD was similar to that of LMWH. From the in vivo Matrigel plugs assay, LHD treated orally could effectively inhibit angiogenesis into the plugs induced by basic fibroblast growth factor, whereas LMWH treated orally could not due to no oral absorption. In addition, when this LHD was orally administered into the tumor bearing mice, it significantly inhibited tumor growth by its antiangiogenic therapeutic mechanism, and when accompanied with doxorubicin, it appeared to have an additive effect. Collectively, LHD having antiangiogenic activity could be orally absorbable and inhibit tumor growth via inhibiting angiogenesis. These findings demonstrate the therapeutic potential of LHD in the clinical trials, which is suggested as a new oral therapeutic remedy for cancer therapy.

Computational proteomics of biomolecular interactions in the sequence and structure space of the tyrosine kinome: Deciphering the molecular basis of the kinase inhibitors selectivity

Understanding and predicting the molecular basis of protein kinases specificity against existing therapeutic agents remains highly challenging and deciphering this complexity presents an important problem in discovery and development of effective cancer drugs. We explore a recently introduced computational approach for in silico profiling of the tyrosine kinases binding specificity with a class of the pyrido-[2,3-d]pyrimidine kinase inhibitors. Computational proteomics analysis of the ligand-protein interactions using parallel simulated tempering with an ensemble of the tyrosine kinases crystal structures reveals an important molecular determinant of the kinase specificity. The pyrido-[2,3-d]pyrimidine inhibitors are capable of dynamically interacting with both active and inactive forms of the tyrosine kinases, accommodating structurally different kinase conformations with a similar binding affinity. Conformational tolerance of the protein tyrosine kinases binding with the pyrido[2,3-d]pyrimidine inhibitors provides the molecular basis for the broad spectrum of potent activities and agrees with the experimental inhibition profiles. The analysis of the pyrido[2,3-d]pyrimidine sensitivities against a number of clinically relevant ABL kinase mutants suggests an important role of conformational adaptability of multitargeted kinase inhibitors in developing drug resistance mechanisms. The presented computational approach may be useful in complementing proteomics technologies to characterize activity signatures of small molecules against a large number of potential kinase targets.

Comparison of some 3-(substituted-benzylidene)-1, 3-dihydro-indolin derivatives as ligands of tyrosine kinase based on binding mode studies and biological assay

A series of 3-(substituted-benylidene)-1, 3-dihydro- indolin-2-one, 3-(substituted-benylidene)-1, 3-dihydro- indolin-2-thione and 2, 2'-dithiobis 3-(substituted-benylidene)-1, 3-dihydro-indole derivatives was investigated as inhibitor of p60c-Src tyrosine kinase by performing receptor docking studies and inhibitory activity toward tyrosine phosphorylation. Some compounds were shown to be docked at the site, where the selective inhibitor PP1 [1-tert-Butyl-3-p-tolyl-1H-pyrazolo[3,4-d]pyrimidine-4-yl-amine] was embedded at the enzyme active site. Evaluation of all compounds for the interactions with the parameters of lowest binding energy levels, capability of hydrogen bond formations and superimposibility on enzyme active site by docking studies, it can be assumed that 3-(substituted- benzylidene)-1, 3-dihydro-indolin-2-one and thione derivatives have better interaction with enzyme active site then 2, 2'-dithiobis 3-(substituted-benzylidene)-1, 3-dihydro indole derivatives. The test results for the inhibitory activity against tyrosine kinase by Elisa method revealed that 3-(substituted-benylidene)-1, 3-dihydro- indolin-2-thione derivatives have more activity then 3-(substituted-benylidene)-1, 3-dihydro- indolin-2-one derivatives.

Coadministration of Sorafenib with Rottlerin Potently Inhibits Cell Proliferation and Migration in Human Malignant Glioma Cells

Mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) are activated in the majority of gliomas and contribute to tumor cell growth and survival. Sorafenib (Bay43-9006; Nexavar) is a dual-action Raf and vascular endothelial growth factor receptor inhibitor that blocks receptor phosphorylation and MAPK-mediated signaling and inhibits growth in a number of tumor types. Because our initial studies of this agent in a series of glioma cell lines showed only partial growth inhibition at clinically achievable concentrations, we questioned whether inhibition of PKC signaling using the PKC-delta inhibitor rottlerin might potentiate therapeutic efficacy. Proliferation assays, apoptosis induction studies, and Western immunoblot analysis were conducted in cells treated with sorafenib and rottlerin as single agents or in combination. Sorafenib and rottlerin reduced proliferation in all cell lines when used as single agents, and the combination produced marked potentiation of growth inhibition. Flow-cytometric measurements of cells stained with Annexin V-propidium iodide and immunocytochemical assessment of cytochrome c and apoptosis-inducing factor release demonstrated that addition of rottlerin resulted in significantly higher levels of apoptosis than sorafenib alone. In addition, the combination of sorafenib and rottlerin reduced or completely inhibited the phosphorylation of extracellular signal-regulated kinase and Akt and down-regulated cell cycle regulatory proteins such as cyclin-D1, cyclin-D3, cyclin-dependent kinase (cdk)4, and cdk6 in a dose- and time-dependent manner. Our results clearly indicate that inhibition of PKC-delta signaling enhances the antiproliferative effect of sorafenib in malignant human glioma cell lines and support the examination of combinations of signaling inhibitors in these tumors.

Functional CT for Quantifying Tumor Perfusion in Antiangiogenic Therapy in a Rat Model

PURPOSE

To determine the histologic basis of perfusion parameters measured at functional computed tomography (CT) and to examine the relationship between changes in perfusion and changes in histologic parameters after antiangiogenic therapy in a rat model.

MATERIALS AND METHODS

This study had institutional animal care and use committee approval. Among 20 Fischer rats with implanted FN13762 tumors in the liver, 10 were treated with SU5416, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor, and 10 were treated with the diluent only as control rats. Six rats chosen at random from each group underwent functional CT for the measurement of tumor blood flow, blood volume, mean transit time, and permeability-surface area product. Tumor tissue slides corresponding to functional CT sections were examined to measure tumor microvascular density, number of luminal vessels, vascular perimeter, and vascular area. Two-tailed Student t testing was used to determine differences in growth, numbers of metastases to major organs, vascularity, and perfusion between SU5416-treated and control tumors. Pearson correlation coefficients were used to investigate relationships between vascular parameters.

RESULTS

Mean tumor volume and number of metastases, respectively, were lower in SU5416-treated rats than in control rats (1580 mm3 +/- 830 [standard deviation] vs 2330 mm3 +/- 960 and 22.4 +/- 11.0 vs 35.2 +/- 17.3); however, these differences were not significant (P = .084 and P = .079). Mean tumor microvascular density was significantly lower in SU5416-treated rats than in control rats (6.4 vessels per field +/- 4.6 vs 17.2 vessels per field +/- 7.5, P < .001); however, vessel perimeter and vessel area, respectively, were significantly larger in treated rats than in control rats (470 microm per field +/- 320 vs 360 microm per field +/- 270, P = .02; and 4010 microm2 per field +/- 2990 vs 2230 microm2 per field +/- 1750, P = .001). Significant correlations were observed between microvascular density and vessel perimeter and area (r = 0.59 and r = 0.25, respectively; P < .01 for both) in SU5416-treated tumors but not control tumors. Blood flow, blood volume, and permeability-surface area product at functional CT were significantly higher in SU5416-treated tumors than in control tumors (P < .001 for all).

CONCLUSION

These results validate the idea that functional CT can help quantify the perfusion function of mature vessels but not changes in microvessel density in antiangiogenic therapy.

Simultaneous determination of Z-3-[(2,4-dimethylpyrrol-5-yl)methylidenyl]-2-indolinone (SU5416) and its interconvertible geometric isomer (SU5886) in rat plasma by LC/MS/MS

Z-3-[(2,4-Dimethylpyrrol-5-yl)methylidenyl]-2-indolinone (SU5416) is a cytostatic substance in development as an anti-angiogenic agent. SU5416 exists as the thermodynamically stable cis or Z-isomer as a solid. Studies have shown that in light exposed solutions of SU5416, the unstable trans or E-isomer, namely SU5886, is formed. The E-isomer converts back to the Z-isomer when protected from light. The E-isomer is unstable for synthesis and isolation; therefore, the analytical standard of the E-isomer is not available. In this study, a simple, fast and reliable LC/MS/MS method has been developed to determinate both isomers simultaneously in rat plasma samples to support the study of disposition kinetics of SU5416. This method is sensitive (limit of quantitation (LOQ=0.5 ng/mL)), reproducible and has a wide linear range (0.5-2500 ng/mL). There was no conversion between E- and Z-isomer during sample preparation procedure and sample determination with LC/MS/MS. Experimental results proved that SU5416 and SU5886 have identical detection response. Therefore, SU5416 (Z-isomer) was used successfully as analytical standard for SU5886 (E-isomer). This method has been applied to rat plasma samples obtained from a pharmacokinetic study. This study underscores the use of LC/MS/MS technique for bioanalytical methods where analytical standards are not available and analytes are interconvertible.

Synthesis and anti-tyrosine kinase activity of 3-(substituted-benzylidene)-1, 3-dihydro-indolin derivatives: investigation of their role against p60c-Src receptor tyrosine kinase with the application of receptor docking studies

A series of 3-(substituted-benzylidene)-1, 3-dihydro-indolin-2-thione derivatives were synthesized as modified congeners of 3-(substituted-benzylidene)-1, 3-dihydro-indolin-2-one series. All the synthesized compounds were examined for their in vitro anti-tyrosine kinase activity against p60c-Src. The activity results revealed that compounds (Z)-3-(4'-Dimethylamino-benzylidene)-1, 3-dihydro-indolin-2-thione (12) (E)-3-(2', 6'-Dichloro-benzylidene)-1, 3-dihydro-indolin-2-thione (13) and (E)-3-(3'-Hydroxy-4'-methoxy-benzylidene)-1, 3-dihydro-indolin-2-thione (19) exhibited anti-tyrosine kinase activity with IC50 value of 21.91, 21.20 and 30.92 microM, respectively. These results are comparable to PP1 [1-tert-Butyl-3-p-tolyl-1H-pyrazolo[3, 4-d]pyrimidine-4-yl-amine] (IC50=0.17 microM), which is reported as a potent and selective p60c-Src tyrosine kinase inhibitor. Some thio congeners are found to be more potent than oxo derivatives; however, no significant correlation was observed between the activity profiles of these two series. Docking program was used to investigate the docking mode of each compound at the active site. Among all of the compounds, only (Z)-3-(2'-Chloro-benzylidene)-1, 3-dihydro-indolin-2-one (8) and (E)-3-(3'-Nitro-benzylidene)-1, 3-dihydro-indolin-2-thione (16) were docked at the active site where the PP1 was embedded.

Philinopside A, a novel marine-derived compound possessing dual anti-angiogenic and anti-tumor effects

Philinopside A is a novel sulfated saponin isolated from the sea cucumber, Pentacta quadrangulari. The effects of philinopside A on angiogenesis and tumor growth were assessed in a series of models in vitro and in vivo. Our results demonstrated that philinopside A significantly inhibited the proliferation, migration and tube formation of human microvascular endothelial cells (HMECs) in a dose-dependent manner, with average IC(50) values of 1.4 +/- 0.17, 0.89 +/- 0.23 and 0.98 +/- 0.19 microM, respectively. Rat aortas culture assay provides a close imitation of in vivo angiogenesis process and 2-10 microM philinopside A suppressed the formation of new microvessels in cultured rat aortas. Philinopside A 2-10 nmol/egg obviously inhibited angiogenesis in chick embryo chorioallantoic membrane assay. In addition, philinopside A manifested strong anti-tumor activities both in vitro and in vivo. Through immunofluorescent analysis, we found the compound reduced mouse sarcoma 180 tumor volume by inducing apoptosis of tumor and tumor-associated endothelial cells. An examination of the effects of philinopside A on the angiogenesis-related receptor tyrosine kinases (RTKs) showed that philinopside A broadly inhibited all tested RTKs, including vascular endothelial growth factor (VEGF) receptor, fibroblast growth factor (FGF) receptor-1, platelet-derived growth factor (PDGF) receptor-beta and epithelial growth factor (EGF) receptor, with IC(50) values ranging from 2.6-4.9 microM. These results suggest that philinopside A is a promising anti-cancer agent that possesses dual cytotoxic and anti-angiogenic effects that were at least partly due to its inhibitory effects on RTKs.

Design, synthesis, and biological evaluation of aminoboronic acids as growth-factor receptor inhibitors of EGFR and VEGFR-1 tyrosine kinases

A series of aminoboronic acids was synthesized based on the structure of lavendustin pharmacophore 1. Their inhibitory activities against the epidermal growth-factor receptor (EGFR) and vascular endothelial growth-factor receptor-1 (VEGFR-1, Flt-1) protein tyrosine kinases, and various protein kinases, PKA, PKC, PTK, and eEF2K were evaluated. Selective inhibition activities were observed in a series of aminoboronic acids. 4-Methoxy-3-((2- methoxyphenylamino)methyl)phenylboronic acid 10 inhibited EGFR tyrosine kinase, whereas 4-(2,5-dihydroxybenzylamino)phenylboronic acid 12 inhibited Flt-1 protein kinase, although lavendustin pharmacophore 1 inhibited both EGFR and Flt-1 kinases at a compound concentration of 1.0 microg mL(-1). The selective inhibition of EGFR by 10 is considered to be due to the substitution of the dihydroxy groups on the benzyl moiety for a boronic acid group at the para position, whereas the selective inhibition of Flt-1 by 12 is due to the substitution of the carboxyl group on the aniline moiety in the lavendustin pharmacophore 1 for a boronic acid group.

Synthesis and antiangiogenic activity of exo -olefinated deoxoartemisinin derivatives

10-exo-Bromoalkylidene and benzylidene deoxoartemisinin derivatives with antiangiogenic activity were synthesized from corresponding 10-alkanesulfonyl dihydroartemisinin and 10-phenylmethanesulfonyl dihydroartemisinin using a highly efficient, mild, and simple Ramberg-Bäcklund rearrangement.

Simultaneous determination of Z-SU5416 and its interconvertible geometric E-isomer in rat plasma by LC/MS/MS

SU5416 is a selective inhibitor of vascular endothelial growth factor (VEGF) receptor, which plays a major role in vascular angiogenesis. SU5416 exists as the thermodynamically stable and pharmacologically active cis isomer (Z-isomer) in the solid state. In light-exposed solutions the unstable trans isomer (E-isomer) is formed. The E-isomer is unstable for synthesis and isolation and the analytical standard of the E-isomer is unavailable. A new, simple, fast and reliable LC/MS/MS method was developed to quantify both isomers simultaneously in rat plasma samples in order to support the study of disposition kinetics of Z- and E-SU5416. This method is sensitive (LOQ = 0.5 ng/ml), reproducible, and has a wide linear range (0.5-2500 ng/ml).

Adenosine-anchored triphosphate subsite probing: distinguishing between HER-2 and HER-4 tyrosine protein kinases

A strategy of full-site occupancy and stereospecific recognition in the triphosphate subsite was used to specifically inhibit two protein kinases HER-2 and HER-4 from the EGFR family. The SAR profiles of a panel of adenosine-anchored bicyclic heterocycles against HER-2 and HER-4 indicated that specificity can be derived for highly homologous protein kinases from stereospecific recognition in the triphosphate-subsite.

A Study on the Interaction between p60c-Src Receptor Tyrosine Kinase and Arylcarboxylic and Arylacetic Acid Derivatives Based on Docking Modes and in Vitro Activity

The fundamental role that receptor tyrosine kinases play in cancer and other proliferative diseases has provided the impetus for an extensive effort on the part of both academic and pharmaceutical laboratories to develop highly specific inhibitors. In this study, inhibitory activity of previously synthesized arylacetic and arylcarboxylic acid derivatives were examined against substrate of tyrosine kinase. It can be assumed that the activity of compounds becomes higher when the -CH(2) linkage exist between aromatic ring and the amide group of the side chain. In addition, when the R(1) and R(2) substitutents are methyl group in both series, the higher activity observed. The data obtained from docking study (DOCK4.0) indicated that compounds 2, 4, 7, 8, 11 render satisfactory interaction with the active site of enzyme, Lys295 of p60(c-Src) tyrosine kinase. Comparison of this interaction and the evaluation of biological data showed that compound 4 is the most active among the entire derivatives.

Metastasis and angiogenesis

Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neovascularization. Removal of inhibiting antiangiogenic factors leads to growth of dormant metastases. Several endogenous inhibitors have been identified so far and some of them have already been successfully applied in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.

Anti-angiogenic chemotherapy in central nervous system tumors

Primary central nervous system tumors are infrequent lesions observed in both pediatric and adult patients that account for a disproportionate amount of cancer related morbidity and mortality. A significant number of advances in neurosurgical and radiation therapy techniques have occurred over the last few decades and yet only small improvements in long-term outcome have resulted. The major reason for this is the ability of these advances to minimize surgical or radiation morbidity on surrounding normal tissue rather than eradicating the microscopic infiltrating disease that remains after up-front standard therapy. As such, a great deal of effort has gone into adjuvant chemotherapy that might complement the standard surgical and radiation approaches. This paper will review the literature on anti-angiogenic therapies in central nervous system (CNS) tumor models and clinical disease, with a focus on anti-angiogenic chemotherapy (also referred to as metronomic or low-dose chemotherapy) and the utilization of this approach in conjunction with standard radiation and surgery. A number of excellent reviews covering related aspects of this topic are also available (1-13).

Growth inhibition activity of thioacetal artemisinin derivatives against human umbilical vein endothelial cells

Thioacetal artemisinin derivatives, in particular, 10alpha-phenylthiodihydroartemisinins (5), 10beta-benzenesulfonyl-9-epi-dihydroartemisinin (9) and 10alpha-mercaptodihydroartemisinin (11), exhibit good growth inhibition activity against HUVEC proliferation at the concentration level of 1 microM.

Thalidomide metabolites and analogues. 3. Synthesis and antiangiogenic activity of the teratogenic and TNFalpha-modulatory thalidomide analogue 2-(2,6-dioxopiperidine-3-yl)phthalimidine

Versatile synthesis of the teratogenic, TNFalpha-modulatory, and antiangiogenic thalidomide analogue 2-(2,6-dioxopiperidine-3-yl)phthalimidine (1) and its direct antiangiogenic properties are described. With thalidomide or thalidomide derivatives as precursors, the synthesis involved either carbonyl reduction/thiation-desulfurization or carbonyl reduction/acyliminium ion reduction protocols. Compared to earlier studies with thalidomide, which was only active with microsomal treatment, 1 exhibited marginal inhibitory activity in the rat aortic ring assay, thereby demonstrating the requirement for metabolic activation.

A study on the synthesis of antiangiogenic (+)-coronarin A and congeners from (+)-sclareolide

Coronarin A 1, epi-coronarin A 2 and some synthetic intermediates 14a and 14b synthesized from sclareolide exhibit good growth inhibition activities on HUVEC proliferation. In particular, coronarin A 1 and epi-coronarin A 2 effectively suppressed the growth factor induced tube formation of HUVEC at the concentration of 10 micro g/mL.

Identification of a novel antiangiogenic agent; 4-(N-imidazol-2-ylmethyl)amino benzopyran analogues

A series of 4-(N-imidazol-2-ylmethyl)aminobenzopyran analogues, originally designed as K(ATP) openers for ischemic diseases, showed antiangiogenic properties through the inhibition of HUVEC tube formation. Especially one of p-Cl substituted analogues (4c) completely inhibited HUVEC tube formation at 10 microM. The compound 4c significantly inhibited tumor growth by 52% on A549 (human non small cell lung carcinoma) in nude mice xenografts without any significant side effects.

Synthesis and investigation of conformationally restricted analogues of lavendustin A as cytotoxic inhibitors of tubulin polymerization

A series of conformationally restricted analogues were synthesized in order to elucidate the possible effects of different amide conformations of lavendustin A derivatives on cytotoxicity in cancer cell cultures and on inhibition of tubulin polymerization. The conformationally restricted analogues were based on the oxazinedione and isoindolone ring systems. In addition, the amide bond was replaced by both cis and trans alkene moieties. Surprisingly, the results indicated very little effect of conformational restriction on biological activity. Because all of the compounds synthesized had similar cytotoxicities and potencies as tubulin polymerization inhibitors, the side chain present on the aniline ring system does not appear to be important in the biological effects of the lavendustins. The hydroquinone ring of lavendustin A may be a more important determinant of the biological activity than the structure surrounding the aniline ring.

Development of biologic markers of response and assessment of antiangiogenic activity in a clinical trial of human recombinant endostatin

PURPOSE

Angiogenesis is a target for the treatment of cancer and other diseases, and its complex biology suggests that establishing the appropriate dose and schedule for antiangiogenic treatment will require extensive study. We present the initial results of a dose-finding clinical trial of recombinant human endostatin (rh-Endo) that examined potential surrogates for response to antiangiogenic therapy.

PATIENTS AND METHODS

Twenty-five patients were treated with escalating doses of rh-Endo. Positron emission tomography (PET) was used to assess tumor blood flow (with [15O]H2O) and metabolism (with [18F]fluorodeoxyglucose) before the start of therapy and then every 4 weeks. To directly assess the effects of rh-Endo on endothelial cells within the tumors, biopsy specimens of tumor tissue were obtained before therapy and again at 8 weeks and evaluated for endothelial cell and tumor cell apoptosis.

RESULTS

Tumor blood flow and metabolism as measured by PET scans generally decreased with increasing doses of rh-Endo; however, the effects were complex and in some analyses nonlinear. Tumor biopsy analysis revealed a significant increase in tumor cell apoptosis (P =.027) and endothelial cell apoptosis (P =.027) after 8 weeks of therapy. However, there was no statistically significant relationship between rh-Endo dose and induction of tumor cell or endothelial cell apoptosis.

CONCLUSION

These initial data suggest that rh-Endo has measurable effects on tumor blood flow and metabolism and induces endothelial and tumor cell apoptosis even in the absence of demonstrable anticancer effects. Further study and validation of these biomarkers in the context of antiangiogenic therapy will be required.

A strategy for the design of multiplex inhibitors for kinase-mediated signalling in angiogenesis

Tumour growth is dependent on multiple factors, including the physiological process of angiogenesis. Several opportunities for inhibiting angiogenesis with targeted therapies have been identified and are currently being evaluated for clinical efficacy. Some of the most promising approaches include small-molecule inhibitors for the tyrosine receptor kinase VEGFR2. Other signal-transduction pathways have also been shown to regulate angiogenesis, including FGFR, PDGFR, Tie and EphB.

Total synthesis and biological evaluation of the nakijiquinones

The Her-2/Neu receptor tyrosine kinase is vastly overexpressed in about 30% of primary breast, ovary, and gastric carcinomas. The nakijiquinones are the only naturally occurring inhibitors of this important oncogene, and structural analogues of the nakijiquinones may display inhibitory properties toward other receptor tyrosine kinases involved in cell signaling and proliferation. Here, we describe the first enantioselective synthesis of the nakijiquinones. Key elements of the synthesis are (i) the reductive alkylation of a Wieland-Miescher-type enone with a tetramethoxyaryl bromide, (ii) the oxidative conversion of the aryl ring into a p-quinoid system, (iii) the regioselective saponification of one of the two vinylogous esters incorporated therein, and (iv) the selective introduction of different amino acids via nucleophilic conversion of the remaining vinylogous ester into the corresponding vinylogous amide. The correct stereochemistry and substitution patterns are completed by conversion of two keto groups into a methyl group and an endocyclic olefin via olefination/reduction and olefination/isomerization sequences, respectively. This synthesis route also gave access to analogues of nakijiquinone C with inverted configuration at C-2 or with an exocyclic instead of an endocyclic double bond. Investigation of the kinase-inhibiting properties of the synthesized derivatives revealed that the C-2 epimer 30 of nakijiquinone C is a potent and selective inhibitor of the KDR receptor, a receptor tyrosine kinase involved in tumor angiogenesis. Molecular modeling studies based on the crystal structure of KDR and a model of the ATP binding site built from a crystal structure of FGF-R revealed an insight into the structural basis for the difference in activity between the natural product nakijiquinone C and the C-2 epimer 30.

[The mechanisms of angiogenesis. Medical and therapeutic applications]

PURPOSE

Endothelial and smooth muscle cells interact with each other to form new blood vessels. In this review, the cellular and molecular mechanism underlying the formation of the primary vascular plexus (vasculogenesis), the sprouting of further blood vessels (angiogenesis) and their maturation via recruitment of smooth muscle cells (arteriogenesis) during physiological and pathological conditions are summarized.

CURRENT KNOWLEDGE AND KEY POINT

The concept of angiogenesis is studied in tumoral and cardiovascular pathology. Promoting the formation of new collateral vessels in ischemic tissues using angiogenic growth factors (therapeutic angiogenesis) is a promising approach in cardiovascular diseases. Conversely, inhibition of the action of key regulators of angiogenesis is a new pathway for the treatment of solid tumors and metastasis.

FUTURE PROSPECTS AND PROJECTS

These concepts are being tested now in clinical trials in the oncology or cardiovascular fields. Some trials are reported in this review with their potential adverse effects, limits and developments in the future.

Antiangiogenesis therapy. Current and future agents

Approaches to cancer therapy for most tumors in adults and children have changed little in 50 years: surgery, radiation, and chemotherapy are standard for many solid tumors. When the concept of angiogenesis in cancer biology was introduced in the 1970s, there was little recognition of the therapeutic potential of attacking a tumor's blood supply. Advances in understanding the molecular processes that regulate tumor blood supply and novel agents that can interfere with them have generated a great deal of scientific interest and excitement. This article reviews the current understanding of angiogenesis and its role in cancer then discusses new therapeutic options in animals and humans, with a focus on pediatric tumors and the potential for treating them.

Tumor angiogenesis as a therapeutic target

Angiogenesis - the formation of new blood vessels within a tumor (or many other tissue types) - has become a hotbed of pharmacological research as well as industrial drug discovery. This is the result of the efforts of a generation of scientists elucidating the complex (patho)physiological, biochemical and molecular events accompanying angiogenesis. It is estimated that >300 drug candidates are currently in various stages of testing, and it is, therefore, impossible to capture all of this in a brief review. Therefore, the emphasis here is on relatively advanced projects that are either in preclinical or clinical development, thus neglecting, to a large extent, the many exciting avenues being pursued in both academic and biotechnology laboratories. Although the potential of the approaches described cannot be overestimated, it is also important to note that there is still no drug on the market that achieves clinical benefit based on a selective modulation or inhibition of angiogenesis.

Regeneration in avian hair cell epithelia: identification of intracellular signals required for S-phase entry

Balance epithelia in birds closely resemble their mammalian counterparts, but their cells turnover rapidly and they quickly regenerate hair cells, leading to functional recovery from damage that would be permanent for a mammal. We isolated and cultured sheets of the chicken's utricular epithelium in bromo-deoxyuridine and specific inhibitors of different intracellular signalling pathways to identify signals that influence turnover and regeneration. Synthesis (S-phase) entry was effectively blocked by inhibition of PI3-K, TOR or MAPK, and significantly decreased by inhibitors of PKC. Comparisons indicate that activated PI3-K and TOR are required for S-phase entry in both avian and mammalian balance epithelia, but activation of the MAPK pathway appears to have a more significant role in avian utricles than in mammals. The dissimilarities in the requirements for these signalling pathways do not appear sufficient to explain the marked difference in regenerative capacity between the ears of birds and mammals.

Simultaneous determination of SU5416 and its phase I and phase II metabolites in rat and dog plasma by LC/MS/MS

SU5416, Z-3-[(2,4-dimethylpyrrol-5-yl)methylidenyl]-2-indolinone, is a cytostatic substance in development as an anti-angiogenic agent. SU5416 has several phase I and phase II metabolites including SU9838, SU6595, SU6689, 5'-hydroxy glucuronide of SU5416 and 5'-acyl glucuronide of SU5416. In order to support the preclinical studies, a liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) method for simultaneous determination of SU5416 and its metabolites in rat and dog plasma was developed. This method is fast, simple, sensitive (LOQ=2.0 ng/ml), reproducible and has a wide linear range (2.0-5000 ng/ml for SU5416, 2.0-2000 ng/ml for SU6689 and 2.0-1000 ng/ml for SU9838 and SU6595). This method was applied to rat and dog plasma samples obtained from pharmacokinetic and toxicokinetic studies.

Antiangiogenic agents and their promising potential in combined therapy

One of the most promising strategies for treating cancer is the addition of antiangiogenic therapy to therapeutic regimens. Angiogenesis, or the growth of new blood vessels from preexisting vessels, is essential both for the growth of a primary tumor and for successful metastasis. As a result of intense research in this field, a number of antiangiogenic agents have been identified and have demonstrated varying degrees of success in inhibiting the growth of solid tumors and metastases in preclinical and clinical studies. The real potential of antiangiogenic agents for cancer therapy resides in strategic combinations with each other, with chemotherapy, with radiation, and with tumor-targeting agents, such as radioimmunotherapy. Along with this new opportunity to develop synergistic therapy comes the challenging complexities of the physiologic systems regulating angiogenesis. These multifaceted systems could intimidate investigators seeking to take advantage of the potential synergy in combined cancer therapy. To aid in these efforts, this overview of key antiangiogenic agent mechanisms, combination strategies and initial studies of the potential synergy with chemotherapy, radiation and radioimmunotherapy is presented.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.

Design, synthesis, and biological evaluation of a series of lavendustin A analogues that inhibit EGFR and Syk tyrosine kinases, as well as tubulin polymerization

A series of N-alkylamide analogues of the lavendustin A pharmacophore were synthesized and tested for inhibition of the epidermal growth factor receptor (EGFR) protein tyrosine kinase and the nonreceptor protein tyrosine kinase Syk. Although several compounds in the series were effective inhibitors of both kinases, it seemed questionable whether their inhibitory effects on these kinases were responsible for the cytotoxic properties observed in a variety of human cancer cell cultures. Accordingly, a COMPARE analysis of the cytotoxicity profile of the most cytotoxic member of the series was performed, and the results indicated that its cytotoxicity profile was similar to that of antitubulin agents. This mechanism of action was supported by demonstrating that most compounds in the series were moderately effective as inhibitors of tubulin polymerization. This suggests that the lavendustin A analogues reported here, as well as some of the previously reported lavendustin A analogues, may be acting as cytotoxic agents by a mechanism involving the inhibition of tubulin polymerization.

From oncogene to drug: development of small molecule tyrosine kinase inhibitors as anti-tumor and anti-angiogenic agents

The confluence of two distinct but related activities in the past 10 years has dramatically accelerated efforts towards the discovery and development of novel drugs to treat cancer. The first is a rapidly emerging understanding that a number of distinct tyrosine kinases play roles in diverse but fundamentally important aspects of tumor progression (growth, survival, metastasis and angiogenesis). The second is the discovery that small molecule compounds have the capacity to potently and selectively inhibit the biochemical function of tyrosine kinases by competing for ATP binding at the enzyme catalytic site. These observations have been conjoined in major efforts to bring forward into clinical development novel cancer drugs with the potential to provide both clinical efficacy and improved tolerability. The focus of this review is on the development of small molecule tyrosine kinase inhibitors, and does not extend to other approaches that could be applied to disrupt the same pathways in clinical tumors (receptor and/or ligand-competitive antibodies, intrabodies, antisense ribonucleotides, ribozymes, phosphatase inhibitors or SH2/SH3-directed agents). Selected tyrosine kinase inhibitors, known or believed to be in development in cancer treatment trials, are summarized as are some of the key issues that must be addressed if these compounds are to be developed into clinically useful cancer chemotherapeutic agents.

Antineoplastic agents from natural sources: achievements and future directions

The influence of natural products upon anticancer drug discovery and design cannot be overestimated. Approximately 60% of all drugs now in clinical trials for the multiplicity of cancers are either natural products, compounds derived from natural products, contain pharmacophores derived from active natural products or are 'old drugs in new clothes', where (modified) natural products are attached to targeting systems. This review covers those materials that the authors are aware of as being in clinical trials through early 2000 and demonstrates how, even today, in the presence of massive numbers of agents from combinatorial libraries, the compounds produced by 'Mother Nature' are still in the forefront of cancer chemotherapeutics as sources of active chemotypes.

3-(3,5-Dimethoxyphenyl)-1,6-naphthyridine-2,7-diamines and related 2-urea derivatives are potent and selective inhibitors of the FGF receptor-1 tyrosine kinase

A series of 3-aryl-1,6-naphthyridine-2,7-diamines and related 2-ureas were prepared and evaluated as inhibitors of the FGF receptor-1 tyrosine kinase. Condensation of 4,6-diaminonicotinaldehyde and substituted phenylacetonitriles gave intermediate naphthyridine-2,7-diamines, and direct reaction of the monoanion of these (NaH/DMF) with alkyl or aryl isocyanates selectively gave the 2-ureas in varying yields (23-93%). For the preparation of more soluble 7-alkylamino-2-ureas, a number of protecting groups for the 2-amine were evaluated (phthaloyl, 4-methoxybenzyl) following selective blocking of the 7-amine (trityl), but these were not superior to the (required) 2-tert-Bu-urea group itself. Direct alkylation of the anion of the (unprotected) 7-amino group with excess 4-(3-chloropropyl)morpholine in DMF gave low (10%) yields of the desired product, but alkylation of the 7-acetamido anion, followed by mild alkaline hydrolysis, raised this to 64%. 3-Phenyl analogues were nonspecific inhibitors of isolated c-Src, FGFR, and PDGFR tyrosine kinases, whereas 3-(2,6-dichlorophenyl) analogues were most effective against c-Src and FGFR, and 3-(3,5-dimethoxyphenyl) derivatives showed high selectivity for FGFR alone. A water-soluble (7-morpholinylpropylamino) analogue retained high FGFR potency (IC(50) 31 nM) and selectivity. Pairwise comparison of the 1, 6-naphthyridines and the corresponding known pyrido[2,3-d]pyrimidine analogues showed little differences in potency or patterns of selectivity, suggesting that the 1-aza atom of the latter is not important for activity. A 7-acetamide derivative inhibited the growth of FGFR-expressing tumor cell lines and was particularly potent against HUVECs (IC(50) 4 nM). This compound was also a very potent inhibitor of HUVEC microcapillary formation (IC(50) 0.01 nM) and Matrigel invasion (IC(50) 7 nM) and showed significant in vivo antitumor effects in a highly vascularized mammary adenocarcinoma 16/c model at nontoxic doses. The compounds are worthy of further evaluation as antiangiogenesis agents.

Genes that regulate metastasis and angiogenesis

Genetic instability and an accumulation of genetic and epigenetic changes during tumor progression lead to an increasingly aggressive and treatment-resistant phenotype, and ultimately metastasis. In recent years it has become well established that angiogenesis, the process by which new vasculature is formed from pre-existing vessels, is an essential component to primary tumor growth and distant metastasis. A greater understanding of the complex multitude of factors involved in tumor angiogenesis and metastasis is fundamental to the development of potential therapeutics to treat malignant disease. As highlighted throughout this review, angiogenesis and metastasis share many common cellular and molecular features. We will briefly discuss the pertinent genes involved in the regulation of angiogenesis and metastasis.

Angiogenesis, metastasis, and endogenous inhibition

Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neo-vascularization. Removal of inhibiting anti-angiogenic factors led to growth of dormant metastases. A number of endogenous inhibitors have been identified and have shown success in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.