Inhibitors of angiogenesis and cancer-related receptor tyrosine kinases

LIF-IGF Axis Contributes to the Proliferation of Neural Progenitor Cells in Developing Rat Cerebrum

In rodent models, leukemia inhibitory factor (LIF) is involved in cerebral development via the placenta, and maternal immune activation is linked to psychiatric disorders in the child. However, whether LIF acts directly on neural progenitor cells (NPCs) remains unclear. This study performed DNA microarray analysis and quantitative RT-PCR on the fetal cerebrum after maternal intraperitoneal or fetal intracerebral ventricular injection of LIF at day 14.5 (E14.5) and determined that the expression of insulin-like growth factors (IGF)-1 and -2 was induced by LIF. Physiological IGF-1 and IGF-2 levels in fetal cerebrospinal fluid (CSF) increased from E15.5 to E17.5, following the physiological surge of LIF levels in CSF at E15.5. Immunostaining showed that IGF-1 was expressed in the cerebrum at E15.5 to E19.5 and IGF-2 at E15.5 to E17.5 and that IGF-1 receptor and insulin receptor were co-expressed in NPCs. Further, LIF treatment enhanced cultured NPC proliferation, which was reduced by picropodophyllin, an IGF-1 receptor inhibitor, even under LIF supplementation. Our findings suggest that IGF expression and release from the NPCs of the fetal cerebrum in fetal CSF is induced by LIF, thus supporting the involvement of the LIF-IGF axis in cerebral cortical development in an autocrine/paracrine manner.

Safety and efficacy profile of lenvatinib in cancer therapy: a systematic review and meta-analysis

To systematically review the safety and efficacy of lenvatinib in the treatment of patients, we retrieved all the relevant clinical trials on the adverse events (AEs) and survival outcomes of lenvatinib through PubMed, Medline, Embase, Web of Science and Cochrane Collaboration's Central register of controlled trial. Fourteen eligible studies involving a total of 978 patients were included in our analysis. The most common all-grade AEs observed in patients treated with lenvatinib were hematuria (56.6%), fatigue (52.2%) and decreased appetite (50.5%). The most frequently observed grade ≥3 AEs were thrombocytopenia (25.4%), hypertension (17.7%) and edema peripheral (15.5%). The incidences of both all-grade and high-grade hypertension were significantly increased. Meanwhile, the controlled trial suggested that progression free survival (PFS) was significantly longer in the lenvatinib group than the placebo group. Subgroup analyses showed that mean PFS for renal cell carcinoma was 10.933±1.828 months (95% CI 7.350-14.515, p < 0.001), and that for thyroid cancer was 18.344±0.083 months (95% CI 18.181-18.506, p < 0.001). In conclusion, lenvatinib is an effective agent in thyroid cancer. Early monitoring and effective management of side effects are crucial for the safe use of this drug.

Pharmacokinetics and excretion of (14)C-lenvatinib in patients with advanced solid tumors or lymphomas

Lenvatinib is an orally available multi-targeted tyrosine kinase inhibitor with anti-angiogenic and antitumor activity. To get more insight into the disposition of lenvatinib, a mass balance study was performed in patients with advanced solid tumors. A single oral 24 mg (100 μCi) dose of (14)C-lenvatinib was administered to six patients, followed by collection of blood, plasma, urine and feces for 7 to 10 days. The collected material was analyzed for total radioactivity, unchanged lenvatinib and selected metabolites. The safety and antitumor effect of a daily oral dose of 24 mg non-labeled lenvatinib were assessed in the extension phase of the study. Peak plasma concentrations of lenvatinib and total radioactivity were reached 1.6 and 1.4 h after administration, respectively, and their terminal phase half-lifes were 34.5 and 17.8 h, respectively. Unchanged lenvatinib systemic exposure accounted for 60 % of the total radioactivity in plasma. Peak concentrations of the analyzed metabolite were over 700-fold lower than the peak plasma concentration of lenvatinib. Ten days after the initial dose, the geometric mean (± CV) recovery of administered dose was 89 % ±10 %, with 64 % ±11 % recovered in feces and 25 % ±18 % in urine. Unchanged lenvatinib in urine and feces accounted for 2.5 % ±68 % of the administered dose, indicating a major role of metabolism in the elimination of lenvatinib. In conclusion, lenvatinib is rapidly absorbed and extensively metabolized, with subsequent excretion in urine and, more predominantly, in feces. Additionally, lenvatinib showed acceptable safety and preliminary antitumor activity.

The therapeutic target Hsp90 and cancer hallmarks

Hsp90 is a major molecular chaperone that is expressed abundantly and plays a pivotal role in assisting correct folding and functionality of its client proteins in cells. The Hsp90 client proteins include a wide variety of signal transducing molecules such as protein kinases and steroid hormone receptors. Cancer is a complex disease, but most types of human cancer share common hallmarks, including self-sufficiency in growth signals, insensitivity to growth-inhibitory mechanism, evasion of programmed cell death, limitless replicative potential, sustained angiogenesis, and tissue invasion and metastasis. A surprisingly large number of Hsp90-client proteins play crucial roles in establishing cancer cell hallmarks. We start the review by describing the structure and function of Hsp90 since conformational changes during the ATPase cycle of Hsp90 are closely related to its function. Many co-chaperones, including Hop, p23, Cdc37, Aha1, and PP5, work together with Hsp90 by modulating the chaperone machinery. Post-translational modifications of Hsp90 and its cochaperones are vital for their function. Many tumor-related Hsp90-client proteins, including signaling kinases, steroid hormone receptors, p53, and telomerase, are described. Hsp90 and its co-chaperones are required for the function of these tumor-promoting client proteins; therefore, inhibition of Hsp90 by specific inhibitors such as geldanamycin and its derivatives attenuates the tumor progression. Hsp90 inhibitors can be potential and effective cancer chemotherapeutic drugs with a unique profile and have been examined in clinical trials. We describe possible mechanisms why Hsp90 inhibitors show selectivity to cancer cells even though Hsp90 is essential also for normal cells. Finally, we discuss the "Hsp90-addiction" of cancer cells, and suggest a role for Hsp90 in tumor evolution.

The therapeutic target Hsp90 and cancer hallmarks

Hsp90 is a major molecular chaperone that is expressed abundantly and plays a pivotal role in assisting correct folding and functionality of its client proteins in cells. The Hsp90 client proteins include a wide variety of signal transducing molecules such as protein kinases and steroid hormone receptors. Cancer is a complex disease, but most types of human cancer share common hallmarks, including self-sufficiency in growth signals, insensitivity to growth-inhibitory mechanism, evasion of programmed cell death, limitless replicative potential, sustained angiogenesis, and tissue invasion and metastasis. A surprisingly large number of Hsp90-client proteins play crucial roles in establishing cancer cell hallmarks. We start the review by describing the structure and function of Hsp90 since conformational changes during the ATPase cycle of Hsp90 are closely related to its function. Many co-chaperones, including Hop, p23, Cdc37, Aha1, and PP5, work together with Hsp90 by modulating the chaperone machinery. Post-translational modifications of Hsp90 and its cochaperones are vital for their function. Many tumor-related Hsp90-client proteins, including signaling kinases, steroid hormone receptors, p53, and telomerase, are described. Hsp90 and its co-chaperones are required for the function of these tumor-promoting client proteins; therefore, inhibition of Hsp90 by specific inhibitors such as geldanamycin and its derivatives attenuates the tumor progression. Hsp90 inhibitors can be potential and effective cancer chemotherapeutic drugs with a unique profile and have been examined in clinical trials. We describe possible mechanisms why Hsp90 inhibitors show selectivity to cancer cells even though Hsp90 is essential also for normal cells. Finally, we discuss the "Hsp90-addiction" of cancer cells, and suggest a role for Hsp90 in tumor evolution.

Current status of HTRF(®) technology in kinase assays

BACKGROUND

Homogeneous time-resolved fluorescence (HTRF) is a fluorescence resonance energy transfer-based technology used to measure bimolecular interactions. It has been applied successfully to kinase assays and has become an important tool in kinase drug discovery.

OBJECTIVE

This article reviews the current status of HTRF technology in biochemical and cellular kinase assays.

METHODS

Recent literature and meeting reports on HTRF kinase assays are reviewed, and their principles, advantages and drawbacks, current status and the potential applications in kinase drug discovery are discussed.

RESULTS/CONCLUSION

HTRF kinase assays are homogeneous, robust, sensitive, easy to miniaturize and high-throughput. This assay format is versatile, as both peptide and protein substrates can be used, and high ATP concentrations are tolerated, which enables the assay to be performed under conditions mimicking the physiological environment. HTRF kinase assays have been applied to both high-throughput screening and compound mechanistic studies. Besides protein kinases, the technology has now been expanded into the lipid kinase family. Furthermore, the utility of HTRF technology in cellular assays is emerging. HTRF kinase assays are a great addition to the toolbox for kinase drug discovery.

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.

Structure-activity relationship of halophenols as a new class of protein tyrosine kinase inhibitors

A series of new benzophenone and diphenylmethane halophenol derivatives were prepared. Their structures were established based on (1)H NMR, (13)C NMR and HRMS data. All prepared compounds were screened for their in vitro protein tyrosine kinase (PTK) inhibitory activities. The effects of modification of the linker, functional groups and substituted positions at the phenyl ring on PTK inhibitory activity were investigated. Twelve halophenols showed significant PTK inhibitory activity. Among them, compounds 6c, 6d, 7d, 9d, 10d, 11d and 13d exhibited stronger activities than that of genistein, the positive reference compound. The results gave a relatively full and definite description of the structure-activity relationship and provided a foundation for further design and structure optimization of the halophenols.

Synthesis of aryl-heteroaryl ureas (AHUs) based on 4-aminoquinoline and their evaluation against the insulin-like growth factor receptor (IGF-1R)

The insulin-like growth factor receptor (IGF-1R) is a receptor tyrosine kinase (RTK) involved in all stages of the development and propagation of breast and other cancers. The inhibition of IGF-1R by small molecules remains a promising strategy to treat cancer. Herein, we explore SAR around previously characterized lead compound (1), which is an aryl-heteroaryl urea (AHU) consisting of 4-aminoquinaldine and a substituted aromatic ring system. A library of novel AHU compounds was prepared based on derivatives of the 4-aminoquinoline heterocycle (including various 2-substituted derivatives, and naphthyridines). The compounds were screened for in vitro inhibitory activity against IGF-1R, and several compounds with improved activity (3-5 microM) were identified. Furthermore, a computational docking study was performed, which identifies a fairly consistent lowest energy mode of binding for the more-active set of inhibitors in this series, while the less-active inhibitors do not adopt a consistent mode of binding.

Acyclic retinoid inhibits angiogenesis by suppressing the MAPK pathway

Acyclic retinoid (ACR) is currently under clinical trial as an agent to suppress the recurrence of hepatocellular carcinoma (HCC) through its ability to induce apoptosis in premature HCC cells. ACR has an anticancer effect in vivo as well, although it shows weak apoptosis-inducing activity against mature HCC cells, suggesting the existence of an additional action mechanism. In this study, we investigated the antiangiogenic activity of ACR. ACR inhibited angiogenesis within chicken chorioallantoic membrane (CAM) in as similar a manner as all-trans retinoic acid (atRA). Although suppression of angiogenesis by atRA was partially rescued by the simultaneous addition of angiopoietin-1, suppression of angiogenesis by ACR was not rescued under the same condition at all. Conversely, although suppression of angiogenesis by ACR was partially inverted by the simultaneous addition of vascular endothelial growth factor (VEGF), suppression of angiogenesis by atRA was not affected under the same condition. These results suggested that mechanisms underlying the suppression of angiogenesis by ACR and atRA were different. ACR selectively inhibited the phosphorylation of VEGF receptor 2 (VEGFR2) and of extracellular signal-regulated kinase (ERK) without changing their protein expression levels, and inhibited endothelial cell growth, migration, and tube formation. The inhibition of the phosphorylation of ERK, endothelial growth, migration, tube formation, and angiogenesis by ACR was rescued by the overexpression of constitutively active mitogen-activated protein kinase (MAPK). Finally, ACR, but not atRA, inhibited HCC-induced angiogenesis in a xenografted CAM model. These results delineate the novel activity of ACR as an antiangiogenic through a strong inhibition of the VEGFR2 MAPK pathway.

Imidazo[1,2-a]pyrazine diaryl ureas: inhibitors of the receptor tyrosine kinase EphB4

Inhibition of receptor tyrosine kinases (RTKs) such as vascular endothelial growth factor receptors (VEGFRs) and platelet-derived growth factor receptors (PDGFRs) has been validated by recently launched small molecules Sutent and Nexavar, both of which display activities against several angiogenesis-related RTKs. EphB4, a receptor tyrosine kinase (RTK) involved in the processes of embryogenesis and angiogenesis, has been shown to be aberrantly up regulated in many cancer types such as breast, lung, bladder and prostate. We propose that inhibition of EphB4 in addition to other validated RTKs would enhance the anti-angiogenic effect and ultimately result in more pronounced anti-cancer efficacy. Herein we report the discovery and SAR of a novel series of imidazo[1,2-a]pyrazine diarylureas that show nanomolar potency for the EphB4 receptor, in addition to potent activity against several other RTKs.

Evaluating the utility of the HTRF Transcreener ADP assay technology: a comparison with the standard HTRF assay technology

The HTRF (homogeneous time-resolved fluorescence) Transcreener ADP assay is a new kinase assay technology marketed by Cis-Bio International (Bagnols-Cèze, France). It measures kinase activity by detecting the formation of ADP using a monoclonal antibody and HTRF detection principles. In this article, we compare this technology with a standard HTRF kinase assay using EGFR [L858R/T790M] mutant enzyme as a case study. We demonstrate that the HTRF Transcreener ADP assay generated similar kinetic constants and inhibitor potency compared with the standard HTRF assay. However, the smaller dynamic window and lower Z' factor of the HTRF Transcreener ADP assay make this format less preferable for high-throughput screening. Based on the assay principle, the HTRF Transcreener ADP assay can detect both kinase and ATPase activities simultaneously. The ability to probe ATPase activity opens up new avenues for assaying kinases with intrinsic ATPase activity without the need to identify substrates, and this can speed up the drug discovery process. However, caution must be exercised because any contaminating ATPase activity will result in an invalid assay. The inability to tolerate high concentrations of ATP in the assay will also limit the application of this technology, especially in compound mechanistic studies such as ATP competition. Overall, the HTRF Transcreener ADP assay provides a new alternative tool to complement existing assay technologies for drug discovery.

Mechanism of inhibition of tumor angiogenesis by beta-hydroxyisovalerylshikonin

Shikonin and beta-hydroxyisovalerylshikonin (beta-HIVS) from Lithospermum erythrorhizon inhibit angiogenesis via inhibition of vascular endothelial growth factor receptors (VEGFR) in an adenosine triphosphate-non-competitive manner, although the underlying molecular mechanism has not been fully understood. In the present study, we found that beta-HIVS inhibited angiogenesis within chicken chorioallantoic membrane approximately threefold more efficiently than shikonin. beta-HIVS also significantly inhibited angiogenesis in two other assays, induced either by Lewis lung carcinoma cells implanted in mouse dorsal skin or by VEGF in s.c. implanted Matrigel plugs and metastasis of Lewis lung carcinoma cells to lung. Therefore, using beta-HIVS as a bioprobe, we investigated the molecular mechanism of shikonin's anti-angiogenic actions. beta-HIVS inhibited the phosphorylation and expression of VEGFR2 and Tie2 without affecting VEGFR1 and fibroblast growth factor receptor 1 levels. beta-HIVS suppressed the phosphorylation but not the expression of extracellular signal-regulated kinase, and an Sp1-dependent transactivation of the VEGFR2 and Tie2 promoters, thereby suppressing the proliferation of vascular endothelial and progenitor cells. This was mimicked by an Sp1 inhibitor mithramycin A and partially rescued by Sp1 overexpression. These results implicate potential use of shikonin and beta-HIVS as leading compounds for clinical application in the future by virtue of their unique properties including: (i) inhibition of VEGFR2 and Tie2 phosphorylation in an adenosine triphosphate-non-competitive manner; (ii) simultaneous inhibition of the phosphorylation and expression of VEGFR2 and Tie2; and (iii) bifunctional inhibition of the growth in endothelial cells and vascular remodeling.

Modeling of growth factor-receptor systems from molecular-level protein interaction networks to whole-body compartment models

Most physiological processes are subjected to molecular regulation by growth factors, which are secreted proteins that activate chemical signal transduction pathways through binding of specific cell-surface receptors. One particular growth factor system involved in the in vivo regulation of blood vessel growth is called the vascular endothelial growth factor (VEGF) system. Computational and numerical techniques are well suited to handle the molecular complexity (the number of binding partners involved, including ligands, receptors, and inert binding sites) and multiscale nature (intratissue vs. intertissue transport and local vs. systemic effects within an organism) involved in modeling growth factor system interactions and effects. This chapter introduces a variety of in silico models that seek to recapitulate different aspects of VEGF system biology at various spatial and temporal scales: molecular-level kinetic models focus on VEGF ligand-receptor interactions at and near the endothelial cell surface; mesoscale single-tissue 3D models can simulate the effects of multicellular tissue architecture on the spatial variation in VEGF ligand production and receptor activation; compartmental modeling allows efficient prediction of average interstitial VEGF concentrations and cell-surface VEGF signaling intensities across multiple large tissue volumes, permitting the investigation of whole-body intertissue transport (e.g., vascular permeability and lymphatic drainage). The given examples will demonstrate the utility of computational models in aiding both basic science and clinical research on VEGF systems biology.

Pharmacophore modeling studies of type I and type II kinase inhibitors of Tie2

In this study, chemical feature based pharmacophore models of type I and type II kinase inhibitors of Tie2 have been developed with the aid of HipHop and HypoRefine modules within Catalyst program package. The best HipHop pharmacophore model Hypo1_I for type I kinase inhibitors contains one hydrogen-bond acceptor, one hydrogen-bond donor, one general hydrophobic, one hydrophobic aromatic, and one ring aromatic feature. And the best HypoRefine model Hypo1_II for type II kinase inhibitors, which was characterized by the best correlation coefficient (0.976032) and the lowest RMSD (0.74204), consists of two hydrogen-bond donors, one hydrophobic aromatic, and two general hydrophobic features, as well as two excluded volumes. These pharmacophore models have been validated by using either or both test set and cross validation methods, which shows that both the Hypo1_I and Hypo1_II have a good predictive ability. The space arrangements of the pharmacophore features in Hypo1_II are consistent with the locations of the three portions making up a typical type II kinase inhibitor, namely, the portion occupying the ATP binding region (ATP-binding-region portion, AP), that occupying the hydrophobic region (hydrophobic-region portion, HP), and that linking AP and HP (bridge portion, BP). Our study also reveals that the ATP-binding-region portion of the type II kinase inhibitors plays an important role to the bioactivity of the type II kinase inhibitors. Structural modifications on this portion should be helpful to further improve the inhibitory potency of type II kinase inhibitors.

Macrocyclic aminopyrimidines as multitarget CDK and VEGF-R inhibitors with potent antiproliferative activities

X-ray structures from CDK2-aminopyrimidine inhibitor complexes led to the idea to stabilize the active conformation of aminopyrimidine inhibitors by incorporating the recognition site into a macrocyclic framework. A modular synthesis approach that relies on a new late-stage macrocyclization protocol that enables fast and efficient synthesis of macrocyclic aminopyrimidines was developed. A set of structurally diverse derivatives was prepared. Macrocyclic aminopyrimidines were shown to be multitarget inhibitors of CDK1/2 and VEGF-RTKs. In addition, potent antiproliferative activities toward various human tumor cells and a human tumor xenograft model were demonstrated.

Design, synthesis and biological evaluation of substituted pyrrolo[2,3-d]pyrimidines as multiple receptor tyrosine kinase inhibitors and antiangiogenic agents

Direct and indirect involvement of receptor tyrosine kinases (RTKs) in tumor growth and metastasis makes them ideal targets for anticancer therapy. A paradigm shift from inhibition of single RTK to inhibition of multiple RTKs has been recently demonstrated. We designed and synthesized eight N(4)-phenylsubstituted-6-(2-phenylethylsubstituted)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines as homologated series of our previously published RTK inhibitors. We reasoned that increased flexibility of the side chain, which determines potency and selectivity, would improve the spectrum of RTK inhibition. These compounds were synthesized using a bis-electrophilic cyclization to afford substituted pyrrolo[2,3-d]pyrimidines followed by chlorination and substitution at the 4-position with various anilines. Five additional compounds of this series were previously reported by Gangjee et al.(1) with activities against IGFR only. Their synthesis, characterization and biological activities against a variety of other RTKs are reported in this study for the first time. The biological evaluation, in whole cell assays, showed several analogs had remarkable inhibitory activity against epithelial growth factor receptor (EGFR), vascular endothelial growth factor receptor-1 (VEGFR-1), platelet-derived growth factor receptor-beta (PDGFR-beta), the growth of A431 cells in culture, and in the chicken embryo chorioallantoic membrane (CAM) angiogenesis assay. The inhibitory data against the RTKs in this study demonstrate that variation of the 6-ethylaryl substituents as well as the N(4)-phenyl substituents of these analogs does indeed control both the potency and specificity of inhibitory activity against RTKs. In addition, homologation of the chain length of the 6-substituent from a methylene to an ethyl increases the spectrum of RTK inhibition. New multi-RTK inhibitors (8, 12) and potent inhibitors of angiogenesis (15, 19) were identified with the best compound, N(4)-(3-trifluromethylphenyl)-6-(2-phenylethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamine (15), with an IC(50) value of 30nM in the CAM angiogenesis inhibition assay.

Dynamical behavior of the vascular endothelial growth factor: Biological implications

The vascular endothelial growth factor (VEGF) seems to be the most important regulator of physiological and pathological angiogenesis, being, for this reason, a favorite target for therapies against angiogenesis-related diseases. VEGF is a homodimer in which the monomers are formed by beta-strands interconnected on the poles by three loops. A recent work showed that an intimate relationship between loops-1 and -3 is required for high affinity binding to the receptors (Kiba et al., J Biol Chem 2003;278:13453-13461). In this work, we report the results of a 10-ns molecular dynamics simulation of VEGF. We analyzed the dynamical behavior of the protein (using a dynamical cross-correlation map) and found that it is governed by a high degree of correlation between the motions of the loops. We also performed a principal component analysis and found an overall motion in which the opposite poles are projected against each other, just like the movement of the wings of a butterfly. From the biological point of view, it is likely that this motion would facilitate receptor binding since VEGF must enter a restricted cavity formed by the two subunits of the receptor.

Synthesis and evaluation of caged Garcinia xanthones

Inspired by the combination of unique structure and potent bioactivities exhibited by several family members of the caged Garcinia xanthones, we developed a synthesis of simplified analogues that maintain the overall caged motif. The caged structure of these compounds was constructed via a site-selective Claisen/Diels-Alder reaction cascade. We found that the fully substituted caged structure, in which are included the C18 and C23 geminal methyl groups, is necessary to maintain bioactivity. Analogue had comparable activity to the natural products of this family, such as gambogic acid. These compounds exhibit cytotoxicity in a variety of tumor cell lines at low micromolar concentrations and were found to induce apoptosis in HUVE cells. In addition, studies with HL-60 and HL-60/ADR cells indicate that these compounds are not affected by the mechanisms of multidrug resistance, conferred by P glycoprotein expression, typical of relapsed cancers and thus represent a new and potent pharmacophore.

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.

Parallel Synthesis of Diarylureas and Their Evaluation as Inhibitors of Insulin-Like Growth Factor Receptor

Diarylurea (DAU) compounds, particularly species composed of a heteroaryl ring system conjugated through a urea linkage to a substituted arene, were previously identified by the screening of a diverse chemical library to be active against the insulin growth factor receptor (IGF-1R). DAU compounds 4{a,b} were synthesized in parallel by the coupling of aryl amines 2{a} with aryl isocyanates 3{b}. Preparative RP-HPLC purification was found necessary to remove an impurity 5{b}, the symmetric urea resulting from the hydrolytic degradation of aryl isocyanates. Two libraries of DAU compounds were prepared to perform preliminary optimization of the two-ring systems for inhibitory activity against IGF-1R. In the first library, we explored a series of heteroaryl ring systems and found the 4-aminoquinaldine ring system to be optimal among those evaluated. The second library fixed the 4-aminoquinaldine ring system and we evaluated a series of substituted arenes conjugated to it. Overall, eight compounds based on the 4-aminoquinaldine heteroaryl system were found to have moderate activity against IGF-1R with IC(50) values better than 40 microM.

Homogeneous time-resolved fluorescence and its applications for kinase assays in drug discovery

The rapidly growing interest in kinases as potential targets for therapeutic intervention has prompted the development of many kinase assay technologies. One exciting example is homogeneous time-resolved fluorescence (HTRF). An HTRF assay utilizes the signal generated by the fluorescence resonance energy transfer between donor and acceptor molecules in close proximity. Dual-wavelength detection helps to eliminate media interference, and the final signal is proportional to the extent of product formation. Thus far, the reported applications of this technology for in vitro kinase assays have mainly focused on high-throughput screening. In this report, we extend the applications of HTRF technology to the areas of enzyme and inhibitor characterization, some aspects of which were previously believed impossible. We describe the methods developed for determining the kinetic parameters of an enzyme, such as K(m) and k(cat), and the procedures for inhibitor mechanistic studies including ATP competitiveness and slow-binding and dissociation kinetics. These assays can be readily applied to any kinase and are valuable in advancing a program through the early stages of drug discovery.

Inhibition of in vivo angiogenesis by N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine

N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), an antibacterial substance isolated from the flesh fly, inhibits human tumor growth in the nude mice model; however, the mechanism of its action is unclear. The in vivo antitumor effect includes the inhibition of tumor cell proliferation and suppression of angiogenesis. Angiogenesis is essential for tumor growth in vivo. In this study, we examined whether 5-S-GAD inhibits tumor cell-induced angiogenesis by performing the mouse dorsal air sac assay. We found that intraperitoneal administration of 5-S-GAD inhibited the angiogenesis induced by S180 mouse sarcoma cells. Furthermore, 5-S-GAD also inhibited vascular endothelial growth factor-induced angiogenesis in the Matrigel plug assay and embryonic angiogenesis in the chick embryo chorioallantoic membrane assay. However, 5-S-GAD did not show any effect on the proliferation, migration, and tube formation of vascular endothelial cells. These results provide the first evidence that a bioactive substance derived from the flesh fly has antiangiogenic activity in vivo, although the mechanisms involved could not be explained.

Biological evaluation of a multi-targeted small molecule inhibitor of tumor-induced angiogenesis

RO4396686 is a small molecule KDR, FGFR, and PDGFR inhibitor with good pharmacokinetic properties in rodents. In a mouse corneal neovascularization assay, this compound inhibited VEGF-induced angiogenesis. Tested in a H460a xenograft tumor model this agent effected significant tumor growth inhibition at doses as low as 50mg/kg.

Scaffold oriented synthesis. Part 1: Design, preparation, and biological evaluation of thienopyrazoles as kinase inhibitors

We report the synthesis of kinase targeted libraries based on the thienopyrazole scaffold. Several thienopyrazole analogs have been identified as submicromolar inhibitors of KDR.

RO4383596, an orally active KDR, FGFR, and PDGFR inhibitor: Synthesis and biological evaluation

(+/-)-1-(anti-3-Hydroxy-cyclopentyl)-3-(4-methoxy-phenyl)-7-phenylamino-3,4-dihydro-1H-pyrimido[4,5-d]pyrimidin-2-one (RO4383596) is a potent and selective inhibitor of the pro-angiogenic receptor tyrosine kinases KDR, FGFR, and PDGFR. This agent has an excellent pharmacokinetic profile and is highly efficacious in rodent models of angiogenesis upon oral administration.