Radiation-enhanced vascular endothelial growth factor (VEGF) secretion in glioblastoma multiforme cell lines--a clue to radioresistance?

Radiation Therapy for Gestational Trophoblastic Neoplasia: Forward-Looking Lessons Learnt

Gestational trophoblastic neoplasia (GTN) includes several rare malignant diseases occurring after pregnancy: invasive moles, choriocarcinoma, placental site trophoblastic tumours, and epithelioid trophoblastic tumours. Multidisciplinary protocols including multi-agent chemotherapy, surgery, and occasionally radiotherapy achieve good outcomes for some high-risk metastatic patients. In this narrative review of the published studies on the topic, we have tried to identify the role of radiotherapy. The available studies are mainly small, old, and retrospective, with incomplete data regarding radiotherapy protocols delivering low doses (which can make this disease appear radioresistant in some cases despite high response rates with palliative doses) to wide fields (whole-brain, whole-liver, etc.), which can increase toxicity. Studies considering modern techniques are needed to overcome these limitations and determine the full potential of radiotherapy beyond its antihemorrhagic and palliative roles.

Mechanistic rationales for combining immunotherapy with radiotherapy

Immunotherapy consisted mainly of immune checkpoint inhibitors (ICIs) has led to significantly improved antitumor response. However, such response has been observed only in tumors possessing an overall responsive tumor immune micro-environment (TIME), in which the presence of functional tumor-infiltrating lymphocytes (TILs) is critical. Various mechanisms of immune escape from immunosurveillance exist, leading to different TIME phenotypes in correlation with primary or acquired resistance to ICIs. Radiotherapy has been shown to induce antitumor immunity not only in the irradiated primary tumor, but also at unirradiated distant sites of metastases. Such antitumor immunity is mainly elicited by radiation's stimulatory effects on antigenicity and adjuvanticity. Furthermore, it may be significantly augmented when irradiation is combined with immunotherapy, such as ICIs. Therefore, radiotherapy represents one potential therapeutic strategy to restore anti-tumor immunity in tumors presenting with an unresponsive TIME. In this review, the generation of anti-tumor immunity, its impairment, radiation's immunogenic properties, and the antitumor effects of combining radiation with immunotherapy will be comprehensively discussed.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

Diffusing alpha-emitters radiation therapy in combination with temozolomide or bevacizumab in human glioblastoma multiforme xenografts

Glioblastoma multiforme (GBM) is at present an incurable disease with a 5-year survival rate of 5.5%, despite improvements in treatment modalities such as surgery, radiation therapy, chemotherapy [e.g., temozolomide (TMZ)], and targeted therapy [e.g., the antiangiogenic agent bevacizumab (BEV)]. Diffusing alpha-emitters radiation therapy (DaRT) is a new modality that employs radium-224-loaded seeds that disperse alpha-emitting atoms inside the tumor. This treatment was shown to be effective in mice bearing human-derived GBM tumors. Here, the effect of DaRT in combination with standard-of-care therapies such as TMZ or BEV was investigated. In a viability assay, the combination of alpha radiation with TMZ doubled the cytotoxic effect of each of the treatments alone in U87 cultured cells. A colony formation assay demonstrated that the surviving fraction of U87 cells treated by TMZ in combination with alpha irradiation was lower than was achieved by alpha- or x-ray irradiation as monotherapies, or by x-ray combined with TMZ. The treatment of U87-bearing mice with DaRT and TMZ delayed tumor development more than the monotherapies. Unlike other radiation types, alpha radiation did not increase VEGF secretion from U87 cells in culture. BEV treatment introduced several days after DaRT implantation improved tumor control, compared to BEV or DaRT as monotherapies. The combination was also shown to be superior when starting BEV administration prior to DaRT implantation in large tumors relative to the seed size. BEV induced a decrease in CD31 staining under DaRT treatment, increased the diffusive spread of 224Ra progeny atoms in the tumor tissue, and decreased their clearance from the tumor through the blood. Taken together, the combinations of DaRT with standard-of-care chemotherapy or antiangiogenic therapy are promising approaches, which may improve the treatment of GBM patients.

Breaking barriers: Neurodegenerative repercussions of radiotherapy induced damage on the blood-brain and blood-tumor barrier

Exposure to radiation during the treatment of CNS tumors leads to detrimental damage of the blood brain barrier (BBB) in normal tissue. Effects are characterized by leakage of the vasculature which exposes the brain to a host of neurotoxic agents potentially leading to white matter necrosis, parenchymal calcification, and an increased chance of stroke. Vasculature of the blood tumor barrier (BTB) is irregular leading to poorly perfused and hypoxic tissue throughout the tumor that becomes resistant to radiation. While current clinical applications of cranial radiotherapy use dose fractionation to reduce normal tissue damage, these treatments still cause significant alterations to the cells that make up the neurovascular unit of the BBB and BTB. Damage to the vasculature manifests as reduction in tight junction proteins, alterations to membrane transporters, impaired cell signaling, apoptosis, and cellular senescence. While radiotherapy treatments are detrimental to normal tissue, adapting combined strategies with radiation targeted to damage the BTB could aid in drug delivery. Understanding differences between the BBB and the BTB may provide valuable insight allowing clinicians to improve treatment outcomes. Leveraging this information should allow advances in the development of therapeutic modalities that will protect the normal tissue while simultaneously improving CNS tumor treatments.

Gamma irradiation exposure for collapsed cell junctions and reduced angiogenesis of 3-D in vitro blood vessels

During radiotherapy, microenvironments neighboring the tumor are also exposed to gamma irradiation; this results in unexpected side effects. Blood vessels can serve as microenvironments for tumors and they play an important role in providing nutrients to tumors. This is mostly related to tumor progression, metastasis, and relapse after therapy. Many studies have been performed to obtain a better understanding of tumor vasculature after radiotherapy with in vitro models. However, compared to 3-D models, 2-D in vitro endothelial monolayers cannot physiologically reflect in vivo blood vessels. We previously remodeled the extracellular matrix (ECM) hydrogel that enhanced the tight barrier formation of 3-D blood vessels and the vascular endothelial growth factor (VEGF) gradient induced angiogenesis in a microfluidic device. In this study, the blood vessel model is further introduced to understand how gamma irradiation affects the endothelial monolayer. After the gamma irradiation exposure, we observed a collapsed endothelial barrier and a reduced angiogenic potential. Changes in the cell behaviors of the tip and stalk cells were also detected in the angiogenesis model after irradiation, which is difficult to observe in 2-D monolayer models. Therefore, the 3-D in vitro blood vessel model can be used to understand radiation-induced endothelial injuries.

Modulation of VEGF Expression and Oxidative Stress Response by Iodine Deficiency in Irradiated Cancerous and Non-Cancerous Breast Cells

Breast cancer remains a major concern and its physiopathology is influenced by iodine deficiency (ID) and radiation exposure. Since radiation and ID can separately induce oxidative stress (OS) and microvascular responses in breast, their combination could additively increase these responses. Therefore, ID was induced in MCF7 and MCF12A breast cell lines by medium change. Cells were then X-irradiated with doses of 0.05, 0.1, or 3 Gy. In MCF12A cells, both ID and radiation (0.1 and 3 Gy) increased OS and vascular endothelial growth factor (VEGF) expression, with an additive effect when the highest dose was combined with ID. However, in MCF7 cells no additive effect was observed. VEGF mRNA up-regulation was reactive oxygen species (ROS)-dependent, involving radiation-induced mitochondrial ROS. Results on total VEGF mRNA hold true for the pro-angiogenic isoform VEGF165 mRNA, but the treatments did not modulate the anti-angiogenic isoform VEGF165b. Radiation-induced antioxidant response was differentially regulated upon ID in both cell lines. Thus, radiation response is modulated according to iodine status and cell type and can lead to additive effects on ROS and VEGF. As these are often involved in cancer initiation and progression, we believe that iodine status should be taken into account in radiation prevention policies.

Chemotherapeutic Stress Induces Transdifferentiation of Glioblastoma Cells to Endothelial Cells and Promotes Vascular Mimicry

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor affecting adults, with a median survival of approximately 21 months. One key factor underlying the limited efficacy of current treatment modalities is the remarkable plasticity exhibited by GBM cells, which allows them to effectively adapt to changes induced by anticancer therapeutics. Moreover, GBM tumors are highly vascularized with aberrant vessels that complicate the delivery of antitumor agents. Recent research has demonstrated that GBM cells have the ability to transdifferentiate into endothelial cells (ECs), illustrating that GBM cells may use plasticity in concert with vascularization leading to the creation of tumor-derived blood vessels. The mechanism behind this transdifferentiation, however, remains unclear. Here, we show that treatment with temozolomide (TMZ) chemotherapy induces time-dependent expression of markers for glioma stem cells (GSCs) and immature and mature ECs. In addition, GBM tumors growing as orthotopic xenografts in nude mice showed increased expression of GSC and EC markers after TMZ treatment. Ex vivo FACS analysis showed the presence of immature and mature EC populations. Furthermore, immunofluorescence analysis revealed increased tumor-derived vessels in TMZ-recurrent tumors. Overall, this study identifies chemotherapeutic stress as a new driver of transdifferentiation of tumor cells to endothelial cells and highlights cellular plasticity as a key player in therapeutic resistance and tumor recurrence.

Axitinib exposure triggers endothelial cells senescence through ROS accumulation and ATM activation

Inhibitors of Vascular Endothelial Growth Factor target both tumor vasculature and cancer cells that have hijacked VEGF Receptors (VEGFRs) signaling for tumor growth-promoting activities. It is important to get precise insight in the specificity of cell responses to these antiangiogenic drugs to maximize their efficiency and minimize off-target systemic toxicity. Here we report that Axitinib, an inhibitor of VEGFRs currently in use as a second line treatment for advanced renal cell carcinoma, promotes senescence of human endothelial cells in vitro. A one-hour pulse of Axitinib is sufficient for triggering cell senescence. Mechanistically, this requires oxidative stress-dependent activation of the Ataxia Telangiectasia Mutated (ATM) kinase. Axitinib-mediated senescence promoting action is prevented by short-term treatment with antioxidants or ATM inhibitors, which conversely fail to prevent senescence induced by the DNA-damaging drug doxorubicin. Coherently, induction of oxidative stress-related genes distinguishes the response of endothelial cells to Axitinib from that to doxorubicin. Importantly, an Axitinib pulse causes cell senescence in glioblastoma cells. However, neither antioxidants nor ATM inhibitors can reverse this phenotype. Thus, antioxidants may selectively protect endothelial cells from Axitinib by decreasing systemic toxicity and maintaining a functional vascularization necessary for efficient delivery of chemotherapeutic drugs within the tumor mass.

Endothelial Microparticles and Vascular Endothelial Growth Factor in Patients With Head and Neck Cancer Undergoing Radiotherapy or Radiochemotherapy

BACKGROUND

Endothelial microparticles (EMPs) released from activated or apoptotic endothelial cells may play a role in coagulation and thrombus formation. However, there is insufficient evidence regarding the impact of EMPs on angiogenesis in patients with cancer.

MATERIALS AND METHODS

Sixteen patients with head and neck cancer (HNC) undergoing radiotherapy/radiochemotherapy (RT/RCT) and 10 healthy controls were studied. Serum EMPs were counted by flow cytometry, and vascular endothelial growth factor (VEGF) was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The mean EMP level was significantly higher in patients with HNC before RT/RCT (1,601±1,479 EMP/μl) compared to the control group (782±698 EMP/μl). The number of EMPs was not notably increased after RT/RCT (1,629±769 EMP/μl). There was no significant correlation between the plasma EMP number and concentration of VEGF before (r=0.131; p=0.625), 1 day after (r=-0.042, p=0.874), nor 3 months after RT/RCT (r=0.454, p=0.076).

CONCLUSION

Released EMPs may not influence promotion of neovascularization in patients with HNC.

Glioblastoma's Next Top Model: Novel Culture Systems for Brain Cancer Radiotherapy Research

Glioblastoma (GBM), the most common and aggressive primary brain tumor in adults, remains one of the least treatable cancers. Current standard of care—combining surgical resection, radiation, and alkylating chemotherapy—results in a median survival of only 15 months. Despite decades of investment and research into the development of new therapies, most candidate anti-glioma compounds fail to translate into effective treatments in clinical trials. One key issue underlying this failure of therapies that work in pre-clinical models to generate meaningful improvement in human patients is the profound mismatch between drug discovery systems—cell cultures and mouse models—and the actual tumors they are supposed to imitate. Indeed, current strategies that evaluate the effects of novel treatments on GBM cells in vitro fail to account for a wide range of factors known to influence tumor growth. These include secreted factors, the brain’s unique extracellular matrix, circulatory structures, the presence of non-tumor brain cells, and nutrient sources available for tumor metabolism. While mouse models provide a more realistic testing ground for potential therapies, they still fail to account for the full complexity of tumor-microenvironment interactions, as well as the role of the immune system. Based on the limitations of current models, researchers have begun to develop and implement novel culture systems that better recapitulate the complex reality of brain tumors growing in situ. A rise in the use of patient derived cells, creative combinations of added growth factors and supplements, may provide a more effective proving ground for the development of novel therapies. This review will summarize and analyze these exciting developments in 3D culturing systems. Special attention will be paid to how they enhance the design and identification of compounds that increase the efficacy of radiotherapy, a bedrock of GBM treatment.

Quantitative imaging of pO2 in orthotopic murine gliomas: hypoxia correlates with resistance to radiation

Hypoxia is considered one of the microenvironmental factors associated with the malignant nature of glioblastoma. Thus, evaluating intratumoural distribution of hypoxia would be useful for therapeutic planning as well as assessment of its effectiveness during the therapy. Electron paramagnetic resonance imaging (EPRI) is an imaging technique which can generate quantitative maps of oxygen in vivo using the exogenous paramagnetic compound, triarylmethyl and monitoring its line broadening caused by oxygen. In this study, the feasibility of EPRI for assessment of oxygen distribution in the glioblastoma using orthotopic U87 and U251 xenograft model is examined. Heterogeneous distribution of pO₂ between 0 and 50 mmHg was observed throughout the tumours except for the normal brain tissue. U251 glioblastoma was more likely to exhibit hypoxia than U87 for comparable tumour size (median pO₂; 29.7 and 18.2 mmHg, p = .028, in U87 and U251, respectively). The area with pO₂ under 10 mmHg on the EPR oximetry (HF10) showed a good correlation with pimonidazole staining among tumours with evaluated size. In subcutaneous xenograft model, irradiation was relatively less effective for U251 compared with U87. In conclusion, EPRI is a feasible method to evaluate oxygen distribution in the brain tumour.

Role of ADAM17 in invasion and migration of CD133-expressing liver cancer stem cells after irradiation

We investigated the biological role of CD133-expressing liver cancer stem cells (CSCs) enriched after irradiation of Huh7 cells in cell invasion and migration. We also explored whether a disintegrin and metalloproteinase-17 (ADAM17) influences the metastatic potential of CSC-enriched hepatocellular carcinoma (HCC) cells after irradiation. A CD133-expressing Huh7 cell subpopulation showed greater resistance to sublethal irradiation and specifically enhanced cell invasion and migration capabilities. We also demonstrated that the radiation-induced MMP-2 and MMP-9 enzyme activities as well as the secretion of vascular endothelial growth factor were increased more predominantly in Huh7^CD133+ cell subpopulations than Huh7^CD133− cell subpopulations. Furthermore, we showed that silencing ADAM17 significantly inhibited the migration and invasiveness of enriched Huh7^CD133+ cells after irradiation; moreover, Notch signaling was significantly reduced in irradiated CD133-expressing liver CSCs following stable knockdown of the ADAM17 gene. In conclusion, our findings indicate that CD133-expressing liver CSCs have considerable metastatic capabilities after irradiation of HCC cells, and their metastatic capabilities might be maintained by ADAM17. Therefore, suppression of ADAM17 shows promise for improving the efficiency of current radiotherapies and reducing the metastatic potential of liver CSCs during HCC treatment.

Role of ADAM17 in invasion and migration of CD133-expressing liver cancer stem cells after irradiation

We investigated the biological role of CD133-expressing liver cancer stem cells (CSCs) enriched after irradiation of Huh7 cells in cell invasion and migration. We also explored whether a disintegrin and metalloproteinase-17 (ADAM17) influences the metastatic potential of CSC-enriched hepatocellular carcinoma (HCC) cells after irradiation. A CD133-expressing Huh7 cell subpopulation showed greater resistance to sublethal irradiation and specifically enhanced cell invasion and migration capabilities. We also demonstrated that the radiation-induced MMP-2 and MMP-9 enzyme activities as well as the secretion of vascular endothelial growth factor were increased more predominantly in Huh7CD133+ cell subpopulations than Huh7CD133- cell subpopulations. Furthermore, we showed that silencing ADAM17 significantly inhibited the migration and invasiveness of enriched Huh7CD133+ cells after irradiation; moreover, Notch signaling was significantly reduced in irradiated CD133-expressing liver CSCs following stable knockdown of the ADAM17 gene. In conclusion, our findings indicate that CD133-expressing liver CSCs have considerable metastatic capabilities after irradiation of HCC cells, and their metastatic capabilities might be maintained by ADAM17. Therefore, suppression of ADAM17 shows promise for improving the efficiency of current radiotherapies and reducing the metastatic potential of liver CSCs during HCC treatment.

Distribution of 4-Hydroxynonenal-Protein Conjugates as a Marker of Lipid Peroxidation and Parameter of Malignancy in Astrocytic and Ependymal Tumors of the Brain

Aims and Background

Lipid peroxidation (LPO) is an autocatalytic process caused by oxidative stress. It results in the production of 4-hydroxynonenal (HNE), which plays a crucial role in hypoxic brain injury, neuronal degeneration and apoptosis. The aim of this study was to evaluate the expression of HNE in 120 astrocytic and 40 ependymal tumors in relation to tumor type, grade of malignancy, angiogenesis, and presence of necrosis and apoptosis.

Methods

Immunohistochemical staining was performed using a monoclonal antibody for the detection of HNE-modified proteins.

Results

HNE-protein adducts were found in all tumors. The incidence of HNE-im-munopositive tumor cells increased with increasing grades of malignancy. Significantly higher HNE expression was found in tumor cells of glioblastomas multiforme than in cells of pilocytic astrocytomas ( P <0.005), and in anaplastic ependymomas than in benign ependymomas ( P <0.01). HNE-immunopositive tumor cells were distributed more diffusely than in perivascular locations ( P <0.05). Pronounced HNE-protein adducts were detected in mitotic, necrotic, and apoptotic cells. HNE was expressed in the endothelium of almost all tumor vessels, but its expression in the walls of the vessels was significantly higher in diffuse and anaplastic astrocytomas than in pilocytic astrocytomas and glioblastomas multiforme ( P <0.05). The number of microvessels containing HNE in their endothelium and walls was significantly associated with the grade of malignancy in both astrocytic ( P <0.001) and ependymal tumors ( P <0.05), although microvessels in pilocytic astrocytomas were significantly more numerous ( P <0.05) than in diffuse astrocytomas.

Conclusions

LPO seems to be a common pathological process in astrocytic and ependymal glial tumors, proportional to the level of malignancy and neovascularization. Therefore, HNE might be involved in the damage of brain cells and the induction of malignancy.

Vascular Endothelial Growth Factor, Irradiation, and Axitinib Have Diverse Effects on Motility and Proliferation of Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is the most common primary brain tumor. It is highly aggressive with an unfavorable prognosis for the patients despite therapies including surgery, irradiation, and chemotherapy. One important characteristic of highly vascularized GBM is the strong expression of vascular endothelial growth factor (VEGF). VEGF has become a new target in the treatment of GBM, and targeted therapies such as the VEGF-receptor blocker axitinib are in clinical trials. Most studies focus on VEGF-induced angiogenesis, but only very few investigations analyze autocrine or paracrine effects of VEGF on the tumor cells. In this study, we examined the impact of VEGF, irradiation, and axitinib on cell proliferation and cell motility in human GBM cell lines U-251 and U-373. VEGF receptor 2 was shown to be expressed within both cell lines by using PCR and immunochemistry. Moreover, we performed 24-h videography to analyze motility, and a viability assay for cell proliferation. We observed increasing effects of VEGF and irradiation on cell motility in both cell lines, as well as strong inhibiting effects on cellular motility by VEGF-receptor blockade using axitinib. Moreover, axitinib diminished irradiation induced accelerating effects. While VEGF stimulation or irradiation did not affect cell proliferation, axitinib significantly decreased cell proliferation in both cell lines. Therefore, the impairment of VEGF signaling might have a crucial role in the treatment of GBM.

Identification of protein biomarkers and signaling pathways associated with prostate cancer radioresistance using label-free LC-MS/MS proteomic approach

Identifying biomarkers and signaling pathways are important for the management of prostate cancer (CaP) radioresistance. In this study, we identified differential proteins and signaling pathways from parental CaP cell lines and CaP radioresistant (RR) sublines using a label-free LC-MS/MS proteomics approach. A total of 309 signaling pathway proteins were identified to be significantly altered between CaP and CaP-RR cells (p ≤ 0.05, fold differences >1.5, ≥80% power). Among these proteins, nineteen are common among three paired CaP cell lines and associated with metastasis, progression and radioresistance. The PI3K/Akt, VEGF and glucose metabolism pathways were identified as the main pathways associated with CaP radioresistance. In addition, the identified potential protein markers were further validated in CaP-RR cell lines and subcutaneous (s.c) animal xenografts by western blotting and immunohistochemistry, respectively and protein aldolase A (ALDOA) was selected for a radiosensitivity study. We found the depletion of ALDOA combined with radiotherapy effectively reduced colony formation, induced more apoptosis and increased radiosensitivity in CaP-RR cells. Our findings indicate that CaP radioresistance is caused by multifactorial traits and downregulation of ALDOA increases radiosensitivity in CaP-RR cells, suggesting that controlling these identified proteins or signaling pathways in combination with radiotherapy may hold promise to overcome CaP radioresistance.

Influence of vascular endothelial growth factor and radiation on gap junctional intercellular communication in glioblastoma multiforme cell lines

Glioblastoma multiforme (GBM) is a highly aggressive glial brain tumor with an unfavorable prognosis despite all current therapies including surgery, radiation and chemotherapy. One characteristic of this tumor is a strong synthesis of vascular endothelial growth factor (VEGF), an angiogenesis factor, followed by pronounced vascularization. VEGF became a target in the treatment of GBM, for example with bevacizumab or the tyrosine kinase inhibitor axitinib, which blocks VEGF receptors. To improve patients’ prognosis, new targets in the treatment of GBM are under investigations. The role of gap junctions in GBM remains unknown, but some experimental therapies affect these intercellular channels to treat the tumor. Gap junctions are composed of connexins to allow the transport of small molecules between adjacent cells through gap junctional intercellular communication (GJIC). Based on data derived from astrocytes in former studies, which show that VEGF is able to enhance GJIC, the current study analyzed the effects of VEGF, radiation therapy and VEGF receptor blockade by axitinib on GJIC in human GBM cell lines U-87 and U-251. While VEGF is able to induce GJIC in U-251 cells but not in U-87 cells, radiation enhances GJIC in both cell lines. VEGF receptor blockade by axitinib diminishes radiation induced effects in U-251 partially, while increases GJIC in U-87 cells. Our data indicate that VEGF and radiation are both modifying components of GJIC in pathologic brain tumor tissue.

Bevacizumab and radiotherapy for the treatment of glioblastoma: brothers in arms or unholy alliance?

Glioblastoma (GBM) represents the most frequent primary brain tumor in adults and carries a dismal prognosis despite aggressive, multimodal treatment regimens involving maximal resection, radiochemotherapy, and maintenance chemotherapy. Histologically, GBMs are characterized by a high degree of VEGF-mediated vascular proliferation. In consequence, new targeted anti-angiogenic therapies, such as the monoclonal anti-VEGF-A antibody bevacizumab, have proven effective in attenuating tumor (neo)angiogenesis and were shown to possess therapeutic activity in several phase II trials. However, the role of bevacizumab in the context of multimodal therapy approaches appears to be rather complex. This review will give insights into current concepts, limitations, and controversies regarding the molecular mechanisms and the clinical benefits of bevacizumab treatment in combination with radio(chemo)therapy - particularly in face of the results of recent phase III trials, which failed to demonstrate convincing improvements in overall survival (OS).

A phase II study of bevacizumab and erlotinib after radiation and temozolomide in MGMT unmethylated GBM patients

Survival for glioblastoma (GBM) patients with an unmethyated MGMT promoter in their tumor is generally worse than methylated MGMT tumors, as temozolomide (TMZ) response is limited. How to better treat patients with unmethylated MGMT is unknown. We performed a trial combining erlotinib and bevacizumab in unmethylated GBM patients after completion of radiation (RT) and TMZ. GBM patients with an unmethylated MGMT promoter were trial eligible. Patient received standard RT (60 Gy) and TMZ (75 mg/m2 × 6 weeks) after surgical resection of their tumor. After completion of RT they started erlotinib 150 mg daily and bevacizumab 10 mg/kg every 2 weeks until progression. Imaging evaluations occurred every 8 weeks. The primary endpoint was overall survival. Of the 48 unmethylated patients enrolled, 46 were evaluable (29 men and 17 women); median age was 55.5 years (29-75) and median KPS was 90 (70-100). All patients completed RT with TMZ. The median number of cycles (1 cycle was 4 weeks) was 8 (2-47). Forty-one patients either progressed or died with a median progression free survival of 9.2 months. At a follow up of 33 months the median overall survival was 13.2 months. There were no unexpected toxicities and most observed toxicities were categorized as CTC grade 1 or 2. The combination of erlotinib and bevacizumab is tolerable but did not meet our primary endpoint of increasing survival. Importantly, more trials are needed to find better therapies for GBM patients with an unmethylated MGMT promoter.

Caspase 3 in dying tumor cells mediates post-irradiation angiogenesis

Cytotoxic radiotherapy unfavorably induces tumor cells to generate various proangiogenic substances, promoting post-irradiation angiogenesis (PIA), which is one of major causes of radiotherapy failure. Though several studies have reported some mechanisms behind PIA, they have not yet described the beginning proangiogenic motivator buried in the irradiated microenvironment. In this work, we revealed that dying tumor cells induced by irradiation prompted PIA via a caspase 3 dependent mechanism. Proteolytic inactivation of caspase 3 in dying tumor cells by transducing a dominant-negative version weakened proangiogenic effects in vitro and in vivo. In addition, inhibition of caspase 3 activity suppressed tumor angiogenesis and tumorigenesis in xenograft mouse model. Importantly, we identified vascular endothelial growth factor (VEGF)-A as a downstream proangiogenic factor regulated by caspase 3 possibly through Akt signaling. Collectively, these findings indicated that besides acting as a key executioner in apoptosis, caspase 3 in dying tumor cells may play a central role in driving proangiogenic response after irradiation. Thus, radiotherapy in combination with caspase 3 inhibitors may be a novel promising therapeutic strategy to reduce tumor recurrence due to restrained PIA.

Effects of epidermal growth factor receptor kinase inhibition on radiation response in canine osteosarcoma cells

BACKGROUND

Radiation therapy is a palliative treatment modality for canine osteosarcoma, with transient improvement in analgesia observed in many cases. However there is room for improvement in outcome for these patients. It is possible that the addition of sensitizing agents may increase tumor response to radiation therapy and prolong quality of life. Epidermal growth factor receptor (EGFR) expression has been documented in canine osteosarcoma and higher EGFR levels have been correlated to a worse prognosis. However, effects of EGFR inhibition on radiation responsiveness in canine osteosarcoma have not been previously characterized. This study examined the effects of the small molecule EGFR inhibitor erlotinib on canine osteosarcoma radiation responses, target and downstream protein expression in vitro. Additionally, to assess the potential impact of treatment on tumor angiogenesis, vascular endothelial growth factor (VEGF) levels in conditioned media were measured.

RESULTS

Erlotinib as a single agent reduced clonogenic survival in two canine osteosarcoma cell lines and enhanced the impact of radiation in one out of three cell lines investigated. In cell viability assays, erlotinib enhanced radiation effects and demonstrated single agent effects. Erlotinib did not alter total levels of EGFR, nor inhibit downstream protein kinase B (PKB/Akt) activation. On the contrary, erlotinib treatment increased phosphorylated Akt in these osteosarcoma cell lines. VEGF levels in conditioned media increased after erlotinib treatment as a single agent and in combination with radiation in two out of three cell lines investigated. However, VEGF levels decreased with erlotinib treatment in the third cell line.

CONCLUSIONS

Erlotinib treatment promoted modest enhancement of radiation effects in canine osteosarcoma cells, and possessed activity as a single agent in some cell lines, indicating a potential role for EGFR inhibition in the treatment of a subset of osteosarcoma patients. The relative radioresistance of osteosarcoma cells does not appear to be related to EGFR signalling exclusively. Angiogenic responses to radiation and kinase inhibitors are similarly likely to be multifactorial and require further investigation.

Biological effects of proton radiation: an update

Proton radiation provides significant dosimetric advantages when compared with gamma radiation due to its superior energy deposition characteristics. Although the physical aspects of proton radiobiology are well understood, biological and clinical endpoints are understudied. The current practice to assume the relative biological effectiveness of low linear energy transfer (LET) protons to be a generic value of about 1.1 relative to photons likely obscures important unrecognised differentials in biological response between these radiation qualities. A deeper understanding of the biological properties induced by proton radiation would have both radiobiological and clinical impact. This article briefly points to some of the literature pertinent to the effects of protons on tissue-level processes that modify disease progression, such as angiogenesis, cell invasion and cancer metastasis. Recent findings hint that proton radiation may, in addition to offering improved radio-therapeutic targeting, be a means to provide a new dimension for increasing therapeutic benefits for patients by manipulating these tissue-level processes.

Improved Methods to Generate Spheroid Cultures from Tumor Cells, Tumor Cells & Fibroblasts or Tumor-Fragments: Microenvironment, Microvesicles and MiRNA

Diagnostic and prognostic indicators are key components to achieve the goal of personalized cancer therapy. Two distinct approaches to this goal include predicting response by genetic analysis and direct testing of possible therapies using cultures derived from biopsy specimens. Optimally, the latter method requires a rapid assessment, but growing xenograft tumors or developing patient-derived cell lines can involve a great deal of time and expense. Furthermore, tumor cells have much different responses when grown in 2D versus 3D tissue environments. Using a modification of existing methods, we show that it is possible to make tumor-fragment (TF) spheroids in only 2–3 days. TF spheroids appear to closely model characteristics of the original tumor and may be used to assess critical therapy-modulating features of the microenvironment such as hypoxia. A similar method allows the reproducible development of spheroids from mixed tumor cells and fibroblasts (mixed-cell spheroids). Prior literature reports have shown highly variable development and properties of mixed-cell spheroids and this has hampered the detailed study of how individual tumor-cell components interact. In this study, we illustrate this approach and describe similarities and differences using two tumor models (U87 glioma and SQ20B squamous-cell carcinoma) with supporting data from additional cell lines. We show that U87 and SQ20B spheroids predict a key microenvironmental factor in tumors (hypoxia) and that SQ20B cells and spheroids generate similar numbers of microvesicles. We also present pilot data for miRNA expression under conditions of cells, tumors, and TF spheroids.

Enhancement of radiosensitivity in human esophageal carcinoma cells by fenofibrate and its potential mechanism

AIMS AND BACKGROUND

Fenofibrate is a specific agonist of PPARα, and is characterized by relatively low systemic toxicity. Recent studies have revealed that fenofibrate suppresses the growth of several cancer lines in vitro, but the exact relation between fenofibrate and irradiation has not been explored. The purpose of this study was to investigate the radiosensitivity enhancement effects of fenofibrate combined with radiation on the human esophageal carcinoma cell lines Eca-109 and TE1, and the potential mechanism underlying these effects.

METHODS AND STUDY DESIGN

The Eca-109 and TE1 cell lines were tested by the CCK-8 assay for cell proliferation. The multitarget click model was used to delineate the survival curve and radiosensitivity was determined after cells were treated with fenofibrate and/or x-ray radiation. Flow cytometry was used to examine the effect of fenofibrate and radiation on the cell cycle. The expression of vascular endothelial growth factor (VEGF) protein was detected by Western blot analysis.

RESULTS

When given alone, fenofibrate had a time- and concentration-dependent cytotoxic effect on cells. The dose-enhancement ratio for combined fenofibrate and radiation increased markedly compared with fenofibrate alone. Further, the ratio of cells in the G2/M phase after fenofibrate and radiation was higher than that after fenofibrate or irradiation alone. The expression of VEGF protein was suppressed after treatment with fenofibrate alone or fenofibrate plus radiation.

CONCLUSIONS

Fenofibrate can enhance the radiosensitivity of human esophageal carcinoma cells by increasing G2/M phase arrest. Modulation of VEGF expression could contribute in vivo to a favorable interaction.

HAb18G/CD147 promotes radioresistance in hepatocellular carcinoma cells: a potential role for integrin β1 signaling

Radiotherapy has played a limited role in the treatment of hepatocellular carcinoma (HCC) due to the risk of tumor radioresistance. A previous study in our laboratory confirmed that CD147 interacts with integrin β1 and plays an important role in modulating the malignant properties of HCC cells. In this study, we further evaluated the role of CD147 in the radioresistance of HCC and as a potential target for improving radiosensitivity. Upon irradiation, the colony formation, apoptosis, cell-cycle distribution, migration, and invasion of SMMC-7721, CD147-knockout SMMC-7721, HepG2, and CD147-knockdown HepG2 cells were determined. A nude mouse xenograft model and a metastatic model of HCC were used to detect the role of CD147 in radioresistance in vivo. Deletion of HAb18G/CD147 significantly enhanced the radiosensitivity of SMMC-7721 and HepG2 cells, and knocking out HAb18G/CD147 in SMMC-7721 cells attenuated irradiation-enhanced migration and invasion. The knockout and antibody blockade of CD147 decreased the tumor growth and metastatic potentials of HCC cells under irradiation. CD147-deleted SMMC-7721 cells showed diminished levels of calpain, cleaved talin, active integrin β1, and decreased p-FAK (Tyr397) and p-Akt (Ser473) levels. FAK and PI3K inhibitors, as well as integrin β1 antibodies, increased the radiation-induced apoptosis of SMMC-7721 cells. Our data provide evidence for CD147 as an important determinant of radioresistance via the regulation of integrin β1 signaling. Inhibition of the HAb18G/CD147 integrin interaction may improve the efficiency of radiosensitivity and provide a potential new approach for HCC therapy.

Radiation promotes malignant progression of glioma cells through HIF-1alpha stabilization

Given its contribution to malignant phenotypes of cancer, tumor hypoxia has been considered as a potential therapeutic problem. In the stressful microenvironment condition, hypoxia inducible factor 1 (HIF1) is well known to mediate the transcriptional adaptation of cells to hypoxia and acts as a central player for the process of hypoxia-driven malignant cancer progression. Here, we found that irradiation causes the HIF1α protein to stabilize, even in normoxia condition through activation of p38 MAPK, thereby promoting angiogenesis in tumor microenvironment and infiltrative property of glioma cells. Notably, irradiation reduced hydroxylation of HIF1α through destabilization of prolyl hydroxylases (PHD)-2. Moreover, radiation also decreased the half-life of protein von Hippel-Lindau (pVHL), which is a specific E3 ligase for HIF1α. Of note, inhibition of p38 MAPK attenuated radiation-induced stabilization of HIF1α through destabilization of PHD-2 and pVHL. In agreement with these results, targeting of either p38 MAPK, HIF1α, pVHL or PHD-2 effectively mitigated the radiation-induced tube formation of human brain-derived micro-vessel endothelial cells (HB-MEC) and infiltration of glioma cells. Taken together, our findings suggest that targeting HIF1α in combination with ionizing radiation might increase the efficacy of radiotherapy for glioma treatment.

Ginsenoside Rg3 enhances radiosensitization of hypoxic oesophageal cancer cell lines through vascular endothelial growth factor and hypoxia inducible factor 1α

Objective

To determine if the pretreatment of hypoxic human oesophageal carcinoma cell lines (EC109, TE1 and KYSE170) with ginsenoside Rg3 (Rg3) increases their radiosensitivity to X-rays.

Methods

The growth inhibitory effect of different Rg3 concentrations was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay. Radiation sensitivity was measured using a clone formation assay and flow cytometry was used to measure the effects of Rg3 on radiation-induced apoptosis. Western blot analysis was used to measure the effects of Rg3 on the levels of hypoxia inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF).

Results

Rg3 inhibited EC109, TE1 and KYSE170 cell growth in a dose- and time-dependent manner. Pretreatment with 10 µmol/ml Rg3 increased EC109, TE1 and KYSE170 radiosensitivity. Rg3 plus radiation significantly increased the apoptosis rate compared with radiation alone. Rg3 also decreased VEGF and HIF-1α protein levels in EC109 cells in a dose-dependent manner. The combination of Rg3 and radiation increased the fragmentation of double-stranded DNA.

Conclusion

Rg3 enhanced the radiosensitivity of human oesophageal carcinoma cell lines cultured under hypoxic conditions possibly by downregulating VEGF and HIF-1α protein levels.

Autotaxin Inhibition with PF-8380 Enhances the Radiosensitivity of Human and Murine Glioblastoma Cell Lines

Purpose: Glioblastoma multiforme (GBM) is an aggressive primary brain tumor that is radio-resistant and recurs despite aggressive surgery, chemo, and radiotherapy. Autotaxin (ATX) is over expressed in various cancers including GBM and is implicated in tumor progression, invasion, and angiogenesis. Using the ATX specific inhibitor, PF-8380, we studied ATX as a potential target to enhance radiosensitivity in GBM.

Methods and Materials: Mouse GL261 and Human U87-MG cells were used as GBM cell models. Clonogenic survival assays and tumor transwell invasion assays were performed using PF-8380 to evaluate role of ATX in survival and invasion. Radiation dependent activation of Akt was analyzed by immunoblotting. Tumor induced angiogenesis was studied using the dorsal skin fold model in GL261. Heterotopic mouse GL261 tumors were used to evaluate the efficacy of PF-8380 as a radiosensitizer.

Results: Pre-treatment of GL261 and U87-MG cells with 1 μM PF-8380 followed by 4 Gy irradiation resulted in decreased clonogenic survival, decreased migration (33% in GL261; P = 0.002 and 17.9% in U87-MG; P = 0.012), decreased invasion (35.6% in GL261; P = 0.0037 and 31.8% in U87-MG; P = 0.002), and attenuated radiation-induced Akt phosphorylation. In the tumor window model, inhibition of ATX abrogated radiation induced tumor neovascularization (65%; P = 0.011). In a heterotopic mouse GL261 tumors untreated mice took 11.2 days to reach a tumor volume of 7000 mm³, however combination of PF-8380 (10 mg/kg) with irradiation (five fractions of 2 Gy) took more than 32 days to reach a tumor volume of 7000 mm³.

Conclusion: Inhibition of ATX by PF-8380 led to decreased invasion and enhanced radiosensitization of GBM cells. Radiation-induced activation of Akt was abrogated by inhibition of ATX. Furthermore, inhibition of ATX led to diminished tumor vascularity and delayed tumor growth. These results suggest that inhibition of ATX may ameliorate GBM response to radiotherapy.

Combining molecular targeted agents with radiation therapy for malignant gliomas

The expansion in understanding the molecular biology that characterizes cancer cells has led to the rapid development of new agents to target important molecular pathways associated with aberrant activation or suppression of cellular signal transduction pathways involved in gliomagenesis, including epidermal growth factor receptor, vascular endothelial growth factor receptor, mammalian target of rapamycin, and integrins signaling pathways. The use of antiangiogenic agent bevacizumab, epidermal growth factor receptor tyrosine kinase inhibitors gefitinib and erlotinib, mammalian target of rapamycin inhibitors temsirolimus and everolimus, and integrin inhibitor cilengitide, in combination with radiation therapy, has been supported by encouraging preclinical data, resulting in a rapid translation into clinical trials. Currently, the majority of published clinical studies on the use of these agents in combination with radiation and cytotoxic therapies have shown only modest survival benefits at best. Tumor heterogeneity and genetic instability may, at least in part, explain the poor results observed with a single-target approach. Much remains to be learned regarding the optimal combination of targeted agents with conventional chemoradiation, including the use of multipathways-targeted therapies, the selection of patients who may benefit from combined treatments based on molecular biomarkers, and the verification of effective blockade of signaling pathways.

Role of IL-8 induced angiogenesis in uveal melanoma

Introduction Uveal melanoma (UM) is a highly vascularised tumour generally treated with radiotherapy (RT). A recent preclinical study from our group [1] demonstrated that RT-associated anti-angiogenic therapy has more than additive effects on cell growth, by modulating vascular endothelial growth factor (VEGF) levels. The pro-angiogenic interleukin-8 (IL-8) is highly expressed in both tumour and endothelial cells and is associated with resistance to VEGF-targeted therapies in various tumour types. The aim of this study is to investigate IL-8 release in response to the anti-angiogenic drug bevacizumab (AV) and RT given alone and in combination. Material and methods The human ocular melanoma cells (OCM-1) and human umbilical vein endothelial cells (HUVEC) were grown in transwell plates. AV was administered at a 2,500 μg/ml dose and cells were irradiated with a 6 Gy dose. IL-8 concentrations were determined by ELISA assay. Protein expression was detected by western blot. Results AV alone or in combination with RT reduces VEGF levels in both cell lines when co-cultured; unexpectedly, RT alone did not increase VEGF levels. In transwell plate AV alone lowered IL-8 secretion in both cell lines. This inhibitory effect was reduced when co-cultured cells are treated with AV + RT, suggesting that RT-induced VEGF may reactivate IL-8 secretion, enhancing an alternative pathway to sustain tumour angiogenesis. Conclusions These data indicate that the UM microenvironment, beside VEGF, can activate IL-8 signalling as an alternative pro-angiogenic pathway.

Synchrotron microbeam radiation therapy induces hypoxia in intracerebral gliosarcoma but not in the normal brain

PURPOSE

Synchrotron microbeam radiation therapy (MRT) is an innovative irradiation modality based on spatial fractionation of a high-dose X-ray beam into lattices of microbeams. The increase in lifespan of brain tumor-bearing rats is associated with vascular damage but the physiological consequences of MRT on blood vessels have not been described. In this manuscript, we evaluate the oxygenation changes induced by MRT in an intracerebral 9L gliosarcoma model.

METHODS

Tissue responses to MRT (two orthogonal arrays (2 × 400Gy)) were studied using magnetic resonance-based measurements of local blood oxygen saturation (MR_SO2) and quantitative immunohistology of RECA-1, Type-IV collagen and GLUT-1, marker of hypoxia.

RESULTS

In tumors, MR_SO2 decreased by a factor of 2 in tumor between day 8 and day 45 after MRT. This correlated with tumor vascular remodeling, i.e. decrease in vessel density, increases in half-vessel distances (×5) and GLUT-1 immunoreactivity. Conversely, MRT did not change normal brain MR_SO2, although vessel inter-distances increased slightly.

CONCLUSION

We provide new evidence for the differential effect of MRT on tumor vasculature, an effect that leads to tumor hypoxia. As hypothesized formerly, the vasculature of the normal brain exposed to MRT remains sufficiently perfused to prevent any hypoxia.

Glioma stem cells and immunotherapy for the treatment of malignant gliomas

Stem cell research has led to the discovery of glioma stem cells (GSCs), and because these cells are resistant to chemotherapy and radiotherapy, analysis of their properties has been rapidly pursued for targeted treatment of malignant glioma. Recent studies have also revealed complex crosstalk between GSCs and their specialized environment (niche). Therefore, targeting not only GSCs but also their niche may be a principle for novel therapies of malignant glioma. One possible novel strategy for targeting GSCs and their niches is immunotherapy with different antitumor mechanism(s) from those of conventional therapy. Recent clinical studies of immunotherapy using peptide vaccines and antibodies have shown promising results. This review describes the recent findings related to GSCs and their niches, as well as immunotherapies for glioma, followed by discussion of immunotherapies that target GSCs for the treatment of malignant glioma.

The enhancement of radiosensitivity in human esophageal squamous cell carcinoma cells by zoledronic acid and its potential mechanism

Esophageal squamous cell carcinoma (ESCC) has a low 5-year patient survival rate. Radiotherapy, as a preoperative or postoperative treatment of surgery, has a crucial role in improving local control and survival of ESCC. Various chemotherapeutic and biologic agents have been used as radio-sensitizers in combination with radiotherapy. Here, we demonstrate that zoledronic acid (ZOL) has a radio-sensitizing effect on ESCC cells. Exposure of ESCC cancer cells to ZOL plus radiation resulted in increased cell death through arresting the cell cycle between S and G2/M phases. ZOL appeared to inhibit proliferation, tube formation and invasion of endothelial cells. These anti-angiogenetic effects were more marked concurrently with irradiation. In addition, synergistic suppressive effects on VEGF expression were observed after combined treatment. Our data suggest that the combination of ZOL and radiation is a promising therapeutic strategy to enhance radiation therapy for ESCC patients.

The VEGF/VEGF-R axis in sporadic vestibular schwannomas correlates with irradiation and disease recurrence

BACKGROUND/AIMS

The molecular mechanisms downstream of mutated neurofibromatosis type 2 (NF2) gene resulting in the growth and development of vestibular schwannoma (VS) are controversial. Several lines of evidence suggest the involvement of the vascular endothelial growth factor (VEGF) pathway in VS development. Given that recent studies of VEGF blockade in patients with NF2-associated VS showed positive effects on VS growth control, we initiated this comprehensive study of the VEGF pathway in sporadic VS.

METHODS

A tissue microarray analysis of 182 sporadic VS was conducted. The expression of VEGF and its receptors as well as the proliferative activity of the tumors were quantified. The expression data were correlated to tumor volumes and diameters as well as to tumor recurrence and previous irradiation.

RESULTS

All studied tumors expressed VEGF and its receptors. Proliferative activity was related to the growth characteristics of the tumors. Moreover, we found significantly higher VEGF levels in recurrent tumors (p = 0.0387) and in preoperatively irradiated tumors (p = 0.0213).

CONCLUSION

Our data suggest a relevant role of the VEGF pathway in VS growth and therapy outcome. Therefore, targeting this pathway using antiangiogenic compounds might be beneficial for patients with sporadic VS, especially those with recurrent or irradiated tumors.

Antitumor activity of Endostar combined with radiation against human nasopharyngeal carcinoma in mouse xenograft models

Radiation treatment for nasopharyngeal carcinoma (NPC) is common and effective. However, local recurrence occurs frequently. Endostar, a novel recombinant human endostatin, is an antiangiogenic drug with a potent antitumor effect. The present study aimed to observe and explore the radiosensitization effects of Endostar on NPC and its underlying mechanism. The NPC subcutaneous transplantation tumor animal model was established to evaluate the antitumor activity of Endostar combined with radiation (Endostar + radiation) treatment compared with monotherapy (Endostar or radiation). Tumor growth and tumor weight were measured to evaluate the antitumor effect. The level of vascular endothelial growth factor (VEGF) and microvessel density (MVD) were measured using immunohistochemical staining of the tumor tissues. Significant antitumor activity was found in the Endostar + radiation group. The tumor inhibition rates of Endostar, radiation and Endostar + radiation were 27.12, 60.45 and 86.11%, respectively. The VEGF levels in the tumor tissue in the Endostar + radiation group were lower than those in the radiation and control groups. The MVD in the tumor tissues in the Endostar + radiation group was 12.2±2.5, lower than that in the Endostar (29.3±3.4), radiation (23.5±3.6) and control (44.7±5.1) groups. These results suggest that Endostar increases the radiation sensitivity of NPC-transplanted tumors in nude mice by lowering VEGF expression. In this study, the NPC animal model was established, which reflects the efficacy of clinical combination therapies and the combination of Endostar and radiation. The mechanisms of the combination therapies should be further investigated using this model.

The addition of Sunitinib to radiation delays tumor growth in a murine model of glioblastoma

OBJECTIVES

Recent preclinical studies suggest that treating glioblastoma (GBM) with a combination of targeted chemotherapy and radiotherapy may enhance the anti-tumor effects of both therapies. However, the effects of these treatments on glioma growth and progression are poorly understood.

METHODS

In this study, we have tested the effects of combination therapy in a mouse glioma model that utilizes a PDGF-IRES-Cre-expressing retrovirus to infect adult glial progenitors in mice carrying conditional deletions of Pten and p53. This model produces tumors with the histological features of GBM with 100% penetrance, making it a powerful system to test novel treatments. Sunitinib is an orally active, small molecule inhibitor of multiple receptor tyrosine kinases critical for tumor growth and angiogenesis, including PDGF receptors. We investigate the addition of Sunitinib to radiotherapy, and use bioluminescence imaging to characterize the effects of treatment on glioma growth and progression.

RESULTS

Treating our PDGF-driven mouse model with either Sunitinib or high-dose radiation alone delayed tumor growth and had a modest but significant effect on survival, while treating with low-dose radiation alone failed to control glioma growth and progression. The addition of Sunitinib to low-dose radiation caused a modest, but significant delay in tumor growth. However, no significant survival benefit was seen as tumors progressed in 100% of animals. Histological analysis revealed a reduction in vascular proliferation and a marked increase in brain invasion. An additional study combining Sunitinib with high-dose radiation revealed a fatal toxicity despite individual monotherapies being well tolerated.

DISCUSSION

These results show that the addition of Sunitinib to radiotherapy fails to significantly alter survival in GBM despite enhancement of the effects of radiation. Furthermore, an enhanced risk of toxicity associated with combined therapy must be considered in the design of future clinical studies.

Knockdown of vascular endothelial cell growth factor expression sensitizes U251 glioma cells to liposomal paclitaxel and radiation treatment in vitro

Glioblastoma is the most aggressive malignancy of the human brain, accounting for 40% of all primary malignant brain tumors. However, there is no effective treatment for this disease. This study was designed to develop anti-vascular endothelial growth factor (VEGF) as a novel adjuvant therapy for glioblastoma. A VEGF shRNA vector was constructed to silence VEGF expression in U251 glioma cells and these cells were treated with various concentrations of liposomal paclitaxel, 6 Gy radiation or liposomal paclitaxel plus radiation. The data demonstrated that the VEGF shRNA vector significantly knocked down VEGF expression, which synergistically sensitized U251 glioma cells to liposomal paclitaxel, radiation or liposomal paclitaxel plus radiation treatment in terms of cell viability, apoptosis, colony formation and morphological changes. Future studies are required to evaluate these effects in vivo.

Effects of irradiation on brain vasculature using an in situ tumor model

PURPOSE

Damage to normal tissue is a limiting factor in clinical radiotherapy (RT). We tested the hypothesis that the presence of tumor alters the response of normal tissues to irradiation using a rat in situ brain tumor model.

METHODS AND MATERIALS

Intravital microscopy was used with a rat cranial window to assess the in situ effect of rat C6 glioma on peritumoral tissue with and without RT. The RT regimen included 40 Gy at 8 Gy/day starting Day 5 after tumor implant. Endpoints included blood-brain barrier permeability, clearance index, leukocyte-endothelial interactions and staining for vascular endothelial growth factor (VEGF) glial fibrillary acidic protein, and apoptosis. To characterize the system response to RT, animal survival and tumor surface area and volume were measured. Sham experiments were performed on similar animals implanted with basement membrane matrix absent of tumor cells.

RESULTS

The presence of tumor alone increases permeability but has little effect on leukocyte-endothelial interactions and astrogliosis. Radiation alone increases tissue permeability, leukocyte-endothelial interactions, and astrogliosis. The highest levels of permeability and cell adhesion were seen in the model that combined tumor and irradiation; however, the presence of tumor appeared to reduce the volume of rolling leukocytes. Unirradiated tumor and peritumoral tissue had poor clearance. Irradiated tumor and peritumoral tissue had a similar clearance index to irradiated and unirradiated sham-implanted animals. Radiation reduces the presence of VEGF in peritumoral normal tissues but did not affect the amount of apoptosis in the normal tissue. Apoptosis was identified in the tumor tissue with and without radiation.

CONCLUSIONS

We developed a novel approach to demonstrate that the presence of the tumor in a rat intracranial model alters the response of normal tissues to irradiation.

The enhancement of radiosensitivity in human esophageal carcinoma cells by thalidomide and its potential mechanism

To investigate the effects of thalidomide on the radiosensitivity of human esophageal cancer cells (TE1 cells) and the potential mechanism underlying these effects. The effects of thalidomide on proliferation of TE1 cells were determined by Methyl thiazolyl tetrazolium assay. The multitarget click model was used to delineate the survival curve using a colony-forming assay, and the radiosensitivity was determined after TE1 cells were treated by thalidomide and/or X-ray radiation. The cell cycle was detected using flow cytometry. Our results are as follows: thalidomide alone suppressed the proliferation of TE1 cells in a dose- and time-dependent manner. The suppressive effects were enhanced by prolonged duration or elevated concentration of thalidomide. However, thalidomide did not affect the cell cycle of TE1 cells. The expression of vascular endothelial growth factor (VEGF) mRNA and protein was suppressed after treatment with thalidomide alone in a dose-dependent manner. Synergistic suppressive effects on VEGF expression were observed after administration of thalidomide and X-ray exposure. In conclusion, thalidomide was able to enhance the radiosensitivity of TE1 cells in vitro, which could be closely related to its suppressive effects on the expression of VEGF in TE1 cells, but had no obvious effects on the cell cycle.

Targeting the NG2/CSPG4 proteoglycan retards tumour growth and angiogenesis in preclinical models of GBM and melanoma

Aberrant expression of the progenitor marker Neuron-glia 2 (NG2/CSPG4) or melanoma proteoglycan on cancer cells and angiogenic vasculature is associated with an aggressive disease course in several malignancies including glioblastoma multiforme (GBM) and melanoma. Thus, we investigated the mechanism of NG2 mediated malignant progression and its potential as a therapeutic target in clinically relevant GBM and melanoma animal models. Xenografting NG2 overexpressing GBM cell lines resulted in increased growth rate, angiogenesis and vascular permeability compared to control, NG2 negative tumours. The effect of abrogating NG2 function was investigated after intracerebral delivery of lentivirally encoded shRNAs targeting NG2 in patient GBM xenografts as well as in established subcutaneous A375 melanoma tumours. NG2 knockdown reduced melanoma proliferation and increased apoptosis and necrosis. Targeting NG2 in two heterogeneous GBM xenografts significantly reduced tumour growth and oedema levels, angiogenesis and normalised vascular function. Vascular normalisation resulted in increased tumour invasion and decreased apoptosis and necrosis. We conclude that NG2 promotes tumour progression by multiple mechanisms and represents an amenable target for cancer molecular therapy.

MMP-2 siRNA inhibits radiation-enhanced invasiveness in glioma cells

Background

Our previous work and that of others strongly suggests a relationship between the infiltrative phenotype of gliomas and the expression of MMP-2. Radiation therapy, which represents one of the mainstays of glioma treatment, is known to increase cell invasion by inducing MMP-2. Thus, inhibition of MMP-2 provides a potential means for improving the efficacy of radiotherapy for malignant glioma.

Methodology/Principal Findings

We have tested the ability of a plasmid vector-mediated MMP-2 siRNA (p-MMP-2) to modulate ionizing radiation-induced invasive phenotype in the human glioma cell lines U251 and U87. Cells that were transfected with p-MMP-2 with and without radiation showed a marked reduction of MMP-2 compared to controls and pSV-transfected cells. A significant reduction of proliferation, migration, invasion and angiogenesis of cells transfected with p-MMP-2 and in combination with radiation was observed compared to controls. Western blot analysis revealed that radiation-enhanced levels of VEGF, VEGFR-2, pVEGFR-2, p-FAK, and p-p38 were inhibited with p-MMP-2-transfected cells. TUNEL staining showed that radiation did not induce apoptosis in U87 and U251 cells while a significant increase in TUNEL-positive cells was observed when irradiated cells were simultaneously transfected with p-MMP-2 as compared to controls. Intracranial tumor growth was predominantly inhibited in the animals treated with p-MMP-2 alone or in combination with radiation compared to controls.

Conclusion/Significance

MMP-2 inhibition, mediated by p-MMP-2 and in combination with radiation, significantly reduced tumor cell migration, invasion, angiogenesis and tumor growth by modulating several important downstream signaling molecules and directing cells towards apoptosis. Taken together, our results demonstrate the efficacy of p-MMP-2 in inhibiting radiation-enhanced tumor invasion and progression and suggest that it may act as a potent adjuvant for radiotherapy in glioma patients.

Evaluation of vascular endothelial growth factor as a prognostic marker for local relapse in early-stage breast cancer patients treated with breast-conserving therapy

PURPOSE

Vascular endothelial growth factor (VEGF) is an important protein involved in the process of angiogenesis that has been found to correlate with relapse-free and overall survival in breast cancer, predominantly in locally advanced and metastatic disease. A paucity of data is available on the prognostic implications of VEGF in early-stage breast cancer; specifically, its prognostic value for local relapse after breast-conserving therapy (BCT) is largely unknown. The purpose of our study was to assess VEGF expression in a cohort of early-stage breast cancer patients treated with BCT and to correlate the clinical and pathologic features and outcomes with overexpression of VEGF.

METHODS AND MATERIALS

After obtaining institutional review board approval, the paraffin specimens of 368 patients with early-stage breast cancer treated with BCT between 1975 and 2005 were constructed into tissue microarrays with twofold redundancy. The tissue microarrays were stained for VEGF and read by a trained pathologist, who was unaware of the clinical details, as positive or negative according the standard guidelines. The clinical and pathologic data, long-term outcomes, and results of VEGF staining were analyzed.

RESULTS

The median follow-up for the entire cohort was 6.5 years. VEGF expression was positive in 56 (15%) of the 368 patients. Although VEGF expression did not correlate with age at diagnosis, tumor size, nodal status, histologic type, family history, estrogen receptor/progesterone receptor status, or HER-2 status, a trend was seen toward increased VEGF expression in the black cohort (26% black vs. 13% white, p=.068). Within the margin-negative cohort, VEGF did not predict for local relapse-free survival (RFS) (96% vs. 95%), nodal RFS (100% vs. 100%), distant metastasis-free survival (91% vs. 92%), overall survival (92% vs. 97%), respectively (all p>.05). Subset analysis revealed that VEGF was highly predictive of local RFS in node-positive, margin-negative patients (86% vs. 100%, p=.029) on univariate analysis, but it did not retain its significance on multivariate analysis (hazard ratio, 2.52; 95% confidence interval, 0.804-7.920, p=.113). No other subgroups were identified in which a correlation was found between VEGF expression and local relapse.

CONCLUSION

To our knowledge, our study is the first to assess the prognostic value of VEGF with the endpoint of local relapse in early-stage breast cancer treated with BCT, an important question given the recent increased use of targeted antiangiogenic agents in early-stage breast cancer. Our study results suggest that VEGF is not an independent predictor of local RFS after BCT, but additional, larger studies specifically analyzing the endpoint of VEGF and local relapse are warranted.

Inhibition of notch signaling in glioblastoma targets cancer stem cells via an endothelial cell intermediate

Glioblastoma multiforme (GBM) is a highly heterogeneous malignant tumor. Recent data suggests the presence of a hierarchical organization within the GBM cell population that involves cancer cells with stem-like behavior, capable of repopulating the tumor and contributing to its resistance to therapy. Tumor stem cells are thought to reside within a vascular niche that provides structural and functional support. However, most GBM studies involve isolated tumor cells grown under various culture conditions. Here, we use a novel three-dimensional organotypic "explant" system of surgical GBM specimens that preserves cytoarchitecture and tumor stroma along with tumor cells. Notch inhibition in explants results in decreased proliferation and self-renewal of tumor cells but is also associated with a decrease in endothelial cells. When endothelial cells are selectively eliminated from the explants via a toxin conjugate, we also observed a decrease in self-renewal of tumor stem cells. These findings support a critical role for tumor endothelial cells in GBM stem cell maintenance, mediated at least in part by Notch signaling. The explant system further highlighted differences in the response to radiation between explants and isolated tumor neurospheres. Combination treatment with Notch blockade and radiation resulted in a substantial decrease in proliferation and in self-renewal in tumor explants while radiation alone was less effective. This data suggests that the Notch pathway plays a critical role in linking angiogenesis and cancer stem cell self-renewal and is thus a potential therapeutic target. Three-dimensional explant systems provide a novel approach for the study of tumor and microenvironment interactions.

Hsp90 as a gatekeeper of tumor angiogenesis: clinical promise and potential pitfalls

Tumor vascularization is an essential modulator of early tumor growth, progression, and therapeutic outcome. Although antiangiogenic treatments appear promising, intrinsic and acquired tumor resistance contributes to treatment failure. Clinical inhibition of the molecular chaperone heat shock protein 90 (Hsp90) provides an opportunity to target multiple aspects of this signaling resiliency, which may elicit more robust and enduring tumor repression relative to effects elicited by specifically targeted agents. This review highlights several primary effectors of angiogenesis modulated by Hsp90 and describes the clinical challenges posed by the redundant circuitry of these pathways. The four main topics addressed include (1) Hsp90-mediated regulation of HIF/VEGF signaling, (2) chaperone-dependent regulation of HIF-independent VEGF-mediated angiogenesis, (3) Hsp90-dependent targeting of key proangiogenic receptor tyrosine kinases and modulation of drug resistance, and (4) consideration of factors such as tumor microenvironment that pose several challenges for the clinical efficacy of anti-angiogenic therapy and Hsp90-targeted strategies.

Effects of irradiation on tumor cell survival, invasion and angiogenesis

Ionizing irradiation is a widely applied therapeutic method for the majority of solid malignant neoplasms, including brain tumors where, depending on localization, this might often be the only feasible primary intervention.Without doubt, it has been proved to be a fundamental tool available in the battlefield against cancer, offering a clear survival benefit in most cases. However, numerous studies have associated tumor irradiation with enhanced aggressive phenotype of the remaining cancer cells. A cell population manages to survive after the exposure, either because it receives sublethal doses and/or because it successfully utilizes the repair mechanisms. The biology of irradiated cells is altered leading to up-regulation of genes that favor cell survival, invasion and angiogenesis. In addition, hypoxia within the tumor mass limits the cytotoxicity of irradiation, whereas irradiation itself may worsen hypoxic conditions, which also contribute to the generation of resistant cells. Activation of cell surface receptors, such as the epidermal growth factor receptor, utilization of signaling pathways, and over-expression of cytokines, proteases and growth factors, for example the matrix metalloproteinases and vascular endothelial growth factor, protect tumor and non-tumor cells from apoptosis, increase their ability to invade to adjacent or distant areas, and trigger angiogenesis. This review will try to unfold the various molecular events and interactions that control tumor cell survival, invasion and angiogenesis and which are elicited or influenced by irradiation of the tumor mass, and to emphasize the importance of combining irradiation therapy with molecular targeting.

Irradiation-induced regulation of plasminogen activator inhibitor type-1 and vascular endothelial growth factor in six human squamous cell carcinoma lines of the head and neck

PURPOSE

It has been shown that plasminogen activator inhibitor type-1 (PAI-1) and vascular endothelial growth factor (VEGF) are involved in neo-angiogenesis. The aim of this study was to investigate the irradiation-induced regulation of PAI-1 and VEGF in squamous cell carcinomas of the head and neck (SCCHN) cell lines of varying radiation sensitivity.

METHODS AND MATERIALS

Six cell lines derived from SCCHN were investigated in vitro. The colorimetric AlamarBlue assay was used to detect metabolic activity of cell lines during irradiation as a surrogate marker for radiation sensitivity. PAI-1 and VEGF secretion levels were measured by enzyme-linked immunosorbent assay 24, 48, and 72 h after irradiation with 0, 2, 6, and 10 Gy. The direct radioprotective effect of exogenous PAI-1 was measured using the clonogenic assay. For regulation studies, transforming growth factor-beta1 (TGF-beta1), hypoxia-inducible factor-1alpha (HIF-1alpha), hypoxia-inducible factor-2alpha (HIF-2alpha), or both HIF-1alpha and HIF-2alpha were downregulated using siRNA.

RESULTS

Although baseline levels varied greatly, irradiation led to a comparable dose-dependent increase in PAI-1 and VEGF secretion in all six cell lines. Addition of exogenous stable PAI-1 to the low PAI-1-expressing cell lines, XF354 and FaDu, did not lead to a radioprotective effect. Downregulation of TGF-beta1 significantly decreased VEGF secretion in radiation-sensitive XF354 cells, and downregulation of HIF-1alpha and HIF-2alpha reduced PAI-1 and VEGF secretion in radiation-resistant SAS cells.

CONCLUSIONS

Irradiation dose-dependently increased PAI-1 and VEGF secretion in all SCCHN cell lines tested regardless of their basal levels and radiation sensitivity. In addition, TGF-beta1 and HIF-1alpha could be partly responsible for VEGF and PAI-1 upregulation after irradiation.

Effect of radiation on vascular endothelial growth factor expression in the C2 canine mastocytoma cell line

OBJECTIVE

To establish the radiosensitivity and effect of irradiation on vascular endothelial growth factor (VEGF) and VEGF receptor (VEGFR) expression in the canine mastocytoma cell line C2.

SAMPLE POPULATION

Canine mastocytoma cell line C2.

PROCEDURES

C2 cells were irradiated with single doses of 2, 4, 6, and 8 Gy. The 3-(4, 5-di-methyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide assay and proliferation assays with (methyl-hydrogen 3) thymidine were used for radiosensitivity experiments. Expression of VEGFR was determined via flow cytometry and apoptotic rate via annexin assay. Human and canine VEGF ELISA kits were evaluated in crossover assay experiments, and the canine kit was used thereafter.

RESULTS

C2 cells secreted VEGF constitutively. Radiation did not induce a significant increase in VEGF secretion, regardless of radiation dose. Consistently, radiation did not up-regulate VEGFR. Cell survival rates decreased in a dose-dependent manner. The apoptotic cell fraction had a dose-dependent increase that reached its maximum 24 to 48 hours after radiation.

CONCLUSIONS AND CLINICAL RELEVANCE

The C2 cell line was radiosensitive, and a fraction (up to 40%) of cells died via apoptosis in a dose-dependent manner. In response to radiation, C2 cells did not upregulate VEGF production or VEGFR. Further studies are needed to determine whether tumor control could be improved by combining radiotherapy with VEGFR inhibitors or apoptosis-modulating agents.