Acute tumour response to a bispecific Ang-2-VEGF-A antibody: insights from multiparametric MRI and gene expression profiling

BACKGROUND

To assess antivascular effects, and evaluate clinically translatable magnetic resonance imaging (MRI) biomarkers of tumour response in vivo, following treatment with vanucizumab, a bispecific human antibody against angiopoietin-2 (Ang-2) and vascular endothelial growth factor-A (VEGF-A).

METHODS

Colo205 colon cancer xenografts were imaged before and 5 days after treatment with a single 10 mg kg(-1) dose of either vanucizumab, bevacizumab (anti-human VEGF-A), LC06 (anti-murine/human Ang-2) or omalizumab (anti-human IgE control). Volumetric response was assessed using T2-weighted MRI, and diffusion-weighted, dynamic contrast-enhanced (DCE) and susceptibility contrast MRI used to quantify tumour water diffusivity (apparent diffusion coefficient (ADC), × 10(6) mm(2) s(-1)), vascular perfusion/permeability (K(trans), min(-1)) and fractional blood volume (fBV, %) respectively. Pathological correlates were sought, and preliminary gene expression profiling performed.

RESULTS

Treatment with vanucizumab, bevacizumab or LC06 induced a significant (P<0.01) cytolentic response compared with control. There was no significant change in tumour ADC in any treatment group. Uptake of Gd-DTPA was restricted to the tumour periphery in all post-treatment groups. A significant reduction in tumour K(trans) (P<0.05) and fBV (P<0.01) was determined 5 days after treatment with vanucizumab only. This was associated with a significant (P<0.05) reduction in Hoechst 33342 uptake compared with control. Gene expression profiling identified 20 human genes exclusively regulated by vanucizumab, 6 of which are known to be involved in vasculogenesis and angiogenesis.

CONCLUSIONS

Vanucizumab is a promising antitumour and antiangiogenic treatment, whose antivascular activity can be monitored using DCE and susceptibility contrast MRI. Differential gene expression in vanucizumab-treated tumours is regulated by the combined effect of Ang-2 and VEGF-A inhibition.

Delayed Hypoxemia Following Traumatic Brain Injury Exacerbates White Matter Injury

Hypoxemia immediately following traumatic brain injury (TBI) has been observed to exacerbate injury. However, it remains unclear whether delayed hypoxemia beyond the immediate postinjury period influences white matter injury. In a retrospective clinical cohort of children aged 4-16 years admitted with severe TBI, 28/74 (35%) patients were found to experience delayed normocarbic hypoxemia within 7 days of admission. Based on these clinical findings, we developed a clinically relevant mouse model of TBI with delayed hypoxemia by exposing 5-week old (adolescent) mice to hypoxic conditions for 30 minutes starting 24 hours after moderate controlled cortical impact (CCI). Injured mice with hypoxemia had increased axonal injury using both β-amyloid precursor protein and NF200 immunostaining in peri-contusional white matter compared with CCI alone. Furthermore, we detected increased peri-contusional white matter tissue hypoxia with pimonidazole and augmented astrogliosis with anti-glial fibrillary acidic protein staining in CCI + delayed hypoxemia compared with CCI alone or sham surgery + delayed hypoxemia. Microglial activation as evidenced by Iba1 staining was not significantly altered by delayed hypoxemia. These clinical and experimental data indicate the prevention or amelioration of delayed hypoxemia effects following TBI may provide a unique opportunity for the development of therapeutic interventions to reduce axonal injury and improve clinical outcomes.

Effect of selective fetectomy on morphology of the mouse placenta

INTRODUCTION

Placental examination is recommended when genetic mutations cause fetal lethality in mice. But how fetal death alters histomorphology of the surviving mouse placenta is not known.

METHODS

Placentas were examined at E17.5 after fetectomy of 1-2 fetal mice per pregnancy at either embryonic day (E) 15.5 (N = 8; Fx-2 group) or E13.5 (N = 5; Fx-4 group), which left 12 ± 2 surviving fetuses per litter.

RESULTS

Fetectomy caused no changes in placental weights and no increases in placental hypoxia (pimonidazole staining). The size and cell morphology of the decidua and junctional zone regions were unchanged and, in the Fx-2 group, these regions became significantly less hypoxic. Significant changes in labyrinth volume included a 30% increase in the Fx-2 group and in both groups, a >50% decrease in % fetal blood space and >40% increase in % labyrinth tissue. Maternal blood sinusoid volume was unchanged. Cell death in the labyrinth was significantly increased (22-fold increase in TUNEL staining) whereas placental mRNA expression of the proliferation marker Mki67 was unchanged. mRNA expression of sFlt1 and Prl3b1 (mPL-II) was unchanged in the labyrinth and junctional zone tissues in the Fx-2 group and in whole placental tissue in the Fx-4 group.

DISCUSSION

Placental examination of the junctional zone and decidual regions after spontaneous fetal death in late gestation is likely to yield useful phenotypic information and abnormalities that may contribute to fetal death. In contrast, labyrinth abnormalities including increased tissue volume and reduced fetoplacental vascularity may not be due to genetic perturbation nor predate fetal death.

Ketoconazole-induced estrogen deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats

This study investigated the relationship among estrogen, placental blood flow and placental weight gain in rats treated with ketoconazole. Oral administration of ketoconazole (25mg/kg/day) on Days 12-14 of pregnancy induced reduction of plasma estradiol-17β (E2) concentration, transient decrease in placental blood flow and increased intensity of a hypoxia-related marker in the placenta on Day 14 of pregnancy. On Day 20 of pregnancy, placental weights of ketoconazole-treated rats increased when compared to controls. Histologically, maternal sinusoidal area of the placenta decreased on Day 14 of pregnancy and the total area of maternal and fetal sinusoids increased on Day 20. All the changes disappeared by concomitant subcutaneous infusion of E2. These results indicate that ketoconazole-induced E2 deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats.

Oxygen as a chemoattractant: confirming cellular hypoxia in paper-based invasion assays

Low oxygen tension, or hypoxia, is a common occurrence in solid tumors. Hypoxia is a master regulator of cellular phenotype, and is associated with increased tumor invasion and aggressiveness as well as adverse patient prognosis. Oxygen has recently been linked with the selective movement of different cancer cell types in three-dimensional invasion assays utilizing paper-based scaffolds. It has remained unclear, however, if cells in these paper-based invasion assays are experiencing hypoxia. In this manuscript, we adapted cell-based methods to measure oxygen tension in our 3D invasion assays: the adduction of pimonidazole to free thiols in the cell, indicative of a reducing environment; the localization of hypoxia inducible factors to the nucleus; and the expression of hypoxia-regulated gene products. We utilized each method to compare the oxygen tension in different locations of the paper-based invasion stacks and found an oxygen gradient is indeed forming. Specifically, we found that the extent of pimonidazole binding, as well as the levels and activities of nucleus-localized HIF-α proteins, increase as the distance between the cells and the source of fresh medium increases. These complementary cell-based readouts not only confirm the selective invasion we observe is due to an oxygen gradient, they also show the gradient is temporal in nature and evolves with increasing culture period.

Mass Spectrometry Imaging of the Hypoxia Marker Pimonidazole in a Breast Tumor Model

Although tumor hypoxia is associated with tumor aggressiveness and resistance to cancer treatment, many details of hypoxia-induced changes in tumors remain to be elucidated. Mass spectrometry imaging (MSI) is a technique that is well suited to study the biomolecular composition of specific tissue regions, such as hypoxic tumor regions. Here, we investigate the use of pimonidazole as an exogenous hypoxia marker for matrix-assisted laser desorption/ionization (MALDI) MSI. In hypoxic cells, pimonidazole is reduced and forms reactive products that bind to thiol groups in proteins, peptides, and amino acids. We show that a reductively activated pimonidazole metabolite can be imaged by MALDI-MSI in a breast tumor xenograft model. Immunohistochemical detection of pimonidazole adducts on adjacent tissue sections confirmed that this metabolite is localized to hypoxic tissue regions. We used this metabolite to image hypoxic tissue regions and their associated lipid and small molecule distributions with MALDI-MSI. We identified a heterogeneous distribution of 1-methylnicotinamide and acetylcarnitine, which mostly colocalized with hypoxic tumor regions. As pimonidazole is a widely used immunohistochemical marker of tissue hypoxia, it is likely that the presented direct MALDI-MSI approach is also applicable to other tissues from pimonidazole-injected animals or humans.

Hypoxia as a Biomarker and for Personalized Radiation Oncology

Tumor hypoxia is a clinically relevant cause of radiation resistance. Direct measurements of tumor oxygenation have been performed predominantly with the Eppendorf histograph and these have defined the reduced prognosis after radiotherapy in poorly oxygenated tumors, especially head-and-neck cancer, cervix cancer and sarcoma. Exogenous markers have been used for immunohistochemical detection of hypoxic tumor areas (pimonidazole) or for positron-emission tomography (PET) imaging (misonidazole). Overexpression of hypoxia-related proteins such as hypoxia-inducible factor-1α (HIF-1α) has also been linked to poor prognosis after radiotherapy and such proteins are considered as potential endogenous hypoxia markers.

Comparative analysis of transcriptomics based hypoxia signatures in head- and neck squamous cell carcinoma

BACKGROUND AND PURPOSE

Hypoxia renders tumors resistant to radiotherapy. However, the paucity of sensitive and reliable methods for detection of tumor hypoxia limits the translation of novel therapy strategies targeting this well-known resistance factor. We sought to investigate the ability of three previously discovered transcriptomics based hypoxia signatures to identify hypoxic tumors and consequently discriminate between patients with poor- vs. good prognosis.

MATERIAL AND METHODS

Three different hypoxia gene signatures developed by Toustrup et al., Eustace et al. and Lendahl et al. were evaluated in an independent cohort consisting of 302 patients with head and neck squamous cell carcinoma (HNSCC). Clinical data as well as genome-wide RNA-sequencing based gene expression data were retrieved from The Cancer Genome Atlas (TCGA). Clustering and statistical analysis were performed using Statistical Utilities for Microarray and Omics data (SUMO) software package.

RESULTS

The 15 gene hypoxia signature developed by Toustrup et al. as well as the 30 gene signature by Lendahl et al. successfully discriminated between HNSCC patients with poor vs. good prognosis. The 26 gene signature developed by Eustace et al. was prognostic in HNSCC patients treated with radiotherapy. The best prognostic value was achieved when a consensus cohort of patients was assigned, i.e., low- or high- degree of tumor hypoxia was found, by all three signatures. Interestingly, the number of signature genes could be successfully reduced to the only common gene across all three signatures, i.e., P4HA1, encoding prolyl-4-hydroxylase, alpha polypeptide I.

CONCLUSIONS

This is the first independent proof for the feasibility of hypoxia gene expression signatures as a prognostic tool in HNSCC patients.

Hyperpolarized magnetic resonance spectroscopy for assessing tumor hypoxia

INTRODUCTION

Hypoxic tumor cells are radioresistant, therefore, identification of hypoxia is crucial. Hyperpolarized magnetic resonance spectroscopy (HPMRS) allows real time measurements of the conversion of pyruvate to lactate, the final step of anaerobic energy production, and may thus allow non-invasive identification of hypoxia or treatment-induced changes in oxygenation. The aim of the study was to investigate the usefulness of HPMRS as a means to assess tumor hypoxia and its dynamics during intervention.

MATERIAL AND METHODS

C3H mammary carcinomas grown in CDF1 mice were used. To manipulate with tumor oxygenation, non-anaesthetized mice were gassed with air, 10% or 100% oxygen prior to administration of hyperpolarized [1-¹³C]pyruvate and HPMRS analysis. A direct assessment of tumor oxygen partial pressure (pO2) distributions were made using the Eppendorf oxygen electrode in a separate, but similarly treated, group of mice.

RESULTS

Even though breathing 100% oxygen improved tumor oxygenation as evidenced by pO2 measurements, the mean (with 1 S.E.) [1-¹³C]lactate/[1-¹³C]pyruvate ratio was unaffected by this intervention, being 34 (30-37) in mice breathing air and 37 (33-42) in mice breathing 100% oxygen. In contrast, and in accordance with pO2 measurements, a significant increase in the [1-¹³C]lactate/[1-¹³C]pyruvate ratio was seen in 10% oxygen-breathing mice with a ratio of 46 (42-50).

CONCLUSIONS

Although, no metabolic change was observed during 100% O2 breathing using HPMRS, the significant increase in the [1-¹³C]lactate/[1-¹³C]pyruvate ratio during 10% oxygen breathing suggests, that HPMRS can detect hypoxia-driven changes in the metabolic fate of pyruvate. To what extent and for what purposes HPMRS may best supplement or complement established techniques like hypoxia PET needs to be unraveled in future research.

Analysis of the intra- and intertumoral heterogeneity of hypoxia in pancreatic cancer patients receiving the nitroimidazole tracer pimonidazole

Background:

Hypoxia is thought to be an adverse feature of pancreatic cancer, but direct measurement in patients is technically challenging. To address this, we characterised the intra/interpatient heterogeneity of hypoxia in surgical specimens from patients who received the 2-nitroimidazole tracer pimonidazole pre-operatively.

Methods:

Pimondazole was given intravenously 16–20 h before pancreatectomy, and the extent and intratumoral heterogeneity of hypoxia determined by image analysis applied to multiple tissue blocks stained by immunohistochemistry. Intra/interpatient heterogeneity was estimated by variance component analysis.

Results:

Pimonidazole staining was analysed in 10 tumours. The extent of labelling varied amongst patients (0–26%), with a broader range of hypoxia in the epithelial (1–39%) compared with the stromal (1–13%) compartments. Variance component analysis demonstrated greater inter- than intrapatient variability of hypoxia, and that multiple (4–5) tumour sections are required to provide a consistent evaluation of its extent in individual tumours.

Conclusions:

There is significant intra- and intertumoral heterogeneity of hypoxia in pancreatic cancers, and these do not appear to be generally more hypoxic than other cancer types. This study establishes the feasibility to assess hypoxia in pancreatic cancer patients using pimonidazole, but questions the reliability of measurements made using a single tissue section.

Extensive Loss of Islet Mass Beyond the First Day After Intraportal Human Islet Transplantation in a Mouse Model

Clinical islet transplantation is characterized by a progressive deterioration of islet graft function, which renders many patients once again dependent on exogenous insulin administration within a couple of years. In this study, we aimed to investigate possible engraftment factors limiting the survival and viability of experimentally transplanted human islets beyond the first day after their transplantation to the liver. Human islets were transplanted into the liver of nude mice and characterized 1 or 30 days after transplantation by immunohistochemistry. The factors assessed were endocrine mass, cellular death, hypoxia, vascular density and amyloid formation in the transplanted islets. One day posttransplantation, necrotic cells, as well as apoptotic cells, were commonly observed. In contrast to necrotic death, apoptosis rates remained high 1 month posttransplantation, and the total islet mass was reduced by more than 50% between 1 and 30 days posttransplantation. Islet mass at 30 days posttransplantation correlated negatively to apoptotic death. Vascular density within the transplanted islets remained less than 30% of that in native human islets up to 30 days posttransplantation and was associated with prevailing hypoxia. Amyloid formation was rarely observed in the 1-day-old transplants, but was commonly observed in the 30-day-old islet transplants. We conclude that substantial islet cell death occurs beyond the immediate posttransplantation phase, particularly through apoptotic events. Concomitant low vascularization with prevailing hypoxia and progressive amyloid development was observed in the human islet grafts. Strategies to improve engraftment at the intraportal site or change of implantation site in the clinical setting are needed.

Uterine artery dysfunction in pregnant ACE2 knockout mice is associated with placental hypoxia and reduced umbilical blood flow velocity

Angiotensin-converting enzyme 2 (ACE2) knockout is associated with reduced fetal weight at late gestation; however, whether uteroplacental vascular and/or hemodynamic disturbances underlie this growth-restricted phenotype is unknown. Uterine artery reactivity and flow velocities, umbilical flow velocities, trophoblast invasion, and placental hypoxia were determined in ACE2 knockout (KO) and C57Bl/6 wild-type (WT) mice at day 14 of gestation. Although systolic blood pressure was higher in pregnant ACE2 KO vs. WT mice (102.3 ± 5.1 vs. 85.1 ± 1.9 mmHg, n = 5-6), the magnitude of difference was similar to that observed in nonpregnant ACE2 KO vs. WT mice. Maternal urinary protein excretion, serum creatinine, and kidney or heart weights were not different in ACE2 KO vs. WT. Fetal weight and pup-to-placental weight ratio were lower in ACE2 KO vs. WT mice. A higher sensitivity to Ang II [pD2 8.64 ± 0.04 vs. 8.5 ± 0.03 (-log EC50)] and greater maximal contraction to phenylephrine (169.0 ± 9.0 vs. 139.0 ± 7.0% KMAX), were associated with lower immunostaining for Ang II receptor 2 and fibrinoid content of the uterine artery in ACE2 KO mice. Uterine artery flow velocities and trophoblast invasion were similar between study groups. In contrast, umbilical artery peak systolic velocities (60.2 ± 4.5 vs. 75.1 ± 4.5 mm/s) and the resistance index measured using VEVO 2100 ultrasound were lower in the ACE2 KO vs. WT mice. Immunostaining for pimonidazole, a marker of hypoxia, and hypoxia-inducible factor-2α were higher in the trophospongium and placental labyrinth of the ACE2 KO vs. WT. In summary, placental hypoxia and uterine artery dysfunction develop before major growth of the fetus occurs and may explain the fetal growth restricted phenotype.

Immunohistochemical evidence of stress and inflammatory markers in mouse models of cutaneous leishmaniosis

Leishmanioses are chronic parasitic diseases and host responses are associated with pro- or anti-inflammatory cytokines involved, respectively, in the control or exacerbation of infection. The relevance of other inflammatory mediators and stress markers has not been widely studied and there is a need to search for biomarkers to leishmaniasis. In this work, the stress and inflammatory molecules p38 mitogen-activated protein kinase, cyclooxygenase-2, migration inhibitory factor, macrophage inflammatory protein 2, heat shock protein 70 kDa, vascular endothelial factor (VEGF), hypoxia-inducible factors (HIF-1α and HIF-2α), heme oxygenase and galectin-3 expression were assessed immunohistochemically in self-controlled lesions in C57BL/6 mice and severe lesions in Balb/c mice infected with Leishmania amazonensis. The results indicated that the majority of molecules were expressed in the cutaneous lesions of both C57BL/6 and Balb/c mice during various phases of infection, suggesting no obvious correlation between the stress and inflammatory molecule expression and the control/exacerbation of leishmanial lesions. However, the cytokine VEGF was only detected in C57BL/6 footpad lesions and small lesions in Balb/c mice treated with antimonial pentavalent. These findings suggest that VEGF expression could be a predictive factor for murine leishmanial control, a hypothesis that should be tested in human leishmaniosis.

YB-1 regulates stress granule formation and tumor progression by translationally activating G3BP1

YB-1, which is upregulated in human sarcomas, controls the availability of the stress granule nucleator G3BP1 and thereby controls stress granule assembly.

Under cell stress, global protein synthesis is inhibited to preserve energy. One mechanism is to sequester and silence mRNAs in ribonucleoprotein complexes known as stress granules (SGs), which contain translationally silent mRNAs, preinitiation factors, and RNA-binding proteins. Y-box binding protein 1 (YB-1) localizes to SGs, but its role in SG biology is unknown. We now report that YB-1 directly binds to and translationally activates the 5′ untranslated region (UTR) of G3BP1 mRNAs, thereby controlling the availability of the G3BP1 SG nucleator for SG assembly. YB-1 inactivation in human sarcoma cells dramatically reduces G3BP1 and SG formation in vitro. YB-1 and G3BP1 expression are highly correlated in human sarcomas, and elevated G3BP1 expression correlates with poor survival. Finally, G3BP1 down-regulation in sarcoma xenografts prevents in vivo SG formation and tumor invasion, and completely blocks lung metastasis in mouse models. Together, these findings demonstrate a critical role for YB-1 in SG formation through translational activation of G3BP1, and highlight novel functions for SGs in tumor progression.

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.

Dynamic oxygenation measurements using a phosphorescent coating within a mammary window chamber mouse model

Phosphorescent lifetime imaging was employed to measure the spatial and temporal distribution of oxygen partial pressure in tissue under the coverslip of a mammary window chamber breast cancer mouse model. A thin platinum-porphyrin coating, whose phosphorescent lifetime varies monotonically with oxygen partial pressure, was applied to the coverslip surface. Dynamic temporal responses to induced modulations in oxygenation levels were measured using this approach.

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.

Gene-environment interaction demonstrates the vulnerability of the embryonic heart

Mammalian embryos develop in a low oxygen environment. The transcription factor hypoxia inducible factor 1a (HIF1α) is a key element in the cellular response to hypoxia. Complete deletion of Hif1α from the mouse conceptus causes extensive placental, vascular and heart defects, resulting in embryonic lethality. However the precise role of Hif1α in each of these organ systems remains unknown. To further investigate, we conditionally-deleted Hif1α from mesoderm, vasculature and heart individually. Surprisingly, deletion from these tissues did not recapitulate the same severe heart phenotype or embryonic lethality. Placental insufficiency, such as occurs in the complete Hif1α null, results in elevated cellular hypoxia in mouse embryos. We hypothesized that subjecting the Hif1α conditional null embryos to increased hypoxic stress might exacerbate the effects of tissue-specific Hif1α deletion. We tested this hypothesis using a model system mimicking placental insufficiency. We found that the majority of embryos lacking Hif1α in the heart died when exposed to non-physiological hypoxia. This was a heart-specific phenomenon, as HIF1α protein accumulated predominantly in the myocardium of hypoxia-stressed embryos. Our study demonstrates the vulnerability of the heart to lowered oxygen levels, and that under such conditions of non-physiological hypoxia the embryo absolutely requires Hif1α to continue normal development. Importantly, these findings extend our understanding of the roles of Hif1α in cardiovascular development.

Treatment with EGCG in NSCLC leads to decreasing interstitial fluid pressure and hypoxia to improve chemotherapy efficacy through rebalance of Ang-1 and Ang-2

AIM

Microvasculature and microenvironment play important roles in proliferation, invasion, metastasis and prognosis in non-small cell lung cancer (NSCLC), which might be altered by many anti-angiogenic drugs. Epigallocatechin-3-gallate (EGCG), a natural anti-angiogenesis agent refined from green tea, was defined to have multiple effects on angiogenesis factors, such as endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and angiopoietins (ANGs). Hypothesizing that EGCG might regulate microvasculature and microenvironment in NSCLC, the effects of EGCG on microvessel density (MVD), expression of Ang-1 and Ang-2, interstitial fluid pressure (IFP), tumor hypoxia, and chemotherapy sensitivity were examined.

METHODS AND RESULTS

EGCG treatment of A549 cells in mice bearing xenografts in vivo led to a significant decrease of MVD detected by CD31, and of Ang-2 expression detected by quantum dots double-label immunofluorescence assessment, while Ang-1 decreased with no significance. Decreased IFP was measured by the Wink-in-needle method, while hypoxia was assessed by polarographic electrode and pimonidazole (PIMO) immunohistochemistry. Assuming that these changes would increase response to chemotherapy, tumor growth studies were p[erformed in nude mice with xenografts, which were then treated with EGCG and the chemotherapeutic agent cisplatin. EGCG therapy combined with cisplatin led to synergistic inhibition of tumor growth, compared with administration of each treatment separately (P < 0.001). According to linear regression analysis, IFP was positively correlated with PIMO staining (R(2) = 0.618, P = 0.002), Ang-2 was correlated with MVD (R(2) = 0.423, P = 0.022), IFP (R(2) = 0.663, P = 0.01) and PIMO staining (R(2) = 0.694, P = 0.01).

CONCLUSION

IFP and delivery of oxygen might be improved by rebalance of Ang-1/Ang-2 under the treatment of EGCG in NSCLC, which also acts as a sensitizer of chemotherapy. These studies established a new mechanism for using EGCG as an adjuvant chemotherapy agent through modifying microvasculature and microenvironment.

Multivoxel ¹H MR spectroscopy is superior to contrast-enhanced MRI for response assessment after anti-angiogenic treatment of orthotopic human glioma xenografts and provides handles for metabolic targeting

BACKGROUND

Anti-angiogenic treatment of glioblastoma characteristically results in therapy resistance and tumor progression via diffuse infiltration. Monitoring tumor progression in these patients is thwarted because therapy results in tumor invisibility in contrast-enhanced (CE) MRI. To address this problem, we examined whether tumor progression could be monitored by metabolic mapping using (1)H MR spectroscopic imaging (MRSI).

METHODS

We treated groups of BALB/c nu/nu mice carrying different orthotopic diffuse-infiltrative glioblastoma xenografts with bevacizumab (anti-vascular endothelial growth factor [VEGF] antibody, n = 13), cabozantinib (combined VEGF receptor 2/c-Met tyrosine kinase inhibitor, n = 11), or placebo (n = 15) and compared CE-MRI with MRS-derived metabolic maps before, during, and after treatment. Metabolic maps and CE-MRIs were subsequently correlated to histology and immunohistochemistry.

RESULTS

In vivo imaging of choline/n-acetyl aspartate ratios via multivoxel MRS is better able to evaluate response to therapy than CE-MRI. Lactate imaging revealed that diffuse infiltrative areas in glioblastoma xenografts did not present with excessive glycolysis. In contrast, glycolysis was observed in hypoxic areas in angiogenesis-dependent compact regions of glioma only, especially after anti-angiogenic treatment.

CONCLUSION

Our data present MRSI as a powerful and feasible approach that is superior to CE-MRI and may provide handles for optimizing treatment of glioma. Furthermore, we show that glycolysis is more prominent in hypoxic areas than in areas of diffuse infiltrative growth. The Warburg hypothesis of persisting glycolysis in tumors under normoxic conditions may thus not be valid for diffuse glioma.

Remote post-conditioning reduces hypoxic damage early after experimental stroke

OBJECTIVES

Given that reliable markers for early ischemic brain damage are lacking, we set out to test whether pimonidazole can be used as a reliable tool in the quantification of hypoxic insults, at early time points following experimental stroke.

METHODS

We have used semi-quantitative Western blotting detection of pimonidazole adducts in a rat model of reversible middle cerebral artery occlusion (MCAO), treated with remote post-conditioning.

RESULTS

First, we demonstrated that a linear relationship exist between pimonidazole binding in the ischemic hemisphere and duration of ischemia, in animals subjected to 5, 15, 30, or 60 minutes of occlusion followed by 120 minutes of reflow. Then we showed a significant reduction in pimonidazole binding in the infarcted hemisphere, when rats with 60 minutes of MCAO, immediately after establishment of cerebral reflow, had 3×15 minutes intermittent hind limb ischemia followed by 24-hour survival. We analysed the middle cerebral arteries from animals with 60 minutes of MCAO and early remote post-conditioning, followed by 30 minutes, 24, or 48 hours of reflow. At 24 hours of reflow increases in phosphorylated protein kinase C-alpha with concomitantly increased levels of p38 phosphorylation were observed.

CONCLUSIONS

Our investigation demonstrates that pimonidazole can be used for quantifying ischemic impact in stroke, even after very short survival times. It furthermore shows that early remote post-conditioning reduces ischemic damage, probably through hyperpolarization and reduced reflow vasospasm in the conduit middle cerebral arteries.

Wound hypoxia in deep tissue after incision in rats

Our previous studies using rat models of incisional pain have shown that tissue lactate levels increase and pH decreases for several days after incision, suggesting the presence of an ischemic-like condition. The purpose of this study was to evaluate the time course and the extent of tissue hypoxia that develops in incised muscle and skin. We directly measured oxygen tension at several time points after incisions of the gastrocnemius muscle, the paraspinal skin, and the plantar hindpaw in anesthetized rats using an oxygen-sensitive microelectrode. In vivo hypoxia of the incised tissues was also evaluated immunohistochemically using a hypoxia marker, pimonidazole hydrochloride. To minimize intersubject variability, unincised contralateral tissues were used as a control. Tissue oxygen tension was decreased in both skeletal muscle and skin compared with control, for several days after incision. When measured directly, oxygen tension decreased immediately and remained low for several days after incisions. Pimonidazole immunostaining revealed hypoxic areas in incised muscle and skin for several days. By postoperative day 10, tissue oxygen tension recovered to that of control tissue. These results support the evidence that a hypoxic condition is present in deep tissue after incisions and that an ischemic-like mechanism may contribute to postoperative pain.

Islet survival and function following intramuscular autotransplantation in the minipig

The liver may not be an optimal site for islet transplantation due to obstacles by an instant blood-mediated inflammatory response (IBMIR), and low revascularization of transplanted islets. Therefore, intramuscular islet transplantation (IMIT) offers an attractive alternative, based on its simplicity, enabling easier access for noninvasive graft imaging and cell explantation. In this study, we explored the outcome of autologous IMIT in the minipig (n = 30). Using the intramuscular injection technique, we demonstrated by direct histological evidence the rapid revascularization of islets autotransplanted into the gracilius muscle. Islet survival assessment was performed using immunohistochemistry staining for insulin and glucagon up to a period of 6 months. Furthermore, we showed the crucial role of minimizing mechanical trauma to the myofibers and limiting exocrine contamination. Intramuscular islet graft function after transplantation was confirmed by documenting the acute insulin response to intravenous glucose in 5/11 pancreatectomized animals. Graft function after IMIT remained however significantly lower than the function measured in 12 out of 18 minipigs who received a similar islet volume in the liver through intraportal infusion. Collectively, these results demonstrated in a clinically relevant preclinical model, suggest IMIT as a promising alternative to intraportal infusion for the transplantation of β cells in certain medical situations.

The teratogenic effect of dofetilide during rat limb development and association with drug-induced bradycardia and hypoxia in the embryo

BACKGROUND

Dofetilide is an antiarrhythmic drug that blocks the cardiac repolarizing current IKr ((IKr, rapid component of the delayed rectifying potassium current). Previous studies have shown that (a) IKr is essential for normal cardiac function of the embryonic heart and (b) dofetilide is teratogenic in rodents. This study was undertaken to examine the mechanism by which dofetilide causes limb defects on gestational day 13 (GD 13) in the rat.

METHODS

Rats were treated with dofetilide (single oral dose, 5 mg/kg) on GD 13 and embryonic heart rates assessed by ultrasound (Vevo770, VisualSonics, Toronto, Ontario, Canada) 2 hr later. Fetuses were examined for malformations on GD 20. In a separate experiment, dofetilide treatment of GD 13 rats was followed 2, 4, 12, or 24 hr with iv dosing with the hypoxia marker, pimonidazole (60 mg/kg). Embryos were collected and heart rates were assessed in vitro and hypoxia in embryo limbs analyzed.

RESULTS

A teratogenic dose of dofetilide at a susceptible stage of development (GD 13) resulted in a period of bradycardia and arrhythmia of the embryonic heart and hypoxia in the developing limbs (GD 13) resulting in limb malformations (GD 20).

CONCLUSIONS

Drugs that induce periods of bradycardia and/or arrhythmia of the embryonic heart and cause the embryo to become hypoxic are potential human teratogens.

Imaging hypoxia in gliomas

Hypoxia plays a central role in tumour development, angiogenesis, growth and resistance to treatment. Owing to constant developments in medical imaging technology, significant advances have been made towards in vitro and in vivo imaging of hypoxia in a variety of tumours, including gliomas of the central nervous system. The aim of this article is to review the literature on imaging approaches currently available for measuring hypoxia in human gliomas and provide an insight into recent advances and future directions in this field. After a brief overview of hypoxia and its importance in gliomas, several methods of measuring hypoxia will be presented. These range from invasive monitoring by Eppendorf polarographic O(2) microelectrodes, positron electron tomography (PET) tracers based on 2-nitroimidazole compounds [(18)F-labelled fluoro-misonidazole ((18)F-MISO) or 1-(2-[((18))F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP-170)], (64)Cu-ATSM Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) or (99m)Tc- and (68)Ga-labelled metronidazole (MN) agents to advanced MRI methods, such as blood oxygenation level dependent (BOLD) MRI, oxygen-enhanced MRI, diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI) and (1)H-magnetic resonance spectroscopy.

Vascular abnormalities associated with acute hypoxia in human melanoma xenografts

BACKGROUND AND PURPOSE

The fraction of hypoxic cells has been shown to differ substantially among human tumors of the same histological type. In this study, a window chamber model was used to identify possible mechanisms leading to the development of highly different hypoxic fractions in A-07 and R-18 human melanoma xenografts.

MATERIALS AND METHODS

Chronic and acute hypoxia was assessed in intradermal tumors using an immunohistochemical and a radiobiological assay. Functional and morphological parameters of the vascular networks of tumors growing in dorsal window chambers were assessed with intravital microscopy.

RESULTS

R-18 tumors showed significantly higher hypoxic fractions than A-07 tumors, and the difference was mostly due to acute hypoxia. Compared to A-07 tumors, R-18 tumors showed low vascular densities, low vessel diameters, long vessel segments, low blood flow velocities, frequent fluctuations in blood flow, and a high fraction of narrow vessels with absent or very low and varying flux of red blood cells.

CONCLUSION

The high fraction of acute hypoxia in R-18 tumors was a consequence of frequent fluctuations in blood flow and red blood cell flux combined with low vascular density. The fluctuations were most likely caused by high geometric resistance to blood flow in the tumor microvasculature.

Micromanaging Iron Homeostasis: hypoxia-inducible micro-RNA-210 suppresses iron homeostasis-related proteins

Iron is fundamental for sustaining life for living organisms, and the iron metabolism is finely regulated at different levels. In cancer cells, deregulation of the iron metabolism induces oxidative stress and drives tumor progression and metastasis; however, the molecular mechanisms of iron homeostasis are not fully understood. Here we found that iron deficiency as well as hypoxia promoted microRNA-210 (miR-210) expression. A central mediator of miR-210 transcriptional activation is the hypoxia-inducible factor (HIF)-1α, and the hypoxia-response element in the miR-210 promoter is confirmed experimentally. This is in agreement with the data from in vivo studies that have demonstrated the presence of miR-210-expressing cells at the chronic hypoxic regions of xenografted tumors. Furthermore we found two essential molecules for iron homeostasis, iron-sulfur cluster scaffold protein (ISCU) and transferrin receptor 1 (TfR), are a direct target of miR-210. Transfection of miR-210 decreases the uptake of transferrin by inhibiting the expression of TfR. In addition, inhibition of miR-210 by anti-miR-210 up-regulates ISCU expression. These findings suggest that miR-210 works as an iron sensor and is involved in the maintenance of iron homeostasis by sustaining the TfR expression level to stimulate cell proliferation and promote cell survival in the hypoxic region within tumors.

Operable non-small cell lung cancer: correlation of volumetric helical dynamic contrast-enhanced CT parameters with immunohistochemical markers of tumor hypoxia

PURPOSE

To assess the relationship between helical dynamic contrast material-enhanced (DCE) computed tomographic (CT) parameters and immunohistochemical markers of hypoxia in patients with operable non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

After institutional review board approval was obtained, 20 prospective patients who were suspected of having NSCLC underwent whole-tumor DCE CT with kinetic modeling (Patlak analysis) 24 hours before scheduled surgery. Flow-extraction product (in milliliters per 100 milliliters per minute) and blood volume (in milliliters per 100 milliliters) were derived. After surgery, matched whole-tumor sections were stained for exogenous and endogenous markers of hypoxia (pimonidazole infused intravenously 24 hours before surgery, immediately after DCE CT; glucose transporter protein). Correlation between DCE CT parameters and immunohistochemical markers was assessed by using the Spearman rank correlation. DCE CT parameters and immunohistochemical markers were also compared according to pathologic subtype, grade, stage, and nodal status by using the Mann-Whitney test. P values less than .05 indicated a statistically significant difference.

RESULT

Fourteen patients with confirmed primary NSCLC underwent resection. There were negative correlations between blood volume and pimonidazole staining (r = -0.48, P = .004), and between flow-extraction product and glucose transporter protein expression (r = -0.50, P = .002). Flow-extraction product was significantly higher in adenocarcinomas than in squamous cell tumors (17.73 vs 11.46; P = .043). Glucose transporter protein expression was significantly lower for adenocarcinomas than for squamous tumors (14.07 vs 33.03; P < .001) and in node negative than in node positive tumors (15.63 vs 23.85; P = .005).

CONCLUSION

Blood volume and flow-extraction product derived at DCE CT correlated negatively with pimonidazole and glucose transporter protein expression, indicating the potential of these CT parameters as imaging biomarkers of hypoxia.

The HIF-pathway inhibitor NSC-134754 induces metabolic changes and anti-tumour activity while maintaining vascular function

Background:

Hypoxia-inducible factor-1 (HIF-1) mediates the transcriptional response to hypoxic stress, promoting tumour progression and survival. This study investigated the acute effects of the small-molecule HIF-pathway inhibitor NSC-134754.

Methods:

Human PC-3LN5 prostate cancer cells were treated with NSC-134754 for 24 h in hypoxia. Orthotopic prostate tumour-bearing mice were treated with a single dose of NSC-134754 for 6, 24 or 48 h. Treatment response was measured using magnetic resonance spectroscopy and imaging. Ex-vivo histological validation of imaging findings was also sought.

Results:

In vitro, NSC-134754 significantly reduced lactate production and glucose uptake (P<0.05), while significantly increasing intracellular glucose (P<0.01) and glutamine uptake/metabolism (P<0.05). Increased glutamine metabolism was independent of c-Myc, a factor also downregulated by NSC-134754. In vivo, a significantly higher tumour apparent diffusion coefficient was determined 24 h post-treatment (P<0.05), with significantly higher tumour necrosis after 48 h (P<0.05). NSC-134754-treated tumours revealed lower expression of HIF-1α and glucose transporter-1, at 6 and 24 h respectively, while a transient increase in tumour hypoxia was observed after 24 h. Vessel perfusion/flow and vascular endothelial growth factor levels were unchanged with treatment.

Conclusion:

NSC-134754 induces metabolic alterations in vitro and early anti-tumour activity in vivo, independent of changes in vascular function. Our data support the further evaluation of NSC-134754 as an anti-cancer agent.

2-Nitroimidazole-tricarbocyanine conjugate as a near-infrared fluorescent probe for in vivo imaging of tumor hypoxia

We developed a novel near-infrared (NIR) fluorescent probe, GPU-167, for in vivo imaging of tumor hypoxia. GPU-167 comprises a tricarbocyanine dye as an NIR fluorophore and two 2-nitroimidazole moieties as exogenous hypoxia markers that undergo bioreductive activation and then selective entrapment in hypoxic cells. After treatment with GPU-167, tumor cells contained significantly higher levels of fluorescence in hypoxia than in normoxia. In vivo fluorescence imaging specifically detected GPU-167 in tumors 24 h after administration. Ex vivo analysis revealed that fluorescence showed a strong correlation with hypoxia inducible factor (HIF)-1 active hypoxic regions. These data suggest that GPU-167 is a promising in vivo optical imaging probe for tumor hypoxia.

Selective tumor hypoxia targeting by hypoxia-activated prodrug TH-302 inhibits tumor growth in preclinical models of cancer

PURPOSE

Tumor hypoxia underlies treatment failure and yields a more aggressive, invasive, and metastatic cancer phenotype. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide mustard (Br-IPM). The purpose of this study is to characterize the antitumor activity of TH-302 and investigate its selective targeting of the hypoxic cells in human tumor xenograft models.

EXPERIMENTAL DESIGN

Antitumor efficacy was assessed by tumor growth kinetics or by clonogenic survival of isolated cells after tumor excision. Hypoxic fractions (HF) were determined by immunohistochemistry and morphometrics of pimonidazole staining. Tumor hypoxia levels were manipulated by exposing animals to different oxygen concentration breathing conditions. The localization and kinetics of TH-302 induced DNA damage was determined by γH2AX immunohistochemistry.

RESULTS

TH-302 antitumor activity was dose-dependent and correlated with total drug exposure. Correlation was found between antitumor activity and tumor HF across 11 xenograft models. Tumor-bearing animals breathing 95% O(2) exhibited attenuated TH-302 efficacy, with whereas those breathing 10% O(2) exhibited enhanced TH-302 efficacy, both compared with air (21% O(2)) breathing. TH-302 treatment resulted in a reduction in the volume of the HF 48 hours after dosing and a corresponding increase in the necrotic fraction. TH-302 induced DNA damage as measured by γH2AX was initially only present in the hypoxic regions and then radiated to the entire tumor in a time-dependent manner, consistent with TH-302 having a "bystander effect."

CONCLUSIONS

The results show that TH-302 has broad antitumor activity and selectively targets hypoxic tumor tissues.

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.

Preclinical evaluation and validation of [18F]HX4, a promising hypoxia marker for PET imaging

Hypoxia has been shown to be an important microenvironmental parameter influencing tumor progression and treatment efficacy. Patient guidance for hypoxia-targeted therapy requires evaluation of tumor oxygenation, preferably in a noninvasive manner. The aim of this study was to evaluate and validate the uptake of [(18)F]HX4, a novel developed hypoxia marker for PET imaging. A heterogeneous accumulation of [(18)F]HX4 was found within rat rhabdomyosarcoma tumors that was significantly (P < 0.0001) higher compared with the surrounding tissues, with temporal increasing tumor-to-blood ratios reaching a plateau of 7.638 ± 0.926 and optimal imaging properties 4 h after injection. [(18)F]HX4 retention in normal tissues was found to be short-lived, homogeneous and characterized by a fast progressive temporal clearance. Heterogeneity in [(18)F]HX4 tumor uptake was analyzed based on 16 regions within the tumor according to the different orthogonal planes at the largest diameter. Validation of heterogeneous [(18)F]HX4 tumor uptake was shown by a strong and significant relationship (r = 0.722; P < 0.0001) with the hypoxic fraction as calculated by the percentage pimonidazole-positive pixels. Furthermore, a causal relationship with tumor oxygenation was established, because combination treatment of nicotinamide and carbogen resulted in a 40% reduction (P < 0.001) in [(18)F]HX4 tumor accumulation whereas treatment with 7% oxygen breathing resulted in a 30% increased uptake (P < 0.05). [(18)F]HX4 is therefore a promising candidate for noninvasive detection and evaluation of tumor hypoxia at a macroscopic level.

A low-oxygenated subpopulation of pancreatic islets constitutes a functional reserve of endocrine cells

OBJECTIVE

The blood perfusion of pancreatic islets is highly variable and tightly regulated by the blood glucose concentration. Thus, oxygen levels are considered crucial for islet metabolism and function. Although islet oxygenation has been extensively studied in vitro, little is known about it in vivo. The current study aimed to investigate the oxygenation of the endocrine pancreas in vivo.

RESEARCH DESIGN AND METHODS

The reductive metabolism of 2-nitroimidazoles, such as pimonidazole, has previously been extensively used in studies of oxygen metabolism both in vitro and in vivo. At tissue oxygen levels <10 mmHg, pimonidazole accumulates intracellularly and may thereafter be detected by means of immunohistochemistry. Islet oxygenation was investigated in normal, 60% partially pancreatectomized, as well as whole-pancreas-transplanted rats. Moreover, leucine-dependent protein biosynthesis was performed using autoradiography to correlate islet oxygenation with metabolic activity.

RESULTS

In vivo, 20-25% of all islets in normal rats showed low oxygenation (pO(2) <10 mmHg). Changes in the islet mass, by means of whole-pancreas transplantation, doubled the fraction of low-oxygenated islets in the endogenous pancreas of transplanted animals, whereas this fraction almost completely disappeared after a 60% partial pancreatectomy. Moreover, oxygenation was related to metabolism, since well-oxygenated islets in vivo had 50% higher leucine-dependent protein biosynthesis, which includes (pro)insulin biosynthesis.

CONCLUSIONS

The current study suggests a novel subpopulation of dormant low-oxygenated islets, which seems to constitute a functional reserve of endocrine cells. This study establishes a novel perspective on the use of the endocrine pancreas in glucose homeostasis.

Immunohistochemical assessment of intrinsic and extrinsic markers of hypoxia in reproductive tissue: differential expression of HIF1α and HIF2α in rat oviduct and endometrium

Hypoxia is thought to be critical in regulating physiological processes within the female reproductive system, including ovulation, composition of the fluid in the oviductal/uterine lumens and ovarian follicle development. This study examined the localisation of exogenous (pimonidazole) and endogenous [hypoxia inducible factor 1α and 2α (HIF1α, -2α), glucose transporter type 1 (GLUT1) and carbonic anhydrase 9 (CAIX)] hypoxia-related antigens within the oviduct and uterus of the rat reproductive tract. The extent to which each endogenous antigen co-compartmentalised with pimonidazole was also assessed. Female Wistar Furth rats (n = 10) were injected intraperitoneally with pimonidazole (60 mg/kg) 1 h prior to death. Reproductive tissues were removed immediately following death and fixed in 4% paraformaldehyde before being embedded in paraffin. Serial sections were cut (6-7 μm thick) and antigens of interest identified using standard immunohistochemical procedures. The mucosal epithelia of the ampulla, isthmus and uterus were immunopositive for pimonidazole in most sections. Co-compartmentalisation of pimonidazole with HIF1α was only expressed in the mucosa of the uterus whilst co-compartmentalisation with HIF2α was observed in the mucosa of the ampulla, isthmus and uterus. Both GLUT1 and CAIX were co-compartmentalised with pimonidazole in mucosa of the isthmus and uterus. This study confirms that mucosal regions of the rat oviduct and uterus frequently experience severe hypoxia and there are compartment specific variations in expression of endogenous hypoxia-related antigens, including the HIF isoforms. The latter observation may relate to target gene specificity of HIF isoforms or perhaps HIF2α's responsiveness to non-hypoxic stimuli such as hypoglycaemia independently of HIF1α.

Metabolic markers in relation to hypoxia; staining patterns and colocalization of pimonidazole, HIF-1α, CAIX, LDH-5, GLUT-1, MCT1 and MCT4

Background

The cellular response of malignant tumors to hypoxia is diverse. Several important endogenous metabolic markers are upregulated under hypoxic conditions. We examined the staining patterns and co-expression of HIF-1α, CAIX, LDH-5, GLUT-1, MCT1 and MCT4 with the exogenous hypoxic cell marker pimonidazole and the association of marker expression with clinicopathological characteristics.

Methods

20 biopsies of advanced head and neck carcinomas were immunohistochemically stained and analyzed. All patients were given the hypoxia marker pimonidazole intravenously 2 h prior to biopsy taking. The tumor area positive for each marker, the colocalization of the different markers and the distribution of the markers in relation to the blood vessels were assessed by semiautomatic quantitative analysis.

Results

MCT1 staining was present in hypoxic (pimonidazole stained) as well as non-hypoxic areas in almost equal amounts. MCT1 expression showed a significant overall correlation (r = 0.75, p < 0.001) and strong spatial relationship with CAIX. LDH-5 showed the strongest correlation with pimonidazole (r = 0.66, p = 0.002). MCT4 and GLUT-1 demonstrated a typical diffusion-limited hypoxic pattern and showed a high degree of colocalization. Both MCT4 and CAIX showed a higher expression in the primary tumor in node positive patients (p = 0.09 both).

Conclusions

Colocalization and staining patterns of metabolic and hypoxia-related proteins provides valuable additional information over single protein analyses and can improve the understanding of their functions and environmental influences.