Exploring the role of HIF-1 in early angiogenesis and response to radiotherapy

Blocking the MIF-CD74 axis augments radiotherapy efficacy for brain metastasis in NSCLC via synergistically promoting microglia M1 polarization

BACKGROUND

Brain metastasis is one of the main causes of recurrence and death in non-small cell lung cancer (NSCLC). Although radiotherapy is the main local therapy for brain metastasis, it is inevitable that some cancer cells become resistant to radiation. Microglia, as macrophages colonized in the brain, play an important role in the tumor microenvironment. Radiotherapy could activate microglia to polarize into both the M1 and M2 phenotypes. Therefore, searching for crosstalk molecules within the microenvironment that can specifically regulate the polarization of microglia is a potential strategy for improving radiation resistance.

METHODS

We used databases to detect the expression of MIF in NSCLC and its relationship with prognosis. We analyzed the effects of targeted blockade of the MIF/CD74 axis on the polarization and function of microglia during radiotherapy using flow cytometry. The mouse model of brain metastasis was used to assess the effect of targeted blockade of MIF/CD74 axis on the growth of brain metastasis.

RESULT

Our findings reveals that the macrophage migration inhibitory factor (MIF) was highly expressed in NSCLC and is associated with the prognosis of NSCLC. Mechanistically, we demonstrated CD74 inhibition reversed radiation-induced AKT phosphorylation in microglia and promoted the M1 polarization in combination of radiation. Additionally, blocking the MIF-CD74 interaction between NSCLC and microglia promoted microglia M1 polarization. Furthermore, radiation improved tumor hypoxia to decrease HIF-1α dependent MIF secretion by NSCLC. MIF inhibition enhanced radiosensitivity for brain metastasis via synergistically promoting microglia M1 polarization in vivo.

CONCLUSIONS

Our study revealed that targeting the MIF-CD74 axis promoted microglia M1 polarization and synergized with radiotherapy for brain metastasis in NSCLC.

Tumor hypoxia and radiotherapy: A major driver of resistance even for novel radiotherapy modalities

Hypoxia in solid tumors is an important predictor of poor clinical outcome to radiotherapy. Both physicochemical and biological processes contribute to a reduced sensitivity of hypoxic tumor cells to ionizing radiation and hypoxia-related treatment resistances. A conventional low-dose fractionated radiotherapy regimen exploits iterative reoxygenation in between the individual fractions, nevertheless tumor hypoxia still remains a major hurdle for successful treatment outcome. The technological advances achieved in image guidance and highly conformal dose delivery make it nowadays possible to prescribe larger doses to the tumor as part of single high-dose or hypofractionated radiotherapy, while keeping an acceptable level of normal tissue complication in the co-irradiated organs at risk. However, we insufficiently understand the impact of tumor hypoxia to single high-doses of RT and hypofractionated RT. So-called FLASH radiotherapy, which delivers ionizing radiation at ultrahigh dose rates (> 40 Gy/sec), has recently emerged as an important breakthrough in the radiotherapy field to reduce normal tissue toxicity compared to irradiation at conventional dose rates (few Gy/min). Not surprisingly, oxygen consumption and tumor hypoxia also seem to play an intriguing role for FLASH radiotherapy. Here we will discuss the role of tumor hypoxia for radiotherapy in general and in the context of novel radiotherapy treatment approaches.

Fucoidan promotes angiogenesis and accelerates wound healing through AKT/Nrf2/HIF-1α signalling pathway

After skin injury, wound repair involves a complex process in which angiogenesis plays a crucial role. Previous research has indicated that fucoidan may aid in wound healing; we therefore hypothesised that fucoidan may speed up the process by promoting angiogenesis. In this study, we investigated the potential molecular mechanism underlying fucoidan's ability to accelerate wound healing by promoting angiogenesis. Using a full-cut wound model, we observed that fucoidan significantly intensified wound closure and promoted granulation formation and collagen deposition. Immunofluorescence staining revealed that fucoidan also promoted wound angiogenesis, specifically by accelerating the migration of new blood vessels to the middle area of the wound. Furthermore, fucoidan demonstrated the ability to enhance the proliferation of human umbilical vein endothelial cells (HUVECs) damaged by hydrogen peroxide (H2 O2 ) and to improve the formation of endothelial tubes. Mechanistic studies revealed that fucoidan upregulated the protein levels of the AKT/Nrf2/HIF-1α signalling pathway, which plays a crucial role in angiogenesis. This was further confirmed using the inhibitor LY294002, which reversed the promotion of endothelial tube formation by fucoidan. Overall, our findings suggest that fucoidan can promote angiogenesis via the AKT/Nrf2/HIF-1α signalling pathway and accelerate wound healing.

Oxidative stress responsive transcription factors in cellular signalling transduction mechanisms

Oxidative stress results from the imbalances in the development of reactive oxygen species (ROS) and antioxidants defence system resulting in tissue injury. A key issue resulting in the modulation of ROS is that it alters hosts molecular, structural and functional properties which is accomplished via various signalling pathways which either activate or inhibit numerous transcription factors (TFs). Some of the regulators include Nuclear erythroid-2 related factors (Nrf-2), CCAAT/enhancer-binding protein delta (CEBPD), Activator Protein-1 (AP-1), Hypoxia-inducible factor 1(HIF-1), Nuclear factor κB (NF-κB), Specificity Protein-1 (SP-1) and Forkhead Box class O (FoxO) transcription factors. The expression of these transcription factors are dependent upon the stress signal and are sometimes interlinked. They are highly specific having their own regulation cellular events. Depending upon the transcription factors and better knowledge on the type of the oxidative stress help researchers develop safe, novel targets which can serve as efficient therapeutic targets for several disease conditions.

Proceedings of the National Cancer Institute Workshop on Charged Particle Radiobiology

In April 2016, the National Cancer Institute hosted a multidisciplinary workshop to discuss the current knowledge of the radiobiological aspects of charged particles used in cancer therapy to identify gaps in that knowledge that might hinder the effective clinical use of charged particles and to propose research that could help fill those gaps. The workshop was organized into 10 topics ranging from biophysical models to clinical trials and included treatment optimization, relative biological effectiveness of tumors and normal tissues, hypofractionation with particles, combination with immunotherapy, "omics," hypoxia, and particle-induced second malignancies. Given that the most commonly used charged particle in the clinic currently is protons, much of the discussion revolved around evaluating the state of knowledge and current practice of using a relative biological effectiveness of 1.1 for protons. Discussion also included the potential advantages of heavier ions, notably carbon ions, because of their increased biological effectiveness, especially for tumors frequently considered to be radiation resistant, increased effectiveness in hypoxic cells, and potential for differentially altering immune responses. The participants identified a large number of research areas in which information is needed to inform the most effective use of charged particles in the future in clinical radiation therapy. This unique form of radiation therapy holds great promise for improving cancer treatment.

Glutamic Pyruvate Transaminase GPT2 Promotes Tumorigenesis of Breast Cancer Cells by Activating Sonic Hedgehog Signaling

Increased glutamine metabolism is a hallmark of cancer. Mitochondrial glutamic pyruvate transaminase (GPT2) catalyzes the reversible transamination between alanine and α-ketoglutarate (α-KG), also known as 2-oxoglutarate, to generate pyruvate and glutamate during cellular glutamine catabolism. However, the precise role of GPT2 in tumorigenesis remains elusive. Here, we report that in breast cancer tissue samples and breast cancer cell lines, GPT2 expression level was markedly elevated and correlated with the pathological grades of breast cancers. GPT2 overexpression increased the subpopulation of breast cancer stem cells in vitro and promoted tumorigenesis in mice. GPT2 reduced α-KG level in cells leading to the inhibition of proline hydroxylase 2 (PHD2) activity involved in the regulation of HIF1α stability. Accumulation of HIF1α, resulting from GPT2-α-KG-PHD2 axial, constitutively activates sonic hedgehog (Shh) signaling pathway. Overall, GPT2 promotes tumorigenesis and stemness of breast cancer cells by activating the Shh signaling, suggesting that GTP2 is a potential target for breast cancer therapy.

Radionuclide I-131 Labeled Albumin-Paclitaxel Nanoparticles for Synergistic Combined Chemo-radioisotope Therapy of Cancer

Development of biocompatible/biodegradable materials with multiple functionalities via simple methods for cancer combination therapy has attracted great attention in recent years. Herein, paclitaxel (PTX), a popular anti-tumor chemotherapeutic drug, is used to induce the self-assembly of human serum albumin (HSA) pre-labeled with radionuclide I-131, obtaining 131I-HSA-PTX nanoparticles for combined chemotherapy and radioisotope therapy (RIT) of cancer. Such 131I-HSA-PTX nanoparticles show prolonged blood circulation time, high tumor specific uptake and excellent intra-tumor penetration ability. Interestingly, as revealed by in vivo photoacoustic imaging and ex vivo immunofluorescence staining, PTX delivered into the tumor by HSA-nanoparticle transportation can remarkably enhance the tumor local oxygen level and suppress the expression of HIF-1α, leading to greatly relieved tumor hypoxia. As the results, the combined in vivo chemotherapy & RIT with 131I-HSA-PTX nanoparticles in the animal tumor model offers excellent synergistic therapeutic efficacy, likely owing to the greatly modulated tumor microenvironment associated with PTX-based chemotherapy. Therefore, in this work, a simple yet effective therapeutic agent is developed for synergistic chemo-RIT of cancer, promising for future clinic translations in cancer treatment.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

Genomic profiling in locally advanced and inflammatory breast cancer and its link to DCE-MRI and overall survival

PURPOSE

We have previously reported that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) perfusion patterns obtained from locally advanced breast cancer (LABC) patients prior to neoadjuvant therapy predicted pathologic clinical response. Genomic analyses were also independently conducted on the same patient population. This retrospective study was performed to test two hypotheses: (1) gene expression profiles are associated with DCE-MRI perfusion patterns, and (2) association between long-term overall survival data and gene expression profiles can lead to the identification of novel predictive biomarkers.

METHODS

We utilised RNA microarray and DCE-MRI data from 47 LABC patients, including 13 inflammatory breast cancer (IBC) patients. Association between gene expression profile and DCE-MRI perfusion patterns (centrifugal and centripetal) was determined by Wilcoxon rank sum test. Association between gene expression level and survival was assessed using a Cox rank score test. Additional genomic analysis of the IBC subset was conducted, with a period of follow-up of up to 11 years. Associations between gene expression and overall survival were further assessed in The Cancer Genome Atlas Data Portal.

RESULTS

Differences in gene expression profiles were seen between centrifugal and centripetal perfusion patterns in the sulphotransferase family, cytosolic, 1 A, phenol-preferring, members 1 and 2 (SULT1A1, SULT1A2), poly (ADP-ribose) polymerase, member 6 (PARP6), and metastasis tumour antigen1 (MTA1). In the IBC subset our analyses demonstrated that differential expression of 45 genes was associated with long-term survival.

CONCLUSIONS

Here we have demonstrated an association between DCE-MRI perfusion patterns and gene expression profiles. In addition we have reported on candidate prognostic biomarkers in IBC patients, with some of the genes being significantly associated with survival in IBC and LABC.

Metabolic reprogramming of cancer-associated fibroblasts by IDH3α downregulation

Cancer-associated fibroblasts (CAFs) provide critical metabolites for tumor growth and undergo metabolic reprogramming to support glycolysis. However, the molecular mechanisms responsible for this change remain unclear. Here, we report that TGF-β1- or PDGF-induced CAFs switch from oxidative phosphorylation to aerobic glycolysis. We identify downregulation of isocitrate dehydrogenase 3α (IDH3α) as a marker for this switch. Furthermore, miR-424 downregulates IDH3α during CAF formation. Downregulation of IDH3α decreases the effective level of α-ketoglutarate (α-KG) by reducing the ratio of α-KG to fumarate and succinate, resulting in PHD2 inhibition and HIF-1α protein stabilization. The accumulation of HIF-1α, in turn, promotes glycolysis by increasing the uptake of glucose, upregulating expression of glycolytic enzymes under normoxic conditions, and inhibiting oxidative phosphorylation by upregulating NDUFA4L2. CAFs from tumor samples exhibit low levels of IDH3α, and overexpression of IDH3α prevents transformation of fibroblasts into CAFs. Our studies reveal IDH3α to be a critical metabolic switch in CAFs.

Submandibular Gland Transfer for the Prevention of Postradiation Xerostomia in Patients with Head and Neck Cancer: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> Submandibular gland transfer has been widely used to prevent postradiation xerostomia in head-and-neck cancers. However, there are still some controversies. <b><i>Methods:</i></b> Six databases were searched, data extraction was performed and the risk of bias was assessed by 2 reviewers independently. The meta-analysis was performed using Review Manager, version 5.2. <b><i>Results:</i></b> A total of 7 trials (12 articles) and 369 participants were included. <b><i>Conclusions:</i></b> The present clinical evidence suggests that submandibular gland transfer might be highly effective to prevent postradiation xerostomia in head-and-neck cancers without serious adverse events. However, more randomized controlled trials are still needed to confirm this conclusion.

Limitations of the dorsal skinfold window chamber model in evaluating anti-angiogenic therapy during early phase of angiogenesis

Background

Angiogenesis is an essential process during tumor development and growth. The murine dorsal skinfold window chamber model has been used for the study of both tumor microvasculature and other vascular diseases, including the study of anti-angiogenic agents in cancer therapy. Hyperspectral imaging of oxygen status of the microvasculature has not been widely used to evaluate response to inhibition of angiogenesis in early tumor cell induced vascular development. This study demonstrates the use of two different classes of anti-angiogenic agents, one targeting the Vascular Endothelial Growth Factor (VEGF) pathway involved with vessel sprouting and the other targeting the Angiopoietin/Tie2 pathway involved in vascular destabilization. Studies evaluated the tumor microvascular response to anti-angiogenic inhibitors in the highly angiogenic renal cell carcinoma induced angiogenesis model.

Methods

Human renal cell carcinoma, Caki-2 cells, were implanted in the murine skinfold window chamber. Mice were treated with either VEGF pathway targeted small molecule inhibitor Sunitinib (100 mg/kg) or with an anti-Ang-2 monoclonal antibody (10 mg/kg) beginning the day of window chamber surgery and tumor cell implantation. Hyperspectral imaging of hemoglobin saturation was used to evaluate both the development and oxygenation of the tumor microvasculature. Tumor volume over time was also assessed over an 11-day period post surgery.

Results

The window chamber model was useful to demonstrate the inhibition of angiogenesis using the VEGF pathway targeted agent Sunitinib. Results show impairment of tumor microvascular development, reduced oxygenation of tumor-associated vasculature and impairment of tumor volume growth compared to control. On the other hand, this model failed to demonstrate the anti-angiogenic effect of the Ang-2 targeted agent. Follow up experiments suggest that the initial surgery of the window chamber model may interfere with such an agent thus skewing the actual effects on angiogenesis.

Conclusions

Results show that this model has great potential to evaluate anti-VEGF, or comparable, targeted agents; however the mere protocol of the window chamber model interferes with proper evaluation of Ang-2 targeted agents. The limitations of this in vivo model in evaluating the response of tumor vasculature to anti-angiogenic agents are discussed.

Up-regulation of microRNA-138 induce radiosensitization in lung cancer cells

Deregulation of microRNAs (miRNAs) is implicated in tumor progression. We attempt to identify the association between miR-138 and Sentrin/SUMO-specific protease 1 (SENP1) as a radiosensitization-related gene and characterize the biological function by which SENP1 was regulated by miR-138 to influence radiosensitization in lung cancer cells. In this study, we showed that miRNA-138 is reduced in both lung cancer clinical specimens and cell lines and is effective to inhibit SENP1 expression. Moreover, high levels of miR-138 are associated with lower levels of lung cancer cell proliferation and colony formation. Then, we investigated the underlying mechanisms responsible for the increase in the radiosensitivity of lung cancer cells when SENP1 is inhibited by miR-138. We further show that the increased radiosensitivity may be the result of an increased γ-H2AX expression, an increased rate of apoptosis, and changes in the cell cycle. In conclusion, our data demonstrate that the miR-138/SENP1 cascade is relative to radiosensitization in lung cancer cells and is a potential radiotherapy target.

Deferoxamine restores callus size, mineralization, and mechanical strength in fracture healing after radiotherapy

BACKGROUND

Therapeutic augmentation of fracture-site angiogenesis with deferoxamine has proven to increase vascularity, callus size, and mineralization in long-bone fracture models. The authors posit that the addition of deferoxamine would enhance pathologic fracture healing in the setting of radiotherapy in a model where nonunions are the most common outcome.

METHODS

Thirty-five Sprague-Dawley rats were divided into three groups. Fracture, irradiated fracture, and irradiated fracture plus deferoxamine. The irradiated fracture and irradiated fracture plus deferoxamine groups received a human equivalent dose of radiotherapy [7 Gy/day for 5 days, (35 Gy)] 2 weeks before mandibular osteotomy and external fixation. The irradiated fracture plus deferoxamine group received injections of deferoxamine into the fracture callus after surgery. After a 40-day healing period, mandibles were dissected, clinically assessed for bony union, imaged with micro-computed tomography, and tension tested to failure.

RESULTS

Compared with irradiated fractures, metrics of callus size, mineralization, and strength in deferoxamine-treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition, the authors observed an increased rate of achieving bony unions in the irradiated fracture plus deferoxamine-treated group when compared with irradiated fracture (67 percent and 20 percent, respectively).

CONCLUSIONS

The authors' data demonstrate nearly total restoration of callus size, mineralization, and biomechanical strength, and a threefold increase in the rate of union with the use of deferoxamine. The authors' results suggest that the administration of deferoxamine may have the potential for clinical translation as a new treatment paradigm for radiation-induced pathologic fractures.

18F-fluorothymidine-pet imaging of glioblastoma multiforme: effects of radiation therapy on radiotracer uptake and molecular biomarker patterns

Introduction. PET imaging is a useful clinical tool for studying tumor progression and treatment effects. Conventional (18)F-FDG-PET imaging is of limited usefulness for imaging Glioblastoma Multiforme (GBM) due to high levels of glucose uptake by normal brain and the resultant signal-to-noise intensity. (18)F-Fluorothymidine (FLT) in contrast has shown promise for imaging GBM, as thymidine is taken up preferentially by proliferating cells. These studies were undertaken to investigate the effectiveness of (18)F-FLT-PET in a GBM mouse model, especially after radiation therapy (RT), and its correlation with useful biomarkers, including proliferation and DNA damage. Methods. Nude/athymic mice with human GBM orthografts were assessed by microPET imaging with (18)F-FDG and (18)F-FLT. Patterns of tumor PET imaging were then compared to immunohistochemistry and immunofluorescence for markers of proliferation (Ki-67), DNA damage and repair (γH2AX), hypoxia (HIF-1α), and angiogenesis (VEGF). Results. We confirmed that (18)F-FLT-PET uptake is limited in healthy mice but enhanced in the intracranial tumors. Our data further demonstrate that (18)F-FLT-PET imaging usefully reflects the inhibition of tumor by RT and correlates with changes in biomarker expression. Conclusions. (18)F-FLT-PET imaging is a promising tumor imaging modality for GBM, including assessing RT effects and biologically relevant biomarkers.

Synergistic antitumor effects of endostar in combination with oxaliplatin via inhibition of HIF and CXCR4 in the colorectal cell line SW1116

Combination treatment with endostar, a novel modified endostatin, and cytotoxic chemotherapies showed a survival benefit in Chinese clinical trials. However, the exact mechanism for this synergism remains unclear. In this study, we report for the first time that the chemokine receptor CXCR4 and the hypoxia-inducible transcription factors (HIF)-1α and HIF-2α are involved in these synergistic antitumor effects in human colorectal cancer SW1116 cells in vitro when endostar treatment is combined with the cytotoxic drug oxaliplatin. Under normoxia, we demonstrate that endostar and oxaliplatin treatments synergize to inhibit SW1116 cell proliferation, Matrigel adhesion and invasion by reduction of CXCR4 expression. Consistently, these antitumor abilities of endostar and oxaliplatin were markedly reduced by silencing of CXCR4 in SW1116 cells. Under low oxygen conditions (hypoxia, 1% oxygen), enhanced proliferation of SW1116 cells exposed to oxaliplatin was observed due to the emergence of drug resistance. Strikingly, endostar overcame oxaliplatin-resistance, most likely as a consequence of reduced HIF-2α and CXCR4 levels. CXCR4, is only dependent on HIF-2α, which promotes more aggressive phenotype and more significant for oxaliplatin resistance in SW1116 cells. Our data not only provide clues to aid understanding of the mechanism of the synergism of endostar and chemotherapy under either normoxia or hypoxia, but also suggests a new strategy of combination endostar and chemotherapy treatments which might potentiate therapeutic efficacies and/or counteract chemotherapy resistance.

New insight into the SDF-1/CXCR4 axis in a breast carcinoma model: hypoxia-induced endothelial SDF-1 and tumor cell CXCR4 are required for tumor cell intravasation

The SDF-1/CXCR4 axis has been implicated in breast cancer metastasis. In contrast to its well-established role in organ-specific homing and colonization of tumor cells, the involvement in intravasation, especially in a hypoxic environment, is still poorly understood. Initially, we detected both, the chemokine SDF-1 and its receptor CXCR4 in microvessels in invasive ductal cancer samples. To elucidate the role of the SDF-1/CXCR4 axis in vascular endothelium for tumor intravasation, we evaluated the effects of CXCR4 activation in human umbilical vein and dermal microvascular endothelial cells (HUVEC and HDMEC) and in cultured mammary carcinoma cells (MDA MB231, and MCF7). We observed an upregulation of SDF-1 and CXCR4 in HUVECs in hypoxia, which led to proliferation, migration, and tube formation. Hypoxia induced adhesion of tumor cells to endothelial cells and stimulated transendothelial migration. The effects of hypoxia were dependent on the activity of the transcription factor hypoxia-inducible factor. Adhesion to and migration through a HUVEC monolayer were significantly reduced by lentiviral inhibition of CXCR4 in breast carcinoma cells or treatment of endothelial cells with an anti-SDF-1 neutralizing antibody. These data show that the interaction of SDF-1 secreted by ECs with tumor cell CXCR4 is sufficient to stimulate transendothelial migration of the tumor cells. Our results suggest that the SDF-1/CXCR4 axis is important in angiogenesis and tumor cell intravasation. Because both proteins were readily identifiable in a significant fraction of human breast cancer samples by immunohistochemistry, CXCR4 may constitute a molecular target for therapy when both, SDF-1, and CXCR4 are expressed.

Application of optical imaging and spectroscopy to radiation biology

Optical imaging and spectroscopy is a diverse field that has been of critical importance in a wide range of areas in radiation research. It is capable of spanning a wide range of spatial and temporal scales, and has the sensitivity and specificity needed for molecular and functional imaging. This review will describe the basic principles of optical imaging and spectroscopy, highlighting a few relevant applications to radiation research.

Basal HIF-1α expression levels are not predictive for radiosensitivity of human cancer cell lines

BACKGROUND AND PURPOSE

High levels of hypoxia inducible factor (HIF)-1α in tumors are reported to be associated with tumor progression and resistance to therapy. To examine the impact of HIF-1α on radioresistance under normoxia, the sensitivity towards irradiation was measured in human tumor cell lines that differ significantly in their basal HIF-1α levels.

MATERIAL AND METHODS

HIF-1α levels were quantified in lysates of H1339, EPLC-272H, A549, SAS, XF354, FaDu, BHY, and CX- tumor cell lines by ELISA. Protein levels of HIF-1α, HIF-2α, carbonic anhydrase IX (CA IX), and GAPDH were assessed by Western blot analysis. Knock-down experiments were performed using HIF-1α siRNA. Clonogenic survival after irradiation was determined by the colony forming assay.

RESULTS

According to their basal HIF-1α status, the tumor cell lines were divided into low (SAS, XF354, FaDu, A549, CX-), intermediate (EPLC-272H, BHY), and high (H1339) HIF-1α expressors. The functionality of the high basal HIF-1α expression in H1339 cells was proven by reduced CA IX expression after knocking-down HIF-1α. Linear regression analysis revealed no correlation between basal HIF-1α levels and the survival fraction at either 2 or 4 Gy in all tumor cell lines investigated.

CONCLUSION

Our data suggest that basal HIF-1α levels in human tumor cell lines do not predict their radiosensitivity under normoxia.

Radiation-induced vascular damage in tumors: implications of vascular damage in ablative hypofractionated radiotherapy (SBRT and SRS)

We have reviewed the studies on radiation-induced vascular changes in human and experimental tumors reported in the last several decades. Although the reported results are inconsistent, they can be generalized as follows. In the human tumors treated with conventional fractionated radiotherapy, the morphological and functional status of the vasculature is preserved, if not improved, during the early part of a treatment course and then decreases toward the end of treatment. Irradiation of human tumor xenografts or rodent tumors with 5-10 Gy in a single dose causes relatively mild vascular damages, but increasing the radiation dose to higher than 10 Gy/fraction induces severe vascular damage resulting in reduced blood perfusion. Little is known about the vascular changes in human tumors treated with high-dose hypofractionated radiation such as stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS). However, the results for experimental tumors strongly indicate that SBRT or SRS of human tumors with doses higher than about 10 Gy/fraction is likely to induce considerable vascular damages and thereby damages the intratumor microenvironment, leading to indirect tumor cell death. Vascular damage may play an important role in the response of human tumors to high-dose hypofractionated SBRT or SRS.

High-resolution in vivo imaging of fluorescent proteins using window chamber models

Fluorescent proteins enable in vivo characterization of a wide and growing array of morphological and functional biomarkers. To fully capitalize on the spatial and temporal information afforded by these reporter proteins, a method for imaging these proteins at high resolution longitudinally is required. This chapter describes the use of window chamber models as a means of imaging fluorescent proteins and other optical parameters. Such models essentially involve surgically implanting a window through which tumor or normal tissue can be imaged using existing microscopy techniques. This enables acquisition of high-quality images down to the cellular or subcellular scale, exploiting the diverse array of optical contrast mechanisms, while also maintaining the native microenvironment of the tissue of interest. This makes these techniques applicable to a wide array of problems in the biomedical sciences.

Computational models of VEGF-associated angiogenic processes in cancer

Tumour angiogenesis allows a growing mass of cancer cells to overcome oxygen diffusion limitation and to increase cell survival. The growth of capillaries from pre-existing blood vessels is the result of numerous signalling cascades involving different molecules and of cellular events involving multiple cell and tissue types. Computational models offer insight into the mechanisms governing angiogenesis and provide quantitative information on parameters difficult to assess by experiments alone. In this article, we summarize results from computational models of tumour angiogenic processes with a focus on the molecular-detailed vascular endothelial growth factor-associated models that have been developed in our laboratory, spanning multiple scales from the molecular to whole body.

Irradiation-dependent effects on tumor perfusion and endogenous and exogenous hypoxia markers in an A549 xenograft model

PURPOSE

Hypoxia is a major determinant of tumor radiosensitivity, and microenvironmental changes in response to ionizing radiation (IR) are often heterogenous. We analyzed IR-dependent changes in hypoxia and perfusion in A549 human lung adenocarcinoma xenografts.

MATERIALS AND METHODS

Immunohistological analysis of two exogenously added chemical hypoxic markers, pimonidazole and CCI-103F, and of the endogenous marker Glut-1 was performed time dependently after IR. Tumor vessels and apoptosis were analyzed using CD31 and caspase-3 antibodies. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and fluorescent beads (Hoechst 33342) were used to monitor vascular perfusion.

RESULTS

CCI-103F signals measuring the fraction of hypoxic areas after IR were significantly decreased by approximately 50% when compared with pimonidazole signals, representing the fraction of hypoxic areas from the same tumors before IR. Interestingly, Glut-1 signals were significantly decreased at early time point (6.5 h) after IR returning to the initial levels at 30.5 h. Vascular density showed no difference between irradiated and control groups, whereas apoptosis was significantly induced at 10.5 h post-IR. DCE-MRI indicated increased perfusion 1 h post-IR.

CONCLUSIONS

The discrepancy between the hypoxic fractions of CCI-103F and Glut-1 forces us to consider the possibility that both markers reflect different metabolic alterations of tumor microenvironment. The reliability of endogenous markers such as Glut-1 to measure reoxygenation in irradiated tumors needs further consideration. Monitoring tumor microvascular response to IR by DCE-MRI and measuring tumor volume alterations should be encouraged.

Application of intravital microscopy in studies of tumor microcirculation

To grow and progress, solid tumors develop a vascular network through co-option and angiogenesis that is characterized by multiple structural and functional abnormalities, which negatively influence therapeutic outcome through direct and indirect mechanisms. As such, the morphology and function of tumor blood vessels, plus their response to different treatments, are a vital and active area of biological research. Intravital microscopy (IVM) has played a key role in studies of tumor angiogenesis, and ongoing developments in molecular probes, imaging techniques, and postimage analysis methods have ensured its continued and widespread use. In this review we discuss some of the primary advantages and disadvantages of IVM approaches and describe recent technological advances in optical microscopy (e.g., confocal microscopy, multiphoton microscopy, hyperspectral imaging, and optical coherence tomography) with examples of their application to studies of tumor angiogenesis.

Relationships between cycling hypoxia, HIF-1, angiogenesis and oxidative stress

This Failla Lecture focused on the inter-relationships between tumor angiogenesis, HIF-1 expression and radiotherapy responses. A common thread that bonds all of these factors together is microenvironmental stress caused by reactive oxygen and nitrogen species formed during tumor growth and angiogenesis or in response to cytotoxic treatment. In this review we focus on one aspect of the crossroad between oxidative stress and angiogenesis, namely cycling hypoxia. Understanding of the relative importance of this feature of the tumor microenvironment has recently expanded; it influences tumor biology in ways that are separate from chronic hypoxia. Cycling hypoxia can influence angiogenesis, treatment responses and metastatic behavior. It represents an important and relatively less well understood feature of tumor biology that requires additional research.

Clinical biomarkers of angiogenesis inhibition

INTRODUCTION

An expanding understanding of the importance of angiogenesis in oncology and the development of numerous angiogenesis inhibitors are driving the search for biomarkers of angiogenesis. We review currently available candidate biomarkers and surrogate markers of anti-angiogenic agent effect.

DISCUSSION

A number of invasive, minimally invasive, and non-invasive tools are described with their potential benefits and limitations. Diverse markers can evaluate tumor tissue or biological fluids, or specialized imaging modalities.

CONCLUSIONS

The inclusion of these markers into clinical trials may provide insight into appropriate dosing for desired biological effects, appropriate timing of additional therapy, prediction of individual response to an agent, insight into the interaction of chemotherapy and radiation following exposure to these agents, and perhaps most importantly, a better understanding of the complex nature of angiogenesis in human tumors. While many markers have potential for clinical use, it is not yet clear which marker or combination of markers will prove most useful.

The expanding universe of hypoxia

Reduced oxygen availability (hypoxia) is sensed and transduced into changes in the activity or expression of cellular macromolecules. These responses impact on virtually all areas of biology and medicine. In this meeting report, we summarize major developments in the field that were presented at the 2008 Keystone Symposium on Cellular, Physiological, and Pathogenic Responses to Hypoxia.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

Hypoxia and free radicals, such as reactive oxygen and nitrogen species, can alter the function and/or activity of the transcription factor hypoxia-inducible factor 1 (HIF1). Interplay between free radicals, hypoxia and HIF1 activity is complex and can influence the earliest stages of tumour development. The hypoxic environment of tumours is heterogeneous, both spatially and temporally, and can change in response to cytotoxic therapy. Free radicals created by hypoxia, hypoxia-reoxygenation cycling and immune cell infiltration after cytotoxic therapy strongly influence HIF1 activity. HIF1 can then promote endothelial and tumour cell survival. As discussed here, a constant theme emerges: inhibition of HIF1 activity will have therapeutic benefit.

The interplay between MYC and HIF in the Warburg effect

c-MYC and the hypoxia-inducible factors (HIFs) are critical factors for tumorigenesis in a large number of human cancers. While the normal function of MYC involves the induction of cell proliferation and enhancement of cellular metabolism, the function of HIF, particularly HIF-1, involves adaptation to the hypoxic microenvironment, including activation of anaerobic glycolysis. When MYC-dependent tumors grow, the hypoxic tumor microenvironment elevates the levels of HIF, such that oncogenic MYC and HIF collaborate to enhance the cancer cell's metabolic needs through increased uptake of glucose and its conversion to lactate. HIF is also able to attenuate mitochondrial respiration through the induction of pyruvate dehydrogenase kinase 1 (PDK1), which in part accounts for the Warburg effect that describes the propensity for cancers to avidly take up glucose and convert it to lactate with the concurrent decrease in mitochondrial respiration. Target genes that are common to both HIF and MYC, such as PDK1, LDHA, HK2, and TFRC, are therefore attractive therapeutic targets, because their coordinate induction by HIF and MYC widens the therapeutic window between cancer and normal tissues.

How lithium treatment generates neutrophilia by enhancing phosphorylation of GSK-3, increasing HIF-1 levels and how this path is important during engraftment

Lithium is commonly used in psychiatry for mood stabilization. Lithium treatment results in neutrophilia, increased platelets and increased circulating CD34+ haematopoietic stem cells, HSC. This paper outlines the newly discovered mechanism by which this occurs. Glycogen synthase kinase-3, GSK-3, phosphorylates and thereby inactivates hypoxia-induced factor-1, HIF-1. HIF-1 is a transcription factor triggering transcription of multiple genes related to adaptation to hypoxia, among which is CXCL12. CXCL12 forms the primary homing gradient for CD34+ HSCs towards the hypoxic, trophic bone marrow niche to which they must go to thrive. Lithium inhibits GSK-3 thereby increasing active HIF-1 that results in a stronger CXCL12 homing gradient. Trophic niche function is enhanced, ultimately resulting in increased production of neutrophils, platelets and CD34+ cells. Sitagliptin is a new drug to treat diabetes that coincidentally inhibits destruction of CXCL12. Thus, lithium and sitagliptin enhance CXCL12 by different paths, potentially increasing trophic niche function. Awareness of this path is important in HSC transplantation.