Prognostic impact of reoxygenation in advanced cancer of the head and neck during the initial course of chemoradiation or radiotherapy alone

Immunologic Effects of Stereotactic Body Radiotherapy in Dogs with Spontaneous Tumors and the Impact of Intratumoral OX40/TLR Agonist Immunotherapy

Stereotactic body radiotherapy (SBRT) is known to induce important immunologic changes within the tumor microenvironment (TME). However, little is known regarding the early immune responses within the TME in the first few weeks following SBRT. Therefore, we used the canine spontaneous tumor model to investigate TME responses to SBRT, and how local injection of immune modulatory antibodies to OX40 and TLR 3/9 agonists might modify those responses. Pet dogs with spontaneous cancers (melanoma, carcinoma, sarcoma, n = 6 per group) were randomized to treatment with either SBRT or SBRT combined with local immunotherapy. Serial tumor biopsies and serum samples were analyzed for immunologic responses. SBRT alone resulted at two weeks after treatment in increased tumor densities of CD3+ T cells, FoxP3+ Tregs, and CD204+ macrophages, and increased expression of genes associated with immunosuppression. The addition of OX40/TLR3/9 immunotherapy to SBRT resulted in local depletion of Tregs and tumor macrophages and reduced Treg-associated gene expression (FoxP3), suppressed macrophage-associated gene expression (IL-8), and suppressed exhausted T cell-associated gene expression (CTLA4). Increased concentrations of IL-7, IL-15, and IL-18 were observed in serum of animals treated with SBRT and immunotherapy, compared to animals treated with SBRT. A paradoxical decrease in the density of effector CD3+ T cells was observed in tumor tissues that received combined SBRT and immunotherapy as compared to animals treated with SBRT only. In summary, these results obtained in a spontaneous large animal cancer model indicate that addition of OX40/TLR immunotherapy to SBRT modifies important immunological effects both locally and systemically.

Spectroscopic investigation of radiation-induced reoxygenation in radiation-resistant tumors

Fractionated radiation therapy is believed to reoxygenate and subsequently radiosensitize surviving hypoxic cancer cells. Measuring tumor reoxygenation between radiation fractions could conceivably provide an early biomarker of treatment response. However, the relationship between tumor reoxygenation and local control is not well understood. We used noninvasive optical fiber-based diffuse reflectance spectroscopy to monitor radiation-induced changes in hemoglobin oxygen saturation (sO2) in tumor xenografts grown from two head and neck squamous cell carcinoma cell lines - UM-SCC-22B and UM-SCC-47. Tumors were treated with 4 doses of 2 Gy over 2 consecutive weeks and diffuse reflectance spectra were acquired every day during the 2-week period. There was a statistically significant increase in sO2 in the treatment-responsive UM-SCC-22B tumors immediately following radiation. This reoxygenation trend was due to an increase in oxygenated hemoglobin (HbO2) and disappeared over the next 48 h as sO2 returned to preradiation baseline values. Conversely, sO2 in the relatively radiation-resistant UM-SCC-47 tumors increased after every dose of radiation and was driven by a significant decrease in deoxygenated hemoglobin (dHb). Immunohistochemical analysis revealed significantly elevated expression of hypoxia-inducible factor (HIF-1) in the UM-SCC-47 tumors prior to radiation and up to 48 h postradiation compared with the UM-SCC-22B tumors. Our observation of a decrease in dHb, a corresponding increase in sO2, as well as greater HIF-1α expression only in UM-SCC-47 tumors strongly suggests that the reoxygenation within these tumors is due to a decrease in oxygen consumption in the cancer cells, which could potentially play a role in promoting radiation resistance.

Optical Imaging Approaches to Investigating Radiation Resistance

Radiation therapy is frequently the first line of treatment for over 50% of cancer patients. While great advances have been made in improving treatment response rates and reducing damage to normal tissue, radiation resistance remains a persistent clinical problem. While hypoxia or a lack of tumor oxygenation has long been considered a key factor in causing treatment failure, recent evidence points to metabolic reprogramming under well-oxygenated conditions as a potential route to promoting radiation resistance. In this review, we present recent studies from our lab and others that use high-resolution optical imaging as well as clinical translational optical spectroscopy to shine light on the biological basis of radiation resistance. Two-photon microscopy of endogenous cellular metabolism has identified key changes in both mitochondrial structure and function that are specific to radiation-resistant cells and help promote cell survival in response to radiation. Optical spectroscopic approaches, such as diffuse reflectance and Raman spectroscopy have demonstrated functional and molecular differences between radiation-resistant and sensitive tumors in response to radiation. These studies have uncovered key changes in metabolic pathways and present a viable route to clinical translation of optical technologies to determine radiation resistance at a very early stage in the clinic.

CT imaging during treatment improves radiomic models for patients with locally advanced head and neck cancer

BACKGROUND AND PURPOSE

The development of radiomic risk models to predict clinical outcome is usually based on pre-treatment imaging, such as computed tomography (CT) scans used for radiation treatment planning. Imaging data acquired during the course of treatment may improve their prognostic performance. We compared the performance of radiomic risk models based on the pre-treatment CT and CT scans acquired in the second week of therapy.

MATERIAL AND METHODS

Treatment planning and second week CT scans of 78 head and neck squamous cell carcinoma patients treated with primary radiochemotherapy were collected. 1538 image features were extracted from each image. Prognostic models for loco-regional tumour control (LRC) and overall survival (OS) were built using 6 feature selection methods and 6 machine learning algorithms. Prognostic performance was assessed using the concordance index (C-Index). Furthermore, patients were stratified into risk groups and differences in LRC and OS were evaluated by log-rank tests.

RESULTS

The performance of radiomic risk model in predicting LRC was improved using the second week CT scans (C-Index: 0.79), in comparison to the pre-treatment CT scans (C-Index: 0.65). This was confirmed by Kaplan-Meier analyses, in which risk stratification based on the second week CT could be improved for LRC (p = 0.002) compared to pre-treatment CT (p = 0.063).

CONCLUSION

Incorporation of imaging during treatment may be a promising way to improve radiomic risk models for clinical treatment adaption, i.e., to select patients that may benefit from dose modification.

Quantitative diffuse reflectance spectroscopy of short-term changes in tumor oxygenation after radiation in a matched model of radiation resistance

There is a critical need to identify patients with radiation-resistant tumors early after treatment commencement. In this study, we use diffuse reflectance spectroscopy (DRS) to investigate changes in vascular oxygenation and total hemoglobin concentration in A549 radiation-sensitive and resistant tumors treated with a clinically relevant dose fraction of 2 Gy. DRS spectra were acquired before, immediately after, 24, and 48 hours after radiation. Our data reveals a significantly higher reoxygenation (sO₂) in the radiation-resistant tumors 24 and 48h after treatment, and provides promising evidence that DRS can discern between the reoxygenation trends of radiation-sensitive and resistant tumors.

Residual tumour hypoxia in head-and-neck cancer patients undergoing primary radiochemotherapy, final results of a prospective trial on repeat FMISO-PET imaging

BACKGROUND

Hypoxia is a well recognised parameter of tumour resistance to radiotherapy, a number of anticancer drugs and potentially immunotherapy. In a previously published exploration cohort of 25 head and neck squamous cell carcinoma (HNSCC) patients on [¹⁸F]fluoromisonidazole positron emission tomography (FMISO-PET) we identified residual tumour hypoxia during radiochemotherapy, not before start of treatment, as the driving mechanism of hypoxia-mediated therapy resistance. Several quantitative FMISO-PET parameters were identified as potential prognostic biomarkers. Here we present the results of the prospective validation cohort, and the overall results of the study.

METHODS

FMISO-PET/CT images of further 25 HNSCC patients were acquired at four time-points before and during radiochemotherapy (RCHT). Peak standardised uptake value, tumour-to-background ratio, and hypoxic volume were analysed. The impact of the potential prognostic parameters on loco-regional tumour control (LRC) was validated by the concordance index (ci) using univariable and multivariable Cox models based on the exploration cohort. Log-rank tests were employed to compare the endpoint between risk groups.

RESULTS

The two cohorts differed significantly in several baseline parameters, e.g., tumour volume, hypoxic volume, HPV status, and intercurrent death. Validation was successful for several FMISO-PET parameters and showed the highest performance (ci=0.77-0.81) after weeks 1 and 2 of treatment. Cut-off values for the FMISO-PET parameters could be validated after week 2 of RCHT. Median values for the residual hypoxic volume, defined as the ratio of the hypoxic volume in week 2 of RCHT and at baseline, stratified patients into groups of significantly different LRC when applied to the respective other cohort.

CONCLUSION

Our study validates that residual tumour hypoxia during radiochemotherapy is a major driver of therapy resistance of HNSCC, and that hypoxia after the second week of treatment measured by FMISO-PET may serve as biomarker for selection of patients at high risk of loco-regional recurrence after state-of-the art radiochemotherapy.

Oxygen and Perfusion Kinetics in Response to Fractionated Radiation Therapy in FaDu Head and Neck Cancer Xenografts Are Related to Treatment Outcome

PURPOSE

To test whether oxygenation kinetics correlate with the likelihood for local tumor control after fractionated radiation therapy.

METHODS AND MATERIALS

We used diffuse reflectance spectroscopy to noninvasively measure tumor vascular oxygenation and total hemoglobin concentration associated with radiation therapy of 5 daily fractions (7.5, 9, or 13.5 Gy/d) in FaDu xenografts. Spectroscopy measurements were obtained immediately before each daily radiation fraction and during the week after radiation therapy. Oxygen saturation and total hemoglobin concentration were computed using an inverse Monte Carlo model.

RESULTS

First, oxygenation kinetics during and after radiation therapy, but before tumor volumes changed, were associated with local tumor control. Locally controlled tumors exhibited significantly faster increases in oxygenation after radiation therapy (days 12-15) compared with tumors that recurred locally. Second, within the group of tumors that recurred, faster increases in oxygenation during radiation therapy (day 3-5 interval) were correlated with earlier recurrence times. An area of 0.74 under the receiver operating characteristic curve was achieved when classifying the local control tumors from all irradiated tumors using the oxygen kinetics with a logistic regression model. Third, the rate of increase in oxygenation was radiation dose dependent. Radiation doses ≤9.5 Gy/d did not initiate an increase in oxygenation, whereas 13.5 Gy/d triggered significant increases in oxygenation during and after radiation therapy.

CONCLUSIONS

Additional confirmation is required in other tumor models, but these results suggest that monitoring tumor oxygenation kinetics could aid in the prediction of local tumor control after radiation therapy.

Evaluation of tumor oxygenation by color duplex sonography: A new approach

OBJECTIVE: Description of a new noninvasive method for the evaluation of tissue oxygenation in head and neck cancer.

STUDY DESIGN AND SETTING: Prospective nonrandomized controlled study in an academic medical center on 20 patients with neck metastases of head and neck cancer. Metastases were investigated using color duplex sonography and pO2 histography. The vascularization in sonography was quantitatively evaluated by color pixel density and compared to the pO2 values of the same nodes.

RESULTS: The correlation between vascularization and flow velocity was 0.71. For the mean/median pO2-values and for the pO2 readings < 10.0 mmHg correlations were r = 0.65/0.76 and 0.71.

CONCLUSION: This sonographic method allows a safe and reliable evaluation of oxygenation in metastases of head and neck cancer.

SIGNIFICANCE: The new approach is an alternative to pO2 histography and may play a future role in the planning of radiotherapy in the neck. (Otolaryngol Head Neck Surg 2005;132:765-9.)

Effects of high-dose microbeam irradiation on tumor microvascular function and angiogenesis

Microbeam radiation therapy (MRT) is a form of cancer treatment in which a single large dose of radiation is spatially fractionated in-line or grid-like patterns. Preclinical studies have demonstrated that MRT is capable of eliciting high levels of tumor response while sparing normal tissue that is exposed to the same radiation field. Since a large fraction of the MRT-treated tumor is in the dose valley region that is not directly irradiated, tumor response may be driven by radiation bystander effects, which in turn elicit a microvascular response. Differential alterations in hemodynamics between the tumor and normal tissue may explain the therapeutic advantages of MRT. Direct observation of these dynamic responses presents a challenge for conventional ex vivo analysis. Furthermore, knowledge gleaned from in vitro studies of radiation bystander response has not been widely incorporated into in vivo models of tumor radiotherapy, and the biological contribution of the bystander effect within the tumor microenvironment is unknown. In this study, we employed noninvasive, serial observations of the tumor microenvironment to address the question of how tumor vasculature and HIF-1 expression are affected by microbeam radiotherapy. Tumors (approximately 4 mm in diameter) grown in a dorsal window chamber were irradiated in a single fraction using either a single, microplanar beam (300 micron wide swath) or a wide-field setup (whole-window chamber) to a total dose of 50 Gy. The tumors were optically observed daily for seven days postirradiation. Microvascular changes in the tumor and surrounding normal tissue differed greatly between the wide-field and microbeam treatments. We present evidence that these changes may be due to dissimilar spatial and temporal patterns of HIF-1 expression induced through radiation bystander effects.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Global gene expression profiling in three tumor cell lines subjected to experimental cycling and chronic hypoxia

Hypoxia is one of the most important features of the tumor microenvironment, exerting an adverse effect on tumor aggressiveness and patient prognosis. Two types of hypoxia may occur within the tumor mass, chronic (prolonged) and cycling (transient, intermittent) hypoxia. Cycling hypoxia has been shown to induce aggressive tumor cell phenotype and radioresistance more significantly than chronic hypoxia, though little is known about the molecular mechanisms underlying this phenomenon. The aim of this study was to delineate the molecular response to both types of hypoxia induced experimentally in tumor cells, with a focus on cycling hypoxia. We analyzed in vitro gene expression profile in three human cancer cell lines (melanoma, ovarian cancer, and prostate cancer) exposed to experimental chronic or transient hypoxia conditions. As expected, the cell-type specific variability in response to hypoxia was significant. However, the expression of 240 probe sets was altered in all 3 cell lines. We found that gene expression profiles induced by both types of hypoxia were qualitatively similar and strongly depend on the cell type. Cycling hypoxia altered the expression of fewer genes than chronic hypoxia (6,132 vs. 8,635 probe sets, FDR adjusted p<0.05), and with lower fold changes. However, the expression of some of these genes was significantly more affected by cycling hypoxia than by prolonged hypoxia, such as IL8, PLAU, and epidermal growth factor (EGF) pathway-related genes (AREG, HBEGF, and EPHA2). These transcripts were, in most cases, validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Our results indicate that experimental cycling hypoxia exerts similar, although less intense effects, on the examined cancer cell lines than its chronic counterpart. Nonetheless, we identified genes and molecular pathways that seem to be preferentially regulated by cyclic hypoxia.

Measurement of reoxygenation during fractionated radiotherapy in head and neck squamous cell carcinoma xenografts

Hypoxic tissues lack adequate oxygenation and it has been long established that tumours commonly exhibit hypoxia and that hypoxia is a factor contributing towards resistance to radiotherapy. To develop computer models and make predictions about the affects of tumour hypoxia on treatment outcome, quantitative tumour oxygenation and reoxygenation data from in vivo systems is required. The aim of this study was to investigate the timing and degree of reoxygenation during radiotherapy in a human head and neck squamous cell carcinoma xenograft mouse model (FaDu). Mice were immobilised using a novel restraining system and exposed unanaesthetised in 3 or 5 Gy fractions, up to a maximum of 40 Gy. Partial pressures of oxygen (pO2) measurements were recorded at six time points throughout the 2 week course of radiotherapy, using a fibre optic system. Tumours receiving 0-30 Gy did not exhibit an increase in pO2. However, the mean pO2 after 2 weeks of accelerated fractionated radiotherapy (40 Gy) was significantly increased (P<0.01) compared to the mean pO2 of tumours not receiving the full schedule (0-30 Gy). These results lead to the conclusion of an average reoxygenation onset time of 2 weeks in this group of xenografts. A relatively large range of pO2 values measured at each dose point in the study indicate a large inter-tumour variation in oxygenation among the tumours. Data from this experimental work will be used to define the range of reoxygenation onset times implemented in a Monte Carlo computer model, simulating hypoxic head and neck cancer growth and radiotherapy.

Detection and characterization of tumor hypoxia using pO2 histography

Data from 125 studies describing the pretreatment oxygenation status as measured in the clinical setting using the computerized Eppendorf pO2 histography system have been compiled in this article. Tumor oxygenation is heterogeneous and severely compromised as compared to normal tissue. Hypoxia results from inadequate perfusion and diffusion within tumors and from a reduced O2 transport capacity in anemic patients. The development of tumor hypoxia is independent of a series of relevant tumor characteristics (e.g., clinical size, stage, histology, and grade) and various patient demographics. Overall median pO2 in cancers of the uterine cervix, head and neck, and breast is 10 mm Hg with the overall hypoxic fraction (pO2 <or= 2.5 mm Hg) being approx. 25%. Metastatic lesions do not substantially deviate from the oxygenation status of (their) primary tumors. Whereas normal tissue oxygenation is independent of the hemoglobin level over the range of 8-15 g/dL, hypoxia is more pronounced in anemic patients and above this range in some cancers. Identification of tumor hypoxia may allow an assessment of a tumor's potential to develop an aggressive phenotype or acquired treatment resistance, both of which lead to poor prognosis. Detection of hypoxia in the clinical setting may therefore be helpful in selecting high-risk patients for individual and/or more intensive treatment schedules.

Induction of plasminogen activator inhibitor type-1 (PAI-1) by hypoxia and irradiation in human head and neck carcinoma cell lines

Background

Squamous cell carcinoma of the head and neck (SCCHN) often contain highly radioresistant hypoxic regions, nonetheless, radiotherapy is a common treatment modality for these tumours. Reoxygenation during fractionated radiotherapy is desired to render these hypoxic tumour regions more radiosensitive. Hypoxia additionally leads to up-regulation of PAI-1, a protein involved in tumour progression and an established prognostic marker for poor outcome. However, the impact of reoxygenation and radiation on PAI-1 levels is not yet clear. Therefore, we investigated the kinetics of PAI-1 expression and secretion after hypoxia and reoxygenation, and determined the influence of ionizing radiation on PAI-1 levels in the two human SCCHN cell lines, BHY and FaDu.

Methods

HIF-1α immunoblot was used to visualize the degree of hypoxia in the two cell lines. Cellular PAI-1 expression was investigated by immunofluorescence microscopy. ELISA was used to quantify relative changes in PAI-1 expression (cell lysates) and secretion (cell culture supernatants) in response to various lengths (2 – 4 h) of hypoxic exposure (< 0.66 % O₂), reoxygenation (24 h, 20 % O₂), and radiation (0, 2, 5 and 10 Gy).

Results

HIF-1α expression was induced between 2 and 24 h of hypoxic exposure. Intracellular PAI-1 expression was significantly increased in BHY and FaDu cells as early as 4 h after hypoxic exposure. A significant induction in secreted PAI-1 was seen after 12 to 24 h (BHY) and 8 to 24 h (FaDu) hypoxia, as compared to the normoxic control. A 24 h reoxygenation period caused significantly less PAI-1 secretion than a 24 h hypoxia period in FaDu cells. Irradiation led to an up-regulation of PAI-1 expression and secretion in both, BHY and FaDu cells.

Conclusion

Our data suggest that both, short-term (~4 – 8 h) and long-term (~20 – 24 h) hypoxic exposure could increase PAI-1 levels in SCCHN in vivo. Importantly, radiation itself could lead to PAI-1 up-regulation in head and neck tumours, whereas reoxygenation of hypoxic tumour cells during fractionated radiotherapy could counteract the increased PAI-1 levels.

Effect of reoxygenation on the hypoxia-induced up-regulation of serine protease inhibitor PAI-1 in head and neck cancer cells

In squamous cell carcinoma of the head and neck (SCCHN), hypoxia is considered a crucial physiological modulator for malignant progression, wherebythe plasminogen activation system is involved in overlapping functions such as moulding of the extracellular matrix, cell proliferation and signal transduction. Little is known about the effects of reoxygenation on the plasminogen activation system in SCCHN cells. Three human SCCHN cell lines (BHY, CAL27, FaDu) and a non-transformed human fibroblast cell line (VH7) were exposed to hypoxic (<0.5% O(2)) conditions for up to 72 h and subsequently reoxygenated at normoxic conditions for 24 h. Urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) protein concentration and former protein activity were determined by ELISA and complex ELISA, respectively. Reoxygenation induced significant changes in cell-associated and secreted PAI-1 protein compared to the normoxic control. Significant increase in cell-associated and secreted uPA protein after reoxygenation was only observed for some of the cell lines. Determination of uPA-PAI-1 complex formation revealed the release of active protein into the cell supernatant. The beneficial role of reoxygenation during radiation therapy is widely accepted. However, reoxygenation does not seem to counteract the effects induced by hypoxia on the plasminogen activation system. Fatally irradiated reoxygenat- ed tumour cells might still produce sufficient amounts of 'harmful' protein and thus initiate a path for invasion and metastasis for surviving tumour cells.

Endogenous markers of two separate hypoxia response pathways (hypoxia inducible factor 2 alpha and carbonic anhydrase 9) are associated with radiotherapy failure in head and neck cancer patients recruited in the CHART randomized trial

PURPOSE

Randomized controlled trials have generally shown a benefit from accelerated radiotherapy in head and neck squamous cell carcinoma (HNSCC). However, the large randomized United Kingdom trial CHART (Continuous Hyperfractionated Accelerated Radiotherapy) failed to show a benefit of strongly accelerated over standard radiotherapy (RT) in 918 patients with HNSCC. In this study, we investigated the impact of tumor hypoxia on the outcome of HNSCC patients in the CHART trial. There are two distinct hypoxia inducible factors (HIFs) that control different gene response pathways and we assessed them both with endogenous markers of hypoxia, hypoxia inducible factor HIF-2 alpha (HIF-2) and carbonic anhydrase CA9, an indicator of HIF-1 alpha (HIF-1) function.

METHODS

Tissue from pre-RT biopsies performed in 198 of 918 patients recruited was analyzed for the immunohistochemical expression of HIF-2 and CA9.

RESULTS

A significant association of high HIF2 and of high CA9 reactivity with poor locoregional control (P < .0001 and P = .0002, respectively) and poor survival (P = .0004 and 0.002, respectively) was noted. In multivariate analysis, HIF-2 and CA9 maintained their independent prognostic significance. Coexpression of both pathways had an additive effect, supporting their independent role. The uni-directional hypothesis, that a benefit from randomization to CHART should be seen in the nonhypoxic tumors, was supported by the data (one-tailed P = .04).

CONCLUSION

Expression of endogenous markers of hypoxia for the HIF-1 and HIF-2 pathway is strongly associated with radiotherapy failure. Using immunohistochemical methods it is possible to identify subgroups of HNSCC patients who are highly curable with radiotherapy, or who are excellent candidates for clinical trials on hypoxia-targeting drugs in two distinct pathways.

Hypoxia in head and neck cancer: How much, how important?

BACKGROUND

Hypoxia develops in tumors because of a less ordered, often chaotic, and leaky vascular supply compared with that in normal tissues. In preclinical models, hypoxia has been shown to be associated with treatment resistance and increased malignant potential. In the clinic, several reports show the presence and extent of tumor hypoxia as a negative prognostic indicator. This article reviews the biology and importance of hypoxia in head and neck cancer.

METHODS

A review of literature was carried out and combined with our own experience on hypoxia measurements using exogenous and endogenous markers.

RESULTS

Hypoxia can increase resistance to radiation and cytotoxic drugs and lead to malignant progression, affecting all treatment modalities, including surgery. Hypoxia measurements using electrodes, exogenous bioreductive markers, or endogenous markers show the presence of hypoxia in most head and neck cancers, and correlations with outcome, although limited, consistently indicate hypoxia as an important negative factor. Each hypoxia measurement method has disadvantages, and no "gold standard" yet exists. Distinctions among chronic, acute, and intermediate hypoxia need to be made, because their biology and relevance to treatment resistance differ. Reliable methods for measuring these different forms in the clinic are still lacking. Several methods to overcome hypoxia have been tested clinically, with radiosensitizers (nimorazole), hypoxic cytotoxins (tirapazamine), and carbogen showing some success. New treatments such as hypoxia-mediated gene therapy await proper clinical testing.

CONCLUSIONS

The hypoxia problem in head and neck cancer needs to be addressed if improvements in current treatments are to be made. Increased knowledge of the molecular biology of intermediate, severe, and intermittent hypoxia is needed to assess their relevance and indicate strategies for overcoming their negative influence.

Hypoxia Is Important in the Biology and Aggression of Human Glial Brain Tumors

We investigated whether increasing levels of tissue hypoxia, measured by the binding of EF5 [2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide] or by Eppendorf needle electrodes, were associated with tumor aggressiveness in patients with previously untreated glial brain tumors. We hypothesized that more extensive and severe hypoxia would be present in tumor cells from patients bearing more clinically aggressive tumors. Hypoxia was measured with the 2-nitroimidazole imaging agent EF5 in 18 patients with supratentorial glial neoplasms. In 12 patients, needle electrode measurements were made intraoperatively. Time to recurrence was used as an indicator of tumor aggression and was analyzed as a function of EF5 binding, electrode values and recursive partitioning analysis (RPA) classification. On the basis of EF5 binding, WHO grade 2 tumors were characterized by modest cellular hypoxia (pO2s approximately 10%) and grade 3 tumors by modest-to-moderate hypoxia (pO2s approximately 10%- 2.5%). Severe hypoxia (approximately 0.1% oxygen) was present in 5 of 12 grade 4 tumors. A correlation between more rapid tumor recurrence and hypoxia was demonstrated with EF5 binding, but this relationship was not predicted by Eppendorf measurements.