Hypoxia and necrosis in rat 9L glioma and Morris 7777 hepatoma tumors: comparative measurements using EF5 binding and the Eppendorf needle electrode

Magnetic boron nitride nanosheets-based on pH-responsive smart nanocarriers for the delivery of doxorubicin for liver cancer treatment

A new drug delivery system (DDS) type complexing magnetic nanoparticles (MNP) along with boron nanosheets (BNN) coated with a pH-responsive polymer-polyethylene glycol (PEG) for the manageable loading/release of the anti-cancerous drug, doxorubicin (DOX), was created (MNP-BNN-PEG-DOX). The X-ray diffraction patterns of the nanocomposites displayed wide diffraction peaks for BNN at 25.1° and 42.3°, belonging to the (002) and (100) planes, correspondingly. Additionally, the characteristic peaks of Fe₃O₄ appeared at 30.5°, 35.9°, 43.6°, 54.1°, 57.5°, and 63.2°, belonging to the (220), (311), (400), (422), (511), and (440) crystal planes, correspondingly. Moreover, the magnetic properties of the nanocomposites revealed that the MNP-BNN remained magnetic after coating with PEG. The saturation magnetization (Ms) of the uncoated-MNP-BNN and MNP-BNN-PEG-1 were 49.4 and 42.3 emu g^-1, respectively. Both in vitro and in vivo analyses shown that DDS might inhibit tumor growth, provoke cancer cell apoptosis, and reduce the cytotoxic effects of DOX. In vivo analysis demonstrated that after treatment with phosphate-buffered saline (PBS), MNP-BNN-PEG-1, free DOX, and MNP-BNN-PEG-1-DOX, the average tumor growth and weight were 1906, 1997, 1188, and 1043 nm and 0.17, 0.20, 0.13, and 0.07 g, respectively. The MNP-BNN-PEG-DOX nanoparticles could be an effective treatment and potential alternative for liver cancer therapy.

Evaluation of CAIX and CAXII Expression in Breast Cancer at Varied O2 Levels: CAIX is the Superior Surrogate Imaging Biomarker of Tumor Hypoxia

PURPOSE

Hypoxia is commonly observed in regions of primary tumors and metastases, and is associated with resistance to treatment, more aggressive tumor phenotypes and poor prognosis. Reliable and validated imaging biomarkers of hypoxia are needed for pre-clinical studies and clinical use. Expression of cell-surface carbonic anhydrases IX and XII (CAIX and CAXII) in tumor cells has been associated with tumor hypoxia. CAIX and CAXII specific antibodies conjugated to fluorescent dye were evaluated for the non-invasive detection of hypoxia in vivo.

PROCEDURES

Human breast cancer cell lines (MCF10A, DCIS, MCF7, ZR-75.1 and MDA-mb231) were characterized for CAIX and CAXII expression by real-time RT-PCR and immunocytochemistry (ICC) under normoxic and hypoxic conditions. Immunohistochemical (IHC) staining of CAIX, CAXII and the commercially available exogenous hypoxia marker, pimonidazole, was performed using sections of ZR-75.1 and MDA-mb-231 orthotopic breast cancer xenograft tumors from nude mice. In vivo fluorescence imaging of ZR-75.1 tumors in animals housed at varied levels of oxygen was used to quantify the relative uptake of the CAIX and CAXII agents and a commercially available sulfonamide-based agent. Corresponding tumor sections were IHC stained for CAIX, CAXII and pimonidazole.

RESULTS

CAIX mRNA expression was significantly higher (p < 0.05) in hypoxia for all cell lines, which was in agreement with protein expression by ICC. CAXII expression was mixed, with a modest hypoxia-related increase in two cell lines (p < 0.05) and no change in others. Quantified IHC staining of ZR-75.1 and MDA-mb-231 tumor sections showed that CAIX and CAXII expression was elevated in regions with pimonidazole staining, but CAXII levels were lower than CAIX. Tumor uptake of the CAIX targeted agent, and IHC staining of CAIX and pimonidazole in corresponding tumor sections were correlated, and co-registered, and shown to be significantly elevated by level of oxygenation (p < 0.001): hypoxia > normoxia > hyperoxia. However, the CAXII and sulfonamide agents were not significantly correlated with hypoxia.

CONCLUSION

These studies suggest that the fluorescently labeled CAIX-specific agent is a more robust indicator of hypoxia in vivo compared to the CAXII-specific agent or the agent specific to the CA active site.

(18)F-fluoromisonidazole positron emission tomography can predict pathological necrosis of brain tumors

PURPOSE

Tumor necrosis is one of the indicators of tumor aggressiveness. (18)F-fluoromisonidazole (FMISO) is the most widely used positron emission tomography (PET) tracer to evaluate severe hypoxia in vivo. Because severe hypoxia causes necrosis, we hypothesized that intratumoral necrosis can be detected by FMISO PET in brain tumors regardless of their histopathology. We applied FMISO PET to various types of brain tumors before tumor resection and evaluated the correlation between histopathological necrosis and FMISO uptake.

METHODS

This study included 59 brain tumor patients who underwent FMISO PET/computed tomography before any treatments. According to the pathological diagnosis, the brain tumors were divided into three groups: astrocytomas (group 1), neuroepithelial tumors except for astrocytomas (group 2), and others (group 3). Two experienced neuropathologists evaluated the presence of necrosis in consensus. FMISO uptake in the tumor was evaluated visually and semi-quantitatively using the tumor-to-normal cerebellum ratio (TNR).

RESULTS

In visual analyses, 26/27 cases in the FMISO-positive group presented with necrosis, whereas 28/32 cases in the FMISO-negative group did not show necrosis. Mean TNRs with and without necrosis were 3.49 ± 0.97 and 1.43 ± 0.42 (p < 0.00001) in group 1, 2.91 ± 0.83 and 1.44 ± 0.20 (p < 0.005) in group 2, and 2.63 ± 1.16 and 1.35 ± 0.23 (p < 0.05) in group 3, respectively. Using a cut-off value of TNR = 1.67, which was calculated by normal reference regions of interest, we could predict necrosis with sensitivity, specificity, and accuracy of 96.7, 93.1, and 94.9 %, respectively.

CONCLUSIONS

FMISO uptake within the lesion indicated the presence of histological micro-necrosis. When we used a TNR of 1.67 as the cut-off value, intratumoral micro-necrosis was sufficiently predictable. Because the presence of necrosis implies a poor prognosis, our results suggest that FMISO PET could provide important information for treatment decisions or surgical strategies of any type of brain tumor.

18F-EF5 PET Is Predictive of Response to Fractionated Radiotherapy in Preclinical Tumor Models

We evaluated the relationship between pre-treatment positron emission tomography (PET) using the hypoxic tracer ¹⁸F-[2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3- pentafluoropropyl) acetamide] (¹⁸F-EF5) and the response of preclinical tumor models to a range of fractionated radiotherapies. Subcutaneous HT29, A549 and RKO tumors grown in nude mice were imaged using ¹⁸F-EF5 positron emission tomography (PET) in order to characterize the extent and heterogeneity of hypoxia in these systems. Based on these results, 80 A549 tumors were subsequently grown and imaged using ¹⁸F-EF5 PET, and then treated with one, two, or four fraction radiation treatments to a total dose of 10–40 Gy. Response was monitored by serial caliper measurements of tumor volume. Longitudinal post-treatment ¹⁸F-EF5 PET imaging was performed on a subset of tumors. Terminal histologic analysis was performed to validate ¹⁸F-EF5 PET measures of hypoxia. EF5-positive tumors responded more poorly to low dose single fraction irradiation relative to EF5-negative tumors, however both groups responded similarly to larger single fraction doses. Irradiated tumors exhibited reduced ¹⁸F-EF5 uptake one month after treatment compared to control tumors. These findings indicate that pre- treatment ¹⁸F-EF5 PET can predict the response of tumors to single fraction radiation treatment. However, increasing the number of fractions delivered abrogates the difference in response between tumors with high and low EF5 uptake pre-treatment, in agreement with traditional radiobiology.

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.

Carbonic anhydrase IX as an imaging and therapeutic target for tumors and metastases

Carbonic anhydrase IX (CAIX) which is a zinc containing metalloprotein, efficiently catalyzes the reversible hydration of carbon dioxide. It is constitutively up-regulated in several cancer types and has an important role in tumor progression, acidification and metastasis. High expression of CAIX generally correlates with poor prognosis and is related to a decrease in the disease-free interval following successful therapy. Therefore, it is considered as a prognostic indicator in oncology.In this review, we describe CAIX regulation and its role in tumor hypoxia, acidification and metastasis. In addition, the molecular imaging of CAIX and its potential for use in cancer detection, diagnosis, staging, and for use in following therapy response is discussed. Both antibodies and small molecular weight compounds have been used for targeted imaging of CAIX expression. The use of CAIX expression as an attractive and promising candidate marker for systemic anticancer therapy is also discussed.

Hypoxia in melanoma: using optical spectroscopy and EF5 to assess tumor oxygenation before and during regional chemotherapy for melanoma

BACKGROUND

There is increasing evidence that tumor hypoxia plays a significant role in the chemoresistance of melanoma, but to our knowledge, real-time tumor oxygenation during isolated limb infusion (ILI) has not been studied. We sought to demonstrate the feasibility of measuring real-time alterations in tissue oxygenation.

METHODS

Consecutive patients with histologically confirmed in-transit melanoma were enrolled onto a prospective single-arm pilot study and administered the hypoxia marker drug EF5. All patients were treated with ILI. Optical spectroscopy readings were obtained at three locations: two discrete target lesions and one normal skin control. Measurements were taken at 11 predefined time points during ILI.

RESULTS

A total of six patients were enrolled onto this pilot study. Intratumor and normal skin optical spectroscopy readings were found to have discrete inflection points throughout the duration of therapy, corresponding with established time points. Baseline hypoxia as measured by both optical spectroscopy and EF5 immunofluorescence was variable, but on the basis of optical spectra, tumors appeared to become more hypoxic compared to normal skin after tourniquet application. The optical hypoxia signature was variable between patients while hemoglobin absorption increased.

CONCLUSIONS

To our knowledge, this is the first use of real-time optical spectroscopy to evaluate oxygenation and perfusion within melanoma lesions during regional chemotherapy. We report our development of this new noninvasive means of assessing tumor vascular function, which has the potential to be a powerful tool for noninvasive examination of the melanoma tumor microenvironment.

Lacking hypoxia-mediated downregulation of E-cadherin in cancers of the uterine cervix

Background:

Experimental studies have established a causal connection between tumour hypoxia, hypoxia-associated proteome changes and downregulation of E-cadherin, the final common pathway of epithelial-to-mesenchymal transition (EMT). Our study aimed at elucidating the interrelationship of these processes in cancers of the uterine cervix in vivo.

Methods:

Tumour oxygenation was assessed in 48 squamous cell carcinomas (SCC) of the uterine cervix using polarographic needle electrodes. The expression pattern of E-cadherin was investigated by immunohistochemistry and western blotting, and was compared with that of the hypoxia-inducible proteins glucose transporter (GLUT)-1 and carbonic anhydrase (CA) IX in biopsy specimens of the oxygenation measurement tracks.

Results:

The majority of cervical cancers (52%) were E-cadherin positive, with a complete absence of the antigen in only 10% of the tumours. No correlation was found between the level of E-cadherin expression and the oxygenation status (mean pO₂, median pO₂ and hypoxic fractions). In patients showing partial expression of E-cadherin (38%), staining was not preferentially diminished in GLUT-1- or CA IX-positive areas, and loss of E-cadherin occurred independently of tumour cell scattering.

Conclusion:

Our data provide no evidence in favour of a hypoxia-induced EMT as a mechanistic basis of cervical cancer invasiveness.

Mechanisms of blood flow and hypoxia production in rat 9L-epigastric tumors

Classical descriptions of tumor physiology suggest two origins for tumor hypoxia; steady-state (diffusion-limited) hypoxia and cycling (perfusion-modulated) hypoxia. Both origins, primarily studied and characterized in murine models, predict relatively small, isolated foci or thin shells of hypoxic tissue interspersed with contrasting oxic tissue. These foci or shells would not be expected to scale with overall tumor size since the oxygen diffusion distance (determined by oxygen permeability and tissue oxygen consumption rate) is not known to vary dramatically from tumor to tumor. We have identified much larger (macroscopic) regions of hypoxia in rat gliosarcoma tumors and in larger human tumors (notably sarcomas and high-grade glial tumors), as indicated by biochemical binding of the hypoxia marker, EF5. Thus, we considered an alternative cause of tumor hypoxia related to a phenomenon first observed in window-chamber tumor models: namely longitudinal arteriole gradients. Although longitudinal arteriole gradients, as originally described, are also microscopic in nature, it is possible for them to scale with tumor size if tumor blood flow is organized in an appropriate manner. In this organization, inflowing blood would arise from relatively well-oxygenated sources and would branch and then coalesce to poorly-oxygenated outflowing blood over distances much larger than the length of conventional arterioles (multi-millimeter scale). This novel concept differs from the common characterization of tumor blood flow as disorganized and/or chaotic. The organization of blood flow to produce extended longitudinal gradients and macroscopic regional hypoxia has many important implications for the imaging, therapy and biological properties of tumors. Herein, we report the first experimental evidence for such blood flow, using rat 9L gliosarcoma tumors grown on the epigastric artery/vein pair.

Measurements of hypoxia ([(18)F]-FMISO, [(18)F]-EF5) with positron emission tomography (PET) and perfusion using PET ([(15)O]-H(2)O) and power Doppler ultrasonography in feline fibrosarcomas*

Abstract The aim of this study was to evaluate if hypoxia in feline fibrosarcomas can be detected. This was done using positron emission tomography (PET), two hypoxia tracers and polarographic pO(2) measurements. Of the seven cats included, five received [(18)F]-fluoromisonidazole and two 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide. Perfusion was evaluated with [(15)O]-H(2)O (n = 4) and with contrast-enhanced power Doppler ultrasonography (n = 5). Hypoxia was detected in three cats. Polarographic pO(2) measurements did not confirm PET results. In the ultrasonographic evaluation, low vascularity and low perfusion were seen with a peripheral vascular pattern and no perfusion in the centre of the tumour. This was in contrast to the [(15)O]-H(2)O scans, where central perfusion of the tumour was also found. In conclusion, it appears that hypoxia exists in this tumour type. The presence of tumour necrosis and heterogeneous hypoxia patterns in these tumours may explain the found discrepancies between the applied techniques.

Evaluation of the relationship between MR estimates of blood oxygen saturation and hypoxia: effect of an antiangiogenic treatment on a gliosarcoma model

PURPOSE

To assess the reproducibility of the magnetic resonance (MR) estimate of blood oxygen saturation (sO(2)) in the rat brain, to evaluate the relationship between low MR estimate of sO(2) values and tissue hypoxia in a hypoxic and necrotic glioscarcoma model (9L gliosarcoma cells), and to evaluate the capability of the MR estimate of sO(2) parameter to help identify modifications induced by an antiangiogenic treatment (sorafenib) in 9L gliosarcoma tumors.

MATERIALS AND METHODS

Experiments were performed with permits from the French Ministry of Agriculture. Forty-eight male rats bearing a 9L gliosarcoma were randomized in untreated and treated (sorafenib) groups. MR blood volume fraction and MR estimate of sO(2) parameters were estimated 1 day before and 1, 3, 5, and 8 days after the start of the treatment. The in vivo MR estimate of sO(2) measurement was correlated with the ex vivo hypoxia assessment by using pimonidazole staining. Paired and unpaired t tests, as well as parametric Pearson tests, were used for the statistical analyses.

RESULTS

In healthy tissues, MR estimate of sO(2) measurements were comparable to literature values and were reproducible (mean across all animals, 68.0% ± 6.5 [standard deviation]). In untreated tumors, MR estimate of sO(2) and immunohistochemical analysis yielded correlated fractional hypoxic-necrotic areas (R(2) = 0.81). In tumors treated with antiangiogenic therapy, tumor MR estimate of sO(2) was decreased with respect to the healthy tissue (P< .001).

CONCLUSION

Results of this study suggest that the MR estimate of sO(2) is a reproducible estimate that could be used as an in vivo probe of hypoxia in brain tumors and as a sensitive reporter of the hypoxic effects of antiangiogenic therapies.

Modeling the spatial distribution of chronic tumor hypoxia: implications for experimental and clinical studies

Tumor oxygenation status is considered one of the important prognostic markers in cancer since it strongly influences the response of cancer cells to various treatments; in particular, to radiation therapy. Thus, a proper and accurate assessment of tumor oxygen distribution before the treatment may highly affect the outcome of the treatment. The heterogeneous nature of tumor hypoxia, mainly influenced by the complex tumor microenvironment, often makes its quantification very difficult. The usual methods used to measure tumor hypoxia are biomarkers and the polarographic needle electrode. Although these techniques may provide an acceptable assessment of hypoxia, they are invasive and may not always give a spatial distribution of hypoxia, which is very useful for treatment planning. An alternative method to quantify the tumor hypoxia is to use theoretical simulations with the knowledge of tumor vasculature. The purpose of this paper is to model tumor hypoxia using a known spatial distribution of tumor vasculature obtained from image data, to analyze the accuracy of polarographic needle electrode measurements in quantifying hypoxia, to quantify the optimum number of measurements required to satisfactorily evaluate the tumor oxygenation status, and to study the effects of hypoxia on radiation response. Our results indicate that the model successfully generated an accurate oxygenation map for tumor cross-sections with known vascular distribution. The method developed here provides a way to estimate tumor hypoxia and provides guidance in planning accurate and effective therapeutic strategies and invasive estimation techniques. Our results agree with the previous findings that the needle electrode technique gives a good estimate of tumor hypoxia if the sampling is done in a uniform way with 5-6 tracks of 20–30 measurements each. Moreover, the analysis indicates that the accurate measurement of oxygen profile can be very useful in determining right radiation doses to the patients.

Targeted therapy of SMMC-7721 liver cancer in vitro and in vivo with carbon nanotubes based drug delivery system

A new type of drug delivery system (DDS) involved chitosan (CHI) modified single walled carbon nanotubes (SWNTs) for controllable loading/release of anti-cancer doxorubicin (DOX) was constructed. CHI was non-covalently wrapped around SWNTs, imparting water-solubility and biocompatibility to the nanotubes. Folic acid (FA) was also bounded to the outer CHI layer to realize selective killing of tumor cells. The targeting DDS could effectively kill the HCC SMMC-7721 cell lines and depress the growth of liver cancer in nude mice, showing superior pharmaceutical efficiency to free DOX. The results of the blood routine and serum biochemical parameters, combined with the histological examinations of vital organs, demonstrating that the targeting DDS had negligible in vivo toxicity. Thus, this DDS is promising for high treatment efficacy and low side effects for future cancer therapy.

In vivo identification and specificity assessment of mRNA markers of hypoxia in human and mouse tumors

BACKGROUND

Tumor hypoxia is linked to poor prognosis, but identification and quantification of tissue hypoxia remains a challenge. The hypoxia-specificity of HIF-1α target genes in vivo has been questioned due to the confounding influence of other microenvironmental abnormalities known to affect gene expression (e.g., low pH). Here we describe a new technique that by exploiting intratumoral oxygenation heterogeneity allows us to identify and objectively rank the most robust mRNA hypoxia biomarkers.

METHODS

Mice carrying human (FaDudd) or murine (SCCVII) tumors were injected with the PET hypoxia tracer FAZA. Four hours post-injection tumors were removed, frozen, and crushed into milligram-sized fragments, which were transferred individually to pre-weighed tubes containing RNAlater and then weighed. For each fragment radioactivity per tissue mass and expression patterns of selected mRNA biomarkers were analyzed and compared.

RESULTS

In both tumour models, fragmentation into pieces weighing 10 to 60 mg resulted in tissue fragments with highly variable relative content of hypoxic cells as evidenced by an up to 13-fold variation in FAZA radioactivity per mass of tissue. Linear regression analysis comparing FAZA retention with patterns of gene expression in individual tissue fragments revealed that CA9, GLUT1 and LOX mRNA levels were equally and strongly correlated to hypoxic extent in FaDudd. The same link between hypoxia and gene expression profile was observed for CA9 and GLUT1, but not LOX, in SCCVII tumors. Apparent in vivo hypoxia-specificity for other putative molecular markers of tissue hypoxia was considerably weaker.

CONCLUSIONS

The portrayed technique allows multiple pairwise measurements of mRNA transcript levels and extent of hypoxia in individual tumors at a smallest possible volumetric scale which (by limiting averaging effects inherent to whole-tumor analysis) strengthen the conclusiveness on true hypoxia-specificity of candidate genes while limiting the required number of tumors. Among tested genes, our study identified CA9, GLUT1 and possibly LOX as highly specific biomarkers of tumor hypoxia in vivo.

The radiation response of cells from 9L gliosarcoma tumours is correlated with [F18]-EF5 uptake

PURPOSE

Tumour hypoxia affects cancer biology and therapy-resistance in both animals and humans. The purpose of this study was to determine whether EF5 ([2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide]) binding and/or radioactive drug uptake correlated with single-dose radiation response in 9L gliosarcoma tumours.

MATERIALS AND METHODS

Twenty-two 9L tumours were grown in male Fischer rats. Rats were administered low specific activity (18)F-EF5 and their tumours irradiated and assessed for cell survival and hypoxia. Hypoxia assays included EF5 binding measured by antibodies against bound-drug adducts and gamma counts of (18)F-EF5 tumour uptake compared with uptake by normal muscle and blood. These assays were compared with cellular radiation response (in vivo to in vitro assay). In six cases, uptake of tumour versus muscle was also assayed using images from a PET (positron emission tomography) camera (PENN G-PET).

RESULTS

The intertumoural variation in radiation response of 9L tumour-cells was significantly correlated with uptake of (18)F-labelled EF5 (i.e., including both bound and non-bound drug) using either tumour to muscle or tumour to blood gamma count ratios. In the tumours where imaging was performed, there was a significant correlation between the image analysis and gamma count analysis. Intertumoural variation in cellular radiation response of the same 22 tumours was also correlated with mean flow cytometry signal due to EF5 binding.

CONCLUSION

To our knowledge, this is the first animal model/drug combination demonstrating a correlation of radioresponse for tumour-cells from individual tumours with drug metabolism using either immunohistochemical or non-invasive techniques.

Preparation of chitosan-polyaspartic acid-5-fluorouracil nanoparticles and its anti-carcinoma effect on tumor growth in nude mice

AIM: To prepare chitosan-polyaspartic acid-5-fluorouracil (CTS-Pasp-5Fu) nanoparticles and investigate its anti-carcinoma effect and toxicity.

METHODS: CTS-Pasp-5Fu nanoparticles were synthesized by ionic gelatification. Male BABL/c nude mice were injected with SGC-7901 gastric carcinoma cell line mass to establish a human gastric carcinoma model. They were randomly allocated into 4 groups: CTS-Pasp-5Fu (containing 5-Fu 1.25 mg/kg), 5-Fu (1.25 mg/kg), CTS-Pasp and normal saline groups. Tumor weight was measured and assay of colony forming unit-granulocyte and macrophage (CFU-GM) was performed. The structural change of cells and tissues was observed and the Bax and Bcl-2 genes were detected.

RESULTS: Compared with normal saline, the inhibition rates of tumor growth for the CTS-Pasp, 5-Fu and CTS-Pasp-5Fu groups were 5.58%, 58.69% and 70.82%, respectively. The tumor inhibition rates for the CTS-Pasp, 5-Fu and CTS-Pasp-5Fu groups were 5.09%, 65.3% and 72.79%, respectively. There was a significant decrease in the number of CFU-GM formation and increase of total bilirubin, and alanine aminotransferase in the 5-Fu group, but no change in those of the other three groups. There was no change in white blood cell count and creatinine among the four groups. Pathological section of liver and nephridial tissues showed that the damage in the 5-Fu group was more severe than that in the CTS-Pasp-5Fu group. 5-Fu and CTS-Pasp-5Fu groups could both down-regulate the Bcl-2 expression and up-regulate the Bax expression to different extent, and the accommodate effect of CTS-Pasp-5Fu was more obvious than 5-Fu.

CONCLUSION: The tumor inhibition rate of CTS-Pasp-5Fu nanoparticles is much higher than that of 5-Fu alone.

Biodisposition and metabolism of [(18)F]fluorocholine in 9L glioma cells and 9L glioma-bearing fisher rats

PURPOSE

[(18)F]Fluorocholine ([(18)F]FCH) was developed as an analog of [(11)C]choline for tumor imaging; however, its metabolic handling remains ill defined. In this study, the metabolism of [(18)F]FCH is evaluated in cultured 9L glioma cells and Fisher 344 rats bearing 9L glioma tumors.

METHODS

9L glioma cells were incubated with [(18)F]FCH and [(14)C]choline under normoxic and hypoxic (1% O(2)) conditions and analyzed for metabolic fate. [(18)F]FCH and [(14)C]choline kinetics and metabolism were studied in Fisher 344 rats bearing subcutaneous 9L tumors.

RESULTS

[(18)F]FCH and [(14)C]choline were similarly metabolized in 9L cells in both normoxic and hypoxic conditions over a 2-h incubation period. In normoxia, radioactivity was predominantly in phosphorylated form for both tracers after 5-min incubation. In hypoxia, the tracers remained mainly in nonmetabolized form at early timepoints (<20 min). Slow dephosphorylation of intracellular [(18)F]phosphofluorocholine (0.043-0.060 min(-1)) and [(14)C]phosphocholine (0.072-0.088 min(-1)) was evidenced via efflux measurements. In rat, both [(18)F]FCH and [(14)C]choline showed high renal and hepatic uptake. Blood clearance of both tracers was rapid with oxidative metabolites, [(18)F]fluorobetaine and [(14)C]betaine, representing the majority of radiolabel in plasma after 5 min postinjection. Oxidation (in liver) and lipid incorporation (in lung) were somewhat slower for [(18)F]FCH relative to [(14)C]choline. The majority of radiolabel in hypoxic subcutaneous tumor, as in hypoxic cultured 9L cells, was found as nonmetabolized [(18)F]FCH and [(14)C]choline.

CONCLUSIONS

[(18)F]FCH mimics choline uptake and metabolism by 9L glioma cells and tumors. However, subtle changes in biodistribution, oxidative metabolism, dephosphorylation, lipid incorporation, and renal excretion show moderate effects of the presence of the radiofluorine atom in [(18)F]FCH. The decrease in phosphorylation of exogenous choline by cancer cells should be considered in interpretation of positron emission tomography images in characteristically hypoxic tumors.

In situ oxygen utilization in the rat intervertebral disc

Nucleus pulposus cells of the intervertebral disc have no endogenous vasculature and have thus been hypothesized to be hypoxic. This hypothesis was tested using 2-nitroimidazole, EF5, a drug that at low oxygen concentrations forms covalent adducts with cellular proteins. After administrating EF5 to rats, sections of the intervertebral disc were analysed for EF5 adducts. Drug adducts were quantified in tissue sections using a fluorescent monoclonal antibody. Although the level of EF5 fluorescence in all intervertebral disc tissues was low, the transition zone at the periphery of the nucleus pulposus exhibited the highest level of EF5 binding. To substantiate this result, tissue nitroreductase levels and drug pharmacology were evaluated. Nitroreductase levels were measured in whole discs under severe hypoxia. We noted that there was robust EF5 binding to cells in the annulus fibrosus and transition zone with modest binding to cells of the nucleus pulposus and endplate. High-performance liquid chromatography analysis indicated limitations in EF5 access to the nucleus pulposus, most probably related to the lack of vasculature and slow drug distribution through the gel-like interior of the disc. However, despite diffusion problems, the drug dose was determined to be sufficient to report the oxygen status of the nucleus pulposus cells. Based on these findings, we conclude that despite poor vascularization, the disc cells accommodate to the local environment by displaying a limited need for oxygen. Accordingly, the cells of the intervertebral disc are not severely hypoxic.

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

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

Dynamics of tumor hypoxia measured with bioreductive hypoxic cell markers

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

Modulation of intratumoral hypoxia by the epidermal growth factor receptor inhibitor gefitinib detected using small animal PET imaging

Blockade of signaling through the epidermal growth factor receptor (EGFR) tyrosine kinase by inhibitors such as gefitinib (Iressa) can inhibit tumor angiogenesis and enhance responses to ionizing radiation. In this study, the ability of gefitinib to modulate intratumoral oxygenation was evaluated in human EGFR-expressing A431 squamous cell carcinoma xenografts using in vivo small animal positron emission tomography (PET) imaging with the hypoxia marker [(18)F]fluoroazomycin arabinoside (FAZA) and by the immunohistochemical detection of hypoxia-induced adducts of the 2-nitroimidazole, pimonidazole. Serial noninvasive PET imaging of A431 xenografts showed a significant reduction in FAZA uptake following treatment with 75 mg/kg/d of gefitinib [tumor to background ratio, 6.1 +/- 1.0 (pretreatment) versus 2.3 +/- 0.6 (posttreatment); P = 0.0004]. Similarly, ex vivo quantitation of FAZA uptake showed significantly reduced FAZA uptake in established A431 xenografts treated with gefitinib compared with vehicle control (tumor to blood ratio for controls versus gefitinib, 8.0 +/- 3.0 versus 2.7 +/- 0.8; P = 0.007; or tumor to muscle ratio controls versus gefitinib, 8.6 +/- 2.8 versus 2.6 +/- 1.0; P = 0.002). The effect of gefitinib treatment seemed to be independent of tumor size. In addition, gefitinib treatment reduced pimonidazole-binding in A431 xenografts measured after 5 and 8 days of gefitinib treatment compared with baseline and with tumors treated with vehicle alone. A strong correlation was observed between pimonidazole binding and FAZA uptake. Together, these findings show that gefitinib reduces intratumoral hypoxia.

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

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

Spatial heterogeneity and oxygen dependence of glucose consumption in R3230Ac and fibrosarcomas of the Fischer 344 rat

To examine the oxygen-dependence of glucose consumption in solid tumors, we monitored gradients of glucose, lactate, and hypoxia in R3230Ac and FSA tumors growing in Fischer 344 rats. Bioluminescence imaging, detection of Hoechst 33342, and immunostaining of the hypoxia marker EF5 [2-8-N-(2,2,3,3,3-pentafluoropropyl)acetamide] were done in serial tumor slices. Glucose and lactate levels were also determined in liver and blood. Cells were further tested for glucose consumption and lactate production in vitro. In both tumor types, EF5 staining indicated similar maximum levels of hypoxia; the most intense staining occurred in perinecrotic regions. Glucose concentrations were highest in liver, declined from blood to tumor edge, further into vital tumor regions, and were lowest close to necrosis. Glucose was significantly lower in FSA than in R3230Ac tumors. Glucose concentrations in R3230Ac tumors were consistently higher in nonhypoxic than in hypoxic areas, with maximum values equal to systemic blood levels. Glucose in FSA tumors was close to zero, regardless of the presence or absence of hypoxia. Lactate did not differ significantly between the tumor types. FSA cells in culture showed a trend towards higher aerobic glucose consumption versus R3230Ac. Both cell lines increased their lactate production to similar levels under hypoxia. We conclude that both R3230Ac and FSA tumors retain the Pasteur effect, i.e., hypoxia triggers increased glycolysis. However, our results imply that increased aerobic glucose utilization leads to low glucose levels in FSA and a situation where supply limits uptake. This explains the repeatedly observed correlation between tumor blood flow and 18F-deoxyglucose uptake.

The relationship between temporal variation of hypoxia, polarographic measurements and predictions of tumour response to radiation

The polarographic oxygen sensor is one of the most used devices for in vivo measurements of oxygen and many other measurement techniques for measuring tumour hypoxia are correlated with electrode measurements. Little is known however about the relationship between electrode measurements and the real tissue oxygenation. This paper investigates the influence of the temporal change of the hypoxic pattern on the electrode measurements and the tumour response. Electrode measurements and tumour response were simulated using a computer program that allows both the calculation of the tissue oxygenation with respect to the two types of hypoxia that might arise in tumours and the virtual insertion of the electrode into the tissue. It was therefore possible to control the amount of each type of hypoxia in order to investigate their influence on the measurement results. Tissues with several vascular architectures ranging from well oxygenated to poorly oxygenated were taken into consideration as might be seen in practice. The influence of the electrode measurements on the treatment outcome was estimated by calculating the tumour control probability for the tumours characterized either by the real or by the measured tumour oxygenation. We have simulated electrode oxygen measurements in different types of tissues, covering a wide range of tumour oxygenations. The results of the simulations showed that the measured distribution depends on the details of the vascular network and not on the type of hypoxia. We have also simulated the effects of the temporal change of the acute hypoxic pattern due to the opening and the closure of different blood vessels during a full fractionated treatment. The results of this simulation suggested that the temporal variation of the hypoxic pattern does not lead to significantly different results for the electrode measurements or the predicted tumour control probabilities. In conclusion, it was found that the averaging effect of the electrode leads to a systematic deviation between the actual oxygen distribution and the measured distribution. However, as the electrode reflects the general trends of the tissue oxygenation it has the potential of being used for the general characterization of tumour hypoxia even if the actual type of hypoxia measured by the electrode cannot be determined. Indeed, the change in time of the acute hypoxic region does not compensate for the lack of oxygenation at a specific moment and therefore does not influence the polarographic oxygen measurements.

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.

Tumor-dependent kinetics of partial pressure of oxygen fluctuations during air and oxygen breathing

The primary purpose of this study was to examine the kinetics of partial pressure of oxygen (pO2) fluctuations in fibrosarcoma (FSA) and 9L tumors under air and O2 breathing conditions. The overall hypothesis was that key factors relating to oxygen tension fluctuations would vary between the two tumor types and as a function of the oxygen content of the breathing gas. To assist in the interpretation of the temporal data, spatial pO2 distributions were measured in 10 FSA and 8 9L tumors transplanted into the subcutis of the hind leg of Nembutal-anesthetized (50 mg/kg) Fischer 344 rats. Recessed-tip oxygen microelectrodes were inserted into the tumor, and linear pO2 measurements were recorded in 50-microm steps along a 3-mm path, and blood pressure was simultaneously measured via femoral arterial access. Additionally, pO2 was measured at a single location for 90 to 120 minutes in FSA (n=11) or 9L tumors (n=12). Rats were switched from air to 100% O2 breathing after 45 minutes. Temporal pO2 records were evaluated for their potential radiobiological significance by assessing the number of times they crossed a 10-mm-Hg threshold. In addition, the data were subjected to Fourier analysis for air and O2 breathing. FSA and 9L tumors had spatial median pO2 measurements of 4 and 1 mm Hg, respectively. 9L had more low pO2 measurements < or =2.5 mm Hg than did FSA, whereas between 2.5 and 10 mm Hg this pattern was reversed. Pimonidazole staining patterns in FSA and 9L tumors supported these results. Temporal pO2 instability was observed in all experiments during air and O2 breathing. Threshold analyses indicated that the 10 mm Hg threshold was crossed 2 to 5 times per hour, independent of tumor type. However, the magnitude of 9L pO2 fluctuations was approximately eight times greater than FSA fluctuations, as assessed with Fourier transform analysis (Wilcoxon, P < 0.005). O2 breathing significantly increased median pO2 in FSA from 3 to 8 mm Hg (P < 0.005) and caused a significant increase in frequency and magnitude of pO2 fluctuations. One hundred percent O2 breathing had no effect on 9L tumor pO2, and it decreased the magnitude of pO2 fluctuations with borderline significance. These results show that these two tumors differ significantly with respect to spatial and temporal oxygenation conditions under air and O2 breathing. Fluctuations of pO2 of the type reported herein are predicted to significantly affect radiotherapy response and could be a source for genetic instability, increased angiogenesis, and metastases.

Tumor oxygen dynamics: correlation of in vivo MRI with histological findings

Tumor oxygenation has long been recognized as a significant factor influencing cancer therapy. We recently established a novel magnetic resonance in vivo approach to measuring regional tumor oxygen tension, FREDOM (Fluorocarbon Relaxometry Using Echo Planar Imaging for Dynamic Oxygen Mapping), using hexafluorobenzene (HFB) as the reporter molecule. We have now investigated oxygen dynamics in the two Dunning prostate R3327 rat tumor sublines, AT1 and H. FREDOM revealed considerable intratumoral heterogeneity in the distribution of pO(2) values in both sublines. The anaplastic faster-growing AT1 tumors were more hypoxic compared with the size-matched, well-differentiated, and slower-growing H tumors. Respiratory challenge with oxygen produced significant increases in mean and median pO(2) in all the H tumors (P<.001), but no response in half of the larger AT1 tumors (>3 cm(3)). Immunohistochemical studies using the hypoxia marker, pimonidazole, and the vascular endothelial cell marker, CD31, confirmed that the H tumors had more extensive vasculature and less hypoxia than the AT1 tumors. These results further validate the utilization of FREDOM to monitor tumor oxygenation and concur with the hypothesis that the level of hypoxia is related to tumor growth rate and poor vascularity.

Acute hypoxia enhances spontaneous lymph node metastasis in an orthotopic murine model of human cervical carcinoma

An orthotopic mouse model of cervical carcinoma has been used to investigate the relationship between acute (cyclic) hypoxia and spontaneous lymph node metastasis in vivo. The human cervical carcinoma cell line ME-180 was stably transfected to express the fluorescent protein DsRed2, which allowed the in vivo optical monitoring of tumor growth and metastasis by fluorescent microscopy. The surgically implanted primary tumors metastasize initially to local lymph nodes and later to lung, a pattern consistent with the clinical course of the disease. The effect of acute hypoxia on the growth and spread of these tumors was examined by exposing tumor-bearing mice to treatment consisting of exposure to 12 cycles of 10 min 7% O(2) followed by 10 min air (total 4 h) daily during tumor growth. After 21 days, the tumors were excised, lymph node and lung metastases were quantified, and the hypoxic fraction and relative vascular area of the primary tumors were assessed by immunohistochemical staining for the hypoxic marker drug EF5 [2-(2-nitro-1H-imidazole-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide] and the vascular marker CD31, respectively. In untreated mice, the primary tumor size was directly correlated with lymph node metastatic burden. The acute hypoxia treatment resulted in a significant decrease in the size of the primary tumors at the time of excision. However, the mice in the acute hypoxia group had an increased number of positive lymph nodes (2-4) as compared with control mice (1-3). Lung metastasis was not affected. The acute hypoxia treatment also decreased the relative vascular area in the primary tumors but did not affect the hypoxic fraction. These results suggest that fluctuating oxygenation in cervical carcinoma tumors may reduce tumor growth rate, but it may also enhance the ability of tumor cells to metastasize to local lymph nodes.

Comparative Measurements of Hypoxia in Human Brain Tumors Using Needle Electrodes and EF5 Binding

Hypoxia is known to be an important prognostic marker in many human cancers. We report the use of two oxygen measurement techniques in human brain tumors and compare these data with semiquantitative histological end points. Oxygenation was measured using the Eppendorf needle electrode and/or EF5 binding in 28 brain tumors. These data were compared with necrosis, mitosis, and endothelial proliferation. In some tumors, absolute EF5 binding was converted to tissue pO(2) based on in vitro calibrations. Eppendorf electrode readings could not be used to identify WHO grade 1/2 versus WHO grade 3/4 tumors, they could not differentiate grade 3 versus grade 4 glial-derived neoplasms, nor did they correlate with necrosis or endothelial proliferation scores. EF5 binding increased as the tumor grade increased and was significantly associated with necrosis and endothelial proliferation. There was no statistically significant correlation between the two hypoxia detection techniques, although both methods indicated similar absolute ranges of tissue pO(2). There was substantial inter- and intratumoral heterogeneity of EF5 binding in WHO grade 4 glial neoplasms. The majority of cells in glial-derived tumor had levels of hypoxia that were mild to moderate (defined herein as 10% to 0.5% pO(2)) rather than severe (defined as approximately 0.1% pO(2)). Immunohistochemical detection of EF5 binding tracks histological parameters in adult brain tumors, with increased binding associated with increasing necrosis and endothelial proliferation. The proportion of moderately to severely hypoxic cells is relatively low, even in the high-grade tumors. Human brain tumors are dominated by oxic to moderately hypoxic cells.

Non-invasive PET and SPECT imaging of tissue hypoxia using isotopically labeled 2-nitroimidazoles

The measurement of pathologically low levels of tissue pO2 is an important diagnostic goal for determining the prognosis of many clinically important diseases including cardiovascular insufficiency, stroke and cancer. A class of bioreductively activated drugs, typified by the 2-nitroimidazoles, has excellent potential for application to this goal. Such drugs bind to cells at a rate which is maximal under conditions of severe hypoxia (e.g. less than 0.05% oxygen) and is inhibited, with Michaelis-Menten kinetics, as a function of increasing oxygen concentration. A number of detection possibilities exist for the drug adducts, including invasive assays which can measure drug adducts in tissue sections at cell-to-cell resolution. Use of such agents in non-invasive assays is important and, to this end, a number of drugs have been conjugated with radioactive isotopes suitable for detection by Nuclear Medicine techniques. In contrast with the invasive assays, resolution and contrast is much more limited with the non-invasive assays. Thus, there are many factors contributing to the balance of pros and cons for the non-invasive vs. invasive use of 2-nitroimidazole drugs as hypoxia detectors. These factors will be summarized in this review, with emphasis on compounds suitable for clinical use. PET (positron emission tomography) imaging with 18F-labeled EF5 (a drug in current clinical trials using invasive assays) will be described.

Comparison of the comet assay and the oxygen microelectrode for measuring tumor oxygenation in head-and-neck cancer patients

PURPOSE

To compare the Eppendorf PO2 histograph and the alkaline comet assay as methods of measuring tumor hypoxia in patients with head-and-neck squamous cell carcinomas.

MATERIALS AND METHODS

As part of a larger clinical trial, 65 patients with head-and-neck squamous cell carcinoma nodal metastasis underwent tumor oxygenation measurements with Eppendorf PO2 histographs and comet assays, performed on fine-needle aspirates at 1 and 2 min after 5 Gy. Fifty-four patients had sufficient tumor cells for comet analysis at 1 min and 26 at both 1 and 2 min. Individual cells were examined for DNA single-strand breaks by alkaline gel electrophoresis, and the distribution of values was quantified using median tail moment (MTM). Nonirradiated tumor cells from pretreatment fine-needle aspirates received 5 Gy in vitro to establish the oxygenated response.

RESULTS

There was a significant correlation between the 1- and 2-min MTM (slope = 0.77 +/- 0.03). There was no relationship between DNA damage in tumor cells irradiated in vitro and in vivo. No correlation was found between Eppendorf PO2 measurements and comet MTM. There was a statistically significant correlation between the treatment response in the node studied and comet MTMs, whereas no correlation was observed between treatment response and Eppendorf measurements.

CONCLUSIONS

Comet assays are reproducible, as shown by biopsies at 1 and 2 min. Intertumor variation in the MTM is not a result of intrinsic radiosensitivity but of tumor hypoxia. There was no correlation between Eppendorf PO2 measurements and comet MTM. Comet assays were better than Eppendorf in predicting treatment response as an end point for short-term outcome. Longer follow-up is needed to determine the role of the comet assay as a predictor for locoregional tumor control and survivals.

Prognostic significance of tumor oxygenation in humans

Low tissue oxygen concentration has been shown to be important in the response of human tumors to radiation therapy, chemotherapy and other treatment modalities. Hypoxia is also known to be a prognostic indicator, as hypoxic human tumors are more biologically aggressive and are more likely to recur locally and metastasize. Herein, we discuss and summarize the various methods under investigation to directly or indirectly measure tissue oxygen in vivo. Secondly, we consider the advantages and disadvantages of each of these techniques. These considerations are made in light of our specific hypotheses that hypoxia should be measured as a continuum, not a binary measurement and that moderate, not severe hypoxia is of great biological consequence.

In vivo colocalization of 2-nitroimidazole EF5 fluorescence intensity and electron paramagnetic resonance oximetry in mouse tumors

BACKGROUND AND PURPOSE

The primary objective of this study was to establish in vivo the relationship between 2-2-nitro-1H-imidazol-1yl-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) adduct formation and intratumoral oxygen concentrations measured by electron paramagnetic resonance (EPR) in a tumor model mimicking a clinical situation. The secondary objective was an attempt to calibrate in situ the immunofluorescence (IF) signal with EPR oximetry.

MATERIALS AND METHODS

IM syngeneic fibrosarcoma (NFSA) bearing C3H mice were used. Three days after injection of a paramagnetic charcoal into the tumor, the mice were anesthetized, injected with the hypoxic marker EF5, and monitored every 20 min for 3 h with a low-frequency EPR spectrometer. Animals were allowed to breath either under 21 or 100% O(2). Tumors were then harvested, frozen, cut into sections including the charcoal and processed for EF5 adducts detection using monoclonal antibodies. Slices were viewed with a fluorescence microscope and 190x140 micrometer areas surrounding the charcoal were digitized and analyzed with the NIH-Image and Adobe Photoshop software. The fluorescence intensity (FI) was measured in the whole pictures and in strips of 10 micrometer around the charcoal.

RESULTS

EF5 binding increased with decreasing pO(2), most substantially at pO(2) below 5 mm Hg. Baseline (ambient air) pO(2) reached 3.2+/-2.1 mm Hg in NFSA tumors. It increased to 9.8+/-3.2 mm Hg under 100% O(2). A statistically significant correlation was observed on an individual tumor basis between the FI in the first 10 micrometer strip around the charcoal and the pO(2) determined by EPR oximetry (Wilcoxon signed rank test: P<0.001).

CONCLUSIONS

The present study confirms the intrinsic relationship between EF5 adduct binding and intratumoral pO(2) in an in vivo environment under biologically-relevant pO(2) values of less than 10 mm Hg.

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

BACKGROUND AND PURPOSE

Tumor oxygenation is recognized as an important determinant of the outcome of radiotherapy and possibly also of other treatment modalities in a number of tumor types and in particular in squamous cell carcinomas. The hypoxic status of various solid tumors has been related to a poor prognosis due to tumor progression towards a more malignant phenotype, with increased metastatic potential, and an increased resistance to treatment. It has been demonstrated in head and neck cancer that hypoxic radioresistance can be successfully counteracted by hypoxia modifying approaches. The microregional distribution and the level of tumor hypoxia depend on oxygen consumption and temporal and spatial variations in blood supply. It is unclear if severely hypoxic cells can resume clonogenicity when O(2) and nutrients become available again as a result of (treatment related) changes in the tumor microenvironment. Non-terminally differentiated hypoxic cells that are capable of proliferation are important for outcome because of their resistance to radiotherapy and possibly other cytotoxic treatments. Various exogenous and endogenous markers for hypoxia are currently available and can be studied in relation to each other, the tumor architecture and the tumor microenvironment. Use of nitroimidazole markers with immunohistochemical detection allows studying tumor cell hypoxia at the microscopic level. Co-registration with other microenvironmental parameters, such as vascular architecture (vascular density), blood perfusion, tumor cell proliferation and apoptosis, offers the possibility to obtain a comprehensive functional image of tumor patho-physiology and to study the effects of different modalities of cancer treatment.

CONCLUSION

A number of functional microregional parameters have emerged that are good candidates for future use as indicators of tumor aggressiveness and treatment response. The key question is whether these parameters can be used as tools for selection of treatment strategies for individual patients. This requires testing of these markers in prospective randomized clinical trials comparing standard treatment against experimental treatments targeting the relevant microregional constituent.

Measurements of hypoxia using pimonidazole and polarographic oxygen-sensitive electrodes in human cervix carcinomas

BACKGROUND AND PURPOSE

The measurement of tumour oxygenation using Eppendorf oxygen-sensitive needle electrodes can provide prognostic information but the method is limited to accessible tumours that are suitable for electrode insertion. In this paper the aim was to study the relationship between such physiological measurements of tumour hypoxia and the labelling of tumours with the hypoxia-specific marker pimonidazole.

MATERIALS AND METHODS

Assessment of tumour oxygen partial pressure (pO(2)) using an Eppendorf pO(2) histograph and immunohistochemical pimonidazole labelling was carried out in 86 patients with primary cervix carcinomas. Pimonidazole was given as a single injection (0.5 g/m(2) i.v.) and 10-24 h later pO(2) measurements were made and biopsies taken. Tumour oxygenation status was evaluated as the median tumour pO(2) and the fraction of pO(2) values </=10 mmHg (HP(10)), </=5 mmHg (HP(5)) and </=2.5 mmHg (HP(2.5)). Hypoxia was detected by immunohistochemistry using monoclonal antibodies directed against reductively activated pimonidazole. Pimonidazole binding was scored using a light microscope. Each tumour was evaluated by the relative area pimonidazole at highest score and the accumulated area of pimonidazole labelling from score 1 to 4. Necrosis was measured in HE stained sections.

RESULTS AND CONCLUSIONS

The degree of hypoxia assessed by either pimonidazole binding or invasive electrode measurements varied significantly between tumours. There was a trend that the most hypoxic tumours measured by oxygen electrodes had the highest score of necrosis, and no or little pimonidazole binding. However, this observation was not consistent and there was no correlation between pimonidazole staining expressed in this way and oxygen electrode measurements of hypoxia.

Oxygen depletion during and after mTHPC-mediated photodynamic therapy in RIF1 and H-MESO1 tumors

During photodynamic therapy (PDT), low oxygenation levels, induced both by oxygen consumption and by vascular occlusion, can lead to an inefficient photochemical reaction that may compromise the efficacy of PDT. In the present studies, tumor oxygenation was measured before, during and after meta-tetrahydroxyphenylchlorin (mTHPC)-mediated PDT of murine RIF1 tumors and human mesothelioma xenografts (H-MESO1). Tumor pO2 was measured in real time with Eppendorf polarography, and the extent of relative hypoxia at specific times was measured by immunohistochemical staining. Significant decreases in median pO2 values, as well as an increase in the number of values below 2.5 mmHg, were seen during and after PDT in RIF1 tumors, although there was a large intertumoral variation. Tumor pO2 values did not change significantly in H-MESO1 tumors. Staining with antibodies against the hypoxia marker EF3 showed significant increases in relative hypoxia after PDT in both tumor types compared with separate groups of untreated controls. Our results are consistent with PDT-induced oxygen depletion (reduced pO2) leading to an increase in relative hypoxia in RIF1 tumors. Extensive necrosis in the H-MESO1 tumors may have prevented the detection of PDT-induced hypoxia using the Eppendorf polarographic needle, whereas immunohistochemistry did reveal increases in relative hypoxia.

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

BACKGROUND

Previous studies have shown that radiation of hypoxic tumors can result in reoxygenation phenomenon. The relevance of this phenomenon for prognosis is unclear. This study analyzes whether the presence of hypoxia, or the extent to which reoxygenation occurs during the initial phase of primary chemoradiation or radiotherapy, can predict the clinical outcome in advanced tumors of the head and neck.

METHODS

The distribution of oxygen partial pressures was determined using pO(2) histography (Kimoc 6650, Sigma pO(2)-Histograph, Eppendorf, Hamburg, Germany). In cervical lymph node metastases of 37 patients with advanced carcinoma of the head and neck (stage IV, UICC), these values were determined before the start of primary chemoradiation or radiotherapy alone (pO(2)x). Thirty-two of 37 patients were reexamined after 1 week of therapy, and measurements were taken again in the same nodes (pO(2)y). The results obtained from these measurements were correlated with both, the initial response to therapy and follow-up results (43 months). RESULTS.: In all patients, pronounced hypoxia (median pO(2), 3.2 mmHg) was found before therapy. In 19 of 32 patients, chemoradiation/radiotherapy induced reoxygenation (deltaO(2) = pO(2)y - pO(2)x), with median deltapO(2) increasing to 6.5 mmHg after 1 week (p =.049). The group of patients with a complete or partial response showed only a slight increase of median deltapO(2) (1 mmHg) compared with a strong reoxygenation effect in the group of patients with no change (mean value of median deltapO(2) = 10.3 mmHg; p =.0062). The group of patients with deltapO(2) values lower than median showed significantly better survival rates compared with the other group (p =.036).

CONCLUSION

These data suggest that reoxygenation under therapy may have prognostic relevance in patients with advanced carcinoma of the head and neck treated by primary chemoradiation or radiation therapy. Remarkably, however, a poor outcome was associated with a higher degree of reoxygenation.

Vascular endothelial growth factor mediated angiogenic potential of pancreatic ductal carcinomas enhanced by hypoxia: an in vitro and in vivo study

Angiogenesis in pancreatic ductal adenocarcinomas depends on the presence of angiogenic factors such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) and is thought to be stimulated by hypoxia. We tested the angiogenic potential of 9 cell lines of pancreatic ductal carcinoma origin by screening mRNA and protein expression of VEGF and bFGF and the release of VEGF into culture medium under normoxic and hypoxic (5% or 0.2% O2) conditions. Angiogenic activity was determined using 2- and 3-D endothelial cell assays. Furthermore, VEGF expression and tumor vascularization were studied in human pancreatic carcinoma tissues from orthotopic xenografts and resection specimens. All cell lines expressed (mRNA, protein) and secreted VEGF, whereas bFGF was only found in 3 cell lines and was secreted into the medium in low concentrations. In addition to the dominant isoforms VEGF121,VEGF165 and VEGF189, 2 isoforms described recently, VEGF145 and VEGF183, were detected. Severe hypoxia (0.2% O2), but not moderate hypoxia (5% O2) raised VEGF mRNA expression and protein secretion in 7/9 and 5/9 cell lines, respectively. Conditioned media from 7/9, 6/9, 8/9 and 7/9 cell lines stimulated endothelial cell proliferation under normoxic (24 and 48 hr) or hypoxic (24 hr, 0.2% and 48 hr 5% O2) conditions, respectively. Conditioned media from 4/9 cell lines also induced capillary-like sprouting under normoxic conditions and from 6/9 under hypoxic (0.2% O2) conditions. In xenografted carcinoma tissues microvessel density was found not to be increased around areas of ischemic necrosis. In resected ductal carcinomas showing tumor necrosis VEGF expression and microvessel density were only increased in 3/12 and 2/13 cases, respectively. In conclusion, in vitro most pancreatic ductal carcinomas show a distinct VEGF related angiogenic potential, as demonstrated by 2- and 3-D endothelial cell proliferation, which may be promoted by severe hypoxia. Surprisingly, perinecrotic tumor areas, which are supposed to be hypoxic, only rarely showed the expected increase in microvessel density and VEGF expression.

Importance of hypoxia in the biology and treatment of brain tumors

The resistance of gliomas to treatment with radiation and antineoplastic drugs may result in part from the effects of the extensive, severe hypoxia that is present in these tumors. It is clear that brain tumors contain extensive regions in which the tumor cells are subjected to unphysiological levels of hypoxia. Hypoxic cells are resistant to radiation. Hypoxia and the perfusion deficits and metabolic changes that accompany hypoxia in vivo also produce resistance to many commonly used anticancer drugs. The resistance of cells that are hypoxic at the time of therapy may influence the efficacy of the treatment of these tumors with radiation, chemotherapy, and combined modality regimens. Moreover, it is becoming increasingly evident from laboratory studies that exposure of cells to adverse microenvironments produces transient changes in gene expression, induces mutations, and selects for cells with altered genotypes, thus driving the evolution of the cell population toward increasing malignancy and increasingly aggressive phenotypes. Hypoxia may therefore be involved in the evolution of cells in low-grade malignancies to the resistant, aggressive phenotype characteristic of glioblastomas. During the past 50 years, many attempts have been made to circumvent the therapeutic resistance induced by hypoxia, by improving tumor oxygenation, by using oxygen-mimetic radiosensitizers, by adjuvant therapy with drugs that are preferentially toxic to hypoxic cells, by using hyperthermia, or by devising radiation sources and regimens that are less affected by hypoxia. Past clinical trials have provided tantalizing suggestions that the outcome of therapy can be improved by many of these approaches, but none has yet produced a significant, reproducible improvement in the therapeutic ratio, which would be needed for any of these approaches to become the standard therapy for these diseases. Several ongoing clinical trials are addressing other, hopefully better regimens; it will be interesting to see the results of these studies.

Theoretical simulation of oxygen tension measurement in the tissue using a microelectrode: II. Simulated measurements in tissues

BACKGROUND AND PURPOSE

The objectives of this study were to make a computer simulation of tissues with different vascular structures and to simulate measurements of oxygen tension using an Eppendorf-like electrode in these tissues and to compare the response to radiation of the tissues with the real oxygen distributions (called input distribution) with the response to radiation of the tissues in which the oxygen distribution is given by the results of the simulated measurements (called output distribution).

MATERIALS AND METHODS

The structure of various tissues and the measurements of oxygen tension using a microelectrode were simulated using a computer program. The mathematical model used combines the description of a gradient of tissue oxygenation and the electrode absorption process.

RESULTS

We have compared the oxygen distributions resulting from diffusion (input) with those obtained from a simulation of measurements (output) for various tissues in the same points. Because the electrode measurement is an averaging process, the calculated oxygen distributions are different from the expected ones and the extreme high and low values are not detected. We have then calculated the survival curves describing the response to radiation if there is a small fraction of truly hypoxic cells (expected values) or a large fraction of cells at intermediate values (observed results) in order to determine the differences between them.

CONCLUSIONS

The results of our study show that oxygen electrode measurements do not give the true distribution of pO(2) values in the tissue. However, our results do not contradict the numerous empirical correlations between the Eppendorf measurements of tumour oxygenation and the outcome of treatments. Measurement results will be misleading for modelling purposes since they do not reflect the actual distributions of oxygen tensions in the measured tissue. Decisions based on such modelling could be very dangerous, especially with respect to the clinical response of tumours to new treatments.

Zonal image analysis of tumour vascular perfusion, hypoxia, and necrosis

A number of laboratories are utilising both hypoxia and perfusion markers to spatially quantify tumour oxygenation and vascular distributions, and scientists are increasingly turning to automated image analysis methods to quantify such interrelationships. In these studies, the presence of regions of necrosis in the immunohistochemical sections remains a potentially significant source of error. In the present work, frozen MCa-4 mammary tumour sections were used to obtain a series of corresponding image montages. Total vessels were identified using CD31 staining, perfused vessels by DiOC(7) staining, hypoxia by EF5/Cy3 uptake, and necrosis by haematoxylin and eosin staining. Our goal was to utilise image analysis techniques to spatially quantitate hypoxic marker binding as a function of distance from the nearest blood vessel. Several refinements to previous imaging methods are described: (1) hypoxia marker images are quantified in terms of their intensity levels, thus providing an analysis of the gradients in hypoxia with increasing distances from blood vessels, (2) zonal imaging masks are derived, which permit spatial sampling of images at precisely defined distances from blood vessels, as well as the omission of necrotic artifacts, (3) thresholding techniques are applied to omit holes in the tissue sections, and (4) distance mapping is utilised to define vascular spacing.

Hypoxic heterogeneity in human tumors: EF5 binding, vasculature, necrosis, and proliferation

We evaluated the levels and distribution of hypoxia in 31 human tumors using fluorescent immunohistochemical detection of binding by the 2-nitroimidazole, EF5. Hypoxia was found to be a heterogeneous property of human tumors. Necrosis was usually found adjacent to the highest level of binding in an individual patient's tumor. However, hypoxia often occurred without necrosis. In the group of tumors studied, the most common relationship between blood vessels (PECAM/CD31) and EF5 staining was consistent with diffusion-limited hypoxia; acute hypoxia occurred infrequently. Within a given patient's tumor, there was an inverse correlation between regions of proliferation (Ki-67) and regions of hypoxia. Again, however, when these parameters were examined in a group of patients, the absence of proliferation did not predict the presence of hypoxia. The relationships between hypoxia and other biologic endpoints are complex, but, within a given tumor's spatial relationships, they are in accord with known physiologic principles. Thus, our data emphasize that the relationships between hypoxia and other biologic parameters vary between patients. Necrosis, proliferation, and blood vessel distribution cannot predict the level or presence of hypoxia in an individual patient's tumor.

The K(m) for Radiosensitization of Human Tumor Cells by Oxygen is Much Greater than 3 mmHg and is Further Increased by Elevated Levels of Cysteine

We studied the role of cysteine as an intracellular radiation protector under conditions in which both oxygen and thiols were monitored at 37 degrees C. In HCT-116 human colon cancer cells, the intracellular cysteine content affects the radiation survival dramatically at intermediate oxygen levels, but not at zero or high oxygen levels. Using a spin-through-oil method with a dual radioactive label detection system, we measured intracellular cysteine and glutathione (GSH) levels for cells in suspension culture. A comparison of the cysteine levels of monolayer cells lysed in situ and of trypsinized monolayer cells in suspension (Horan et al., Cytometry 29, 76-82, 1997) revealed that, upon trypsinization from monolayer culture and transfer to a spinner apparatus at 37 degrees C, HCT-116 cells lose most of their intracellular cysteine. Over the 60-min time course of control experiments, these cells do not recover intracellular cysteine despite the availability of cystine (the disulfide of cysteine) in the medium. When cells in spinner culture are provided with exogenous cysteine, they initially concentrate it to 10-fold the extracellular concentration, with the concentration factor decreasing to about 5-fold over the course of an hour. The intracellular GSH concentration changes little throughout this period, regardless of the changes in cysteine levels. The same apparatus was used to assess the survival of HCT-116 cells irradiated at 37 degrees C under conditions of constant pO(2) monitoring. For cells without added cysteine, the oxygen concentration for half-maximal radiation sensitivity was about 7.5 mmHg (intermediate hypoxia), more than twice the commonly accepted value (3 mmHg). At 7.5 mmHg, cells with added cysteine (intracellular concentration 3.5 mM) were almost as radioresistant as severely hypoxic cells (approximately 0.005% oxygen). Cells in parallel experiments in which the cells were grown in monolayers on glass Petri dishes had intermediate cysteine values and also intermediate radiosensitivity. We conclude that the radiation response of cells at intermediate oxygen levels is controlled predominantly by intracellular cysteine levels and that the cysteine levels commonly found in tumors may increase the K(m) for radiosensitivity to values much higher than suggested previously.

Effects of radiation on tumor intravascular oxygenation, vascular configuration, development of hypoxia, and clonogenic survival

The underlying physiological mechanisms leading to tumor reoxygenation after irradiation have elicited considerable interest, but they remain somewhat unclear. The current study was undertaken to determine the effects of a single dose of 10 Gy gamma radiation on both tumor pathophysiology and radiobiologically hypoxic fraction. Immunohistochemical staining and perfusion markers were used to quantify tumor vasculature, uptake of the hypoxia marker EF5 to assess the distribution of hypoxia, and intravascular HbO(2) measurements to determine oxygen availability. Tumor radiosensitivity was measured by a clonogenic assay. At 24 h postirradiation, oxygen availability increased, perfused vessel numbers decreased, EF5 uptake decreased, and the radiobiologically hypoxic fraction was unchanged. Together, these results demonstrate that tumor hypoxia develops at an increased distance from perfused blood vessels after irradiation, suggesting a decrease in oxygen consumption at 24 h. By 72 h postirradiation, all physiological parameters had returned to the levels in volume-matched, nonirradiated controls. These studies clearly show that single measures of either tumor oxygenation or vascular structure are inadequate for assessing the effects of radiation on tumor clonogenicity. Although such direct measurements have previously proven valuable in predicting tumor response to therapy or oxygen manipulation, a combination of parameters is required to adequately describe the mechanisms underlying these changes after irradiation.

Invasive oxygen measurements and pimonidazole labeling in human cervix carcinoma

PURPOSE

This study was designed to compare tumor hypoxia assessed by invasive O2 sensitive electrodes and pimonidazole labeling in primary human cervix carcinomas.

METHODS AND MATERIALS

Twenty-eight patients with primary cervix carcinomas (FIGO Stage Ib-IVa) were investigated. Both invasive pO2 measurements and pimonidazole labeling were obtained in all patients. Before treatment, patients were given pimonidazole as a single injection (0.5 g/m2 i.v.). Ten to 24 h later, oxygenation measurements were done by Eppendorf histography, and after this procedure biopsies were taken for pimonidazole-binding analysis. Tumor oxygen partial pressure (pO2) was evaluated as the median tumor pO2 and the fraction of pO2 values < or = 10 mmHg (HF10). Biopsies were formalin fixed and paraffin embedded, and hypoxia was detected by immunohistochemistry using monoclonal antibodies directed against reductively activated pimonidazole. Pimonidazole binding was evaluated by a semiquantitative scoring system.

RESULTS

Both Eppendorf measurements and pimonidazole binding showed large intra-and intertumor variability. A comparison between pimonidazole binding expressed as the fraction of fields at the highest score and HF10 showed a trend for the most well-oxygenated tumors having a low fraction of fields; however, the correlation did not reach statistical significance (p = 0.43, r = 0.165; Spearman's rank correlation test).

CONCLUSION

Hypoxia measured in human uterine cervix carcinomas is heterogeneously expressed both within and between tumors when assessed by either invasive pO2 measurements or pimonidazole binding. Despite a trend that tumors with high pO2 values expressed less pimonidazole binding, no correlation was seen between the two assays in this preliminary report.