Targeting the Vascular Endothelial Growth Factor Pathway in the Treatment of Human Malignancy

Recombinant expressing angiopep-2 fused anti-VEGF single chain Fab (scFab) could cross blood-brain barrier and target glioma

In 2009, the FDA approved bevacizumab for the treatment of adult patients diagnosed with recurrent glioblastoma. However, the poor permeability of the macromolecules across the blood–brain barrier, determined by multifactorial anatomical and physiological milieu, restricts the clinical therapeutic effect of bevacizumab. The low-density lipoprotein receptor related protein 1 (LRP1) is highly expressed in the endothelial cells of the brain capillary and the glioma cells. Angiopep-2 (ANG) is a 19-aa oligopeptide that can bind to LRP1 and penetrate the blood–brain barrier by receptor-mediated transport. Therefore, ANG can be used as a dual-targeting drug delivery carrier into the brain and the glioma sites. In this study, ANG gene was fused with the C-terminal domain of single-chain antigen binding fragment (scFab) of the anti-VEGF antibody and recombinant scFab-ANG protein was expressed and purified using Rosatte (DE3) strain. We confirmed that ANG could carry anti-VEGF-scFab, penetrate a three-dimensional model of the brain tumor, and cross the hCMEC/D3 monolayer in the in vitro blood–brain barrier model. The animal experiments demonstrated that 3 h after the tail intravenous protein injection, the fluorescent signals in the brains of the mice in the scFab-ANG group were stronger than that in the scFab group. Furthermore, the study of the in situ rat glioma model shows that scFab-ANG could target glioma while anti-VEGF-scFab could not. These findings indicate that scFab-ANG had stronger transepithelial permeability and glioma targeting capacity. Thus, it can be a potential candidate drug for glioblastoma therapy.

Screening Approaches for Targeting Ribonucleoprotein Complexes: A New Dimension for Drug Discovery

RNA-binding proteins (RBPs) are pleiotropic factors that control the processing and functional compartmentalization of transcripts by binding primarily to mRNA untranslated regions (UTRs). The competitive and/or cooperative interplay between RBPs and an array of coding and noncoding RNAs (ncRNAs) determines the posttranscriptional control of gene expression, influencing protein production. Recently, a variety of well-recognized and noncanonical RBP domains have been revealed by modern system-wide analyses, underlying an evolving classification of ribonucleoproteins (RNPs) and their importance in governing physiological RNA metabolism. The possibility of targeting selected RNA-protein interactions with small molecules is now expanding the concept of protein "druggability," with new implications for medicinal chemistry and for a deeper characterization of the mechanism of action of bioactive compounds. Here, taking SF3B1, HuR, LIN28, and Musashi proteins as paradigmatic case studies, we review the strategies applied for targeting RBPs, with emphasis on the technological advancements to study protein-RNA interactions and on the requirements of appropriate validation strategies to parallel high-throughput screening (HTS) efforts.

Improving gastric cancer preclinical studies using diverse in vitro and in vivo model systems

BACKGROUND

"Biomarker-driven targeted therapy," the practice of tailoring patients' treatment to the expression/activity levels of disease-specific genes/proteins, remains challenging. For example, while the anti-ERBB2 monoclonal antibody, trastuzumab, was first developed using well-characterized, diverse in vitro breast cancer models (and is now a standard adjuvant therapy for ERBB2-positive breast cancer patients), trastuzumab approval for ERBB2-positive gastric cancer was largely based on preclinical studies of a single cell line, NCI-N87. Ensuing clinical trials revealed only modest patient efficacy, and many ERBB2-positive gastric cancer (GC) patients failed to respond at all (i.e., were inherently recalcitrant), or succumbed to acquired resistance.

METHOD

To assess mechanisms underlying GC insensitivity to ERBB2 therapies, we established a diverse panel of GC cells, differing in ERBB2 expression levels, for comprehensive in vitro and in vivo characterization. For higher throughput assays of ERBB2 DNA and protein levels, we compared the concordance of various laboratory quantification methods, including those of in vitro and in vivo genetic anomalies (FISH and SISH) and xenograft protein expression (Western blot vs. IHC), of both cell and xenograft (tissue-sectioned) microarrays.

RESULTS

The biomarker assessment methods strongly agreed, as did correlation between RNA and protein expression. However, although ERBB2 genomic anomalies showed good in vitro vs. in vivo correlation, we observed striking differences in protein expression between cultured cells and mouse xenografts (even within the same GC cell type). Via our unique pathway analysis, we delineated a signaling network, in addition to specific pathways/biological processes, emanating from the ERBB2 signaling cascade, as a potential useful target of clinical treatment. Integrated analysis of public data from gastric tumors revealed frequent (10 - 20 %) amplification of the genes NFKBIE, PTK2, and PIK3CA, each of which resides in an ERBB2-derived subpathway network.

CONCLUSION

Our comprehensive bioinformatics analyses of highly heterogeneous cancer cells, combined with tumor "omics" profiles, can optimally characterize the expression patterns and activity of specific tumor biomarkers. Subsequent in vitro and in vivo validation, of specific disease biomarkers (using multiple methodologies), can improve prediction of patient stratification according to drug response or nonresponse.

Randomized phase II study of nintedanib in metastatic castration-resistant prostate cancer postdocetaxel

This open-label, phase II trial assessed the efficacy and safety of two doses of nintedanib, a triple angiokinase inhibitor targeting vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor signaling, in patients with metastatic castration-resistant prostate cancer (mCRPC) following progression on docetaxel-based regimens. Patients were randomized to nintedanib 150 mg (arm A, n=40) or 250 mg (arm B, n=41) twice daily for 6 months unless disease progression or adverse events (AEs) led to discontinuation. The primary endpoint was the prostate-specific antigen (PSA) response rate (confirmed PSA decline of ≥20% from baseline). Eighty-one patients were enrolled. The PSA response rate was 0% (0/32) in arm A versus 11.1% (4/36) in arm B (P=0.12); 5.6% of patients (2/36) in arm B showed a PSA reduction of at least 50%. In arm B, the rate of PSA increase was significantly decelerated on treatment versus before treatment (P=0.002). The median progression-free survival was 73.5 and 76.0 days for arm A and arm B, respectively (P=0.3). AEs included gastrointestinal disorders, asthenia, hypertension, and reversible elevated transaminases. The incidence of drug-related serious AEs (no drug-related deaths) was 20.0% (arm A) and 24.4% (arm B). The primary endpoint was not met. Nintedanib (250 mg) showed only modest activity with manageable AEs in patients with mCRPC post-docetaxel.

Effect of Avastin on the number and structure of tumor blood vessels of nude mice with A549 lung adenocarcinoma

The aim of the present study was to investigate the effect of Avastin on the number and structure of tumor blood vessels of nude mice with A549 lung adenocarcinoma. A total of 30 nude mice were randomly divided into three groups, namely the control, the Avastin I (Avastin 3 mg/kg) and the Avastin II (Avastin 6 mg/kg) groups. Following treatment, ELISA was used to detect the expression level of vascular endothelial growth factor (VEGF) in tumor tissues. The microvascular density in tumor tissues and tumor vascular pericyte coverage was detected by immunofluorescence. The tumor growth and survival rate of mice in the three groups were also analyzed. Compared with the control group, the Avastin I and II groups exhibited significantly decreased VEGF levels and microvascular density in the tumor tissues, with the decrease in the Avastin II group being more prominent (P<0.05). After 7 days of treatment, the vascular pericyte coverage in the tumor tissues of mice in the Avastin I and II groups was significantly increased compared with that in the control group mice (P<0.05). Compared with the control group, the mice in the Avastin I and II groups exhibited a significantly decreased tumor growth rate and this effect was dose-dependent. The survival rate of mice in the Avastin I and II groups was significantly increased compared with that of the mice in the control group (P<0.05). In conclusion, Avastin significantly decreased the microvascular density of the tumor in nude mice with A549 lung adenocarcinoma and also significantly increased tumor vascular pericyte coverage, inhibited tumor growth and increased the survival rate of the mice, through its potent antiangiogenic activity.

Endothelial-mesenchymal transition in normal human esophageal endothelial cells cocultured with esophageal adenocarcinoma cells: role of IL-1β and TGF-β2

Endothelial-mesenchymal transition (EndoMT) has been recognized as a key determinant of tumor microenvironment in cancer progression and metastasis. Endothelial cells undergoing EndoMT lose their endothelial markers, acquire the mesenchymal phenotype, and become more invasive with increased migratory abilities. Early stages of esophageal adenocarcinoma (EAC) are characterized by strong microvasculature whose impact in tumor progression remains undefined. Our aim was to determine the role of EndoMT in EAC by investigating the impact of tumor cells on normal primary human esophageal microvascular endothelial cells (HEMEC). HEMEC were either cocultured with OE33 adenocarcinoma cells or treated with IL-1β and transforming growth factor-β2 (TGF-β2) for indicated periods and analyzed for EndoMT-associated changes by real-time PCR, Western blotting, immunofluorescence staining, and functional assays. Additionally, human EAC tissues were investigated for detection of EndoMT-like cells. Our results demonstrate an increased expression of mesenchymal markers [fibroblast-specific protein 1 (FSP1), collagen1α2, vimentin, α-smooth muscle actin (α-SMA), and Snail], decreased expression of endothelial markers [CD31, von Willebrand factor VIII (vWF), and VE-cadherin], and elevated migration ability in HEMEC following coculture with OE33 cells. The EndoMT-related changes were inhibited by IL-1β and TGF-β2 gene silencing in OE33 cells. Recombinant IL-1β and TGF-β2 induced EndoMT in HEMEC. Although the level of VEGF expression was elevated in EndoMT cells, the angiogenic property of these cells was diminished. In vivo, by immunostaining EndoMT-like cells were detected at the invasive front of EAC. Our findings underscore a significant role for EndoMT in EAC and provide new insights into the mechanisms and significance of EndoMT in the context of tumor progression.

Isolation and genome-wide expression and methylation characterization of CD31+ cells from normal and malignant human prostate tissue

Endothelial cells (ECs) are an important component involved in the angiogenesis. Little is known about the global gene expression and epigenetic regulation in tumor endothelial cells. The identification of gene expression and epigenetic difference between human prostate tumor-derived endothelial cells (TdECs) and those in normal tissues may uncover unique biological features of TdEC and facilitate the discovery of new anti-angiogenic targets. We established a method for isolation of CD31⁺ endothelial cells from malignant and normal prostate tissues obtained at prostatectomy. TdECs and normal-derived ECs (NdECs) showed >90% enrichment in primary culture and demonstrated microvascular endothelial cell characteristics such as cobblestone morphology in monolayer culture, diI-acetyl-LDL uptake and capillary-tube like formation in Matrigel^®. In vitro primary cultures of ECs maintained expression of endothelial markers such as CD31, von Willebrand factor, intercellular adhesion molecule, vascular endothelial growth factor receptor 1, and vascular endothelial growth factor receptor 2. We then conducted a pilot study of transcriptome and methylome analysis of TdECs and matched NdECs from patients with prostate cancer. We observed a wide spectrum of differences in gene expression and methylation patterns in endothelial cells, between malignant and normal prostate tissues. Array-based expression and methylation data were validated by qRT-PCR and bisulfite DNA pyrosequencing. Further analysis of transcriptome and methylome data revealed a number of differentially expressed genes with loci whose methylation change is accompanied by an inverse change in gene expression. Our study demonstrates the feasibility of isolation of ECs from histologically normal prostate and prostate cancer via CD31⁺ selection. The data, although preliminary, indicates that there exist widespread differences in methylation and transcription between TdECs and NdECs. Interestingly, only a small proportion of perturbed genes were overlapped between American (AA) and Caucasian American (CA) patients with prostate cancer. Our study indicates that identifying gene expression and/or epigenetic differences between TdECs and NdECs may provide us with new anti-angiogenic targets. Future studies will be required to further characterize the isolated ECs and determine the biological features that can be exploited in the prognosis and therapy of prostate cancer.

Vasostatin inhibits VEGF-induced endothelial cell proliferation, tube formation and induces cell apoptosis under oxygen deprivation

Anti-angiogenesis treatment has been a promising new form of cancer therapy. Endothelial cells are critical for vascular homeostasis and play important roles in angiogenesis, vascular and tissue remodeling. Vasostatin, the 180 amino acid N-terminal fragment of the calreticulin protein, is reported to be a potent endogenous inhibitor of angiogenesis, suppressing tumor growth. However, the mechanism of these effects has not been sufficiently investigated. This study was performed to investigate the possible mechanism of vasostatin effects on primary cultured human umbilical vein endothelial cells (HUVEC). We found that vasostatin could inhibit the cell viability of HUVEC and induce cell apoptosis through mitochondrial pathways via activation of caspase-3 under oxygen deprivation conditions. Meanwhile, vasostatin also inhibited vascular endothelial growth factor-induced proliferation and tube formation of HUVEC. The possible mechanism of vasostatin-inhibited proliferation of HUVEC could be through down-regulation of endothelial nitric oxide synthase. These findings suggest that vasostatin could regulate endothelial cell function and might be used in anti-angiogenesis treatment.

Superparamagnetic iron oxide nanoparticles mediated (131)I-hVEGF siRNA inhibits hepatocellular carcinoma tumor growth in nude mice

Background

Hepatocellular carcinoma (HCC) is a primary liver tumor and is the most difficult human malignancy to treat. In this study, we sought to develop an integrative approach in which real-time tumor monitoring, gene therapy, and internal radiotherapy can be performed simultaneously. This was achieved through targeting HCC with superparamagnetic iron oxide nanoparticles (SPIOs) carrying small interfering RNA with radiolabled iodine 131 (¹³¹I) against the human vascular endothelial growth factor (hVEGF).

Methods

hVEGF siRNA was labeled with ¹³¹I by the Bolton-Hunter method and conjugated to SilenceMag, a type of SPIOs. ¹³¹I-hVEGF siRNA/SilenceMag was then subcutaneously injected into nude mice with HCC tumors exposed to an external magnetic field (EMF). The biodistribution and cytotoxicity of ¹³¹I-hVEGF siRNA/SilenceMag was assessed by SPECT (Single-Photon Emission Computed Tomography) and MRI (Magnetic Resonance Imaging) studies and blood kinetics analysis. The body weight and tumor size of nude mice bearing HCC were measured daily for the 4-week duration of the experiment.

Results

¹³¹I-hVEGF siRNA/SilenceMag was successfully labeled; with a satisfactory radiochemical purity (>80%) and biological activity in vitro. External application of an EMF successfully attracted and retained more ¹³¹I-hVEGF siRNA/SilenceMag in HCC tumors as shown by SPECT, MRI and biodistribution studies. The tumors treated with ¹³¹I-hVEGF siRNA/SilenceMag grew nearly 50% slower in the presence of EMF than those without EMF and the control. Immunohistochemical assay confirmed that the tumor targeted by ¹³¹I-hVEGF siRNA/SilenceMag guided by an EMF had a lower VEGF protein level compared to that without EMF exposure and the control.

Conclusions

EMF-guided ¹³¹I-hVEGF siRNA/SilenceMag exhibited an antitumor effect. The synergic therapy of ¹³¹I-hVEGF siRNA/SilenceMag might be a promising future treatment option against HCC with the dual functional properties of tumor therapy and imaging.

Selective aminopeptidase-N (CD13) inhibitors with relevance to cancer chemotherapy

Aminopeptidase-N (APN/CD13) is highly expressed on the surface of numerous types of cancer cells and particularly on the endothelial cells of neoangiogenic vessels during tumourigenesis. This metallo-aminopeptidase has been identified as a potential target for cancer chemotherapy. In this work, we evaluated the efficacy of a novel series of benzosuberone analogues, which were previously reported to be highly potent, selective APN inhibitors with Ki values in the micromolar to sub-nanomolar range. Endothelial cell morphogenesis as well as cell motility were inhibited in vitro in a dose-dependent manner at concentrations that correlated with the potency of the compounds, thus confirming the key role of APN in these established models of angiogenesis. We report toxicity studies in mice showing that these compounds are well tolerated. We report the effects of the compounds, used alone or in combination with rapamycin, on the growth of a select panel of tumours that were subcutaneously xenografted onto Swiss nude mice. Our data indicate that the in vivo efficacy of these new APN inhibitors during the initial phase of tumour growth can be ascribed to their anti-angiogenic activities. However, we also provide evidence that these compounds are effective against established solid tumours. For colonic tumours, the anti-tumour effect depends on the level of APN expression in epithelial cells, and APN expression is associated with down-regulation of the transcription factor HIF-1α. These effects seem to be distinct from those of rapamycin. Our finding that the anti-tumour effect of the inhibitors in the colon requires APN expression strongly suggests that APN plays a crucial function in tumour cells that is distinct from its known role in neovascularisation.

In vivo evolution of tumor-derived endothelial cells

The growth of a malignant tumor beyond a certain, limited size requires that it first develop an independent blood supply. In addition to providing metabolic support, this neovasculature also allows tumor cells to access the systemic circulation, thus facilitating metastatic dissemination. The neovasculature may originate either from normal blood vessels in close physical proximity to the tumor and/or from the recruitment of bone marrow-derived endothelial cell (EC) precursors. Recent studies have shown that human tumor vasculature ECs may also arise directly from tumor cells themselves and that the two populations have highly similar or identical karyotypes. We now show that, during the course of serial in vivo passage, these tumor-derived ECs (TDECs) progressively acquire more pronounced EC-like properties. These include higher-level expression of EC-specific genes and proteins, a greater capacity for EC-like behavior in vitro, and a markedly enhanced propensity to incorporate into the tumor vasculature. In addition, both vessel density and size are significantly increased in neoplasms derived from mixtures of tumor cells and serially passaged TDECs. A comparison of early- and late-passage TDECs using whole-genome single nucleotide polymorphism profiling showed the latter cells to have apparently evolved by a process of clonal expansion of a population with a distinct pattern of interstitial chromosomal gains and losses affecting a relatively small number of genes. The majority of these have established roles in vascular development, tumor suppression or epithelial-mesenchymal transition. These studies provide direct evidence that TDECs have a strong evolutionary capacity as a result of their inherent genomic instability. Consequently such cells might be capable of escaping anti-angiogenic cancer therapies by generating resistant populations.

Phloroglucinol inhibits the bioactivities of endothelial progenitor cells and suppresses tumor angiogenesis in LLC-tumor-bearing mice

BACKGROUND

There is increasing evidence that phloroglucinol, a compound from Ecklonia cava, induces the apoptosis of cancer cells, eventually suppressing tumor angiogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

This is the first report on phloroglucinol's ability to potentially inhibit the functional bioactivities of endothelial progenitor cells (EPCs) and thereby attenuate tumor growth and angiogenesis in the Lewis lung carcinoma (LLC)-tumor-bearing mouse model. Although Phloroglucinol did not affect their cell toxicity, it specifically inhibited vascular endothelial growth factor (VEGF) dependent migration and capillary-like tube formation of EPCs. Our matrigel plug assay clearly indicated that orally injected phloroglucinol effectively disrupts VEGF-induced neovessel formation. Moreover, we demonstrated that when phloroglucinol is orally administered, it significantly inhibits tumor growth and angiogenesis as well as CD45(-)/CD34(+) progenitor mobilization into peripheral blood in vivo in the LLC-tumor-bearing mouse model.

CONCLUSIONS/SIGNIFICANCE

These results suggest a novel role for Phloroglucinol: Phloroglucinol might be a modulator of circulating EPC bioactivities, eventually suppressing tumorigenesis. Therefore, phloroglucinol might be a candidate compound for biosafe drugs that target tumor angiogenesis.

(99)mTc-(CO)(3) His-annexin A5 micro-SPECT demonstrates increased cell death by irinotecan during the vascular normalization window caused by bevacizumab

Colorectal tumors are dependent on angiogenesis for growth, and vascular endothelial growth factor (VEGF) is a key mediator of tumor angiogenesis. Antiangiogenic drugs can induce a transient normalization of the tumor vasculature with improved delivery of coadministered chemotherapy. The efficacy of antihuman VEGF antibody (bevacizumab) with or without irinotecan was evaluated in a colorectal cancer xenograft using (99m)Tc-(CO)(3) His-annexin A5.

METHODS

Colo205-bearing mice were treated with a single dose of bevacizumab (5 mg/kg) during 2, 4, or 6 d. Microvessel density, pericyte coverage (α-smooth-muscle actin immunostaining), collagen-covered tumor vessels (Masson trichrome staining), and tumor hypoxic fraction (pimonidazole staining) were determined at the 3 different time points after treatment with bevacizumab. To investigate the possible synergistic effects of combination therapy with bevacizumab and irinotecan, Colo205-bearing mice were treated with a single dose of bevacizumab 2, 4, or 6 d before administration of a single dose of irinotecan (100 mg/kg) or 0.9% NaCl. The apoptosis-detecting radiotracer (99m)Tc-(CO)(3) His-annexin A5 was injected (18.5 MBq) in mice 12, 24, and 48 h after the start of the irinotecan or NaCl treatment, and micro-SPECT was subsequently performed 3.5 h after injection of the radiotracer. Results were correlated to histologic analysis for apoptosis (caspase-3 activation).

RESULTS

Four days after bevacizumab administration, microvessel density decreased significantly, and α-smooth-muscle actin and collagen-covered vessels, compared with control tumors, were increased, suggesting normalization of the tumor vasculature. Hypoxic fraction was slightly reduced 4 d after treatment with bevacizumab. SPECT analyses demonstrated a significant increase in tumoral (99m)Tc-(CO)(3) His-annexin A5 uptake 4 d after bevacizumab treatment and 24 h after irinotecan administration (232.78 ± 24.82 percentage injected dose/tumor weight [g]/body weight [kg], P < 0.05), compared with each monotherapy, indicating a synergistic effect of both therapies.

CONCLUSION

(99m)Tc-(CO)(3) His-annexin A5 micro-SPECT demonstrates increased antitumor activity of irinotecan during the transient vascular normalization period caused by bevacizumab. Our data outline the importance of timing of combined anti-VEGF treatment with chemotherapy.

Pleiotropic stromal effects of vascular endothelial growth factor receptor 2 antibody therapy in renal cell carcinoma models

The benefits of inhibiting vascular endothelial growth factor (VEGF) signaling in cancer patients are predominantly attributed to effects on tumor endothelial cells. Targeting non-endothelial stromal cells to further impact tumor cell growth and survival is being pursued through the inhibition of additional growth factor pathways important for the survival and/or proliferation of these cells. However, recent data suggest that VEGF receptor (VEGFR)-specific inhibitors may target lymphatic vessels and pericytes in addition to blood vessels. Here, in fact, we demonstrate that DC101 (40 mg/kg, thrice a week), an antibody specific to murine VEGFR2, significantly reduces all three of these stromal components in subcutaneous (SKRC-29) and orthotopic (786-O-LP) models of renal cell carcinoma (RCC) established in nu/nu athymic mice. Sunitinib (40 mg/kg, once daily), a receptor tyrosine kinase inhibitor of VEGFR2 and other growth factor receptors, also caused significant loss of tumor blood vessels in RCC models but had weaker effects than DC101 on pericytes and lymphatic vessels. In combination, sunitinib did not significantly add to the effects of DC101 on tumor blood vessels, lymphatic vessels, or pericytes. Nevertheless, sunitinib increased the effect of DC101 on tumor burden in the SKRC-29 model, perhaps related to its broader specificity. Our data have important implications for combination therapy design, supporting the conclusion that targeting VEGFR2 alone in RCC has the potential to have pleiotropic effects on tumor stroma.

Prognostic significance of epidermal growth factor receptor and vascular endothelial growth factor receptor in colorectal adenocarcinoma

The purpose of this study was to evaluate the association between the expression of growth factors and the clinicopathological variables of colorectal adenocarcinoma. Immunohistochemistry and fluorescence in situ hybridization (FISH) were used to evaluate the amplification and expression of epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), VEGF-D, VEGF receptor (VEGFR)-2, VEGFR-3, transforming growth factor (TGF)-β1, and insulin-like growth factor-1 receptor (IGF-1R) in a tissue microarray of 292 colorectal adenocarcinomas. The expression of EGFR, VEGF, VEGF-D, VEGFR-2 and VEGFR-3 was detected in 5.1%, 10.0%, 6.8%, 5.2%, and 57.2%. EGFR expression was associated with angioinvasion (p < 0.05) and lymph node metastasis (p < 0.005). VEGFR-3 expression was higher in the rectum than in the colon (p < 0.05). VEGF expression correlated with VEGF-D (p < 0.05) and VEGFR-3 (p < 0.005) expression, while VEGF-D expression showed no significant association with VEGFR-2 or VEGFR-3. EGFR amplification was present in 10.6% and was not associated with EGFR protein expression. VEGFR-2 and VEGFR-3 expression levels were related to poor patient survival. Stage, perineural invasion, and lymph node metastasis were independent prognostic factors based on a Cox analysis. VEGFR-2 and VEGFR-3 expression are markers of a poor prognosis in patients with surgically resected colorectal adenocarcinoma, whereas EGFR has a minor influence.

Dual blockade of phosphatidylinositol 3'-kinase and mitogen-activated protein kinase pathways overcomes paclitaxel-resistance in colorectal cancer

Paclitaxel, one of key drugs to treat a wide range of malignancies, exhibits relative low sensitivity for colorectal cancer. The present study was to examine whether and how phosphatidylinositol 3'-kinase (PI3K) signals affect the sensitivity of colorectal cancer to paclitaxel. Four colorectal cancer cell lines were exposed to paclitaxel in the presence of PI3K signal inhibitors, such as LY294002, siRNA for Akt, or rapamycin, with or without MAPK inhibitor, PD98059. Cell viability and apoptosis were determined by MTT assay, cell cycle analysis in flow cytometer and Hoechst nuclear staining. To analyze the PI3K activity, the expression in phosphorylated Akt and downstream effectors of p70S6 kinase (S6K) were evaluated by Western blot analysis. Paclitaxel alone (5-10 nM) did not induce the apoptosis in all four cell lines. Although LY294002 alone did not affect the cell viability, it suppressed the Akt and S6K activities and induced the sub-G1 arrest/apoptosis when paclitaxel was co-administered, as well as the Akt siRNA and rapamycin did. Simultaneous blockade of PI3K and MAPK pathways more suppressed the S6K activity and further increased the apoptosis. In conclusion, PI3K is involved in low susceptibility of colorectal cancer to paclitaxel and dual PI3K/MAPK targeting agents may evolve a new paclitaxel-based chemotherapy for colorectal cancer.

r84, a novel therapeutic antibody against mouse and human VEGF with potent anti-tumor activity and limited toxicity induction

Vascular endothelial growth factor (VEGF) is critical for physiological and pathological angiogenesis. Within the tumor microenvironment, VEGF functions as an endothelial cell survival factor, permeability factor, mitogen, and chemotactic agent. The majority of these functions are mediated by VEGF-induced activation of VEGF receptor 2 (VEGFR2), a high affinity receptor tyrosine kinase expressed by endothelial cells and other cell types in the tumor microenvironment. VEGF can also ligate other cell surface receptors including VEGFR1 and neuropilin-1 and -2. However, the importance of VEGF-induced activation of these receptors in tumorigenesis is still unclear. We report the development and characterization of r84, a fully human monoclonal antibody that binds human and mouse VEGF and selectively blocks VEGF from interacting with VEGFR2 but does not interfere with VEGF:VEGFR1 interaction. Selective blockade of VEGF binding to VEGFR2 by r84 is shown through ELISA, receptor binding assays, receptor activation assays, and cell-based functional assays. Furthermore, we show that r84 has potent anti-tumor activity and does not alter tissue histology or blood and urine chemistry after chronic high dose therapy in mice. In addition, chronic r84 therapy does not induce elevated blood pressure levels in some models. The ability of r84 to specifically block VEGF:VEGFR2 binding provides a valuable tool for the characterization of VEGF receptor pathway activation during tumor progression and highlights the utility and safety of selective blockade of VEGF-induced VEGFR2 signaling in tumors.

Targeting of VEGF-dependent transendothelial migration of cancer cells by bevacizumab

Cancer progression is often associated with the formation of malignant effusions. Vascular endothelial growth factor (VEGF) is a major regulator of vascular permeability and has been implicated as mediator of tumor progression. We examined the production and secretion of VEGF(165) in various primary cancer cells derived from malignant effusions, and the role of exogenous VEGF(165) as a mediator of effusion formation. VEGF(165) was constantly secreted by all cultured tumor cells in an mTOR-dependent manner, as it was inhibited by the mTOR inhibitor rapamycin. Secreted VEGF(165) showed functional activity by inducing endothelial leakiness and tumor cell-transendothelial migration in vitro, effects which could be reverted by the anti-VEGF antibody bevacizumab. Thus, mTOR inhibitors as well as bevacizumab should be considered as potential agents in cancer patients suffering from malignant effusions.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

In vivo method for establishing synergy between antibodies to epidermal growth factor receptor and vascular endothelial growth factor receptor-2

Targeted therapy for cancer is shifting towards an approach of inhibiting multiple pathways, justified in part by the ability of cancer cells to overcome the inhibition of a single pathway. However the literature is replete with preclinical data supporting the anticancer potential of numerous combinations of targeted agents, making it difficult to select the combination strategies to invest in through clinical development. One characteristic of a combination strategy that can be utilized for prioritization is synergy. Synergy indicates that the effect of the combination is greater than that predicted from the monotherapy potencies. Here we describe a detailed method for establishing synergy between two treatments in vivo. We utilized this method to establish that antibodies targeting the epidermal growth factor receptor and vascular endothelial growth factor receptor-2 are synergistic with regard to antitumor effects, in a BxPC-3 subcutaneous xenograft model for pancreatic cancer.

siRNA targeting VEGF inhibits hepatocellular carcinoma growth and tumor angiogenesis in vivo

BACKGROUND/AIMS

We have investigated whether siRNA targeted against VEGF inhibits functional properties of endothelial cells in vitro and HCC tumor growth and blood vessel formation in vivo.

METHODS

The influence of siRNA-VEGF on endothelial cell proliferation, apoptosis and tube formation were analyzed in vitro. Antitumoral effects were examined in an orthotopic tumor model after ex vivo transfer or intraperitoneal treatment of siRNA, respectively. Intratumoral microvessel density was assessed by CD31 staining.

RESULTS

VEGF expression was inhibited in Hepa129 by 70% and in SVEC4-10 by 48% within two days after transfection. In vitro, endothelial cell proliferation and tube formation was reduced by 23% and 38%, respectively. Interference with VEGF signaling was demonstrated by reduced pAKT in hepatoma cells. Tumor growth was inhibited by ex vivo transfer or intraperitoneal application of siRNA-VEGF by 83% or 63% in orthotopic tumors within 14 days. VEGF protein was reduced in both models by 29% and 44%. Microvessel density dropped to 34% for tumors from ex vivo transfected cells and 39% for systemic treated tumors.

CONCLUSIONS

The results show that VEGF knockdown can be associated with reduced endothelial cell proliferation and tube formation in vitro and decreased tumor growth and microvessel density in vivo.

Bile acids induce overexpression of homeobox gene CDX-2 and vascular endothelial growth factor (VEGF) in human Barrett's esophageal mucosa and adenocarcinoma cell line

OBJECTIVE

Barrett's esophagus (BE) is an acquired precancerous condition that develops from mucosal injury incurred after chronic gastroesophageal acid and bile reflux. The mechanism of progression of carcinogenesis in BE is still not fully understood. Recently, the role of bile acids and the homeobox gene transcription factor CDX-2 has been suggested in the pathogenesis of BE. The aims of the present study were 1) to compare the mRNA and protein expression of CDX-2 in biopsies obtained from patients with BE and normal squamous epithelium and 2) to study the effect of two different bile salts, ursodeoxycholic acid (UDCA) and deoxycholic acid (DCA), on the mRNA expression of CDX-2 and vascular endothelial growth factor (VEGF) in Barrett's the adenocarcinoma cell line (OE-33).

MATERIAL AND METHODS

CDX-2 expression was measured in Barrett's mucosa and normal esophageal mucosa obtained from 15 patients with BE histologically diagnosed by immunohistochemistry, Western blot, and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In in vitro experiments, OE-33 cells were incubated with DCA (100 microM) and UDCA (100 microM) in neutral and shortly acidified media (pulse acidification). The expression of CDX-2 and VEGF was assessed by quantitative RT-PCR.

RESULTS

Both mRNA and protein expression of CDX-2 were significantly up-regulated in Barrett's mucosa as compared to normal esophageal mucosa. In neutral medium, OE-33 cells showed an increase in CDX-2 expression after incubation with DCA or UDCA. After short acidification of the medium, expression of CDX-2 in OE-33 cells was significantly higher than that in cells incubated in neutral pH. The addition of DCA and UDCA did not cause any further alteration in CDX-2 expression. In neutral and acidified medium, VEGF mRNA expression was only significantly up-regulated by DCA, but not by UDCA.

CONCLUSIONS

Bile acids, especially in acidic medium, increase expression of CDX-2. DCA appears to be a stronger stimulant of the expression of VEGF than UDCA in the Barrett's carcinoma cell line, indicating a stronger carcinogenic potential of this bile salt.

Enhancement of therapeutic effectiveness by combining liposomal honokiol with cisplatin in ovarian carcinoma

Honokiol, a well-tolerated natural product, can inhibit the proliferation of cancer cells. But its water insolubility hampers its systemic administration for therapy of cancer. As a drug delivery system, the pegylated liposome (PEGL) can increase the water solubility and targeting of the drug. Honokiol has been successfully encapsulated by PEGL in our laboratory. We wondered whether the combination treatment with pegylated liposomal honokiol (H-PEGL) and cisplatin (DDP) could improve the antitumor efficacy in ovarian carcinoma. H-PEGL could introduce apoptosis of SKOV3 cells in vitro, which was quantified by flow cytometric analysis, and the cellular morphologic changes were determined by propidium iodide staining. In a human ovarian carcinoma mouse model, combination treatment with H-PEGL (0.4 mg/day for 30 days; intraperitoneal) and DDP (5 mg/kg on days 7, 11, 15, 19; intraperitoneal) acted synergistically to inhibit tumor growth by 91.48% without notable toxicity, but H-PEGL and DDP alone only inhibit tumor growth by 66.83% and 52.5% as compared to the NaCl solution control, respectively. Assessment of microvessel density and apoptosis index by CD31 and terminal deoxynucleotidyl transferase-mediated nick end labeling immunohistochemistry respectively suggested that the antitumor activity of H-PEGL is mediated by angiogenesis inhibition and introduction of apoptosis. Our results showed us a splendid prospect of the clinical application of combination treatment on patients suffering from ovarian cancer with H-PEGL and DDP.