Tumour cell proliferation under hypoxic conditions in human head and neck squamous cell carcinomas

Clinical relevance and therapeutic predictive ability of hypoxia biomarkers in head and neck cancer tumour models

Tumour hypoxia promotes poor patient outcomes, with particularly strong evidence for head and neck squamous cell carcinoma (HNSCC). To effectively target hypoxia, therapies require selection biomarkers and preclinical models that can accurately model tumour hypoxia. We established 20 patient-derived xenograft (PDX) and cell line-derived xenograft (CDX) models of HNSCC that we characterised for their fidelity to represent clinical HNSCC in gene expression, hypoxia status and proliferation and that were evaluated for their sensitivity to hypoxia-activated prodrugs (HAPs). PDX models showed greater fidelity in gene expression to clinical HNSCC than cell lines, as did CDX models relative to their paired cell lines. PDX models were significantly more hypoxic than CDX models, as assessed by hypoxia gene signatures and pimonidazole immunohistochemistry, and showed similar hypoxia gene expression to clinical HNSCC tumours. Hypoxia or proliferation status alone could not determine HAP sensitivity across our 20 HNSCC and two non-HNSCC tumour models by either tumour growth inhibition or killing of hypoxia cells in an ex vivo clonogenic assay. In summary, our tumour models provide clinically relevant HNSCC models that are suitable for evaluating hypoxia-targeting therapies; however, additional biomarkers to hypoxia are required to accurately predict drug sensitivity.

Prostate cancer radiogenomics reveals proliferative gene expression programs associated with distinct MRI-based hypoxia levels

BACKGROUND AND PURPOSE

The biology behind individual hypoxia levels in patient tumors is poorly understood. Here, we used radiogenomics to identify associations between magnetic resonance imaging (MRI)-based hypoxia levels and biological processes derived from gene expression data in prostate cancer.

MATERIALS AND METHODS

For 85 prostate cancer patients, MRI-based hypoxia images were constructed by combining diffusion-weighted images reflecting oxygen consumption and supply. The ability to differentiate hypoxia levels in these images was verified by comparison with matched biopsy sections stained for the hypoxia marker pimonidazole. For MRI-defined hypoxia levels, corresponding hypoxic fractions were calculated and correlated with biopsy gene expression profiles. Biological processes were predicted by gene set enrichment analysis (GSEA) and validated by immunohistochemistry (Ki67 proliferation marker, reactive stroma grade) and RT-PCR (MYC).

RESULTS

Genes with correlation between expression level and hypoxic fraction were identified for 56 MRI-based hypoxia levels. At all levels, GSEA identified proliferation as the predominant biological process enriched among the correlating genes. Two independent proliferative gene signatures were developed. The Peak1 signature, upregulated at moderate/severe hypoxia, reflected MYC upregulation and high Ki67-proliferation index of cancer cells in pimonidazole-positive regions. The Peak2 signature, upregulated at mild to non-hypoxic levels, was associated with fibroblast gene signature and reactive stroma grade. High scores of both Peak1 and Peak2 indicated elevated risk of biochemical recurrence in multiple cohorts.

CONCLUSION

Radiogenomics identified two gene expression programs activated at different hypoxia levels, reflecting proliferation of cancer cells and stroma cells. Genes involved in these programs could be candidate targets for intervention.

Impact of Tumour Hypoxia on Evofosfamide Sensitivity in Head and Neck Squamous Cell Carcinoma Patient-Derived Xenograft Models

Tumour hypoxia is a marker of poor prognosis and failure of chemoradiotherapy in head and neck squamous cell carcinoma (HNSCC), providing a strategy for therapeutic intervention in this setting. To evaluate the utility of the hypoxia-activated prodrug evofosfamide (TH-302) in HNSCC, we established ten early passage patient-derived xenograft (PDX) models of HNSCC that were characterised by their histopathology, hypoxia status, gene expression, and sensitivity to evofosfamide. All PDX models closely resembled the histology of the patient tumours they were derived from. Pimonidazole-positive tumour hypoxic fractions ranged from 1.7-7.9% in line with reported HNSCC clinical values, while mRNA expression of the Toustrup hypoxia gene signature showed close correlations between PDX and matched patient tumours, together suggesting the PDX models may accurately model clinical tumour hypoxia. Evofosfamide as a single agent (50 mg/kg IP, qd × 5 for three weeks) demonstrated antitumour efficacy that was variable across the PDX models, ranging from complete regressions in one p16-positive PDX model to lack of significant activity in the three most resistant models. Despite all PDX models showing evidence of tumour hypoxia, and hypoxia being essential for activation of evofosfamide, the antitumour activity of evofosfamide only weakly correlated with tumour hypoxia status determined by pimonidazole immunohistochemistry. Other candidate evofosfamide sensitivity genes-MKI67, POR, and SLFN11-did not strongly influence evofosfamide sensitivity in univariate analyses, although a weak significant relationship with MKI67 was observed, while SLFN11 expression was lost in PDX tumours. Overall, these data confirm that evofosfamide has antitumour activity in clinically-relevant PDX tumour models of HNSCC and support further clinical evaluation of this drug in HNSCC patients. Further research is required to identify those factors that, alongside hypoxia, can influence sensitivity to evofosfamide and could act as predictive biomarkers to support its use in precision medicine therapy of HNSCC.

Arterial Spin Labeling and Dynamic Susceptibility Contrast-enhanced MR Imaging for evaluation of arteriovenous shunting and tumor hypoxia in glioblastoma

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and carries a dismal prognosis. Significant challenges in the care of patients with GBM include marked vascular heterogeneity and arteriovenous (AV) shunting, which results in tumor hypoxia and inadequate delivery of systemic treatments to reach tumor cells. In this study, we investigated the utility of different MR perfusion techniques to detect and quantify arteriovenous (AV) shunting and tumor hypoxia in patients with GBM. Macrovascular shunting was present in 33% of subjects, with the degree of shunting ranging from (37–60%) using arterial spin labeling perfusion. Among the dynamic susceptibility contrast-enhanced perfusion curve features, there were a strong negative correlation between hypoxia score, DSC perfusion curve recovery slope (r = −0.72, P = 0.018) and angle (r = −0.73, P = 0.015). The results of this study support the possibility of using arterial spin labeling and pattern analysis of dynamic susceptibility contrast-enhanced MR Imaging for evaluation of arteriovenous shunting and tumor hypoxia in glioblastoma.

Voxel based comparison and texture analysis of 18F-FDG and 18F-FMISO PET of patients with head-and-neck cancer

Background

Hypoxia can induce radiation resistance and is an independent prognostic marker for outcome in head and neck cancer. As ¹⁸F-FMISO (FMISO), a hypoxia tracer for PET, is far less common than ¹⁸F-FDG (FDG) and two separate PET scans result in doubled cost and radiation exposure to the patient, we aimed to predict hypoxia from FDG PET with new techniques of voxel based analysis and texture analysis.

Methods

Thirty-eight patients with head-and-neck cancer underwent consecutive FDG and FMISO PET scans before any treatment. ROIs enclosing the primary cancer were compared in a voxel-by-voxel manner between FDG and FMISO PET. Tumour hypoxia was defined as the volume with a tumour-to-muscle ratio (TMR) > 1.25 in the FMISO PET and hypermetabolic volume was defined as >50% SUVmax in the FDG PET. The concordance rate was defined as percentage of voxels within the tumour which were both hypermetabolic and hypoxic. 38 different texture analysis (TA) parameters were computed based on the ROIs and correlated with presence of hypoxia.

Results

Within the hypoxic tumour regions, the FDG uptake was twice as high as in the non-hypoxic tumour regions (SUVmean 10.9 vs. 5.4; p<0.001). A moderate correlation between FDG and FMISO uptake was found by a voxel-by-voxel comparison (r = 0.664 p<0.001). The average concordance rate was 25% (± 22%). Entropy was the TA parameter showing the highest correlation with hypoxia (r = 0.524 p<0.001).

Conclusion

FDG uptake was higher in hypoxic tumour regions than in non-hypoxic regions as expected by tumour biology. A moderate correlation between FDG and FMISO PET was found by voxel-based analysis. TA yielded similar results in FDG and FMISO PET. However, it may not be possible to predict tumour hypoxia even with the help of texture analysis.

Prolyl hydroxylase domain protein 3 and asparaginyl hydroxylase factor inhibiting HIF-1 levels are predictive of tumoral behavior and prognosis in hepatocellular carcinoma

Hypoxia-inducible factors (HIFs) are key regulators in oxygen homeostasis. Their stabilization and activity are regulated by prolyl hydroxylase domain (PHD)-1, -2, -3 and factor inhibiting HIF (FIH). This study investigated the relation between these oxygen sensors and the clinical behaviors and prognosis of hepatocellular carcinoma (HCC). Tissue microarray and RT-PCR analysis of tumor tissues and adjacent non-tumor liver tissues revealed that mRNA and protein levels of both PHD3 and FIH were lower within tumors. The lower expression of PHD3 in tumor was associated with larger tumor size, incomplete tumor encapsulation, vascular invasion and higher Ki-67 LI (p < 0.05). The lower expression of FIH in tumor was associated with incomplete tumor encapsulation, vascular invasion, as well as higher TNM stage, BCLC stage, microvascular density and Ki-67 LI (p < 0.05). Patients with reduced expression of PHD3 or FIH had markedly shorter disease-free survival (DFS), lower overall survival (OS), or higher recurrence (p < 0.05), especially early recurrence. Patients with simultaneously reduced expression of PHD3 and FIH exhibited the least chance of forming tumor encapsulation, highest TNM stage (p < 0.0083), lowest OS and highest recurrence rate (p < 0.05). Multivariate analysis indicated that a lower expression of FIH independently predicted a poor prognosis in HCC. These findings indicate that downregulation of PHD3 and FIH in HCC is associated with more aggressive tumor behavior and a poor prognosis. PHD3 and FIH may be potential therapeutic targets for HCC treatment.

The tumour hypoxia marker pimonidazole reflects a transcriptional programme associated with aggressive prostate cancer

Background:

The hypoxia marker pimonidazole is a candidate biomarker of cancer aggressiveness. We investigated the transcriptional programme associated with pimonidazole staining in prostate cancer.

Methods:

Index tumour biopsies were taken by image guidance from an investigation cohort of 52 patients, where 43 patients received pimonidazole before prostatectomy. Biopsy location within the index tumour was verified for 46 (88%) patients, who were included for gene expression profiling and immunohistochemistry. Two independent cohorts of 59 and 281 patients were used for validation.

Results:

Expression of genes in proliferation, DNA repair and hypoxia response was a major part of the transcriptional programme associated with pimonidazole staining. A signature of 32 essential genes was constructed and showed positive correlation to Ki67 staining, confirming the increased proliferation in hypoxic tumours as suggested from the gene data. Positive correlations were also found to tumour stage and lymph node status, but not to blood prostate-specific antigen level, consistent with the findings for pimonidazole staining. The association with aggressiveness was confirmed in validation cohorts, where the signature correlated with Gleason score and had independent prognostic impact, respectively.

Conclusions:

Pimonidazole staining reflects an aggressive hypoxic phenotype of prostate cancer characterised by upregulation of proliferation, DNA repair and hypoxia response genes.

Modeling the relationship between fluorodeoxyglucose uptake and tumor radioresistance as a function of the tumor microenvironment

High fluorodeoxyglucose positron emission tomography (FDG-PET) uptake in tumors has often been correlated with increasing local failure and shorter overall survival, but the radiobiological mechanisms of this uptake are unclear. We explore the relationship between FDG-PET uptake and tumor radioresistance using a mechanistic model that considers cellular status as a function of microenvironmental conditions, including proliferating cells with access to oxygen and glucose, metabolically active cells with access to glucose but not oxygen, and severely hypoxic cells that are starving. However, it is unclear what the precise uptake levels of glucose should be for cells that receive oxygen and glucose versus cells that only receive glucose. Different potential FDG uptake profiles, as a function of the microenvironment, were simulated. Predicted tumor doses for 50% control (TD₅₀) in 2 Gy fractions were estimated for each assumed uptake profile and for various possible cell mixtures. The results support the hypothesis of an increased avidity of FDG for cells in the intermediate stress state (those receiving glucose but not oxygen) compared to well-oxygenated (and proliferating) cells.

Systematic analysis of 18F-FDG PET and metabolism, proliferation and hypoxia markers for classification of head and neck tumors

Background

Quantification of molecular cell processes is important for prognostication and treatment individualization of head and neck cancer (HNC). However, individual tumor comparison can show discord in upregulation similarities when analyzing multiple biological mechanisms. Elaborate tumor characterization, integrating multiple pathways reflecting intrinsic and microenvironmental properties, may be beneficial to group most uniform tumors for treatment modification schemes. The goal of this study was to systematically analyze if immunohistochemical (IHC) assessment of molecular markers, involved in treatment resistance, and ¹⁸F-FDG PET parameters could accurately distinguish separate HNC tumors.

Methods

Several imaging parameters and texture features for ¹⁸F-FDG small-animal PET and immunohistochemical markers related to metabolism, hypoxia, proliferation and tumor blood perfusion were assessed within groups of BALB/c nu/nu mice xenografted with 14 human HNC models. Classification methods were used to predict tumor line based on sets of parameters.

Results

We found that ¹⁸F-FDG PET could not differentiate between the tumor lines. On the contrary, combined IHC parameters could accurately allocate individual tumors to the correct model. From 9 analyzed IHC parameters, a cluster of 6 random parameters already classified 70.3% correctly. Combining all PET/IHC characteristics resulted in the highest tumor line classification accuracy (81.0%; cross validation 82.0%), which was just 2.2% higher (p = 5.2×10^-32) than the performance of the IHC parameter/feature based model.

Conclusions

With a select set of IHC markers representing cellular processes of metabolism, proliferation, hypoxia and perfusion, one can reliably distinguish between HNC tumor lines. Addition of ¹⁸F-FDG PET improves classification accuracy of IHC to a significant yet minor degree. These results may form a basis for development of tumor characterization models for treatment allocation purposes.

Modelling the interplay between hypoxia and proliferation in radiotherapy tumour response

A tumour control probability computational model for fractionated radiotherapy was developed, with the goal of incorporating the fundamental interplay between hypoxia and proliferation, including reoxygenation over a course of radiotherapy. The fundamental idea is that the local delivery of oxygen and glucose limits the amount of proliferation and metabolically-supported cell survival a tumour sub-volume can support. The model has three compartments: a proliferating compartment of cells receiving oxygen and glucose; an intermediate, metabolically-active compartment receiving glucose; and a highly hypoxic compartment of starving cells. Following the post-mitotic cell death of proliferating cells, intermediate cells move into the proliferative compartment and hypoxic cells move into the intermediate compartment. A key advantage of the proposed model is that the initial compartmental cell distribution is uniquely determined from the assumed local growth fraction (GF) and volume doubling time (TD) values. Varying initial cell state distributions, based on the local (voxel) GF and TD, were simulated. Tumour response was simulated for head and neck squamous cell carcinoma using relevant parameter values based on published sources. The tumour dose required to achieve a 50% local control rate (TCD50) was found for various GFs and TD's, and the effect of fraction size on TCD50 was also evaluated. Due to the advantage of reoxygenation over a course of radiotherapy, conventional fraction sizes (2-2.4 Gy fx(-1)) were predicted to result in smaller TCD50's than larger fraction sizes (4-5 Gy fx(-1)) for a 10 cc tumour with GFs of around 0.15. The time to eliminate hypoxic cells (the reoxygenation time) was estimated for a given GF and decreased as GF increased. The extra dose required to overcome accelerated stem cell accumulation in longer treatment schedules was estimated to be 0.68 Gy/day (in EQD26.6), similar to published values derived from clinical data. The model predicts, for a 2 Gy/weekday fractionation, that increased initial proliferation (high GF) should, surprisingly, lead to moderately higher local control values. Tumour hypoxia is predicted to increase the required dose for local control by approximately 30%. Predicted tumour regression patterns are consistent with clinical observations. This simple yet flexible model shows how the local competition for chemical resources might impact local control rates under varying fractionation conditions.

Biological characteristics of intratumoral [F-18]‑fluoromisonidazole distribution in a rodent model of glioma

Accurate imaging to identify hypoxic regions in tumors is key for radiotherapy planning. [F-18]‑fluoro-misonidazole ([F-18]-FMISO) is widely used for tumor hypoxia imaging and has the potential to optimize radiotherapy planning. However, the biological characteristics of intratumoral [F-18]-FMISO distribution have not yet been fully investigated. In hypoxic cells, the hypoxia-inducible factor-1 (HIF-1) target proteins that induce cellular proliferation and glucose metabolism, glucose transporter-1 (Glut-1) and hexokinase-II (HK-II), are upregulated. In this study, we determined the intratumoral distribution of [F-18]-FMISO by autoradiography (ARG) and compared it with pimonidazole uptake, expression of Glut-1, tumor proliferative activity (Ki-67 index) and glucose metabolism ([C-14]2-fluoro-2-deoxy-D-glucose uptake; [C-14]-FDG) in a glioma rat model. Five C6 glioma‑bearing rats were injected with [F-18]-FMISO and [C-14]-FDG. After 90 min, the rats were injected with pimonidazole and 60 min later, the rats were sacrificed and tumor tissues were sectioned into slices. The adjacent slices were used for ARG and immunohistochemical (IHC) analyses of pimonidazole, Glut-1 and Ki-67. [F-18]-FMISO ARG images were divided into regions of high [F-18]-FMISO uptake (FMISO+) and low [F-18]-FMISO uptake (FMISO-). Pimonidazole and Glut-1 expression levels, Ki-67 index and [C-14]-FDG distribution were evaluated in the regions of interest (ROIs) placed on FMISO+ and FMISO-. [F-18]-FMISO distribution was generally consistent with pimonidazole distribution. The percentage of positively stained areas (% positive) of Glut-1 in FMISO+ was significantly higher compared to FMISO- (24 ± 8% in FMISO+ and 9 ± 4% in FMISO-; P<0.05). There were no significant differences in Ki-67 index and [C-14]-FDG uptake between FMISO+ and FMISO- (for Ki-67, 10 ± 5% in FMISO+ and 12 ± 5% in FMISO-, P=ns; for [C-14]-FDG, 1.4 ± 0.3% ID/g/kg in FMISO+ and 1.3 ± 0.3% ID/g/kg in FMISO-, P = ns). Intratumoral [F-18]-FMISO distribution reflected tumor hypoxia and expression of the hypoxia‑related gene product Glut-1; it did not, however, reflect tumor proliferation or glucose metabolism. Our findings help elucidate the biological characteristics of intratumoral [F-18]-FMISO distribution that are relevant to radiotherapy planning.

Hypoxia-induced autophagic response is associated with aggressive phenotype and elevated incidence of metastasis in orthotopic immunocompetent murine models of head and neck squamous cell carcinomas (HNSCC)

Hypoxia confers resistance to chemoradiation therapy and promotes metastasis in head and neck squamous cell carcinomas (HNSCC). We investigated the effects of hypoxia in tumor phenotype using immunocompetent murine HNSCC models. Balb/c mice were injected intraorally with murine squamous cell carcinoma cells LY-2 and B4B8. Intratumoral hypoxia fraction was evaluated by the immunohistochemical detection of hypoxic probe pimonidazole and carbonic anhydrase IX (CAIX). Tumor cell apoptosis and autophagy in hypoxic areas of these tumors were examined immunohistochemically. Hypoxia-induced apoptotic and autophagic responses in vitro were examined by treating LY2 cells with CoCl(2). B4B8 tumors exhibited a non-aggressive phenotype characterized by its slow growth rate and the lack of metastatic spread. LY2 tumors demonstrated an aggressive phenotype characterized by rapid growth rate with regional and distant metastasis. Intratumoral hypoxia fraction in B4B8 tumors was significantly lower than in LY2 tumors. The hypoxic areas in B4B8 tumors exhibited increased apoptosis rate than that of LY2 tumors. In contrast, the hypoxic areas in LY2 tumors revealed autophagy. The induction of hypoxia in vitro elicited autophagy and not apoptosis in LY2 cells. The induction of autophagy coupled with blockage of apoptosis in hypoxic areas promotes tumor cell survival and confers aggressive phenotype in immunocompetent murine HNSCC models.

The Relationship among Hypoxia, Proliferation, and Outcome in Patients with De Novo Glioblastoma: A Pilot Study

The hypoxia and proliferation index increase with grade in human glial tumors, but there is no agreement whether either has prognostic importance in glioblastomas. We evaluated these end points individually and together in 16 de novo human glioblastomas using antibodies against the 2-nitroimidazole hypoxia detection agent EF5 and the proliferation detection agent Ki-67. Frozen tumor tissue sections were fluorescence-stained for nuclei (Hoechst 33342), hypoxia (anti-EF5 antibodies), and proliferation (anti-Ki-67 antibodies). EF5 binding adjacent to Ki-67+ cells, overall EF5 binding, the ratio of these values, and the proliferation index were evaluated. Patients were classified using recursive partitioning analysis and followed up until recurrence and/or death. Recursive partitioning analysis was statistically significant for survival (P = .0026). Overall EF5 binding, EF5 binding near Ki-67+ cells, and proliferation index did not predict recurrence. Two additional survival analyses based on ratios of the overall EF5 binding to EF5 binding near Ki-67+ cells were performed. High and low ratio values were determined by two cutoff points: (a) the 50% value for the ratio [EF5/Ki-67(Binding)]/[Tumor(binding)] = Ratio(EF5 50%) and (b) the median EF5 value (75.6%) of the ratio [EF5/Ki-67(Binding)]/[Tumor(binding)] = Ratio(patients median). On the basis of the Ratio(EF5 50%), recurrence (P = .0074) and survival (P = .0196) could be predicted. Using the Ratio(patients median), only survival could be predicted (P = .0291). In summary, patients had a worse prognosis if the [EF5/Ki-67(Binding)]/[Tumor(binding)] ratio was high. A hypothesis for the mechanisms and translational significance of these findings is discussed.

Hypoxia in larynx carcinomas assessed by pimonidazole binding and the value of CA-IX and vascularity as surrogate markers of hypoxia

Tumour hypoxia as driving force in tumour progression and treatment resistance has been well established. Assessment of oxygenation status of tumours may provide important prognostic information and improve selection of patients for treatment. In this study, a large homogenous group of 103 laryngeal carcinomas has been investigated in the presence of hypoxia by pimonidazole binding and the usefulness of Carbonic anhydrase IX (CA-IX) and vascular parameters as surrogate markers of hypoxia. These parameters are further related to clinical and biological characteristics. One hundred and three patients with T2-T4 larynx carcinoma were included. They were given the hypoxia marker pimonidazole intravenously (i.v.) 2h prior to taking a biopsy. Expression of all the parameters was examined by immunohistochemistry, excluding large necrotic areas. Among tumours a large variation in pimonidazole positivity (hypoxic fraction based on pimonidazole, HFpimo) (range 0-19%) and CA-IX expression (hypoxic fraction based on CA-IX staining, HFCA-IX) (range 0-34%) was observed. In 67% of the tumours, hypoxia involved 1% of the viable tumour area. HFpimo and HFCA-IX correlated significantly albeit weak (p=0.04). Both parameters showed weak inverse correlations with the relative vascular area (RVA) (p=0.01). HFpimo was further associated with histopathological grade, with poorly differentiated tumours being more hypoxic. The fraction of the tumour area positive for both pimonidazole and CA-IX correlated significantly with N stage. From these results, it was concluded that CA-IX and RVA have only limited value for measuring hypoxia and are not as robust as pimonidazole, probably due to the influence of other factors in the microenvironment. A combination of staining patterns of exogenous and endogenous markers might give important additive information about tumour biology and behaviour.

A theoretical framework for prescribing radiotherapy dose distributions using patient-specific biological information

We present a formalism for using functional imaging both to derive patient-specific radiobiological properties and consequently to prescribe optimal nonuniform radiotherapy dose distributions. The ability to quantitatively assess the response to an initial course of radiotherapy would allow the derivation of radiobiological parameters for individual patients. Both an iterative optimization and an analytical approach to this problem were investigated and illustrated by application to the linear-quadratic model of cell killing using simulated parametric data for a modeled tumor. Potential gains in local control were assessed by comparing uniform dose distributions with optimized dose distributions of equal integral dose. The effect on local prescribed dose of variations in effective radiosensitivity, tumor burden, and proliferation rate was investigated, with results suggesting that dose variations would be significant but clinically achievable. The sensitivity of derived parameters to image noise and the effect of varying the initial fractionation and imaging schedule were assessed. The analytical approach proved remarkably robust, with 10% image noise resulting in dose errors of approximately 1% for a clinically relevant set of parameters. Potential benefits were demonstrated by using this formalism to prescribe nonuniform dose distributions for model tumors using a range of literature-derived parameters. The redistribution of dose improved tumor control probability by factors between 1.03 and 4.27 for a range of model tumors.

No detectable hypoxia in malignant salivary gland tumors: preliminary results

PURPOSE

Hypoxia is detected in most solid tumors and is associated with malignant progression and adverse treatment outcomes. However, the oxygenation status of malignant salivary gland tumors has not been previously studied. The aim of this study was to investigate the potential clinical relevance of hypoxia in this tumor type.

METHODS AND MATERIALS

Twelve patients scheduled for surgical resection of a salivary gland tumor were preoperatively injected with the hypoxia marker pimonidazole and the proliferation marker iododeoxyuridine. Tissue samples of the dissected tumor were immunohistochemically stained for blood vessels, pimonidazole, carbonic anhydrase-IX, glucose transporters-1 and -3 (Glut-1, Glut-3), hypoxia-inducible factor-1alpha, iododeoxyuridine, and epidermal growth factor receptor. The tissue sections were quantitatively assessed by computerized image analysis.

RESULTS

The tissue material from 8 patients was of sufficient quality for quantitative analysis. All tumors were negative for pimonidazole binding, as well as for carbonic anhydrase-IX, Glut-1, Glut-3, and hypoxia-inducible factor-1alpha. The vascular density was high, with a median value of 285 mm(-2) (range, 209-546). The iododeoxyuridine-labeling index varied from <0.1% to 12.2% (median, 2.2%). Epidermal growth factor receptor expression levels were mostly moderate to high. In one-half of the cases, nuclear expression of epidermal growth factor receptor was observed.

CONCLUSION

The absence of detectable pimonidazole binding, as well as the lack of expression of hypoxia-associated proteins in all tumors, indicates that malignant salivary gland tumors are generally well oxygenated. It is unlikely that hypoxia is a relevant factor for their clinical behavior and treatment responsiveness.