Heme oxygenase-1 and its metabolites affect pancreatic tumor growth in vivo

Background  

Pancreatic cancer (PaCa) is a fatal human cancer due to its exceptional resistance to all current anticancer therapies. The cytoprotective enzyme heme oxygenase-1 (HO-1) is significantly overexpressed in PaCa and seems to play an important role in cancer resistance to anticancer treatment. The inhibition of HO-1 sensitized PaCa cells to chemo- and radiotherapy in vitro.     

Loss of BNIP3 expression is a late event in pancreatic cancer contributing to chemoresistance and worsened prognosis

Altered expression of apoptosis-regulating genes plays an important role in the aggressive growth behavior and chemoresistance of pancreatic ductal adenocarcinoma. In the present study, the hypoxia-inducible proapoptotic gene, BNIP3, was analysed in terms of expression, effect on patient survival, and chemo-responsiveness in pancreatic cancer cell lines. cDNA microarray, real-time light cycler quantitative polymerase chain reaction, laser-capture microdissection, and immunohistochemistry analyses were used to evaluate BNIP3 expression in normal and diseased pancreatic specimens. Modulation of BNIP3 expression was achieved using specific siRNA molecules. The effect of chemotherapeutic agents on pancreatic cancer cells was assessed utilizing 3-(4,5-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromide assays. BNIP3 mRNA levels were 3.0- and 6.3-fold lower in chronic pancreatitis and pancreatic cancer compared to the normal pancreas, respectively. Microdissection analysis confirmed the reduction of BNIP3 expression in pancreatic cancer cells compared to normal duct cells. By immunohistochemistry, BNIP3 was predominantly expressed in the acinar cells of the normal and diseased pancreas. Interestingly, while BNIP3 was undetectable in the cancer cells of 59% of the cases, 75-100% of PanIN2/3 lesions displayed BNIP3 immunoreactivity. Loss of BNIP3 expression correlated with poorer survival of patients (8 vs 14 months for BNIP3 negative vs positive tumors). Hypoxia induced BNIP3 expression in four out of eight pancreatic cancer cell lines, while it was absent under normoxic and hypoxic conditions in the remaining four. Downregulation of BNIP3 resulted in increased resistance to 5-fluoro-uracil and gemcitabine. In conclusion, loss of BNIP3 expression occurs late in pancreatic cancer, contributes to resistance to chemotherapy, and correlates with a worsened prognosis.     

Predominant Bcl-XL knockdown disables antiapoptotic mechanisms: tumor necrosis factor-related apoptosis-inducing ligand-based triple chemotherapy overcomes chemoresistance in pancreatic cancer cells in vitro

Pancreatic cancer is lethal because of its invasiveness, rapid progression, and profound resistance to chemotherapy and radiation therapy. To identify the molecular mechanisms underlying this, we have examined the expression and potency of three major death receptors: tumor necrosis factor receptor (TNF-R), TNF-related apoptosis-inducing ligand receptor (TRAIL-R), and Fas in mediating cytotoxicity in four invasive pancreatic cancer cell lines. We have analyzed the expression of major antiapoptotic factors, cell cycle regulators and death receptor decoys (DcR) in comparison with normal pancreas tissues and five other human malignant tumor cell lines. We have found that different pancreatic cancer cell lines coexpress high-level TRAIL-R, Fas, and TNF-R1 but are strongly resistant to apoptosis triggered by the death receptors. DcR2 and DcR3 overexpression may partly contribute to the resistance of pancreatic cancer cells to TRAIL-R- and Fas-mediated cytotoxicity. Bcl-XL and Bcl-2 are predominantly overexpressed in pancreatic cancer cell lines, respectively. Bcl-XL is also predominantly overexpressed in prostate, colorectal, and intestinal cancer cells. The knockdown of the predominant Bcl-XL overexpression significantly reduces the viability of pancreatic cancer cells to TNFalpha- and TRAIL-mediated apoptosis by sublethal-dose single and combined antitumor drugs, including geldanamycin, PS-341, Trichostatin A, and doxorubicine. Geldanamyin and PS-341 synergistically block NFkappaB activation, suppress Akt/PKB pathway, and down-regulate Bcl-XL, Bcl-2, cIAP-1, and cyclin D1 expression. This combined regimen dramatically enhances TRAIL cytotoxic effects and breaks through chemoresistance. Bcl-XL plays a vital role in pancreatic cancer chemoresistance. Geldanamycin, PS-341, and TRAIL triple combination may be a novel therapeutic strategy for pancreatic cancer.     

mda-7 gene transfer sensitizes breast carcinoma cells to chemotherapy, biologic therapies and radiotherapy: correlation with expression of bcl-2 family members

Current therapies used in the treatment of breast cancer are limited by systemic toxicity, rapid drug metabolism and intrinsic and acquired drug resistance. We have previously shown that adenoviral-mediated transfer of the melanoma differentiation-associated gene-7 (mda-7) elicits growth inhibition and apoptosis in various tumor types. Here, we evaluate the effects of Ad-mda7, alone and in combination with other therapies, against a panel of nine breast tumor cell lines and their normal counterparts; we report selective Ad-mda7-mediated p53-independent growth inhibition, G2/M cell cycle arrest, and apoptosis. In vivo, Ad-mda7 induced p53-independent tumor growth inhibition (P<0.004) in multiple xenograft models. We then evaluated the combination of Ad-mda7 with agents commonly used to treat breast cancer: radiotherapy (XRT), Tamoxifen, Taxotere, Adriamycin, and Herceptin. These agents exhibit diverse modes of action, including formation of bulky adducts, inhibition of DNA replication (Adriamycin, XRT), damage to microtubules (Taxotere), nonsteroidal estrogen antagonists (Tamoxifen), or Her2/neu receptor blockade (Herceptin). Treated with conventional anticancer drugs or radiation, MDA-7-expressing cells display additive or synergistic cytotoxicity and apoptosis that correlates with decreased BCL-2 expression and BAX upregulation. In vivo, animals that received Ad-mda7 and XRT underwent significant reduction of tumor growth (P<0.002). This is the first report of the synergistic effects of Ad-mda7 combined with chemotherapy or radiotherapy on human breast carcinoma cells.     

CNT1 expression influences proliferation and chemosensitivity in drug-resistant pancreatic cancer cells

Overcoming the inherent chemoresistance of pancreatic cancers remains a major goal of therapeutic investigations in this disease. In this study, we discovered a role for the human concentrative nucleoside transporter-1 (hCNT1; SLC28A1), a high-affinity pyrimidine nucleoside transporter, in determining the chemosensitivity of human pancreatic cancer cells to gemcitabine, the drug used presently as a standard of care. Compared with normal pancreas and pancreatic ductal epithelial cells, hCNT1 expression was frequently reduced in pancreatic tumors and tumor cell lines. In addition, hCNT1-mediated (3)H-gemcitabine transport was lower in pancreatic cancer cell lines and correlated with cytotoxic IC(50) estimations of gemcitabine. In contrast to gemcitabine-sensitive pancreatic cancer cell lines, MIA PaCa-2, a gemcitabine-resistant pancreatic cancer cell line, exhibited relatively restrictive, cell cycle-dependent hCNT1 expression and transport. hCNT1 translation was suppressed in the late G1-enriched MIA PaCa-2 cell population possibly in an miRNA-dependent manner, which corresponded with the lowest hCNT1-mediated gemcitabine transport during this phase. Although hCNT1 protein was induced during G1/S transition, increased hCNT1 trafficking resulted in maximal cell surface recruitment and transport-overshoot in the G2/M phase-enriched cell population. hCNT1 protein was directed predominantly to proteasomal or lysosomal degradation in S or G2/M phase MIA PaCa-2 cells, respectively. Pharmacological inhibition of hCNT1 degradation moderately increased cell surface hCNT1 expression and cellular gemcitabine transport in MIA PaCa-2 cells. Constitutive hCNT1 expression reduced clonogenic survival of MIA PaCa-2 cells and steeply augmented gemcitabine transport and chemosensitization. In addition to supporting a putative tumor suppressor role for hCNT1, our findings identify hCNT1 as a potential candidate to render drug-resistant pancreatic cancer cells amenable to chemotherapy.     

Inhibition of constitutive NF-kappa B activity by I kappa B alpha M suppresses tumorigenesis

We have demonstrated that nuclear factor-kappa B (NF-kappa B) is constitutively activated in human pancreatic adenocarcinoma and human pancreatic cancer cell lines but not in normal pancreatic tissues or in immortalized, nontumorigenic pancreatic epithelial cells, suggesting that NF-kappa B plays a critical role in the development of pancreatic adenocarcinoma. To elucidate the role of constitutive NF-kappa B activity in human pancreatic cancer cells, we generated pancreatic tumor cell lines that express a phosphorylation defective I kappa B alpha (S32, 36A) (I kappa B alpha M) that blocks NF-kappa B activity. In this study, we showed that inhibiting constitutive NF-kappa B activity by expressing I kappa B alpha M suppressed the tumorigenicity of a nonmetastatic human pancreatic cancer cell line, PANC-1, in an orthotopic nude mouse model. Immunohistochemical analysis showed that PANC-1-derived tumors expressed vascular endothelial growth factor (VEGF) and induced angiogenesis. Inhibiting NF-kappa B signaling by expressing I kappa B alpha M significantly reduced expression of Bcl-x(L) and Bcl-2. The cytokine-induced expression of VEGF and Interleukin-8 in PANC-1 cells is also decreased. Taken together, these results suggest that the inhibition of NF-kappa B signaling can suppress tumorigenesis of pancreatic cancer cells and that the NF-kappa B signaling pathway is a potential target for anticancer agents.     

Loss of methylthioadenosine phosphorylase and elevated ornithine decarboxylase is common in pancreatic cancer.

PURPOSE: Loss of the methylthioadenosine phosphorylase (MTAP) gene at 9p21 is observed frequently in a variety of human cancers. We have shown previously that MTAP can act as a tumor suppressor gene and that its tumor suppressor function is related to its effect on polyamine homeostasis. Ornithine decarboxylase is a key enzyme in the regulation of polyamine metabolism. The aim of this study is to analyze MTAP and ornithine decarboxylase (ODC) expression in primary pancreatic tumor specimens. EXPERIMENTAL DESIGN: We measured MTAP and ODC activity in protein extracts derived from 30 surgically resected tumor samples and eight normal pancreas samples. In a subset of six samples, we also examined MTAP DNA using interphase fluorescence in situ hybridization. In addition, we examined the effect of the ODC inhibitor difluoromethylornithine on two pancreatic adenocarcinoma-derived cell lines. Result: MTAP activity was 2.8-fold reduced in adenocarcinomas and 6.3-fold reduced in neuroendocrine tumors compared with control pancreas. Conversely, ODC activity was 3.6-fold elevated in adenocarcinomas and 3.9-fold elevated in neuroendocrine tumors compared with control pancreas. Using interphase fluorescence in situ hybridization, we found in tumor samples that 43 to 75% of the nuclei had lost at least one copy of MTAP locus, indicating that loss of MTAP activity was at least partially because of deletion of the MTAP locus. We also show that inhibition of ODC by difluoromethylornithine caused decreased cell growth and increased apoptosis in two MTAP-deleted pancreatic adenocarcinoma-derived cell lines. CONCLUSIONS: MTAP activity is frequently lost, and ODC activity is frequently elevated in both pancreatic adenocarcinoma and neuroendocrine tumors. Inhibition of ODC activity caused decreased cell growth and increased apoptosis in pancreatic tumor-derived cell lines. These findings suggest that MTAP and polyamine metabolism could be potential therapeutic targets in the treatment of pancreatic cancer.     

In vivo selection and characterization of metastatic variants from human pancreatic adenocarcinoma by using orthotopic implantation in nude mice

We determined whether the implantation of human pancreatic cancer cells into the pancreas of nude mice can be used to select variants with increasing metastatic potential. COLO 357 line fast-growing cells were injected into the spleen or pancreas of nude mice. Hepatic metastases were harvested, and tumor cells were reinjected into the spleen or pancreas. This cycle was repeated several times to yield cell lines L3.6sl (spleen to liver) and L3.6pl (pancreas to liver). The variant cells produced significantly higher incidence and number of lymph node and liver metastases than the parental cells. Their increased metastatic potential was associated with increased expression (mRNA and protein) of the proangiogenic molecules basic fibroblast growth factor, vascular endothelial growth factor, and interleukin-8. The metastatic cells also exhibited increased motility and invasiveness, which were associated with increased expression of collagenase type IV (MMP-9) and decreased expression of E-cadherin. Collectively, the data show that the orthotopic implantation of human pancreatic cancer cells in nude mice is a relevant model with which to study the biology of pancreatic cancer metastasis and to select variant cell lines with enhanced metastatic potential.     

Targeted delivery of gemcitabine to pancreatic adenocarcinoma using cetuximab as a targeting agent

One of the key challenges in anticancer therapy is the toxicity and poor bioavailability of the anticancer drugs. Nanotechnology can play a pivotal role by delivering drugs in a targeted fashion to the malignant cells that will reduce the systemic toxicity of the anticancer drug. In this report, we show a stepwise development of a nanoparticle-based targeted delivery system for in vitro and in vivo therapeutic application in pancreatic cancer. In the first part of the study, we have shown the fabrication and characterization of the delivery system containing gold nanoparticle as a delivery vehicle, cetuximab as a targeting agent, and gemcitabine as an anticancer drug for in vitro application. Nanoconjugate was first characterized physico-chemically. In vitro targeting efficacy, tested against three pancreatic cancer cell lines (PANC-1, AsPC-1, and MIA Paca2) with variable epidermal growth factor receptor (EGFR) expression, showed that gold uptake correlated with EGFR expression. In the second part, we showed the in vivo therapeutic efficacy of the targeted delivery system. Administration of this targeted delivery system resulted in significant inhibition of pancreatic tumor cell proliferation in vitro and orthotopic pancreatic tumor growth in vivo. Tumor progression was monitored noninvasively by measuring bioluminescence of the implanted tumor cells. Pharmacokinetic experiments along with the quantitation of gold both in vitro and in vivo further confirmed that the inhibition of tumor growth was due to targeted delivery. This strategy could be used as a generalized approach for the treatment of a variety of cancers characterized by overexpression of EGFR.     

Synergistic antipancreatic tumor effect by simultaneously targeting hypoxic cancer cells with HSP90 inhibitor and glycolysis inhibitor.

PURPOSE: We sought to examine the synergistic antipancreatic cancer effect by simultaneously targeting hypoxic cancer cells with heat-shock protein 90 (HSP90) inhibitor and blockade of energy production. EXPERIMENTAL DESIGN: The anticancer effects of an HSP90 inhibitor (geldanamycin) in pancreatic cells were investigated in hypoxia and normoxia. A hexokinase II inhibitor, 3-broma-pyruvate (3BrPA), was evaluated for selective glycolysis inhibition in hypoxia as a sensitizer of HSP90 inhibitor against pancreatic cancer. The HSP90 client protein degradation was monitored by Western blot. The synergistic antitumor effect of geldanamycin and 3BrPA was evaluated in a xenograft pancreatic cancer model and monitored by a noninvasive dynamic contrast-enhanced magnetic resonance imaging. RESULTS: Hypoxia enhanced HIF-1alpha expression by 11-fold in pancreatic cancer cells, and HSP90 inhibitor exhibited a seven- to eightfold higher anticancer effect in hypoxia compared with normoxia via HSP90 client protein degradation. 3BrPA selectively inhibited glycolysis and sensitized geldanamycin against pancreatic cancer cells by 17- to 400-fold through HSP90 client protein degradation. The synergistic anticancer effect of reduced doses of geldanamycin and 3-BrPA was confirmed in xenograft models in vivo by more than 75% tumor growth inhibition. CONCLUSIONS: The combination of HSP90 inhibitors and glycolysis inhibitors provides preferential inhibition of cancer cells in hypoxia through HSP90 client protein degradation and selective glycolysis inhibition. This may provide a new therapeutic regimen to battle chemotherapy-resistant pancreatic cancers, by enhancing the synergistic therapeutic efficacy and reducing dose-limiting toxicity.     

HERG1 functions as an oncogene in pancreatic cancer and is downregulated by miR-96

Pancreatic cancer is an aggressive malignancy with an extremely poor prognosis. The human ether-a-go-go-related potassium channel (HERG1) is a human rapid delayed rectifier, which is involved in many crucial cellular events. In this article, we find that HERG1 expression is dramatically increased both in pancreatic cancer tissues and cell lines, and that increased HERG1 expression is significantly related to the development of pancreatic cancer. HERG1 silencing in pancreatic cancer-derived cell lines PANC-1 and CFPAC-1 strongly inhibits their malignant capacity in vitro as well as tumorigenicity and metastasis in nude mice. In addition, HERG1 is identified as a direct target of miR-96, which is downregulated in pancreatic cancer tissues and cell lines. Ectopic expression of miR-96 represses the HERG1 expression in pancreatic cancer and significantly inhibits malignant behavior of pancreatic cancer cells in vitro and in vivo.Collectively, our findings suggest that miR-96 acts as a tumor suppressor in pancreatic cancer and may therefore serve as a useful therapeutic target for the development of new anticancer therapy.     

Syndecan-1 expression is up-regulated in pancreatic but not in other gastrointestinal cancers

Syndecan-1 belongs to the syndecan family of cell surface transmembrane heparan-sulfate proteoglycans, which participate in cell proliferation, cell migration and cell-matrix interactions. Decreased expression of syndecan-1 has been observed in some gastrointestinal malignancies, and it is thought that high levels of syndecan-1 correlate with the maintenance of epithelial morphology and inhibition of invasiveness. In our study, we characterized the expression of syndecan-1 in normal, chronic pancreatitis and primary and metastatic human pancreatic cancer tissues, in cultured pancreatic cancer cell lines and in esophageal, gastric, colon, and liver cancers. Pancreatic cancer cell lines expressed syndecan-1 mRNA and protein at variable levels. In addition, these cells also released syndecan-1 into the culture medium. Pancreatic cancer tissues markedly over-expressed syndecan-1 mRNA in comparison with both chronic pancreatitis (2.4-fold increase, p < 0.01) and normal pancreatic samples (10.6-fold increase, p < 0.01). There was no difference in syndecan-1 mRNA expression between early and advanced tumors. By in situ hybridization and immunohistochemistry, syndecan-1 expression was evident at relatively low levels in the ductal cells and less frequently in acinar cells of the normal pancreas. In chronic pancreatitis, syndecan-1 was present at low to moderate levels in areas with atrophic acinar cells and ductular complexes. In contrast, in pancreatic cancer tissues, syndecan-1 was present at moderate to high levels in the majority of the cancer cells within the tumor mass and also in metastatic lesions of pancreatic tumors. Syndecan-1 mRNA levels in other gastrointestinal malignancies (esophageal, gastric, colon and liver cancers) were not significantly different from the levels observed in the corresponding normal samples. Together, our findings suggest that syndecan-1 expression by pancreatic cancer cells may be of importance in the pathobiology of this disorder and that its role in pancreatic cancer seems to be different from that in other gastrointestinal malignancies.     

紫杉醇作用卵巢癌细胞系HO-8910后CYP1B1 mRNA及蛋白表达差异的研究

背景与目的:用紫杉醇(paclitaxel,PTX)对卵巢癌细胞系HO-8910进行体外化疗后,观察CYP1B1表达的变化,以期探讨CYP1B1基因表达与肿瘤细胞耐药的关系. 材料与方法:以不同浓度PTX(分别为30、15、7.5、3.75、1.88、0.94、0.47 μg/mi)处理H0-8910细胞.采用四甲基偶氮唑蓝(MTT)比色法检测PTX对HO-8910细胞体外生长的抑制作用,实验同时设只加培养液的对照组.以5 μg/ml PTX分别处理HO-8910细胞24 h、48 h、72 h和50#g/ml PTX处理细胞24 h后,用RT-PCR技术检测存活的卵巢癌细胞中CYP1B1 mRNA的表达水平,用Western blot检测细胞CYP1B1蛋白表达.结果:PTX能抑制HO-8910细胞生长,7种不同浓度的PTX作用72 h后,细胞的抑制率分别为89.10%、76.82%、67.39%、57.27%、46.21%、37.02%、17.56%,随着药物浓度的下降,其抑制率明显降低,各浓度组细胞抑制率间的差异具有统计学意义(P<0.05).经PTX处理后存活的HO-8910细胞中CYP1B1 mRNA及蛋白的表达量增加,高于对照组;5 μg/ml PTX处理HO-8910细胞48 h、72 h和50 μg/ml的PTX处理24 h组,CYP1B1蛋白的表达量高于5 μg/ml PTX处理24 h组(P<0.05).结论:CYP1B1在卵巢癌细胞系中呈高表达,CYP1B1基因在卵巢癌细胞系H0-8910体外PTX化疗中起抑制作用.     

HMGA-targeted phosphorothioate DNA aptamers increase sensitivity to gemcitabine chemotherapy in human pancreatic cancer cell lines

Elevated high mobility group A (HMGA) protein expression in pancreatic cancer cells is correlated with resistance to the chemotherapy agent gemcitabine. Here, we demonstrate use of HMGA-targeted AT-rich phosphorothioate DNA (AT-sDNA) aptamers to suppress HMGA carcinogenic activity. Cell growth of human pancreatic cancer cells (AsPC-1 and Miapaca-2) transfected with AT-sDNA were monitored after treatment with gemcitabine. Significant increases in cell death in AT-sDNA transfected cells compared to non-AT-rich sDNA treated cells were observed in both cell lines. The data indicate the potential use of HMGA targeted DNA aptamers to enhance chemotherapy efficacy in pancreatic cancer treatment.     

Anticancer Effects of the Nitric Oxide-Modified Saquinavir Derivative Saquinavir-NO against Multidrug-Resistant Cancer Cells

The human immunodeficiency virus (HIV) protease inhibitor saquinavir shows anticancer activity. Although its nitric oxide-modified derivative saquinavir-NO (saq-NO) was less toxic to normal cells, it exerted stronger inhibition of B16 melanoma growth in syngeneic C57BL/6 mice than saquinavir did. Saq-NO has been shown to block proliferation, upregulate p53 expression, and promote differentiation of C6 glioma and B16 cells. The anticancer activity of substances is frequently hampered by cancer cell chemoresistance mechanisms. Therefore, we here investigated the roles of p53 and the ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), and breast cancer resistance protein 1 (BCRP1) in cancer cell sensitivity to saq-NO to get more information about the potential of saq-NO as anticancer drug. Saq-NO exerted anticancer effects in lower concentrations than saquinavir in a panel of human cancer cell lines. Neither p53 mutation or depletion nor expression of P-gp, MRP1, or BCRP1 affected anticancer activity of saq-NO or saquinavir. Moreover, saq-NO sensitized P-gp-, MRP1-, or BCRP1-expressing cancer cells to chemotherapy. Saq-NO induced enhanced sensitization of P-gp- or MRP1-expressing cancer cells to chemotherapy compared with saquinavir, whereas both substances similarly sensitized BCRP1-expressing cells. Washout kinetics and ABC transporter ATPase activities demonstrated that saq-NO is a substrate of P-gp as well as of MRP1. These data support the further investigation of saq-NO as an anticancer drug, especially in multidrug-resistant tumors.     

Cooperative antitumor effect of multitargeted kinase inhibitor ZD6474 and ionizing radiation in glioblastoma.

PURPOSE: Glioblastoma multiforme is an aggressive disease in which vascular endothelial growth factor (VEGF) and the EGF receptor (EGFR) are implicated in tumor growth, relapse, and resistance to radiotherapy and chemotherapy. The VEGF receptors VEGFR-1 (flt-1) and VEGFR-2 (KDR), typically present on endothelial cells, have also been identified in human glioblastoma tissues and cell lines. In addition, EGFR is dysregulated in the majority of human glioblastomas and EGFR overexpression correlates with shorter survival. We have investigated the antitumor and antiangiogenic effect of ZD6474, an inhibitor of both VEGFR and EGFR signaling as a single agent and in combination with ionizing radiation. EXPERIMENTAL DESIGN: We have used ZD6474 and/or ionizing radiation in human glioblastoma cell lines D54 and U251 in vitro and in nude mice bearing established xenografts. The effects of treatment on tumor blood vessels and protein expression were evaluated by Western blot and immunohistochemistry. RESULTS: As single agents, ionizing radiation and ZD6474 caused a dose-dependent inhibition of soft agar growth in D54 and U251 cell lines, whereas a cooperative effect was obtained in combination. Treatment of mice bearing D54 xenografts with either ZD6474 or radiotherapy alone caused tumor growth inhibition that was reversible upon treatment cessation. A cooperative and long-lasting inhibition of tumor growth was obtained with ZD6474 in combination with concomitant radiotherapy. The antiproliferative effect was accompanied by inhibition of VEGF protein expression and inhibition of angiogenesis as measured by vessel counting. CONCLUSION: This study shows the antitumor activity of ZD6474 in combination with ionizing radiation in glioblastoma both in vitro and in vivo, and provides a scientific rationale to evaluate ZD6474 alone or in combination with radiotherapy in patients affected by this disease.