Tumor hypoxia at the micro-regional level: clinical relevance and predictive value of exogenous and endogenous hypoxic cell markers

An acidic environment changes cyclin D1 localization and alters colony forming ability in gliomas

The human glioma cell lines, U87 and T98G, were evaluated for their ability to survive and form colonies in an acidic environment of pH(ext) 6.0. In contrast to U87, which showed an 80-90% survival rate, only 40% of T98G cells survived 6 days at pH(ext) 6.0 and lost their colony forming ability when returned to a normocidic environment. Although both U87 and T98G cells maintain an intracellular pH (pH(i)) of 7.0 at pH(ext) 6.0 and arrest mostly in G1 phase of the cell cycle, only T98G demonstrated a major loss of cyclin D1 that was prevented by the proteasome inhibitor MG132. Colony forming ability was restored by stably transfecting T98G cells with a cyclin D1-expressing plasmid. Both U87 and T98G cells demonstrated increased cytoplasmic localization of cyclin D1 during exposure at pH(ext) 6.0. Upon prolonged (24 h) incubation at pH(ext) 6.0, nuclear cyclin D1 was nearly absent in T98G in contrast to U87 cells. Thus, an acidic environment triggers cytoplasmic localization and proteasomal degradation of cyclin D1.

Reproducibility of intratumor distribution of (18)F-fluoromisonidazole in head and neck cancer

PURPOSE

Hypoxia is one of the main causes of the failure to achieve local control using radiotherapy. This is due to the increased radioresistance of hypoxic cells. (18)F-fluoromisonidazole ((18)F-FMISO) positron emission tomography (PET) is a noninvasive imaging technique that can assist in the identification of intratumor regions of hypoxia. The aim of this study was to evaluate the reproducibility of (18)F-FMISO intratumor distribution using two pretreatment PET scans.

METHODS AND MATERIALS

We enrolled 20 head and neck cancer patients in this study. Of these, 6 were excluded from the analysis for technical reasons. All patients underwent an (18)F-fluorodeoxyglucose study, followed by two (18)F-FMISO studies 3 days apart. The hypoxic volumes were delineated according to a tumor/blood ratio >or=1.2. The (18)F-FMISO tracer distributions from the two (18)F-FMISO studies were co-registered on a voxel-by-voxel basis using the computed tomography images from the PET/computed tomography examinations. A correlation between the (18)F-FMISO intensities of the corresponding spatial voxels was derived.

RESULTS

A voxel-by-voxel analysis of the (18)F-FMISO distributions in the entire tumor volume showed a strong correlation in 71% of the patients. Restraining the correlation to putatively hypoxic zones reduced the number of patients exhibiting a strong correlation to 46%.

CONCLUSION

Variability in spatial uptake can occur between repeat (18)F-FMISO PET scans in patients with head and neck cancer. Blood data for one patient was not available. Of 13 patients, 6 had well-correlated intratumor distributions of (18)F-FMISO-suggestive of chronic hypoxia. More work is required to identify the underlying causes of changes in intratumor distribution before single-time-point (18)F-FMISO PET images can be used as the basis of hypoxia-targeting intensity-modulated radiotherapy.

Downregulation of BCL-2 induces downregulation of carbonic anhydrase IX, vascular endothelial growth factor, and pAkt and induces radiation sensitization

OBJECTIVES

Our group previously demonstrated that expression of the oncogene, Bcl-2, was associated with radiation resistance. The aim of the present study was to determine whether Bcl-2 expression in radiation-resistant tumors was associated with expression of carbonic anhydrase IX (CAIX), vascular endothelial growth factor (VEGF), and pAkt and whether downregulation of Bcl-2 could modulate the expression of CAIX, VEGF, and pAkt.

METHODS

Two prostate cancer cell lines, PC-3-Bcl-2 and PC-3-Neo, were injected into the subcutaneous flanks of 192 athymic male nude mice; 96 received PC-3 Bcl-2 and 96 PC-3-Neo. The mice were then treated with antisense Bcl-2 oligodeoxynucleotide (ASODN), reverse control ODN, or vehicle only (mock treatment) with or without irradiation (4 Gy). The tumors were monitored for growth (ie, volume) over time, resected at various points, and processed and sectioned for protein analyses.

RESULTS

Bcl-2 ASODN treatment was associated with downregulation of Bcl-2, VEGF, pAkt, and CAIX. PC-3-Bcl-2 and PC-3-Neo prostate tumor xenografts in mice treated with the combination of Bcl-2 ASODN and irradiation were significantly (ie, one third) smaller than those in mice treated with reverse control ODN alone, Bcl-2 ASODN alone, irradiation alone, or reverse control ODN plus irradiation (P = 0.0001). An increased tumor response to the combined therapy was associated with decreased expression of Bcl-2, VEGF, and pAkt proteins.

CONCLUSIONS

These findings have demonstrated an intimate relationship among CAIX, VEGF, pAkt, and Bcl-2 in prostate tumors. Thus, CAIX might prove effective as a potential marker of tumor radiation resistance. Downregulation of CAIX might lead to radiation sensitization. Consequently, the combination of CAIX reduction and radiotherapy warrants further consideration as a new strategy for therapy.

Expression and prognostic significance of a panel of tissue hypoxia markers in head-and-neck squamous cell carcinomas

PURPOSE

To investigate the expression pattern of hypoxia-induced proteins identified as being involved in malignant progression of head-and-neck squamous cell carcinoma (HNSCC) and to determine their relationship to tumor pO(2) and prognosis.

METHODS AND MATERIALS

We performed immunohistochemical staining of hypoxia-induced proteins (carbonic anhydrase IX [CA IX], BNIP3L, connective tissue growth factor, osteopontin, ephrin A1, hypoxia inducible gene-2, dihydrofolate reductase, galectin-1, IkappaB kinase beta, and lysyl oxidase) on tumor tissue arrays of 101 HNSCC patients with pretreatment pO(2) measurements. Analysis of variance and Fisher's exact tests were used to evaluate the relationship between marker expression, tumor pO(2), and CA IX staining. Cox proportional hazard model and log-rank tests were used to determine the relationship between markers and prognosis.

RESULTS

Osteopontin expression correlated with tumor pO(2) (Eppendorf measurements) (p = 0.04). However, there was a strong correlation between lysyl oxidase, ephrin A1, and galectin-1 and CA IX staining. These markers also predicted for cancer-specific survival and overall survival on univariate analysis. A hypoxia score of 0-5 was assigned to each patient, on the basis of the presence of strong staining for these markers, whereby a higher score signifies increased marker expression. On multivariate analysis, increasing hypoxia score was an independent prognostic factor for cancer-specific survival (p = 0.015) and was borderline significant for overall survival (p = 0.057) when adjusted for other independent predictors of outcomes (hemoglobin and age).

CONCLUSIONS

We identified a panel of hypoxia-related tissue markers that correlates with treatment outcomes in HNSCC. Validation of these markers will be needed to determine their utility in identifying patients for hypoxia-targeted therapy.

Glucose transporter-1 expression in squamous cell carcinoma of the tongue

PURPOSE

Tumor cells are known to express hypoxia-related proteins such as glucose transporter-1 (Glut-1). These hypoxia-induced changes may allow tumor cells to survive under sustained hypoxic microenvironments, and the surviving tumor cell under hypoxia may develop a more aggressive phenotype and so result in a poor prognosis.

MATERIALS AND METHODS

The Glut-1 expression was analyzed by immunohistochemistry, and its association with the prognosis was assessed in 60 patients with squamous cell carcinoma of the tongue.

RESULTS

The Glut-1 expression was diffuse with a membranous pattern, and the median percentage of Glut-1 positive tumor cells was 60% (range: 0.0 approximately 90.0%). A high Glut-1 expression (the percentage of positive tumor cells >or= the median value, 60%) was associated with the location of primary lesion, lymph node metastasis status and disease stage (p<0.05). The expression of Glut-1 was correlated with the Ki-67 expression (r=0.406, p=0.001). Microvessel density, as represented by CD31 staining, was also correlated with the Glut-1 expression although its significance is weak (r=0.267, p=0.039). On the univariate analysis, the group with a high Glut-1 expression showed poorer overall survival than the group with a low Glut-1 expression (p<0.05). However, the Glut-1 expression failed to show any independent prognostic significance on the multivariate analysis.

CONCLUSION

The expression of Glut-1 may be useful for predicting the prognosis and determining the treatment strategy for the management of squamous cell carcinoma of the tongue.

Drug Resistance and the Solid Tumor Microenvironment

Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.

Fluorine-18-labeled fluoromisonidazole positron emission and computed tomography-guided intensity-modulated radiotherapy for head and neck cancer: a feasibility study

PURPOSE

Hypoxia renders tumor cells radioresistant, limiting locoregional control from radiotherapy (RT). Intensity-modulated RT (IMRT) allows for targeting of the gross tumor volume (GTV) and can potentially deliver a greater dose to hypoxic subvolumes (GTV(h)) while sparing normal tissues. A Monte Carlo model has shown that boosting the GTV(h) increases the tumor control probability. This study examined the feasibility of fluorine-18-labeled fluoromisonidazole positron emission tomography/computed tomography ((18)F-FMISO PET/CT)-guided IMRT with the goal of maximally escalating the dose to radioresistant hypoxic zones in a cohort of head and neck cancer (HNC) patients.

METHODS AND MATERIALS

(18)F-FMISO was administered intravenously for PET imaging. The CT simulation, fluorodeoxyglucose PET/CT, and (18)F-FMISO PET/CT scans were co-registered using the same immobilization methods. The tumor boundaries were defined by clinical examination and available imaging studies, including fluorodeoxyglucose PET/CT. Regions of elevated (18)F-FMISO uptake within the fluorodeoxyglucose PET/CT GTV were targeted for an IMRT boost. Additional targets and/or normal structures were contoured or transferred to treatment planning to generate (18)F-FMISO PET/CT-guided IMRT plans.

RESULTS

The heterogeneous distribution of (18)F-FMISO within the GTV demonstrated variable levels of hypoxia within the tumor. Plans directed at performing (18)F-FMISO PET/CT-guided IMRT for 10 HNC patients achieved 84 Gy to the GTV(h) and 70 Gy to the GTV, without exceeding the normal tissue tolerance. We also attempted to deliver 105 Gy to the GTV(h) for 2 patients and were successful in 1, with normal tissue sparing.

CONCLUSION

It was feasible to dose escalate the GTV(h) to 84 Gy in all 10 patients and in 1 patient to 105 Gy without exceeding the normal tissue tolerance. This information has provided important data for subsequent hypoxia-guided IMRT trials with the goal of further improving locoregional control in HNC patients.

The potential role of intrinsic hypoxia markers as prognostic variables in cancer

Tumor hypoxia is related to tumor progression and therapy resistance, which leads to poor patient outcome. It has been suggested that measuring the hypoxic status of a tumor helps to predict patient outcome and to select more targeted treatment. However, current methods using needle electrodes or exogenous markers have limitations due to their invasiveness or necessity for preinjection. Recent studies showed that hypoxia-regulated genes could be alternatively used as endogenous hypoxia markers. This is a review of 15 hypoxia-regulated genes, including hypoxia-inducible factor-1 and its targets, and their correlation with tumor hypoxia and patient outcome from 213 studies. Though most of the studies showed significance of these genes in predicting prognosis, there was no definitive prognostic and hypoxia marker. In conclusion, this review suggests the need for further studies with standardized methods to examine gene expression, as well as the use of multiple gene expressions.

Analysis of oxygen transport in a diffusion-limited model of engineered heart tissue

Cardiac tissue engineering has made notable progress in recent years with the advent of an experimental model based on neonatal cardiomyocytes entrapped in collage gels and purified basement membrane extract, known as "engineered heart tissues" (EHTs). EHTs are a formidable display of tissue-level contractile function and cellular-level differentiation, although they suffer greatly from mass transport limitations due to the high density of metabolically active cells and the diffusion-limited nature of the hydrogel. In this report, a mathematical model was developed to predict oxygen levels inside a one-dimensional, diffusion-limited model of EHT. These predictions were then compared to values measured in corresponding experiments with a hypoxia-sensitive stain (pimonidazole). EHTs were cast between two plastic discs, which allowed for mass transfer with the culture medium to occur in only the radial direction. EHTs were cultured for up to 36 h in the presence of pimonidazole, after which time they were snap-frozen, histologically sectioned, and stained for bound pimonidazole. Quantitative image analysis was performed to measure the distance from the culture medium at which hypoxia first occurs under various conditions. As tested by variation of simple design parameters, the trends in oxygen profiles predicted by the model are in reasonable agreement with those obtained experimentally, although a number of ambiguities related to the specific model parameters led to a general overprediction of oxygen concentrations. Based on the sensitivity analysis in the present study, it is concluded that diffusion-reaction models may offer relatively precise predictions of oxygen concentrations in diffusion-limited tissue constructs.

Lack of prognostic and predictive value of CA IX in radiotherapy of squamous cell carcinoma of the head and neck with known modifiable hypoxia: An evaluation of the DAHANCA 5 study

BACKGROUND AND PURPOSE

CA IX is suggested to be an endogenous marker of hypoxia in tumours like squamous cell carcinomas of the head and neck (HNSCC). The aim of the present study was to investigate whether CA IX served as a prognostic factor for outcome in a large population of HNSCC and if CA IX was able to discriminate the tumours that did benefit from hypoxic modification with nimorazole.

MATERIALS AND METHODS

Paraffin-embedded formalin-fixed pre-treatment tumour tissue was available from 320 of the 414 patients treated in the randomized DAHANCA 5 protocol with primary radiotherapy+/-the hypoxic radiosensitizer nimorazole. CA IX was measured using immunohistochemistry and results were divided into four groups of CA IX expression: <1%, 1-10%, 10-30% and >30% of the tumour area with positive membrane staining. Locoregional control and disease-specific survival were used as endpoints.

RESULTS

Expression of CA IX was not correlated to any of the tumour or patient characteristics investigated. Furthermore, CA IX did not serve as a prognostic marker in the total cohort as well as in the group of 150 patients treated without nimorazole. Finally, no relation was found between the different expression levels of CA IX and the influence of nimorazole when locoregional control or disease-specific survival was used as endpoints.

CONCLUSIONS

This is to date one of the largest studies of CA IX in HNSCC. The data suggest that CA IX have no prognostic or predictive potential in patients with cancer in the head and neck treated with conventional radiotherapy and concomitant nimorazole.

Phosphorylation of eIF2alpha is required for mRNA translation inhibition and survival during moderate hypoxia

BACKGROUND AND PURPOSE

Human tumors are characterized by temporal fluctuations in oxygen tension. The biological pathways that respond to the dynamic tumor microenvironment represent potential molecular targets for cancer therapy. Anoxic conditions result in eIF2alpha dependent inhibition of overall mRNA translation, differential gene expression, hypoxia tolerance and tumor growth. The signaling pathway which governs eIF2alpha phosphorylation has therefore emerged as a potential molecular target. In this study, we investigated the role of eIF2alpha in regulating mRNA translation and hypoxia tolerance during moderate hypoxia. Since other molecular pathways that regulate protein synthesis are frequently mutated in cancer, we also assessed mRNA translation in a panel of cell lines from different origins.

MATERIALS AND METHODS

Immortalized human fibroblast, transformed mouse embryo fibroblasts (MEFs) and cells from six cancer cell lines were exposed to 0.2% or 0.0% oxygen. We assayed global mRNA translation efficiency by polysome analysis, as well as proliferation and clonogenic survival. The role of eIF2alpha was assessed in MEFs harboring a homozygous inactivating mutation (S51A) as well as in U373-MG cells overexpressing GADD34 (C-term) under a tetracycline-dependent promoter. The involvement of eIF4E regulation was investigated in HeLa cells stably expressing a short hairpin RNA (shRNA) targeting 4E-BP1.

RESULTS

All cells investigated inhibited mRNA translation severely in response to anoxia and modestly in response to hypoxia. Two independent genetic cell models demonstrated that inhibition of mRNA translation in response to moderate hypoxia was dependent on eIF2alpha phosphorylation. Disruption of eIF2alpha phosphorylation caused sensitivity to hypoxia and anoxia.

CONCLUSIONS

Disruption of eIF2alpha phosphorylation is a potential target for hypoxia-directed molecular cancer therapy.

Dynamics of tumor hypoxia measured with bioreductive hypoxic cell markers

Hypoxic cells are common in tumors and contribute to malignant progression, distant metastasis and resistance to radiotherapy. It is well known that tumors are heterogeneous with respect to the levels and duration of hypoxia. Several strategies, including high-oxygen-content gas breathing, radiosensitizers and hypoxic cytotoxins, have been developed to overcome hypoxia-mediated radioresistance. However, with these strategies, an increased tumor control rate is often accompanied by more severe side effects. Consequently, development of assays for prediction of tumor response and early monitoring of treatment responses could reduce both over- and undertreatment, thereby avoiding unnecessary side effects. The purpose of this review is to discuss different assays for measurement of hypoxia that can be used to detect changes in oxygen tension. The main focus is on exogenous bioreductive hypoxia markers (2-nitroimidazoles) such as pimonidazole, CCI-103F, EF5 and F-misonidazole. These are specifically reduced and bind to macromolecules in viable hypoxic cells. A number of these bioreductive drugs are approved for clinical use and can be detected with methods ranging from noninvasive PET imaging (low resolution) to microscopic imaging of tumor sections (high resolution). If the latter are stained for multiple markers, hypoxia can be analyzed in relation to different microenvironmental parameters such as vasculature, proliferation and endogenous hypoxia-related markers, for instance HIF1alpha and CA-IX. In addition, temporal and spatial changes in hypoxia can be analyzed by consecutive injection of two different hypoxia markers. Therefore, bioreductive exogenous hypoxia markers are promising as tools for development of predictive assays or as tools for early treatment monitoring and validation of potential endogenous hypoxia markers.

Tumor microenvironment in head and neck squamous cell carcinomas: Predictive value and clinical relevance of hypoxic markers. A review

BACKGROUND

Hypoxia and tumor cell proliferation are important factors determining the treatment response of squamous cell carcinomas of the head and neck. Successful approaches have been developed to counteract these resistance mechanisms although usually at the cost of increased short- and long-term side effects. To provide the best attainable quality of life for individual patients and the head and neck cancer patient population as a whole, it is of increasing importance that tools be developed that allow a better selection of patients for these intensified treatments.

METHODS

A literature review was performed with special focus on the predictive value and clinical relevance of endogenous hypoxia-related markers.

RESULTS

New methods for qualitative and quantitative assessment of functional microenvironmental parameters such as hypoxia, proliferation, and vasculature have identified several candidate markers for future use in predictive assays. Hypoxia-related markers include hypoxia inducible factor (HIF)-1alpha, carbonic anhydrase IX, glucose transporters, erythropoietin receptor, osteopontin, and others. Although several of these markers and combinations of markers are associated with treatment outcome, their clinical value as predictive factors remains to be established.

CONCLUSIONS

A number of markers and marker profiles have emerged that may have potential as a predictive assay. Validation of these candidate assays requires testing in prospective trials comparing standard treatment against experimental treatments targeting the related microregional constituent.

Microenvironmental transformations by VEGF- and EGF-receptor inhibition and potential implications for responsiveness to radiotherapy

The microregional distribution and dynamics of tumor cell hypoxia and proliferation are important determinants of tumor aggressiveness and resistance to treatment. Modulation of these elements by biological targeted drugs such as EGFR- and VEGFR-inhibitors may improve the effect of radiotherapy significantly. These combinations are being evaluated in clinical trials and evidence of their effectiveness is accumulating. However, the mechanistic basis of this cooperative effect and the role and behavior of the microregional tumor phenotype under EGF- and VEGF-blockage is poorly understood. Unfolding of these interactions and effects further downstream is necessary to exploit these biological modifiers most profitably to unravel questions such as: (1) can microregional phenotypes be modulated by EGFR- or VEGFR-blockage and how do downstream effects in the signaling pathways relate to these changes? (2) How do the microregional changes induced by EGFR- and VEGF-blockage affect the responsiveness of tumors to ionizing radiation? Answering these questions will improve our understanding of tumor growth related phenotypic transformations at the microregional level and how these can be influenced by modulation of the EGF- and VEGF-signaling pathways. This knowledge can be used to identify and improve therapeutic combinations with the novel biological modifiers and test a variety of biological-based treatment approaches.

Pimonidazole labelling and response to fractionated irradiation of five human squamous cell carcinoma (hSCC) lines in nude mice: The need for a multivariate approach in biomarker studies

OBJECTIVE

To investigate the influence on local control after fractionated radiotherapy of hypoxia measured in unirradiated tumours using the hypoxic marker Pimonidazole, using multivariate approaches.

MATERIAL AND METHODS

Five human squamous cell carcinoma lines (FaDu, UT-SCC-15, UT-SCC-14, XF354, and UT-SCC-5) were transplanted subcutaneously into the right hind-leg of NMRI nude mice. Histological material was collected from 60 unirradiated tumours after injection of Pimonidazole. The relative hypoxic area within the viable tumour area (Pimonidazole hypoxic fraction, pHF) was determined in seven serial 10 microm cross-sections per tumour by fluorescence microscopy and computerized image analysis. Local tumour control was evaluated in a total of 399 irradiated tumours at 120 days after 30 fractions given within 6 weeks with total doses between 30 and 115 Gy.

RESULTS

Tumour lines showed pronounced heterogeneity in both pHF and TCD50. Mean pHF values varied between 5% and 37%, TCD50 values between 47 and 130 Gy. A Cox Proportional Hazards model of time to recurrence with two covariates, dose and pHF, yielded significant contributions of both parameters on local control (p < 0.005) but violated the proportional hazards assumption, suggesting that other factors also influence tumour control. Introduction of histological grade as an example of a confounding factor into the model improved the fit significantly. Local control rates decreased with increasing pHF and this effect was more pronounced at higher doses.

CONCLUSIONS

This study confirms that tumour hypoxia measured using Pimonidazole in untreated tumours is a significant determinant of local control after fractionated irradiation. The data support the use of multivariate approaches for the evaluation of a single prognostic biomarker such as Pimonidazole, and more generally, suggest that they are required to establish accurate prognostic factors for tumour response.

Practical integration of [18F]-FDG-PET and PET-CT in the planning of radiotherapy for non-small cell lung cancer (NSCLC): The technical basis, ICRU-target volumes, problems, perspectives

The value of positron emission tomography using [18F]-fluoro-deoxy-glucose (FDG-PET) for pretherapeutic evaluation of patients with non-small cell lung cancer (NSCLC) is beyond doubt. Due to the increasing availability of PET and PET-CT scanners the method is now widely available, and its technical integration has become possible for radiotherapy planning systems. Due to the depiction of malignant tissue with high diagnostic accuracy, the use of FDG-PET in radiotherapy planning of NSCLC is very promising. However, by uncritical application, PET could impair rather than improve the prognosis of patients. Therefore, in the present paper we give an overview of technical factors influencing PET and PET-CT data, and their consequences for radiotherapy planning. We further review the relevant literature concerning the diagnostic value of FDG-PET and on the integration of FDG-PET data in RT planning for NSCLC. We point out the possible impact in gross tumor volume (GTV) definition and describe methods of target volume contouring of the primary tumor, as well as concepts for the integration of diagnostic information on lymph node involvement into the clinical target volume (CTV), and the possible implications of PET data on the definition of the planning target volume (PTV). Finally, we give an idea of the possible future use of tracers other than [18F]-FDG in lung cancer.

PET imaging of tumour hypoxia

This article has been retracted from Cancer Imaging. The correct citation is Padhani AR, Krohn KA, Lewis JS, Alber M. Imaging oxygenation of human tumours.

PET imaging of tumour hypoxia

Tumour hypoxia represents a significant challenge to the curability of human tumours leading to treatment resistance and enhanced tumour progression. Tumour hypoxia can be detected by non-invasive and invasive techniques but the inter-relationships between these remains largely undefined. [¹⁸F]Fluoromisonidazole-3-fluoro-1-(2 ^′-nitro-1 ^′-imidazolyl)-2-propanol ([¹⁸F]MISO) and Cu-diacetyl-bis(N⁴-methylthiosemicarbazone (Cu-ATSM)-positron emission tomography (PET), and blood oxygen level-dependent (BOLD)-magnetic resonance imaging (MRI) are the lead contenders for human application based on their non-invasive nature, ease of use and robustness, measurement of hypoxia status, validity, ability to demonstrate heterogeneity and general availability; PET techniques are the primary focus of this review.

Imaging oxygenation of human tumours

Tumour hypoxia represents a significant challenge to the curability of human tumours leading to treatment resistance and enhanced tumour progression. Tumour hypoxia can be detected by non-invasive and invasive techniques but the inter-relationships between these remains largely undefined. ¹⁸F-MISO and Cu-ATSM-PET, and BOLD-MRI are the lead contenders for human application based on their non-invasive nature, ease of use and robustness, measurement of hypoxia status, validity, ability to demonstrate heterogeneity and general availability, these techniques are the primary focus of this review. We discuss where developments are required for hypoxia imaging to become clinically useful and explore potential new uses for hypoxia imaging techniques including biological conformal radiotherapy.

p21(WAF1)-mediated transcriptional targeting of inducible nitric oxide synthase gene therapy sensitizes tumours to fractionated radiotherapy

Cancer gene therapy that utilizes toxic transgene products requires strict transcriptional targeting to prevent adverse normal tissue effects. We report on the use of a promoter derived from the cyclin dependent kinase inhibitor, p21((WAF1)), to control transgene expression. We demonstrate that this promoter is relatively silent in normal cells (L132, FSK, HMEC-1) compared to the almost constitutive expression obtained in tumour cells (DU145, LNCaP, HT29 and MCF-7) of varying p53 status, a characteristic that will be important in gene therapy protocols. In addition, we found that the p21((WAF1)) promoter could be further induced by both external beam radiation (up to eight-fold in DU145 cells), intracellular-concentrated radionuclides ([(211)At]MABG) (up to 3.5-fold in SK-N-BE(2c) cells) and hypoxia (up to four-fold in DU145 cells). We have previously achieved significant radiosensitization of tumour cells both in vitro and in vivo by using inducible nitric oxide synthase (iNOS) gene therapy to generate the potent radiosensitizer, nitric oxide (NO(.-)). Here, we report that a clinically relevant schedule of p21((WAF1))-driven iNOS gene therapy significantly sensitized both p53 wild-type RIF-1 tumours and p53 mutant HT29 tumours to fractionated radiotherapy. Our data highlight the utility of this p21((WAF1))/iNOS-targeted approach.

Imaging hypoxia after oxygenation-modification: comparing [18F]FMISO autoradiography with pimonidazole immunohistochemistry in human xenograft tumors

PURPOSE

Hypoxia is one of the reasons for radiation therapy resistance. Positron emission tomography using (18)F-labeled misonidazole ([(18)F]FMISO) is a non-invasive method of imaging tumor hypoxia. Aim of this study was to validate [(18)F]FMISO against the clinically most widely used hypoxic cell marker pimonidazole under different oxygenation conditions.

MATERIALS AND METHODS

One human head and neck squamous cell carcinoma (SCCNij3) and two human glioblastoma (E102 and E106) xenograft tumor lines were studied after injection of [(18)F]FMISO and pimonidazole. Control mice were compared with a second group breathing carbogen to reduce tumor hypoxia and with a third group with clamped tumors to increase hypoxia. Tumor sections were analyzed on a phosphor imaging system and consecutively stained immunohistochemically (IHC) for visualization of pimonidazole. Pixel-by-pixel analysis was performed and the hypoxic fraction, obtained after segmentation of the pimonidazole signal, was related to the mean optical density of [(18)F]FMISO and pimonidazole.

RESULTS

A moderate pixel-by-pixel correlation between [(18)F]FMISO autoradiography and pimonidazole IHC was found for the control tumors, after carbogen breathing and after clamping for SCCNij3. For E102 and E106, mean signal intensities for pimonidazole significantly decreased after carbogen breathing and increased after clamping, mean [(18)F]FMISO signal intensities increased significantly after clamping and a significant correlation between the hypoxic fractions and the mean [(18)F]FMISO signal intensities was found.

CONCLUSIONS

[(18)F]FMISO autoradiography and pimonidazole immunohistochemistry can both be used to visualize treatment induced changes in tumor hypoxia. However, the response to these modifications differs widely between xenograft tumor lines.

Comparison between pimonidazole binding, oxygen electrode measurements, and expression of endogenous hypoxia markers in cancer of the uterine cervix

BACKGROUND

Although tumor hypoxia has been associated with a more aggressive phenotype and lower cure rate, there is no consensus as to the method best suited for routine measurement. Binding of the chemical hypoxia marker, pimonidazole, and expression of the endogenous hypoxia markers HIF-1alpha and CAIX were compared for their ability to detect hypoxia in tumor biopsies from 67 patients with advanced carcinoma of the cervix.

METHODS

Two biopsies were taken one day after administration of pimonidazole and were analyzed for pimonidazole binding using flow cytometry or immunohistochemistry. CAIX and HIF-1alpha expression and degree of colocalization were measured in sequential antibody-stained sections. Patient subsets were examined for tumor oxygen tension using an Eppendorf electrode, S phase DNA content, or change in HIF-1alpha expression over the course of treatment.

RESULTS

Approximately 6% of the tumor area stained positive for pimonidazole, HIF-1alpha, or CAIX. The CAIX positive fraction correlated with the pimonidazole positive fraction (r = 0.60). Weaker but significant correlations were observed between pimonidazole and HIF-1alpha (r = 0.31) and CAIX and HIF-1alpha (r = 0.41). Taking the extent of marker colocalization into consideration increased the confidence that all markers were identifying hypoxic regions. Over 65% of stained areas showed a high degree of colocalization with the other markers. Oxygen microelectrode measurements and S phase fraction were not correlated with the hypoxic fraction measured using the three hypoxia markers. HIF-1alpha levels tended to decrease with time after the start of therapy.

CONCLUSIONS

Endogenous hypoxia marker binding shows reasonable agreement, in extent and location, with binding of pimonidazole. CAIX staining pattern is a better match to the pimonidazole staining pattern than is HIF-1alpha, and high CAIX expression in the absence (or low levels) of HIF-1alpha may indicate a different biology.

Effects of hyperoxygenation on FDG-uptake in head-and-neck cancer

PURPOSE

Tumor hyperoxygenation results in high response rates to ARCON (accelerated radiotherapy with carbogen and nicotinamide). The effect of hyperoxygenation on tumor metabolism using [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) was investigated.

METHODS

Within one week, FDG-PET was performed without and with hyperoxygenation by carbogen breathing and/or nicotinamide administration in 22 patients, eligible for ARCON for head-and-neck cancer. Maximum standardized uptake values (SUV(max)) in both scans and the relative change were calculated in the primary tumor and in normal muscle.

RESULTS

Alteration of the tumor oxygenation state induced profound, but variable, metabolic changes (median DeltaSUV(max) -4%; range -61% to +30%). Metabolism in normal muscle was not affected. In three patients who did not achieve local tumor control, the SUV(max) after hyperoxygenation differed less than 5% change as compared to baseline, whereas 13 of the 16 patients with local tumor control showed a larger difference (p<0.05).

CONCLUSION

Given the heterogeneous response pattern of nicotinamide and carbogen on FDG-uptake in head-and-neck carcinoma, the prognostic significance of semiquantitative FDG-PET before and after hyperoxygenation remains uncertain and requires confirmation in larger clinical studies before introducing the procedure as a predictive tool for oxygenation modifying treatments.

c-Jun kinase mediates expression of VEGF induced at transcriptional level by Rac1 and Cdc42Hs but not by RhoA

Tumour angiogenesis is mediated by increased levels of vascular endothelial growth factor (VEGF). We have studied the mechanism by which endogenous activation of Rho oncoproteins regulates VEGF expression in COS-7 and NIH3T3 cells. We carried out transient and stable transfection with constitutively activated rhoA, rac1, and cdc42 mutants in COS-7 and NIH3T3 cells, respectively in the absence of external stimuli. Western blot and inmunohistochemistry assays of those cells revealed increased VEGF protein expression. Cotransfection with constitutively activated rhoA, rac1, and cdc42 mutants and a VEGF promoter-reporter construct showed an increase in VEGF promoter transcriptional activity induced by Rho oncoproteins in COS-7 and NIH3T3. c-Jun kinase had been described as a MAPK involved in Rho oncoproteins pathways. Interestingly, we found that c-Jun kinase chemical inhibition as well as transient transactivation assays using dominant negative c-Jun kinase mutant abolished the VEGF promoter transcriptional induction by Rac1 and Cdc42 but not by RhoA. These findings indicate that Rho oncoprotein endogenously activated regulates VEGF expression through a transcriptional mechanism, and that the c-Jun kinase activity is a mediator in the expression of VEGF induced by Rac1 and Cdc42 oncoproteins, but not of that induced by RhoA.

Hypoxia protects HepG2 cells against etoposide-induced apoptosis via a HIF-1-independent pathway

Tumor hypoxia has been described to increase the resistance of cancer cells to radiation therapy and chemotherapy. It also supports the invasiveness and metastatic potential of the tumor. However, few data are available on the transduction pathway set up under hypoxia and leading to this resistance against anti-cancer therapies. HIF-1, the main transcription factor activated by hypoxia, has been recently shown to participate to this process although its role as an anti- or a pro-apoptotic protein is still controversy. In this study, we showed that hypoxia protected HepG2 cells against etoposide-induced apoptosis. The effect of hypoxia on cell death was assayed by measuring different parameters of the apoptotic pathway, like DNA fragmentation, caspase activity and PARP-1 cleavage. The possible implication of HIF-1 in the anti-apoptotic role of hypoxia was investigated using HIF-1alpha siRNA. Our results indicated that HIF-1 is not involved in the hypoxia-induced anti-apoptotic pathway. Another transcription factor, AP-1, was studied for its potential role in the hypoxia-induced protection against apoptosis. Specific inhibition of AP-1 decreased the protection effect of hypoxia against etoposide-induced apoptosis. Together, all these data underline that hypoxia could mediate its anti-apoptotic role via different transcription factors depending on the cellular context and pro-apoptotic stimuli.

Hypoxia in human colorectal adenocarcinoma: comparison between extrinsic and potential intrinsic hypoxia markers

PURPOSE

To detect and quantify hypoxia in colorectal adenocarcinomas by use of pimonidazole and iododeoxyuridine (IdUrd) as extrinsic markers and carbonic anhydrase IX (CA IX), microvessel density (MVD), epidermal growth-factor receptor (EGFR), and vascular endothelial growth factor (VEGF) as intrinsic markers of hypoxia.

METHODS AND MATERIAL

Twenty patients with an adenocarcinoma of the left colon and rectum treated by primary surgery were injected with pimonidazole and IdUrd. Serial sections of tumor biopsies were single stained for VEGF, EGFR, Ki67, and double stained for blood vessels in combination with either pimonidazole, IdUrd, or CA IX. Percentage of expression was scored as well as colocalization of pimonidazole with CA IX.

RESULTS

The median percentage of hypoxia, as judged by pimonidazole staining, was 16.7% (range, 0-52.4%). The expression of pimonidazole correlated inversely with the total MVD and endothelial cord MVD (R = -0.55, p = 0.01; R = -0.47, p = 0.04). Good colocalization was found between pimonidazole and CA IX in only 30% of tumors, with no correlation overall between pimonidazole and CA IX, VEGF, or EGFR or between the different intrinsic markers. Cells around some vessels (0.08-11%) were negative for IdUrd but positive for Ki 67, which indicated their lack of perfusion at the time of injection.

CONCLUSION

Chronic and acute hypoxic regions are present in colorectal tumors, as shown by pimonidazole and IdUrd staining. Only in a minority of tumors did an association exist between the areas stained by pimonidazole and those positive for CA IX. Pimonidazole also did not correlate with expression of other putative intrinsic hypoxia markers (VEGF, EGFR).

Targeted anti-vascular endothelial growth factor receptor-2 therapy leads to short-term and long-term impairment of vascular function and increase in tumor hypoxia

Because antiangiogenic therapies inhibit the growth of new tumor-associated blood vessels, as well as prune newly formed vasculature, they would be expected to reduce the supply of oxygen and thus increase tumor hypoxia. However, it is not clear if antiangiogenic treatments lead only to consistent and sustained increases in hypoxia, or transient decreases in tumor hypoxia along with periods of increased hypoxia. We undertook a detailed analysis of an orthotopically transplanted human breast carcinoma (MDA-MB-231) over a 3-week treatment period using DC101, an anti-vascular endothelial growth factor receptor 2 antibody. We observed consistent reductions in microvascular density, blood flow (measured by high-frequency micro-ultrasound), and perfusion. These effects resulted in an increase in the hypoxic tumor fraction, measured with an exogenous marker, pimonidazole, concurrent with an elevation in hypoxia-inducible factor-1alpha expression, an endogenous marker. The increase in tumor hypoxia was evident within 5 days and remained so throughout the entire course of treatment. Vascular perfusion and flow were impaired at days 2, 5, 7, 8, 14, and 21 after the first injection, but not at 4 hours. A modest increase in the vessel maturation index was detected after the 3-week treatment period, but this was not accompanied by an improvement in vascular function. These results suggest that sustained hypoxia and impairment of vascular function can be two consistent consequences of antiangiogenic drug treatment. The implications of the results are discussed, particularly with respect to how they relate to different theories for the counterintuitive chemosensitizing effects of antiangiogenic drugs, even when hypoxia is increased.

Combining radiotherapy and angiogenesis inhibitors: clinical trial design

Radiotherapy (RT) plays a vital role in the multimodality treatment of cancer. Recent advances in RT have primarily involved improvements in dose delivery. Future improvements in tumor control and disease outcomes will likely involve the combination of RT with targeted therapies. Preclinical evaluations of angiogenesis inhibitors in combination with RT have yielded promising results with increased tumor "cure." It remains to be seen whether these improvements in tumor control in the laboratory will translate into improved outcomes in the clinic. Multiple differences between these agents and cytotoxic chemotherapy must be taken into account when designing clinical trials evaluating their effectiveness in combination with RT. We discuss important considerations for designing clinical trials of angiogenesis inhibitors with RT.

Carbonic anhydrase IX expression and tumor oxygenation status do not correlate at the microregional level in locally advanced cancers of the uterine cervix

PURPOSE

Carbonic anhydrase IX (CA IX) can be induced by hypoxia in vitro and shows an immunohistochemical expression pattern that is predominantly found in perinecrotic tumor areas and correlates with exogenous markers of hypoxia, such as pimonidazole. CA IX might therefore serve as an endogenous marker of tumor hypoxia, although comparisons of CA IX immunostaining with direct oxygenation measurements using pO2 microsensors have thus far yielded contradictory results.

EXPERIMENTAL DESIGN

Because tumor heterogeneity may be among the factors responsible for the discrepancy between the two methods, CA IX expression in tissue samples originating from oxygen microelectrode tracks of locally advanced cervical cancers was assessed in this study. Seventy-seven biopsy specimens were analyzed immunohistochemically using an anti-CA IX rabbit polyclonal antibody and semiquantitative scoring.

RESULTS

CA IX expression showed no correlation with the oxygenation variables median pO2 and hypoxic fraction 2.5, 5, or 10. Cases with higher International Federation of Gynecology and Obstetrics stages (IIb-IVa) exhibited stronger expression of CA IX (P = 0.035) and CA IX expression tended to be more prevalent in node-positive patients (P = 0.051).

CONCLUSIONS

These data indicate that CA IX cannot be recommended as a substitute for oxygen microelectrode measurements. That the expression of CA IX does not correlate with the oxygenation status may be due to the degree to which other factors, such as nutrient (e.g., glucose) deficiency or the action of oncogenic mutations, can modulate the in vivo expression of this protein, rendering a strict association with tumor hypoxia too unreliable for clinical use.

Hypoxia regulates cross-talk between Syk and Lck leading to breast cancer progression and angiogenesis

Hypoxia is a key parameter that controls tumor angiogenesis and malignant progression by regulating the expression of several oncogenic molecules. The nonreceptor protein-tyrosine kinases Syk and Lck play crucial roles in the signaling mechanism of various cellular processes. The enhanced expression of Syk in normal breast tissue but not in malignant breast carcinoma has prompted us to investigate its potential role in mammary carcinogenesis. Accordingly, we hypothesized that hypoxia/reoxygenation (H/R) may play an important role in regulating Syk activation, and Lck may be involved in this process. In this study, we have demonstrated that H/R differentially regulates Syk phosphorylation and its subsequent interaction and cross-talk with Lck in MCF-7 cells. Moreover, Syk and Lck play differential roles in regulating Sp1 activation and expressions of melanoma cell adhesion molecule (MelCAM), urokinase-type plasminogen activator (uPA), matrix metalloproteinase-9 (MMP-9), and vascular endothelial growth factor (VEGF) in response to H/R. Overexpression of wild type Syk inhibited the H/R-induced uPA, MMP-9, and VEGF expression but up-regulated MelCAM expression. Our data also indicated that MelCAM acts as a tumor suppressor by negatively regulating H/R-induced uPA secretion and MMP-9 activation. The mice xenograft study showed the cross-talk between Syk and Lck regulated H/R-induced breast tumor progression and further correlated with the expressions of MelCAM, uPA, MMP-9, and VEGF. Human clinical specimen analysis supported the in vitro and in vivo findings. To our knowledge, this is first report that the cross-talk between Syk and Lck regulates H/R-induced breast cancer progression and further suggests that Syk may act as potential therapeutic target for the treatment of breast cancer.

Tirapazamine causes vascular dysfunction in HCT-116 tumour xenografts

BACKGROUND AND PURPOSE

Tirapazamine is a hypoxic cytotoxin currently undergoing Phase II/III clinical evaluation in combination with radiation and chemotherapeutics for the treatment of non-hematological cancers. Tissue penetration studies using multicellular models have suggested that tirapazamine exposure may be limited to cells close to blood vessels. However, animal studies show tirapazamine enhances the anti-tumour activity of radiation and chemotherapy and clinical studies with tirapazamine, so far, are promising. To investigate this apparent paradox we examined the microregional effects of tirapazamine in vivo by mapping drug effects with respect to the position of blood vessels in tumour cryosections.

PATIENTS AND METHODS

Tirapazamine was administered i.p. to mice bearing HCT-116 tumours, which were excised at various times after treatment. Images of multiple-stained cryosections were overlaid to provide microregional information on the relative position of proliferating cells, hypoxia, perfusion and vasculature.

RESULTS

We observed extensive and permanent vascular dysfunction in a large proportion of tumours from mice treated with tirapazamine. In the affected tumours, blood flow ceased in the centrally located tumour vessels, leaving a rim of functional vessels around the periphery of the tumour. This vascular dysfunction commenced within 24 h after tirapazamine administration and the areas affected appeared to be replaced by necrosis over the following 24-48 h.

CONCLUSIONS

Because the majority of hypoxic cells are located in the center of tumours we propose that the activity of tirapazamine in vivo may be related to its effects on tumour vasculature and that its activity against hypoxic cells located distal to functional blood vessels may not be as important as previously believed.

Response of the plasma hypoxia marker osteopontin to in vitro hypoxia in human tumor cells

BACKGROUND

Osteopontin (OPN) is recognized as a tumor-associated protein and has recently been shown to be a potential plasma marker of tumor hypoxia in head and neck cancer patients. We sought to detect patterns of OPN accumulation and secretion in human tumor cells during in vitro hypoxia.

MATERIALS AND METHODS

The human tumor cell lines A 549 lung carcinoma, U 87 malignant glioma, HT 1080 fibrosarcoma, FaDu pharyngeal carcinoma and HT 29 and HCT 116 colorectal carcinoma were treated with 1, 6 or 24 h of hypoxia (0.1% O2) or 24 h followed by 4 h or 20 of reoxygenation. OPN concentration in the supernatant was measured by ELISA, OPN protein and mRNA levels by Western and Northern blotting.

RESULTS

In FaDu, HT 29 and HCT 116, OPN levels in the supernatant remained below 10 ng/ml under all conditions. In A 549, HT 1080 and U 87, mean aerobic OPN concentrations were 2296, 164 and 115 ng/ml, respectively. No increase of OPN in the medium during 24h of hypoxia, but moderate increases during subsequent 24-hour-reoxygenation were observed in these three cell lines. Intracellular OPN protein was present to a similar extent in all six-cell lines under aerobic conditions and also did not accumulate during hypoxia treatment. OPN mRNA response to hypoxia and reoxygenation was very heterogeneous between cell lines.

CONCLUSION

Reoxygenation rather than hypoxia appears to induce OPN secretion from human tumor cells in a cell-type specific manner.

The hypoxic proteome is influenced by gene-specific changes in mRNA translation

BACKGROUND AND PURPOSE

Hypoxia causes a rapid reduction in mRNA translation efficiency. This inhibition does not affect all mRNA species to the same extent and can therefore contribute significantly to hypoxia-induced differential protein expression. Our aim in this study was to characterize changes in gene expression during acute hypoxia and evaluate the contribution of regulation via mRNA translation on these changes. For each gene, the contribution of changes in mRNA abundance versus mRNA translation was determined.

MATERIALS AND METHODS

DU145 prostate carcinoma cells were exposed to 4h of hypoxia (<0.02% O2). Efficiently translated mRNAs were isolated by sedimentation through a sucrose gradient. Affymetrix microarray technology was used to evaluate both the transcriptional and translational contribution to gene expression. Results were validated by quantitative PCR.

RESULTS

One hundred and twenty genes were more than 4-fold upregulated by hypoxia in the efficiently translated fraction of mRNA, in comparison to only 76 genes at the level of transcription. Of the 50 genes demonstrating the largest changes in translation, 11 were found to be more than 2-fold over represented in the translated fraction in comparison to their overall transcriptional level. The gene with the highest translational contribution to its induction was CITED-2, which is a negative regulator of HIF-1 transcriptional activity.

CONCLUSIONS

Gene-specific regulation of mRNA translation contributes significantly to differential gene expression during hypoxia.

Comparison of different methods of CAIX quantification in relation to hypoxia in three human head and neck tumor lines

PURPOSE

In head and neck cancer, it has been shown that hypoxic tumors respond poorly to therapy. Methods to identify hypoxic tumors are, therefore, of importance to select patients for oxygenation modifying or other intensified treatments. The aim of this study was to compare tumor cell hypoxia assessed by the hypoxic cell marker pimonidazole (PIMO) with expression of the endogenous hypoxia-related marker carbonic anhydrase IX (CAIX) in three human head and neck tumor lines.

MATERIAL AND METHODS

Forty-five tumors of three human head and neck tumor lines, SCCNij3, SCCNij59 and MEC82, xenografted in athymic mice, were used. CAIX was quantified by biodistribution (% injected dose/g tumor) after injecting 3-5 microl 111In-labeled G250 mouse antibody 3 days prior to euthanizing. In a tissue section from the same tumor, fractions of tumor area positive for PIMO, CAIX and Hoechst 33342 (perfusion marker) were assessed after immunohistochemical staining, using a digital image analysis system.

RESULTS

SCCNij3 and MEC82 were relatively hypoxic tumor lines with fractions of tumor area positive for pimonidazole of 0.16 and 0.15, respectively. SCCNij59 was a better-oxygenated tumor line with a PIMO-fraction of 0.03. The three tumor lines showed different levels and patterns of CAIX immunohistochemical staining, but only in MEC82 there was a good correlation between PIMO-fraction and CAIX-fraction (r2=0.92, P<0.0001). Correlations between 111In-G250 uptake and CAIX-fraction or PIMO-fraction within tumor lines were weak or absent.

CONCLUSIONS

Assessment of CAIX expression depends largely on the techniques and tumor lines used. Furthermore, the immunohistochemical staining pattern of CAIX relative to PIMO differs between human tumor lines of similar anatomical origin. Therefore, the use of CAIX as endogenous marker of tumor hypoxia remains questionable.

Activation of RhoB by Hypoxia Controls Hypoxia-Inducible Factor-1α Stabilization through Glycogen Synthase Kinase-3 in U87 Glioblastoma Cells

Hypoxia is a crucial factor in tumor aggressiveness and resistance to treatment, particularly in glioma. Our previous results have shown that inhibiting the small GTPase RhoB increased oxygenation of U87 human glioblastoma xenografts, in part, by regulating angiogenesis. We investigated here whether RhoB might also control a signaling pathway that would permit glioma cells to adapt to hypoxia. We first showed that silencing RhoB with siRNA induced degradation and inhibition of the transcriptional activity of the hypoxia-inducible factor by the proteasome in U87 hypoxic cells. This RhoB-dependent degradation of hypoxia-inducible factor-1alpha in hypoxic conditions was mediated by the Akt/glycogen synthase kinase-3beta pathway. While investigating how hypoxia could activate this signaling pathway, using the GST-Rhotekin RBD pulldown assay, we showed the early activation of RhoB by reactive oxygen species under hypoxic conditions and, subsequently, its participation in the ensuing cellular adaptation to hypoxia. Overall, therefore, our results have not only highlighted a new signaling pathway for hypoxia controlled by the small GTPase RhoB, but they also strongly implicate RhoB as a potentially important therapeutic target for decreasing tumor hypoxia.

Hypoxia in relation to vasculature and proliferation in liver metastases in patients with colorectal cancer

PURPOSE

To investigate hypoxia measured by pimonidazole binding, glucose transporter 1 (GLUT1) and carbonic anhydrase IX (CA-IX) expression, proliferation, and vascularity in liver metastases of colorectal cancer and to compare GLUT1 and CA-IX expression in corresponding primary tumors.

METHODS AND MATERIALS

Twenty-five patients with liver metastases of colorectal cancer, planned for metastasectomy, were included. The hypoxia marker pimonidazole and proliferation marker iododeoxyuridine were administered before surgery. After immunofluorescent staining of the frozen metastases, pimonidazole binding, vascularity, and proliferation were analyzed quantitatively. Thirteen paraffin-embedded primary tumors were stained immunohistochemically for GLUT1 and CA-IX expression, which was analyzed semiquantitatively in primary tumors and corresponding liver metastases.

RESULTS

In liver metastases, pimonidazole binding showed a pattern consistent with diffusion-limited hypoxia. The mean pimonidazole-positive fraction was 0.146; the mean distance from vessels to pimonidazole-positive areas was 80 microm. When expressed, often co-localization was observed between pimonidazole binding and GLUT1 or CA-IX expression, but microregional areas of mismatch were also observed. No correlation between the level of pimonidazole binding and GLUT1 or CA-IX expression was observed. In some patients, a large fraction (up to 30%) of proliferating cells was present in pimonidazole-stained areas. Expression of CA-IX in primary tumors and metastases showed a significant correlation, which was absent for GLUT1 expression.

CONCLUSIONS

Compared with other tumor types, liver metastases of colorectal cancer contain large amounts of hypoxic cells. The lack of correlation with pimonidazole binding brings into question the value of GLUT1 and CA-IX as endogenous markers of hypoxia.

Plasma osteopontin, hypoxia, and response to the hypoxia sensitiser nimorazole in radiotherapy of head and neck cancer: results from the DAHANCA 5 randomised double-blind placebo-controlled trial

BACKGROUND

The concentration of osteopontin (SPP1) in plasma is associated with tumour hypoxia. The DAHANCA 5 trial found that the hypoxia radiosensitiser nimorazole significantly improved the outcome of radiotherapy for patients with head and neck cancer compared with placebo. However, whether all patients benefit from such modification of hypoxia is unclear. We aimed to assess whether the concentration of plasma osteopontin could predict response to the hypoxia radiosensitiser.

METHODS

Plasma concentrations of osteopontin were measured by use of ELISA from stored samples of 320 patients randomised in the DAHANCA 5 trial. Samples were grouped into tertiles according to high (167-1382 microg/L), intermediate (69-166 microg/L), or low (0-68 microg/L) concentrations of plasma osteopontin, and analysed for locoregional tumour control and disease-specific survival at 5 years.

FINDINGS

Overall, locoregional tumour failure and disease-specific mortality were more frequent in patients assigned placebo than in those assigned nimorazole (relative risk [RR] 0.51 [95% CI 0.32-0.79] and 0.54 [0.35-0.85], respectively). Locoregional tumour failure was more frequent in patients with high concentrations of osteopontin assigned placebo than in those with high concentrations assigned nimorazole (0.19 [0.08-0.44]), as was disease-specific mortality (0.25 [0.11-0.59]). However, neither locoregional tumour failure nor disease-specific mortality differed between groups for patients with low concentrations of plasma osteopontin (0.79 [0.26-1.70]) and (0.69 [0.31-1.51]) or for those with intermediate concentrations (0.90 [0.41-1.98] and 0.89 [0.41-1.96], respectively).

INTERPRETATION

High plasma concentrations of osteopontin are associated with a poor outlook after radiotherapy for patients with head and neck cancer, but can be improved by use of nimorazole. High concentrations of osteopontin can predict clinically relevant hypoxia, and might identify patients who will benefit from modification of hypoxia during radiotherapy.

Analysis of the prognostic impact of tumor embolization before definitive radiotherapy for cervical carcinoma

PURPOSE

To assess whether embolization compromises the radiocurability of primary cervical cancer.

METHODS AND MATERIALS

Two hundred fifty-four patients with primary cervical cancer (International Federation of Gynecology and Obstetrics [FIGO] stages IB: 47; II: 91; IIIB: 102; IV: 14) were treated with external beam irradiation and Ir-192 high-dose-rate brachytherapy over a period of 15 years. Of these, 24 patients (9.4%) (FIGO stages IB: 1; II: 8; IIIB: 12; IV: 3) had had bilateral embolization of the internal iliac arteries before referral. The median age of the entire cohort was 66 years (range, 34-85 years). Tumor size was >5 cm and paraortic nodes were enlarged (> or =1 cm) on pretreatment CAT scan in 39.4% and 9.1% of patients, respectively. All patients with hemoglobin levels (hb-l) < or =11 g/dL (28.3%) received packed red cell transfusions (PRCT) before and/or during radiotherapy in an attempt to maintain levels >11 g/dL throughout treatment. Cross-table tests were used to compare the distribution of FIGO stage, tumor size, lymph node status, and pretreatment and treatment hb-l of embolized and nonembolized patients. The impact of embolization, along with the above-listed tumor characteristics, on disease-specific survival (DSS), pelvic control (PC), and distant metastases-free survival (MFS) was determined by univariate and multivariate analyses.

RESULTS

Embolized patients presented at a statistically significant younger median age (55 vs. 67 years; p = 0.003), with larger tumors (66.7% vs. 36.5%; p = 0.007), and lower pretreatment hb-l (75% vs. 23.5%; p < 0.001) than nonembolized patients. There was no significant difference in stage distribution or lymph node status, and although embolized patients responded better to PRCT (50% vs. 29.6%), this difference was not statistically significant. Univariate analysis showed a trend toward decreased DSS (p = 0.09) and PC (p = 0.07) for embolized patients but no effect on MFS, whereas all other variables tested were significantly correlated with DSS, PC, and MFS (all p < 0.001). In the multivariate model, tumor embolization, FIGO stage, and pretreatment hb-l ceased to impact significantly on outcome. Tumor size remained the most powerful independent predictor for all endpoints tested, followed by treatment hb-l. Paraortic node status was significantly correlated with DSS and MFS.

CONCLUSION

Although a trend toward poorer DSS and PC was observed in embolized patients, no impact on radiocurability could be demonstrated in multivariate analysis after controlling for the major tumor characteristics and treatment hb-l.

A noninvasive approach for assessing tumor hypoxia in xenografts: developing a urinary marker for hypoxia

Tumor hypoxia modifies the efficacy of conventional anticancer therapy and promotes malignant tumor progression. Human chorionic gonadotropin (hCG) is a glycoprotein secreted during pregnancy that has been used to monitor tumor burden in xenografts engineered to express this marker. We adapted this approach to use urinary beta-hCG as a secreted reporter protein for tumor hypoxia. We used a hypoxia-inducible promoter containing five tandem repeats of the hypoxia-response element (HRE) ligated upstream of the beta-hCG gene. This construct was stably integrated into two different cancer cell lines, FaDu, a human head and neck squamous cell carcinoma, and RKO, a human colorectal cancer cell line. In vitro studies showed that tumor cells stably transfected with this plasmid construct secrete beta-hCG in response to hypoxia or hypoxia-inducible factor 1alpha (HIF-1alpha) stabilizing agents. The hypoxia responsiveness of this construct can be blocked by treatment with agents that affect the HIF-1alpha pathways, including topotecan, 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)indazole (YC-1), and flavopiridol. Immunofluorescent analysis of tumor sections and quantitative assessment with flow cytometry indicate colocalization between beta-hCG and 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5) and beta-hCG and pimonidazole, two extrinsic markers for tumor hypoxia. Secretion of beta-hCG from xenografts that contain these stable constructs is directly responsive to changes in tumor oxygenation, including exposure of the animals to 10% O2 and tumor bed irradiation. Similarly, urinary beta-hCG levels decline after treatment with flavopiridol, an inhibitor of HIF-1 transactivation. This effect was observed only in tumor cells expressing a HRE-regulated reporter gene and not in tumor cells expressing a cytomegalovirus-regulated reporter gene. The 5HRE beta-hCG reporter system described here enables serial, noninvasive monitoring of tumor hypoxia in a mouse model by measuring a urinary reporter protein.

Reduced Expression of Hypoxia-Inducible Factor-1α in Perinecrotic Regions of Solid Tumors

Hypoxia that develops in solid tumors stabilizes the hypoxia-inducible factor-1alpha (HIF-1alpha) subunit of the HIF-1 transcription factor, leading to up-regulation of dozens of hypoxia-regulated genes that increase glycolysis and oxygen delivery. HIF-1alpha and its downstream target gene CA9 have both been used as surrogate hypoxia markers, and, in general, high expression predicts for a poor response to treatment. Combinations of hypoxia markers offer the opportunity to measure changes in tumor oxygenation that may be relevant to tumor response to treatment. We compared the degree of colocalization of two endogenous markers for hypoxia, HIF-1alpha and carbonic anhydrase IX (CAIX), with a chemical marker for hypoxia, pimonidazole. Unexpectedly, expression of HIF-1alpha was reduced in the most hypoxic regions that border necrosis in xenograft tumors composed of SiHa cervical carcinoma, WiDr colon carcinoma, or M006 astrocytoma cells. Similar results were obtained for samples from three cervical cancer biopsies. However, CAIX was present in these perinecrotic cells that were also capable of metabolizing and binding a chemical marker for hypoxia, pimonidazole. In vitro experiments using tumor cells and tumor cubes incubated under anoxic conditions indicated that nutrient deprivation seems to be largely responsible for the lack of HIF-1alpha expression in perinecrotic regions. The half-life of CAIX was sufficiently long that, once formed, it remained for days in the absence of continued HIF-1alpha expression. These results have implications for the use of HIF-1alpha as an indicator of tumor hypoxia and aggressiveness as well as development of hypoxia-directed antitumor therapies based on the expression of HIF-1alpha.

Prognostic value of tumor oxygenation in 397 head and neck tumors after primary radiation therapy. An international multi-center study

PURPOSE

To analyze the relationship between pre-treatment measurements of tumor oxygen tension (pO2) and survival in advanced head and neck cancer.

PATIENTS AND METHODS

Eppendorf pO2 measurements in 397 patients from seven centers were analyzed using the fraction of pO2 values < or =2.5 mmHg (HP2.5), < or =5 mmHg (HP5) and median tumor pO2 (mmHg) as descriptors. All patients had intended curative radiation therapy alone or as pre- or post-operative radiotherapy or radio-chemotherapy according to the practice at each center.

RESULTS

The degree of hypoxia varied between tumors with an overall median tumor pO2=9 mmHg (range 0-62 mmHg), a median HP2.5=19% (range 0-97%) and HP5=38%, (range 0-100%). By quadratic regression median tumor pO2 correlated with Hb (2P=0.026, n=357), while HP2.5 or HP5 did not. HP2.5 above the population median was the only parameter that associated with poor overall survival (Kaplan Meier analysis, P=0.006). In a multivariate Cox Proportional Hazards analysis, stratified according to institution HP2.5 was by far the most statistically significant factor in explaining the variability in survival. After adjusting for HP2.5, clinical stage, radiation dose and surgery hemoglobin concentration was not significant in the model. The prognostic model shows that the 5-year survival is almost constant for HP2.5 values in the range from 0 to 20%, whereas the 5-year survival approaches 0% in the most hypoxic tumors.

CONCLUSION

This study provides evidence that tumor hypoxia is associated with a poor prognosis in patients with advanced head and neck cancer.

Does heterogeneity of pimonidazole labelling correspond to the heterogeneity of radiation-response of FaDu human squamous cell carcinoma?

BACKGROUND AND PURPOSE

Pimonidazole is a marker for hypoxic cells which are radioresistant and thereby important for the outcome of radiotherapy. The present study evaluates heterogeneity in pimonidazole binding within and between tumours and relates the results to the heterogeneity of radiation response in the same tumour cell line.

MATERIALS AND METHODS

FaDu, a poorly differentiated human squamous cell carcinoma line, was transplanted subcutaneously into the right hind-leg of NMRI nude mice. Tumours were irradiated with graded single doses either under ambient or clamped blood flow conditions and local tumour control was evaluated after 120 days. Complete dose-response curves for local tumour control were generated and the slope, a measure of heterogeneity of radiation response, was determined. In parallel, 12 unirradiated tumours were examined histologically. Seven serial 10 microm cross-sections per tumour were evaluated using fluorescence microscopy and computerised image analysis to determine the pimonidazole hypoxic fraction (pHF). Heterogeneity in pHF was quantified by its coefficient of variation (CV). Poisson-based model calculations considering the intertumoural heterogeneity of pHF were performed and the slopes of the predicted and the observed dose-response curves were compared.

RESULTS

The mean pHF was 11% [CV 50%] when one central section per tumour was evaluated. Measurements of multiple sections per tumour resulted in a mean pHF of 12% [CV 46%] (P=0.7). Intertumoural heterogeneity in pHF was more pronounced than heterogeneity in individual tumours by a factor of 2. Model calculations based on the variability in pHF resulted in similar slopes of the dose-response curve for local tumour control in comparison with the observed slope when the heterogeneity in an unknown and arbitrarily chosen additional radiobiologically relevant parameter, in this example clonogen density, was taken into account.

CONCLUSIONS

While the average pimonidazole hypoxic fraction in FaDu tumours corresponds well to the radiobiological hypoxic fraction, the variability of pHF in FaDu tumours was not sufficient to explain the heterogeneity of radiation response in the same tumour line. Information on at least one additional parameter is expected to substantially enhance the predictive power of histological markers of tumour hypoxia.

Influence of oxygen concentration and pH on expression of hypoxia induced genes

BACKGROUND AND PURPOSE

This study was designed to determine the oxygen dependency for expression of the endogenous hypoxic markers carbonic anhydrase IX (protein: CAIX/gene: CA9), glucose transporter 1 (GLUT1/GLUT1), osteopontin (OPN/OPN) and lactate dehydrogenase A (LDH-A/LDHA), and how this expression was influenced by extracellular pH (pHe).

MATERIALS AND METHODS

Human cervix squamous cell carcinoma (SiHa) cells were used in all experiments. These cells were gassed in an enclosed environment under either anoxia (95% N2+5% CO2) for various times (0-30 h) or under different oxygen concentrations (0-21% O2) for 24 h at normal pHe (7.4) or low pHe (6.3). Response to radiation (7 Gy) was estimated using a clonogenic assay. Gene expression was determined by real-time PCR (normalized to the housekeeping gene, TFRC) and protein expression by Western blots.

RESULTS

Under normal pHe conditions, CA9, GLUT1 and LDHA gene expression was upregulated within 1-3h of anoxia, reaching near maximal values by 6h. OPN showed a slow increase over 24 h. At 24 h the relative increase was 135, 12, 90 and 5 times for CA9, GLUT1, OPN and LDHA, respectively. No induction was seen with the EGF receptor (EGFR). Gassing cells with differing oxygen concentrations for 24h resulted in a maximum level of expression for CA9 at 1% oxygen, whereas with GLUT1 and LDHA maximal expression occurred at 0.01% oxygen, but at 0% oxygen with OPN. The oxygen dependency for radiation response was identical to that seen for GLUT1 and LDHA. Expression of CA9, GLUT1, OPN and LDHA was inhibited under hypoxic conditions when pHe was reduced to 6.3. Expression of CAIX protein mimicked the CA9 gene expression patterns.

CONCLUSION

The expression of all the endogenous markers were upregulated by hypoxia, but the timing and oxygen dependencies were different and their expression was influenced by low pHe. This raises concerns about the generalised use of these agents as markers for hypoxia.

The prognostic value of the hypoxia markers CA IX and GLUT 1 and the cytokines VEGF and IL 6 in head and neck squamous cell carcinoma treated by radiotherapy +/- chemotherapy

Background

Several parameters of the tumor microenvironment, such as hypoxia, inflammation and angiogenesis, play a critical role in tumor aggressiveness and treatment response. A major question remains if these markers can be used to stratify patients to certain treatment protocols.

The purpose of this study was to investigate the inter-relationship and the prognostic significance of several biological and clinicopathological parameters in patients with head and neck squamous cell carcinoma (HNSCC) treated by radiotherapy ± chemotherapy.

Methods

We used two subgroups of a retrospective series for which CT-determined tumoral perfusion correlated with local control. In the first subgroup (n = 67), immunohistochemistry for carbonic anhydrase IX (CA IX) and glucose transporter-1 (GLUT-1) was performed on the pretreatment tumor biopsy. In the second subgroup (n = 34), enzyme linked immunosorbent assay (ELISA) was used to determine pretreatment levels of the cytokines vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) in serum. Correlation was investigated between tumoral perfusion and each of these biological markers, as well as between the markers mutually. The prognostic value of these microenvironmental parameters was also evaluated.

Results

For CA IX and GLUT-1, the combined assessment of patients with both markers expressed above the median showed an independent correlation with local control (p = 0.02) and disease-free survival (p = 0.04) with a trend for regional control (p = 0.06).

In the second subgroup, IL-6 pretreatment serum level above the median was the only independent predictor of local control (p = 0.009), disease-free survival (p = 0.02) and overall survival (p = 0.005).

Conclusion

To our knowledge, we are the first to report a link in HNSCC between IL-6 pretreatment serum levels and radioresistance in vivo. This link is supported by the strong prognostic association of pretreatment IL-6 with local control, known to be the most important parameter to judge radiotherapy responses.

Furthermore, the combined assessment of CA IX and GLUT-1 correlated independently with prognosis. This is a valuable indication that a combined approach is important in the investigation of prognostic markers.

Oxygen distribution in murine tumors: characterization using oxygen-dependent quenching of phosphorescence

In the present work, a novel method for detecting hypoxia in tumors, phosphorescence quenching, was used to evaluate tissue and tumor oxygenation. This technique is based on the concept that phosphorescence lifetime and intensity are inversely proportional to the oxygen concentration in the tissue sample. We used the phosphor Oxyphor G2 to evaluate the oxygen profiles in three murine tumor models: K1735 malignant melanoma, RENCA renal cell carcinoma, and Lewis lung carcinoma. Oxygen measurements were obtained both as histograms of oxygen distribution within the sample and as an average oxygen pressure within the tissue sampled; the latter allowing real-time oxygen monitoring. Each of the tumor types examined had a characteristic and consistent oxygen profile. K1735 tumors were all well oxygenated, with a peak oxygen pressure of 37.8 ± 5.1 Torr; RENCA tumors had intermediate oxygen pressures, with a peak oxygen pressure of 24.8 ± 17.9 Torr; and LLC tumors were all severely hypoxic, with a peak oxygen pressure of 1.8 ± 1.1 Torr. These results correlated well with measurements of tumor cell oxygenation measured by nitroimidazole (EF5) binding and were consistent with assessments of tumor blood flow by contrast enhanced ultrasound and tumor histology. The results show that phosphorescence quenching is a reliable, reproducible, and noninvasive method capable of providing real-time determination of oxygen concentrations within tumors.

Carbonic anhydrase IX as a marker for poor prognosis in soft tissue sarcoma

PURPOSE

Hypoxia is associated with malignant progression and poor outcome in several human tumors, including soft tissue sarcoma. Recent studies have suggested that carbonic anhydrase (CA) IX is an intrinsic marker of hypoxia, and that CA IX correlates with poor prognosis in several types of carcinoma. The aim of this study was to quantify the extent of CA IX expression and to investigate whether CA IX is a marker for poor prognosis in soft tissue sarcoma patients at high risk of developing metastasis.

EXPERIMENTAL DESIGN

Archival paraffin-embedded blocks were retrieved from 47 patients with deep, large, high-grade soft tissue sarcoma. Sections from two separate and representative tumor areas were immunostained for CA IX, and the CA IX-positive area fraction was quantified by image analysis, excluding areas of normal stroma and necrosis that were identified from serial H&E-stained sections. Patients were then subject to survival analysis.

RESULTS

CA IX-positive area fractions of viable tumor tissue varied significantly between tumors (range, 0-0.23; median, 0.004), with positive membranous CA IX staining in 66% (31 of 47) of the tumors. Patients with CA IX-positive tumors had a significantly lower disease-specific and overall survival than patients with CA IX-negative tumors (P = 0.033 and P = 0.044, respectively).

CONCLUSIONS

These data suggest that CA IX, a potential intrinsic marker of hypoxia, predicts for poor prognosis in patients with deep, large, high-grade soft tissue sarcoma. Larger studies are required to determine whether CA IX has independent prognostic value in this group of tumors.