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

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.

Overcoming radioresistance with the hypoxia-activated prodrug CP-506: A pre-clinical study of local tumour control probability

BACKGROUND AND PURPOSE

Tumour hypoxia is an established radioresistance factor. A novel hypoxia-activated prodrug CP-506 has been proven to selectively target hypoxic tumour cells and to cause anti-tumour activity. The current study investigates whether CP-506 improves outcome of radiotherapy in vivo.

MATERIALS AND METHODS

Mice bearing FaDu and UT-SCC-5 xenografts were randomized to receive 5 daily injections of CP-506/vehicle followed by single dose (SD) irradiation. In addition, CP-506 was combined once per week with fractionated irradiation (30 fractions/6 weeks). Animals were followed-up to score all recurrences. In parallel, tumours were harvested to evaluate pimonidazole hypoxia, DNA damage (γH2AX), expression of oxidoreductases.

RESULTS

CP-506 treatment significantly increased local control rate after SD in FaDu, 62% vs. 27% (p = 0.024). In UT-SCC-5, this effect was not curative and only marginally significant. CP-506 induced significant DNA damage in FaDu (p = 0.009) but not in UT- SCC-5. Hypoxic volume (HV) was significantly smaller (p = 0.038) after pretreatment with CP-506 as compared to vehicle in FaDu but not in less responsive UT-SCC-5. Adding CP-506 to fractionated radiotherapy in FaDu did not result in significant benefit.

CONCLUSION

The results support the use of CP-506 in combination with radiation in particular using hypofractionation schedules in hypoxic tumours. The magnitude of effect depends on the tumour model, therefore it is expected that applying appropriate patient stratification strategy will further enhance the benefit of CP-506 treatment for cancer patients. A phase I-IIA clinical trial of CP-506 in monotherapy or in combination with carboplatin or a checkpoint inhibitor has been approved (NCT04954599).

Patient-Derived Xenograft and Organoid Models for Precision Medicine Targeting of the Tumour Microenvironment in Head and Neck Cancer

Patient survival from head and neck squamous cell carcinoma (HNSCC), the seventh most common cause of cancer, has not markedly improved in recent years despite the approval of targeted therapies and immunotherapy agents. Precision medicine approaches that seek to individualise therapy through the use of predictive biomarkers and stratification strategies offer opportunities to improve therapeutic success in HNSCC. To enable precision medicine of HNSCC, an understanding of the microenvironment that influences tumour growth and response to therapy is required alongside research tools that recapitulate the features of human tumours. In this review, we highlight the importance of the tumour microenvironment in HNSCC, with a focus on tumour hypoxia, and discuss the fidelity of patient-derived xenograft and organoids for modelling human HNSCC and response to therapy. We describe the benefits of patient-derived models over alternative preclinical models and their limitations in clinical relevance and how these impact their utility in precision medicine in HNSCC for the discovery of new therapeutic agents, as well as predictive biomarkers to identify patients' most likely to respond to therapy.

Repeat FMISO-PET imaging weakly correlates with hypoxia-associated gene expressions for locally advanced HNSCC treated by primary radiochemotherapy

BACKGROUND

Hypoxia is an important factor of tumour resistance to radiotherapy, chemotherapy and potentially immunotherapy. It can be measured e.g. by positron emission tomography (PET) imaging or hypoxia-associated gene expressions from tumour biopsies. Here we correlate [¹⁸F]fluoromisonidazole (FMISO)-PET/CT imaging with hypoxia-associated gene expressions on a cohort of 50 head and neck squamous cell carcinoma (HNSCC) patients and compare their prognostic value for response to radiochemotherapy (RCTx).

METHODS

FMISO-PET/CT images of 50 HNSCC patients were acquired at four time-points before and during RCTx. For 42 of these patients, hypoxia-associated gene expressions were evaluated by nanoString technology based on a biopsy obtained before any treatment. The FMISO-PET parameters tumour-to-background ratio and hypoxic volume were correlated to the expressions of 58 hypoxia-associated genes using the Spearman correlation coefficient ρ. Three hypoxia-associated gene signatures were compared regarding their correlation with the FMISO-PET parameters using their median expression. In addition, the correlation with tumour volume was analysed. The impact of both hypoxia measurement methods on loco-regional tumour control (LRC) and overall survival (OS) was assessed by Cox regression.

RESULTS

The median expression of hypoxia-associated genes was weakly correlated to hypoxia measured by FMISO-PET imaging (ρ ≤ 0.43), with higher correlations to imaging after weeks 1 and 2 of treatment (p < 0.001). Moderate correlations were obtained between FMISO-PET imaging and tumour volume (ρ ≤ 0.69). Prognostic models for LRC and OS based on the FMISO-PET parameters could not be improved by including hypoxia classifiers.

CONCLUSION

We observed low correlations between hypoxia FMISO-PET parameters and expressions of hypoxia-associated genes. Since FMISO-PET showed a superior patient stratification, it may be the preferred biomarker over hypoxia-associated genes for stratifying patients with locally advanced HNSCC treated by primary RCTx.

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.

Reprogramming of tumor metabolism by targeting mitochondria improves tumor response to irradiation

BACKGROUND

The Warburg phenotype identified decades ago describes tumor cells with increased glycolysis and decreased mitochondrial respiration even in the presence of oxygen. This particular metabolism also termed 'aerobic glycolysis' reflects an adaptation of tumor cells to proliferation in a heterogeneous tumor microenvironment. Although metabolic alterations in cancer cells are common features, their impact on the response to radiotherapy is not yet fully elucidated. This study investigated the impact of cellular oxygen consumption inhibition on the tumor response to radiotherapy.

MATERIAL AND METHODS

Warburg-phenotype tumor cells with impaired mitochondrial respiration (MD) were produced and compared in respect to their metabolism to the genetically matched parental cells (WT). After characterization of their metabolism we compared the response of MD cells to irradiation in vivo and in vitro to the genetically matched parental cells (WT).

RESULTS

We first confirmed that MD cells were exclusively glycolytic while WT cells exhibited mitochondrial respiration. We then used these cells for assessing the response of WT and MD tumors to a single dose of radiation and showed that the in vivo tumor growth delay of the MD group was increased, indicating an increased radiosensitivity compared to WT while the in vitro ability of both cell lines to repair radiation-induced DNA damage was similar.

CONCLUSION

Taken together, these results indicate that in addition to intrinsic radiosensitivity parameters the tumor response to radiation will also depend on their metabolic rate of oxygen consumption.

Intra- and intertumor heterogeneities in total, chronic, and acute hypoxia in xenografted squamous cell carcinomas. Detection and quantification using (immuno-)fluorescence techniques

BACKGROUND

Heterogeneously distributed hypoxia is a major characteristic of solid tumors. (Immuno-)fluorescence detection of hypoxia in experimental tumors is frequently assessed in a single central section; however, this may not necessarily be representative of the whole tumor. In order to determine whether analysis of one central section is exemplary of the whole tumor and whether different volumes have an impact on tumor oxygenation, we assessed the fractions of total (TH), chronic (CH), and acute hypoxia (AH) throughout different layers of tumors of varying volumes.

MATERIALS AND METHODS

Xenografted FaDu human squamous cell carcinomas of different volumes were investigated for intra- and intertumor heterogeneities. Tissue blocks located at the apical, central, and basal layer were sliced from individual tumors. Four serial cryosections were analyzed from each tissue block. Vital tumor tissue was explored for the distribution of Hoechst 33342 (perfusion), pimonidazole (hypoxia), and CD31 (endothelium) to assess TH, CH, and AH.

RESULTS

Fractions of TH, CH, and AH were consistently similar in the serial sections of individual tissue blocks. However, significant differences were found between the apical, central, and basal blocks that were even opposite depending on the tumor volume. Pooled data from all three tissue blocks revealed significantly higher fractions of hypoxia in the large tumors than in the small tumors.

CONCLUSION

FaDu tumors exhibit a heterogeneous and volume-dependent oxygenation status. Assessing the average fractions of TH, CH, and AH from central blocks corresponds best to the average of the entire tumor. However, information on intratumor heterogeneities is lost, especially when considering tumors of substantially different volumes.

Effects of three modifiers of glycolysis on ATP, lactate, hypoxia, and growth in human tumor cell lines in vivo

BACKGROUND

High pretreatment tumor lactate content is associated with poor outcome after fractionated irradiation in human squamous cell carcinoma (hSCC) xenografts. Therefore, decreasing lactate content might be a promising approach for increasing tumor radiosensitivity. As the basis for such experiments, the effects of the biochemical inhibitors pyruvate dehydrogenase kinase dichloroacetate (DCA), lactate dehydrogenase oxamate, and monocarboxylic acid transporter-1 α-cyano-4-hydroxycinnamate (CHC) on tumor micromilieu and growth were investigated.

MATERIALS AND METHODS

Oxygen consumption (OCR) and extracellular acidification rates (ECAR) were measured in FaDu and UT-SCC-5 hSCC in response to DCA in vitro. Mice bearing FaDu, UT-SCC-5, and WiDr colorectal adenocarcinoma received either DCA in drinking water or DCA injected twice a day, or CHC injected daily. WiDr was also treated daily with oxamate. FaDu and UT-SCC-5 were either excised 8 days after treatment for histology or tumor growth was monitored. WiDr tumors were excised at 8 mm. Effect of inhibitors on ATP, lactate, hypoxia, and Ki67 labeling index (LI) was evaluated.

RESULTS

DCA increased OCR and decreased ECAR in vitro. None of the treatments with inhibitors significantly changed lactate content, hypoxia levels, and Ki67 LI in the three tumor lines in vivo. ATP concentration significantly decreased after only daily twice injections of DCA in FaDu accompanied by a significant increase in necrotic fraction. Tumor growth was not affected by any of the treatments.

CONCLUSION

Overall, tumor micromilieu and tumor growth could not be changed by glycolysis modifiers in the three tumor cell lines in vivo. Further studies are necessary to explore the impact of metabolic targets on radiation response.

Quantifying heterogeneity in human tumours using MRI and PET

Most tumours, even those of the same histological type and grade, demonstrate considerable biological heterogeneity. Variations in genomic subtype, growth factor expression and local microenvironmental factors can result in regional variations within individual tumours. For example, localised variations in tumour cell proliferation, cell death, metabolic activity and vascular structure will be accompanied by variations in oxygenation status, pH and drug delivery that may directly affect therapeutic response. Documenting and quantifying regional heterogeneity within the tumour requires histological or imaging techniques. There is increasing evidence that quantitative imaging biomarkers can be used in vivo to provide important, reproducible and repeatable estimates of tumoural heterogeneity. In this article we review the imaging methods available to provide appropriate biomarkers of tumour structure and function. We also discuss the significant technical issues involved in the quantitative estimation of heterogeneity and the range of descriptive metrics that can be derived. Finally, we have reviewed the existing clinical evidence that heterogeneity metrics provide additional useful information in drug discovery and development and in clinical practice.

Cancer stem cells at the crossroads of current cancer therapy failures--radiation oncology perspective

Despite continuous improvements in cancer management, locoregional recurrence or metastatic spread still occurs in a high proportion of patients after radiotherapy or combined treatments. One underlying reason might be a low efficacy of current treatments on eradication of cancer stem cells (CSCs). It has been recognised for a long time, that only the small subpopulation of CSCs can cause recurrences and that all CSCs need to be killed for permanent tumour cure. However, only recently novel technologies have allowed to enrich CSCs and to investigate their biology. An emerging experimental and clinical database provides first hints that cell populations accumulated by putative stem cell markers or tumours that highly express such markers may be more radioresistant than their marker-negative counterparts. Other data support a higher tolerance of CSCs to hypoxia and preferential location in specific microenvironmental niches. However, conflicting data, methodological problems of the assays and a generally small database on only few tumour types necessitate further large and well-designed prospective experimental and clinical investigations that specifically address this question to corroborate this hypothesis. If such investigations confirm biological differences between CSCs and non-CSCs, this would imply that novel treatment strategies need to be tested specifically for their effect on CSCs. Another implication is that also biomarkers for prediction of local tumour control after radiotherapy or combined treatments need to reflect the behaviour of CSCs and not of the bulk of all cancer cells. This review discusses the importance of CSCs for treatment failure and challenges occurring from the CSC concept for cancer diagnosis, treatment and prediction of outcome. It is concluded that CSC-based endpoints and biomarkers are eventually expected to considerably improve tumour cure rates in the clinics through individualised tailoring of treatment.

Glycolytic metabolism and tumour response to fractionated irradiation

BACKGROUND AND PURPOSE

To study whether pre-therapeutic lactate or pyruvate predict for tumour response to fractionated irradiation and to identify possible coherencies between intermediates of glycolysis and expression levels of selected proteins.

MATERIALS AND METHODS

Concentrations of lactate, pyruvate, glucose and ATP were quantified via bioluminescence imaging in tumour xenografts derived from 10 human head and neck squamous cell carcinoma (HNSCC) lines. Tumours were irradiated with 30 fractions within 6 weeks. Expression levels of the selected proteins in tumours were measured at the mRNA and protein level. Tumour-infiltrating leucocytes were quantified after staining for CD45.

RESULTS

Lactate but not pyruvate concentrations were significantly correlated with tumour response to fractionated irradiation. Lactate concentrations in vivo did not reflect lactate production rates in vitro. Metabolite concentrations did not correlate with GLUT1, PFK-L or LDH-A at the transcriptional or protein level. CD45-positive cell infiltration was low in the majority of tumours and did not correlate with lactate concentration.

CONCLUSIONS

Our data support the hypothesis that the antioxidative capacity of lactate may contribute to radioresistance in malignant tumours. Non-invasive imaging of lactate to monitor radiation response and testing inhibitors of glycolysis to improve outcome after fractionated radiotherapy warrant further investigations.

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.

Biological imaging in radiation therapy: role of positron emission tomography

In radiation therapy (RT), staging, treatment planning, monitoring and evaluation of response are traditionally based on computed tomography (CT) and magnetic resonance imaging (MRI). These radiological investigations have the significant advantage to show the anatomy with a high resolution, being also called anatomical imaging. In recent years, so called biological imaging methods which visualize metabolic pathways have been developed. These methods offer complementary imaging of various aspects of tumour biology. To date, the most prominent biological imaging system in use is positron emission tomography (PET), whose diagnostic properties have clinically been evaluated for years. The aim of this review is to discuss the valences and implications of PET in RT. We will focus our evaluation on the following topics: the role of biological imaging for tumour tissue detection/delineation of the gross tumour volume (GTV) and for the visualization of heterogeneous tumour biology. We will discuss the role of fluorodeoxyglucose-PET in lung and head and neck cancer and the impact of amino acids (AA)-PET in target volume delineation of brain gliomas. Furthermore, we summarize the data of the literature about tumour hypoxia and proliferation visualized by PET. We conclude that, regarding treatment planning in radiotherapy, PET offers advantages in terms of tumour delineation and the description of biological processes. However, to define the real impact of biological imaging on clinical outcome after radiotherapy, further experimental, clinical and cost/benefit analyses are required.

Detection of different hypoxic cell subpopulations in human melanoma xenografts by pimonidazole immunohistochemistry

This study aimed at developing immunohistochemical assays for different subpopulations of hypoxic cells in tumors. BALB/c-nu/nu mice bearing A-07 or R-18 tumors were given a single dose of 90 mg/kg body weight or three doses (3 h apart) of 30 mg/kg body weight of pimonidazole hydrochloride intravenously. The fraction of pimonidazole-labeled cells was assessed in paraffin-embedded and frozen tumor sections and compared with the fraction of radiobiologically hypoxic cells. The staining pattern in paraffin-embedded sections indicated selective staining of chronically hypoxic cells. Frozen sections showed a staining pattern consistent with staining of both chronically and acutely/repetitively hypoxic cells. Fraction of pimonidazole-labeled cells in paraffin-embedded sections was lower than the fraction of radiobiologically hypoxic cells (single-dose and triple-dose experiment). In frozen sections, fraction of pimonidazole-labeled cells was similar to (single-dose experiment) or higher than (triple-dose experiment) fraction of radiobiologically hypoxic cells. Three different subpopulations of hypoxic cells could be quantified by pimonidazole immunohistochemistry: the fraction of cells that are hypoxic because of limitations in oxygen diffusion, the fraction of cells that are hypoxic simultaneously because of fluctuations in blood perfusion, and the fraction of cells that are exposed to one or more periods of hypoxia during their lifetime because of fluctuations in blood perfusion.

Application of radiotherapy and chemotherapy protocols to pre-clinical tumor models

This unit (1) provides background into understanding how agents that target specific molecules or receptors (molecular-targeted agents), in particular, agents affecting the tumor vasculature (perivasculature network in tumors), interact with and modify radiation therapy; (2) details factors affecting interpretation of results in murine tumor model experiments utilizing radiation therapy and drug combinations; and (3) provides specific protocols for the application of radiation therapy, both alone and in combination with chemotherapy and/or molecular-targeted agents.

EGFR-TK inhibition before radiotherapy reduces tumour volume but does not improve local control: Differential response of cancer stem cells and nontumourigenic cells?

BACKGROUND AND PURPOSE

Waiting times before radiotherapy may reduce tumour control probability due to proliferation of tumour cells. The aim of the experiment was to test whether the growth inhibiting effect of epidermal growth factor receptor (EGFR)-inhibitors after surgery or tumour transplantation results in a lower tumour mass at time of irradiation and can thereby improve local tumour control.

MATERIALS AND METHODS

The EGFR-tyrosine kinase inhibitor BIBX1382BS was applied over 14days starting from microscopically non-in-sano-resection of FaDu tumours or from tumour transplantation, followed by irradiation (5f/5d). Endpoint was local tumour control. In addition, vital tumour areas, pimonidazole hypoxic fraction, BrdU labelling index, and colony forming ability in vitro were tested in control tumours and after BIBX1382BS treatment (starting from transplantation).

RESULTS

The tumour volume at start of irradiation was significantly lower in the BIBX1382BS treated tumours as compared to the control groups by factors of 11 (post-surgery setting) and 2.7 (transplantation setting). However, the reduced volume did not translate into improved local control after irradiation. The TCD(50) values after surgery were 25.4Gy [95% CI 18; 33Gy] in the control group and 30.5Gy [24; 37] in the BIBX1382BS group (p=0.25). Treatment after transplantation resulted in TCD(50) values of 41.1Gy [35; 47] in the control group and 41.1Gy [33; 49] in the BIBX1382BS group (p=1). While the proportion of S-phase cells decreased after BIBX1382BS treatment, no differences were observed between the pimonidazole hypoxic fractions and in vitro colony forming ability.

CONCLUSIONS

EGFR-TK inhibition with BIBX1382BS over 14days between macroscopically complete tumour resection or tumour transplantation and start of radiotherapy significantly reduced tumour volume but did not improve local tumour control. One possible explanation is that the EGFR-TK inhibitor has a higher activity in nontumourigenic cancer cells compared to cancer stem cells. This hypothesis, along with the observation that tumours of similar size were significantly more radiosensitive after surgery than without surgery, warrants further investigation.

Effect of increase of radiation dose on local control relates to pre-treatment FDG uptake in FaDu tumours in nude mice

OBJECTIVES

To investigate whether heterogeneity in [(18)F]2-fluoro-2-deoxy-d-glucose (FDG) uptake in a single tumour line, i.e. in tumours with identical genetic background, relates to radiation response.

MATERIALS AND METHODS

Sixty-two human FaDu head and neck squamous cell carcinomas in nude mice with a diameter of 7mm entered the study. FDG-PET scanning was performed without anaesthesia on an animal PET scanner immediately prior to irradiation in order to determine maximum standardized uptake values (SUV(max)). Single dose irradiations of 25 or 35Gy were applied under normal blood flow conditions using 200kV X-rays (0.5mm Cu, approximately 1.2Gy min(-1)). The mice were observed for 120 days after irradiation, experimental endpoint was local tumour control evaluated using the Kaplan-Meier method.

RESULTS

Analyzing all 62 animals, tumour control probability after irradiation with 25Gy was significantly lower than after irradiation with 35Gy (29% vs. 57%, log rank p=0.016). Pre-treatment SUV(max) values ranged from 0.72 to 3.47, the median SUV(max) value was 1.59. In tumours with FDG uptake less than the median SUV(max), local control was 37% after 25Gy vs. 47% after 35Gy (p=0.37). In contrast, substantial differences in local tumour control were found in tumours with FDG uptake above the median SUV(max) (24% vs. 71%, p=0.006). Multivariate Cox analysis revealed a significant decrease of hazard of recurrence with increasing dose and SUV(max).

CONCLUSIONS

An increase of radiation dose had a greater effect on local control in FaDu tumours with higher FDG uptake than in tumours with lower FDG uptake. This supports the hypothesis that pre-treatment FDG-PET may provide useful information for heterogeneous radiation dose prescription in subvolumes of tumours of individual patients. As only one tumour model was studied and single doses were applied, confirmatory investigations using further tumour models and fractionated radiotherapy are warranted.

Pre-treatment number of clonogenic cells and their radiosensitivity are major determinants of local tumour control after fractionated irradiation

OBJECTIVE

The response of tumours to fractionated radiotherapy is determined by many factors including repopulation, reoxygenation, the number of clonogenic cells, and their intrinsic radiosensitivity. However, after single radiation doses given under conditions of clamp hypoxia, the dose to control a tumour locally is dependent only on the number of clonogenic cells and their cellular radiosensitivity. Therefore, these parameters were investigated using local control after single doses given under hypoxia, to predict the outcome of fractionated irradiation.

MATERIALS AND METHODS

Ten hSCC cell lines (FaDu, UT-SCC-15, UT-SCC-14, XF354, UT-SCC-5, UT-SCC-45, SAS, CAL-33, UT-SCC-8, and HSC-4) were transplanted subcutaneously into the right hind-leg of NMRI nude mice. At 7mm in diameter, tumours were irradiated either with graded single doses under clamp blood flow conditions (n=873) or with 30 graded fractions within 6 weeks (n=905) under ambient conditions. Local tumour control was determined 120 days after irradiation. Radiation response was quantified in terms of TCD(50), i.e. the dose required to control 50% of tumours locally.

RESULTS

Ten tumour lines investigated showed a pronounced heterogeneity in both TCD(50(30fx/6w)) after fractionated irradiation and TCD(50(SDclamp)) after single dose irradiation. TCD(50(30fx/6w)) varied between 45Gy for UT-SCC-45 and 127Gy for SAS; TCD(50(SDclamp)) varied between 42Gy for UT-SCC-14 and 66Gy for CAL-33. Two tumours were excluded from further analysis due to immunogenicity or non-defined TCD(50). Linear regression analysis revealed a significant positive correlation between TCD(50(SDclamp)) and TCD(50(30fx/6w)) (R(2)=0.82, p=0.002).

CONCLUSIONS

Significant association between TCD(50(SDclamp)) and TCD(50(30fx/6w)) suggests that the pre-treatment number of clonogenic tumour cells and their cellular radiosensitivity have a major impact on local control after fractionated radiotherapy.

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.

Tumor lactate content predicts for response to fractionated irradiation of human squamous cell carcinomas in nude mice

BACKGROUND AND PURPOSE

The present study was performed to test the hypothesis that lactate accumulation correlates with the radioresistance of malignant tumors due to the radical scavenging capacity of lactate or metabolic intermediates of glycolysis, such as pyruvate.

MATERIALS AND METHODS

Five human head and neck squamous cell carcinoma cell lines (HNSCCs) xenografted in nude mice were treated with a clinically relevant irradiation protocol with 30 fractions within 6 weeks. The radiation dose necessary to locally control 50% of the tumors (TCD50) ranged from 47.4 to 129.8 Gy. Concentrations of glucose, lactate, and ATP in viable tumor regions as potential indicators of glycolytic activity were assessed with structure-associated quantitative bioluminescence imaging.

RESULTS

Mean lactate concentrations of the different tumor cell lines were in the range of 7.3-25.9 micromol/g. TCD50 values were positively correlated with tumor lactate levels (R = 0.9824, p = 0.0028).

CONCLUSIONS

The data obtained support the hypothesis that tissue lactate content correlates with radioresistance in solid human tumors. Furthermore, the results suggest that tumor lactate content determined non-invasively by proton magnetic resonance spectroscopy imaging may be used to predict for radioresistance of malignancies in the clinic; the data also imply that transient inhibition of glycolysis during treatment might possibly sensitize tumors to irradiation.

Strain and tumour specific variations in the effect of hypoxia on osteopontin levels in experimental models

PURPOSE

To investigate the relationship between tumour hypoxia and serum and tumour osteopontin (OPN) levels.

MATERIALS AND METHODS

Experiments were performed in CDF1 or C3H/Km mice implanted with a C3H mammary carcinoma (CDF1) or SCCVII squamous cell carcinoma (C3H/Km), respectively. Mice were either untreated or gassed with 10% oxygen for 1-72 h. Serum and tumour OPN levels were measured with an ELISA and tumour OPN mRNA levels using RT-PCR. Tumour oxygenation was estimated using the Eppendorf histograph with the percentage of pO(2) values <or=5 mm Hg (HF5) as the endpoint.

RESULTS

OPN levels were 50-fold higher in the serum of non-tumour bearing CDF1 mice compared to C3H/Km mice. A tumour related increase in serum OPN levels was observed in CDF1 but not in C3H/Km mice. Low oxygen breathing increased HF5 in both tumour models and in the C3H mammary carcinoma model both serum and tumour OPN decreased after prolonged hypoxia (24h and more). When 12h of hypoxia was followed by 24h reoxygenation there was a twofold increase in serum OPN levels. No changes were observed in the SCCVII model. No changes in tumour OPN mRNA expression were observed during hypoxia and reoxygenation in these tumour models.

CONCLUSION

Clear strain and tumour specific differences in the effect of hypoxia on OPN levels have been observed in two different mouse tumour models. These data emphasize the complexity in the relationship between poor oxygenation (and/or reoxygenation) of tumours and serum levels of OPN.

The prognostic value of endogenous hypoxia-related markers for head and neck squamous cell carcinomas treated with ARCON

BACKGROUND AND PURPOSE

Hypoxic radioresistance is an important cause for treatment failure in a number of tumor types including head and neck cancers. Recent studies suggest that outcome can be improved by oxygenation modifying treatments such as ARCON. A robust endogenous marker of hypoxia might be a valuable aid to select patients for such treatments. The aim of this investigation was to study associations between the putative endogenous hypoxia markers CA-IX, Glut-1 and Glut-3 and clinical tumor and patient characteristics and to evaluate the prognostic value of these markers.

PATIENTS AND METHODS

Tumor biopsies from 58 patients treated with ARCON in a phase II trial were included. Tumor sections were immunohistochemically stained for CA-IX, Glut-1 and Glut-3. Sections were scored for relative tumor area stained by the markers (CA-IX and Glut-3) and for intensity of staining (Glut-1 and Glut-3). Further, sections were stained for CD34, an endothelial marker to assess microvascular density.

RESULTS

Staining of CA-IX and Glut-3 was observed at some distance from vessels and adjacent to necrosis. Glut-1 staining was generally very diffuse. The distribution of clinical characteristics was equal between tumors with high and low marker expression. Significant differences were found for locoregional control (P = 0.04) and for freedom of distant metastases (P = 0.02) in favour of patients with high CA-IX positivity (>25% of tumor area). High Glut-3 expression was associated with a better locoregional control (P = 0.04). Higher Glut-1 intensity was associated with an increased rate of distant metastases (P = 0.0005) and a worse overall survival (P = 0.001).

CONCLUSIONS

The inconsistent associations with outcome of CA-IX and the glucose transporters indicate that different factors play a role in up-regulation of these markers. Compared to studies with conventional treatment, the correlation between CA-IX expression and Glut-3 expression and outcome was reversed after treatment with ARCON. This does not support the potential of any of these proteins as very specific and robust hypoxia markers.

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.