Molecular imaging of hypoxia with radiolabelled agents. Eur J Nucl Med Mol Imaging. 2009;36:1674-1686. [PMID: 19565239 PMCID: PMC2758191 DOI: 10.1007/s00259-009-1195-9]

Concomitant [18F]F-FAZA and [18F]F-FDG Imaging of Gynecological Cancer Xenografts: Insight into Tumor Hypoxia

BACKGROUND/AIM

Herein we assessed the feasibility of imaging protocols using both hypoxia-specific [18F]F-FAZA and [18F]F-FDG in bypassing the limitations derived from the non-specific findings of [18F]F-FDG PET imaging of tumor-related hypoxia.

MATERIALS AND METHODS

CoCl2-generated hypoxia was induced in multidrug resistant (Pgp+) or sensitive (Pgp-) human ovarian (Pgp- A2780, Pgp+ A2780AD), and cervix carcinoma (Pgp- KB-3-1, Pgp+ KB-V-1) cell lines to establish corresponding tumor-bearing mouse models. Prior to [18F]F-FDG/[18F]F-FAZA-based MiniPET imaging, in vitro [18F]F-FDG uptake measurements and western blotting were used to verify the presence of hypoxia.

RESULTS

Elevated GLUT-1, and hexokinase enzyme-II expression driven by CoCl2-induced activation of hypoxia-inducible factor-1α explains enhanced cellular [18F]F-FDG accumulation. No difference was observed in the [18F]F-FAZA accretion of Pgp+ and Pgp- tumors. Tumor-to-muscle ratios for [18F]F-FAZA measured at 110-120 min postinjection (6.2±0.1) provided the best contrasted images for the delineation of PET-oxic and PET-hypoxic intratumor regions. Although all tumors exhibited heterogenous uptake of both radiopharmaceuticals, greater differences for [18F]F-FAZA between the tracer avid and non-accumulating regions indicate its superiority over [18F]F-FDG. Spatial correlation between [18F]F-FGD and [18F]F-FAZA scans confirms that hypoxia mostly occurs in regions with highly active glucose metabolism.

CONCLUSION

The addition of [18F]F-FAZA PET to [18F]F-FGD imaging may add clinical value in determining hypoxic sub-regions.

Molecular imaging of tumor hypoxia: Evolution of nitroimidazole radiopharmaceuticals and insights for future development

Though growing evidence has been collected in support of the concept of dose escalation based on the molecular level images indicating hypoxic tumor sub-volumes that could be radio-resistant, validation of the concept is still a work in progress. Molecular imaging of tumor hypoxia using radiopharmaceuticals is expected to provide the required input to plan dose escalation through Image Guided Radiation Therapy (IGRT) to kill/control the radio-resistant hypoxic tumor cells. The success of the IGRT, therefore, is heavily dependent on the quality of images obtained using the radiopharmaceutical and the extent to which the image represents the true hypoxic status of the tumor in spite of the heterogeneous nature of tumor hypoxia. Available literature on radiopharmaceuticals for imaging hypoxia is highly skewed in favor of nitroimidazole as the pharmacophore given their ability to undergo oxygen dependent reduction in hypoxic cells. In this context, present review on nitroimidazole radiopharmaceuticals would be immensely helpful to the researchers to obtain a birds-eye view on what has been achieved so far and what can be tried differently to obtain a better hypoxia imaging agent. The review also covers various methods of radiolabeling that could be utilized for developing radiotracers for hypoxia targeting applications.

Recent Developments in PET and SPECT Radiotracers as Radiopharmaceuticals for Hypoxia Tumors

Hypoxia, a deficiency in the levels of oxygen, is a common feature of most solid tumors and induces many characteristics of cancer. Hypoxia is associated with metastases and strong resistance to radio- and chemotherapy, and can decrease the accuracy of cancer prognosis. Non-invasive imaging methods such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) using hypoxia-targeting radiopharmaceuticals have been used for the detection and therapy of tumor hypoxia. Nitroimidazoles are bioreducible moieties that can be selectively reduced under hypoxic conditions covalently bind to intracellular macromolecules, and are trapped within hypoxic cells and tissues. Recently, there has been a strong motivation to develop PET and SPECT radiotracers as radiopharmaceuticals containing nitroimidazole moieties for the visualization and treatment of hypoxic tumors. In this review, we summarize the development of some novel PET and SPECT radiotracers as radiopharmaceuticals containing nitroimidazoles, as well as their physicochemical properties, in vitro cellular uptake values, in vivo biodistribution, and PET/SPECT imaging results.

Recent Advances of 68Ga-Labeled PET Radiotracers with Nitroimidazole in the Diagnosis of Hypoxia Tumors

Positron emission tomography (PET) is a noninvasive molecular imaging method extensively applied in the detection and treatment of various diseases. Hypoxia is a common phenomenon found in most solid tumors. Nitroimidazole is a group of bioreducible pharmacophores that selectively accumulate in hypoxic regions of the body. Over the past few decades, many scientists have reported the use of radiopharmaceuticals containing nitroimidazole for the detection of hypoxic tumors. Gallium-68, a positron-emitting radioisotope, has a favorable half-life time of 68 min and can be conveniently produced by ⁶⁸Ge/⁶⁸Ga generators. Recently, there has been significant progress in the preparation of novel ⁶⁸Ga-labeled complexes bearing nitroimidazole moieties for the diagnosis of hypoxia. This review provides a comprehensive overview of the current status of developing ⁶⁸Ga-labeled radiopharmaceuticals with nitroimidazole moieties, their pharmacokinetics, and in vitro and in vivo studies, as well as PET imaging studies for hypoxic tumors.

Semifluorinated Alkanes as New Drug Carriers-An Overview of Potential Medical and Clinical Applications

Fluorinated compounds have been used in clinical and biomedical applications for years. The newer class of semifluorinated alkanes (SFAs) has very interesting physicochemical properties including high gas solubility (e.g., for oxygen) and low surface tensions, such as the well-known perfluorocarbons (PFC). Due to their high propensity to assemble to interfaces, they can be used to formulate a variety of multiphase colloidal systems, including direct and reverse fluorocarbon emulsions, microbubbles and nanoemulsions, gels, dispersions, suspensions and aerosols. In addition, SFAs can dissolve lipophilic drugs and thus be used as new drug carriers or in new formulations. In vitreoretinal surgery and as eye drops, SFAs have become part of daily clinical practice. This review provides brief background information on the fluorinated compounds used in medicine and discusses the physicochemical properties and biocompatibility of SFAs. The clinically established use in vitreoretinal surgery and new developments in drug delivery as eye drops are described. The potential clinical applications for oxygen transport by SFAs as pure fluids into the lungs or as intravenous applications of SFA emulsions are presented. Finally, aspects of drug delivery with SFAs as topical, oral, intravenous (systemic) and pulmonary applications as well as protein delivery are covered. This manuscript provides an overview of the (potential) medical applications of semifluorinated alkanes. The databases of PubMed and Medline were searched until January 2023.

Advances in PET and MRI imaging of tumor hypoxia

Tumor hypoxia is a complex and evolving phenomenon both in time and space. Molecular imaging allows to approach these variations, but the tracers used have their own limitations. PET imaging has the disadvantage of low resolution and must take into account molecular biodistribution, but has the advantage of high targeting accuracy. The relationship between the signal in MRI imaging and oxygen is complex but hopefully it would lead to the detection of truly oxygen-depleted tissue. Different ways of imaging hypoxia are discussed in this review, with nuclear medicine tracers such as [¹⁸F]-FMISO, [¹⁸F]-FAZA, or [⁶⁴Cu]-ATSM but also with MRI techniques such as perfusion imaging, diffusion MRI or oxygen-enhanced MRI. Hypoxia is a pejorative factor regarding aggressiveness, tumor dissemination and resistance to treatments. Therefore, having accurate tools is particularly important.

Hypoxia-Inducible Factors-Based Single Nucleotide Polymorphism in Breast Cancer with More Cancer Susceptibility

Hypoxia-inducible factors (HIFs) are a collection of transcriptional factors that engage in the regulation of oxygen homeostasis. They are hypoxia-responsive stress factors whose expression is linked to tumor growth and angiogenesis. HIF is a crucial player in the progression of breast cancer. Patients with high levels of hypoxia-inducible HIFs in their primary tumor biopsies had a higher chance of metastasis, the leading cause of breast cancer-related death. HIF polymorphisms have been shown in several epidemiological studies to influence breast cancer susceptibility. In the oxygendependent degradation domain, several short nucleotide polymorphisms (SNPs) of the HIF gene have been connected with higher HIF activity. To find SNP that make up the genetic diversity that underpins the phenotypic difference found between individuals in their susceptibility to cancer and the course of their disease, researchers used a variety of potential pathway-based approaches.

Research progress on tumor hypoxia-associative nanomedicine

Hypoxia at the solid tumor site is generally related to the unrestricted proliferation and metabolism of cancerous cells, which can cause tumor metastasis and aggravate tumor progression. Besides, hypoxia plays a substantial role in tumor treatment, and it is one of the main reasons that malignant tumors are difficult to cure and have a poor prognosis. On account of the tumor specific hypoxic environment, many hypoxia-associative nanomedicine have been proposed for tumor treatment. Considering the enhanced targeting effect, designing hypoxia-associative nanomedicine can not only minimize the adverse effects of drugs on normal tissues, but also achieve targeted therapy at the lesion site. Mostly, there can be three strategies for the treatment of hypoxic tumor, including improvement of hypoxic environment, hypoxia responsive drug release and hypoxia activated prodrug. The review describes the design principle and applications of tumor hypoxia-associative nanomedicine in recent years, and also explores its development trends in solid tumor treatment. Moreover, this review presents the current limitations of tumor hypoxia-associative nanomedicine in chemotherapy, radiotherapy, photodynamic therapy, sonodynamic therapy and immunotherapy, which may provide a reference for clinic translation of tumor hypoxia-associative nanomedicine.

Synthesis of a 2-nitroimidazole derivative N-(4-[18F]fluorobenzyl)-2-(2-nitro-1H-imidazol-1-yl)-acetamide ([18 F]FBNA) as PET radiotracer for imaging tumor hypoxia

BACKGROUND

Tissue hypoxia is a pathological condition characterized by reducing oxygen supply. Hypoxia is a hallmark of tumor environment and is commonly observed in many solid tumors. Non-invasive imaging techniques like positron emission tomography (PET) are at the forefront of detecting and monitoring tissue hypoxia changes in vivo.

RESULTS

We have developed a novel ¹⁸F-labeled radiotracer for hypoxia PET imaging based on cytotoxic agent benznidazole. Radiotracer N-(4-[¹⁸F]fluorobenzyl)-2-(2-nitro-1H-imidazol-1-yl)acetamide ([¹⁸F]FBNA) was synthesized through acylation chemistry with readily available 4-[¹⁸F]fluorobenzyl amine. Radiotracer [¹⁸F]FBNA was obtained in good radiochemical yields (47.4 ± 5.3%) and high radiochemical purity (> 95%). The total synthesis time was 100 min, including HPLC purification and the molar activity was greater than 40 GBq/µmol. Radiotracer [¹⁸F]FBNA was stable in saline and mouse serum for 6 h. [¹⁸F]FBNA partition coefficient (logP = 1.05) was found to be more lipophilic than [¹⁸F]EF-5 (logP = 0.75), [¹⁸F]FMISO (logP = 0.4) and [¹⁸F]FAZA (logP =  - 0.4). In vitro studies showed that [¹⁸F]FBNA accumulates in gastric cancer cell lines AGS and MKN45 under hypoxic conditions.

CONCLUSIONS

Hence, [¹⁸F]FBNA represents a novel and easy-to-prepare PET radioligand for imaging hypoxia.

Association of Hypoxia-Inducible Factor 1α Gene Polymorphisms With Breast Cancer Susceptibility: A Meta-Analysis

PURPOSE

Overexpression of the hypoxia-inducible factor 1α (HIF1A) gene is significantly associated with different types of cancers, including breast cancer. In this study, the effects of single-nucleotide polymorphisms rs11549465, rs11549467, and rs2057482 of the HIF1A gene and their association with breast cancer were systematically investigated through meta-analysis.

MATERIALS AND METHODS

After a systematic review, nine case-control studies of the HIF1A rs11549465 C/T polymorphism, six case-control studies of the HIF1A rs11549467 G/A polymorphism, and one case-control study of the HIF1A rs2057482 C/T polymorphism were included in this meta-analysis. The summary pooled odds ratios with 95% CIs were evaluated to detect the relationship between HIF1A polymorphisms and breast cancer susceptibility.

RESULTS

Subgroup-stratified analyses showed that the T and TT genotypes of the HIF1A rs11549465 C/T polymorphism were significantly associated with increased breast cancer risk in the Asian population under three genetic models (allele, homozygous, and recessive). HIF1A rs11549467 G/A analyses indicated that the A and AA genotypes were significantly associated with increased breast cancer risk in the Asian population under allele and dominant models. However, no association with breast cancer was observed in the White population for the HIF1A rs11549465 C/T and rs11549467 G/A polymorphisms. In addition, the HIF1A rs2057482 C/T polymorphism showed no association with breast cancer under any genetic models or by ethnicity-stratified analyses.

CONCLUSION

The results of this meta-analysis suggested that the HIF1A rs11549465 C/T and rs1154946 G/A polymorphisms were significantly associated with increased breast cancer risk in the Asian population, but no associations were found in the White population. Thus, HIF1A could be an important biomarker for population-based breast cancer screening.

Blood Oxygen Sensor Using a Boron-Doped Diamond Electrode

The electrochemical behavior of oxygen (O₂) in blood was studied using boron-doped diamond (BDD) electrodes. Cyclic voltammogram of O₂ in a 0.1 M phosphate buffer solution solution containing 1 × 10^-6 M of bovine hemoglobin exhibits a reduction peak at -1.4 V (vs Ag/AgCl). Moreover, the scan rate dependence was investigated to study the reduction reaction mechanism, which was attributable to the reduction of O₂ to H₂O₂ via two electrons. A linear calibration curve was observed in the concentration range of 86.88-314.63 mg L^-1 (R² = 0.99) with a detection limit of 1.0 mg L^-1 (S/B = 3). The analytical performance was better than those with glassy carbon or platinum electrodes as the working electrode. In addition, an application to bovine blood was performed. The O₂ concentration in the blood measured on the BDD electrodes was compared to that measured using an OxyLite Pro fiber-optic oxygen sensor device. Both methods gave similar values of the O₂ concentration in the range of ∼40 to 150 mmHg. This result confirms that BDD electrodes could potentially be used to detect the O₂ concentration in blood.

Hypoxia Imaging As a Guide for Hypoxia-Modulated and Hypoxia-Activated Therapy

Significance: Oxygen imaging techniques, which can probe the spatiotemporal heterogeneity of tumor oxygenation, could be of significant clinical utility in radiation treatment planning and in evaluating the effectiveness of hypoxia-activated prodrugs. To fulfill these goals, oxygen imaging techniques should be noninvasive, quantitative, and capable of serial imaging, as well as having sufficient temporal resolution to detect the dynamics of tumor oxygenation to distinguish regions of chronic and acute hypoxia. Recent Advances: No current technique meets all these requirements, although all have strengths in certain areas. The current status of positron emission tomography (PET)-based hypoxia imaging, oxygen-enhanced magnetic resonance imaging (MRI), ¹⁹F MRI, and electron paramagnetic resonance (EPR) oximetry are reviewed along with their strengths and weaknesses for planning hypoxia-guided, intensity-modulated radiation therapy and detecting treatment response for hypoxia-targeted prodrugs. Critical Issues: Spatial and temporal resolution emerges as a major concern for these areas along with specificity and quantitative response. Although multiple oxygen imaging techniques have reached the investigative stage, clinical trials to test the therapeutic effectiveness of hypoxia imaging have been limited. Future Directions: Imaging elements of the redox environment besides oxygen by EPR and hyperpolarized MRI may have a significant impact on our understanding of the basic biology of the reactive oxygen species response and may extend treatment possibilities.

Imaging of Tumor Hypoxia With Radionuclide-Labeled Tracers for PET

The hypoxic state in a solid tumor refers to the internal hypoxic environment that appears as the tumor volume increases (the maximum radius exceeds 180-200 microns). This state can promote angiogenesis, destroy the balance of the cell’s internal environment, and lead to resistance to radiotherapy and chemotherapy, as well as poor prognostic factors such as metastasis and recurrence. Therefore, accurate quantification, mapping, and monitoring of hypoxia, targeted therapy, and improvement of tumor hypoxia are of great significance for tumor treatment and improving patient survival. Despite many years of development, PET-based hypoxia imaging is still the most widely used evaluation method. This article provides a comprehensive overview of tumor hypoxia imaging using radionuclide-labeled PET tracers. We introduced the mechanism of tumor hypoxia and the reasons leading to the poor prognosis, and more comprehensively included the past, recent and ongoing studies of PET radiotracers for tumor hypoxia imaging. At the same time, the advantages and disadvantages of mainstream methods for detecting tumor hypoxia are summarized.

[18F]-FDG-PET/CT and [18F]-FAZA-PET/CT Hypoxia Imaging of Metastatic Thyroid Cancer: Association with Short-Term Progression After Radioiodine Therapy

PURPOSE

To examine the relationships between 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]-FDG) and hypoxia tracer [¹⁸F]fluoro-azomycinarabinofuranoside ([¹⁸F]-FAZA) and between ¹³¹I and [¹⁸F]-FAZA uptake in patients with metastatic thyroid cancer and to evaluate imaging features associated with short-term progression after ¹³¹I therapy.

PROCEDURES

The study population was 20 patients (17 women and 3 men; mean age, 67 years) with metastatic thyroid cancer who underwent both [¹⁸F]-FDG- and [¹⁸F]-FAZA-positron emission tomography (PET)/X-ray computed tomography (CT) examinations before ¹³¹I therapy. Short-term response to radioiodine was assessed (mean follow-up, 19 months ± 9). PET parameters including [¹⁸F]-FDG-SUVmax, [¹⁸F]-FAZA-SUVmax, and [¹⁸F]-FAZA-tumor-to-muscle [T/M] were obtained. Mann-Whitney U, Wilcoxon signed-rank, or χ² tests were used to assess differences between two quantitative variables or compare categorical data. Predictive factors for short-term progression were investigated with logistic regression analysis.

RESULTS

Eleven lymph node metastatic lesions were identified in 9 patients and 46 distant metastatic lesions (lung, 19; bone, 17; and liver, 10) in 14 patients. A total of 24 ¹³¹I-positive and 33 ¹³¹I-negative lesions were detected. SUVmax was significantly lower with [¹⁸F]-FAZA-PET/CT (1.3 ± 0.6) than with [¹⁸F]-FDG-PET/CT (6.4 ± 5.9, p < 0.001). No significant correlation was observed between [¹⁸F]-FAZA-PET/CT and ¹³¹I imaging concerning visibility (p = 0.36). After ¹³¹I therapy, 31 of 57 metastatic lesions displayed short-term progression. Multivariate logistic regression revealed that [¹⁸F]-FDG-SUVmax (p = 0.022) and [¹⁸F]-FAZA-T/M (p = 0.002) showed significant associations with short-term progression.

CONCLUSIONS

Although [¹⁸F]-FAZA uptake was low in metastatic thyroid cancers, not only glucose metabolism but also hypoxic conditions may be associated with progression after ¹³¹I therapy in patients with metastatic thyroid cancer.

Mitochondria targeted near-infrared chemodosimeter for upconversion luminescence bioimaging of hypoxia

We report a mitochondria-targeted near-infrared probe (NRh-O) for frequency upconversion luminescence (FUCL) imaging of hypoxia. Under hypoxic conditions, NRh-O rapidly responds to release the FUCL product NRh (λ_ex/em = 850/825 nm) with high sensitivity and selectivity in mitochondria. This highlights the potential application of a hypoxia-responsive probe in early clinical diagnosis.

In vivo noninvasive preclinical tumor hypoxia imaging methods: a review

Tumors exhibit areas of decreased oxygenation due to malformed blood vessels. This low oxygen concentration decreases the effectiveness of radiation therapy, and the resulting poor perfusion can prevent drugs from reaching areas of the tumor. Tumor hypoxia is associated with poorer prognosis and disease progression, and is therefore of interest to preclinical researchers. Although there are multiple different ways to measure tumor hypoxia and related factors, there is no standard for quantifying spatial and temporal tumor hypoxia distributions in preclinical research or in the clinic. This review compares imaging methods utilized for the purpose of assessing spatio-temporal patterns of hypoxia in the preclinical setting. Imaging methods provide varying levels of spatial and temporal resolution regarding different aspects of hypoxia, and with varying advantages and disadvantages. The choice of modality requires consideration of the specific experimental model, the nature of the required characterization and the availability of complementary modalities as well as immunohistochemistry.

FDG PET correlates weakly with HIF-1 expression in solid tumors: a meta-analysis

BACKGROUND

Hypoxia-inducible factor (HIF)-1α plays a key role in hypoxic adaptation of tumor cells. Overexpression of HIF-1α is associated with tumor aggressiveness and worse prognosis in several malignancies. Presumably, expression of HIF-1a may be reflected by positron emission tomography with 2-deoxy-2 [fluorine-18] fluoro-D-glucose (18F-FDG PET). There are inconsistent data about relationships between FDG PET and HIF-1α.

PURPOSE

To provide evident data about associations between maximum standardized uptake value (SUV_max) and HIF-1α expression in solid tumors.

MATERIAL AND METHODS

MEDLINE, SCOPUS, and EMBASE databases were screened for relationships between SUV and HIF-1α up to August 2019. Overall, 21 studies with 1154 patients were identified. The following data were extracted from the literature: authors; year of publication; number of patients; and correlation coefficients.

RESULTS

Correlation coefficients between SUV_max and HIF-1α were in the range of -0.51-0.71. The pooled correlation coefficient was 0.27 (95% confidence interval [CI] = 0.14-0.41). Furthermore, correlation coefficients for some tumor entities were calculated. For this sub-analysis, data for primary tumors with >2 reports were included. The calculated correlation coefficients in the analyzed subgroups were as follows: head and neck squamous cell carcinoma: ρ = 0.25 (95% CI = 0.07-0.42); non-small lung cell cancer: ρ = 0.27 (95% CI = -0.14-0.67); uterine cervical cancer: ρ = -0.09 (95% CI = -0.89-0.71); thymic tumors: ρ = 0.39 (95% CI = 0.04-0.58).

CONCLUSION

SUV_max of FDG PET correlated weakly with expression of HIF-1α both in overall sample and tumor subgroups. Therefore, FDG PET cannot be used for prediction of hypoxia in clinical practice.

Azo-Based Hypoxia-Responsive Self-Assembly Near-Infrared Fluorescent Nanoprobe for In Vivo Real-Time Bioimaging of Tumors

Hypoxia is an obvious characteristic of cancer, especially solid tumors. which may give rise to the expansion of invasion and metastasis. Exploring near-infrared (NIR) nanoprobes that could accurately evaluate the degree of hypoxia will contribute to the assessment of the degree of malignant neoplasms, so as to adopt more accurate and individualized treatment options Here, we have developed a self-assembled NIR organic nanoprobe to specifically and authoritatively detect the oxygen concentration in vivo and in vitro to evaluate the level of hypoxia. The organic nanoprobe mainly contains two motifs: a fluorophore moiety NRh-NH₂ for NIR fluorescence imaging and hypoxia-sensitive moiety Azonaphthalene derivatives for quenching NIR emissions, detecting oxygen in hypoxic regions and improving the hydrophilicity. The nanoprobes were used for detection of oxygen in a variety of living cells under different conditions and real-time bioimaging of neoplasms in live mice. This design strategy provides ideas for the development of nanoprobes for the diagnosis of tumors and other hypoxia-related diseases.

An overview of the developments and potential applications of 68Ga-labelled PET/CT hypoxia imaging

Non-invasive imaging of hypoxia plays a role in monitoring the body's adaptive response or the development of pathology under hypoxic conditions. Various techniques to image hypoxia have been investigated with a shift towards the use of molecular imaging using PET/CT. The role of hypoxia-specific radiopharmaceuticals such as radiolabelled nitroimidazoles is well documented particularly in the oncologic setting. With the increasing utilisation of in-house labelling with a PET benchtop generator, such as the ⁶⁸Ge/⁶⁸Ga generator, the use of ⁶⁸Ga-labelled hypoxic radiopharmaceuticals in the clinical setting is developing. Since hypoxia plays a role in various pathologic states including infectious disease such as TB, there is a need to explore the potential application of ⁶⁸Ga-labelled hypoxia seeking radiopharmaceuticals beyond oncology. The purpose of this review is to describe the developments of ⁶⁸Ga-labelled hypoxic radiopharmaceuticals including the various chelators that have been investigated. Further, the role of hypoxia imaging in various pathologies is discussed with particular emphasis on the potential clinical applications of hypoxia PET/CT in TB.

Mechanisms controlling bacterial infection in myeloid cells under hypoxic conditions

Various factors of the tissue microenvironment such as the oxygen concentration influence the host-pathogen interaction. During the past decade, hypoxia-driven signaling via hypoxia-inducible factors (HIF) has emerged as an important factor that affects both the pathogen and the host. In this chapter, we will review the current knowledge of this complex interplay, with a particular emphasis given to the impact of hypoxia and HIF on the inflammatory and antimicrobial activity of myeloid cells, the bacterial responses to hypoxia and the containment of bacterial infections under oxygen-limited conditions. We will also summarize how low oxygen concentrations influence the metabolism of neutrophils, macrophages and dendritic cells. Finally, we will discuss the consequences of hypoxia and HIFα activation for the invading pathogen, with a focus on Pseudomonas aeruginosa, Mycobacterium tuberculosis, Coxiella burnetii, Salmonella enterica and Staphylococcus aureus. This includes a description of the mechanisms and microbial factors, which the pathogens use to sense and react to hypoxic conditions.

Conjugated Photosensitizers for Imaging and PDT in Cancer Research

Early cancer detection and perfect understanding of the disease are imperative toward efficient treatments. It is straightforward that, for choosing a specific cancer treatment methodology, diagnostic agents undertake a critical role. Imaging is an extremely intriguing tool since it assumes a follow up to treatments to survey the accomplishment of the treatment and to recognize any conceivable repeating injuries. It also permits analysis of the disease, as well as to pursue treatment and monitor the possible changes that happen on the tumor. Likewise, it allows screening the adequacy of treatment and visualizing the state of the tumor. Additionally, when the treatment is finished, observing the patient is imperative to evaluate the treatment methodology and adjust the treatment if necessary. The goal of this review is to present an overview of conjugated photosensitizers for imaging and therapy.

Synthesis of 99mTc-labeled 2-Mercaptobenzimidazole as a novel radiotracer to diagnose tumor hypoxia

Discovery of ^99mTc-labeled imidazole derivatives as a potential radiotracer for hypoxic tumor imaging is considered to be of great interest because of non-invasive detection capabilities. 2-Mercaptobenzimidazole (2-MBI) was successfully synthesized, characterized and radiolabeled with [^99mTc (CO)₃(H₂O)₃]⁺ intermediate to form ^99mTc-2-MBI complex with radiochemical purity of ≥95% yield as observed by instant-thin layer chromatography (ITLC) and radio-high performance liquid chromatography (radio-HPLC). The ^99mTc-2-MBI complex was observed to be stable in saline and serum with no noticeable decomposition at room temperature and 37 °C, respectively, over a time period of 24 h. Biodistribution results in Balb/c mice bearing S180 tumor show that ^99mTc-2-MBI highly internalized in tumor tissue, also possess preferably high tumor/muscle and tumor/blood ratios 4.14 ± 0.77 and 3.91 ± 0.63, respectively at 24 h incubation. Scintigraphic imaging study shows ^99mTc-2-MBI is visibly accumulated in hypoxic tumor tissue, suggesting it would be a promising radiotracer for early stage diagnosis of tumor hypoxia.

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Radiolabeled imidazole derivatives are non-invasive imaging radiotracers

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Benzoimidazole as basic subunit of biomolecules

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Hypoxia or oxygen deprivation plays key role in tumor progression and resistance to therapy

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Imidazole moiety reduce into reactive intermediary metabolites to show high accumulation in viable hypoxic cells

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^99mTc-2-MBI radiotracer possess enhanced tumor/muscle and tumor/blood ratios

Precision Radiotherapy: 18F-FDG PET-based radiotherapy planning in Head and Neck cancers

Precision medicine is gaining importance in this era of molecular imaging where the molecular features of a disease can be noninvasively assessed and treated with personalized medicine. This is especially suited for head and neck cancers (HNCa). Early stage HNCa are ideally managed with radiotherapy (RT) or surgery. Head and neck (HN) is a complex region and its tumors respond to RT differently due to dissimilar structures and moving organs such as tongue. Radiation oncologists are always in the process of trying and investigating newer RT techniques in order to achieve precise and targetted therapy to tumour/s. One such innovation is Intensity modulated RT (IMRT) using 3 Dimensional conformal RT (3DCRT). This 3DCRT resizes the radiation beams to match the shape of the tumor. Such focused dose escalation may improve local control in HNCa. Image guided RT in conjunction with IMRT is the most advanced form of RT planning being used these days. Simulation computerized tomography (CT) images are usually incorporated into RT planning module. But limitations of CT such as poor soft tissue contrast than magnetic resonance imaging and inability to clearly define solid / cystic / necrotic areas and viable tumour exist. Functional imaging such as Positron Emission Tomography (PET) has established its superiority over CT in delineating the actual site and extent of HN tumors. A combination of IMRT with BTV (Biological Tumour Volume) may be the most ideal technique to deliver a homogeneous radiation boost to tumour. This review shall discuss PET based RT planning, challenges, practical tips, and how to optimize therapy with the least side effects to the normal surrounding tissues.

Optimization of treatment planning for hypoxic tumours and re-modulation of radiation intensity in heavy-ion radiotherapy

Aim

The purpose of this study is to optimize treatment planning in carbon ion radiotherapy, taking into account the effect of tumour hypoxia.

Background

In conventional hadron therapy, the goal is to create a homogenous dose in the tumour area and, thus, achieve a uniform cell survival level. Since the induction of a specific damage to cells is directly influenced by the level of hypoxia in the tissue, the varying oxygen pressure in the different regions of hypoxic tumours would disrupt the uniformity of the cell survival level.

Materials and methods

Using the Geant4 Monte Carlo Code, the physical dose profile and dose-averaged linear energy transfer were calculated in the tumour. Then, the oxygen enhancement ratio in different areas of the tumour were compared with different pressures.

Results

Modulations of radiation intensities as well as energies of ion beams were calculated, both considering and disregarding the effect of hypoxia, and the required dose profiles were compared with each other. Cell survival levels were also compared between the two methods. An equation was obtained for re-modulating the beams in the presence of hypoxia, and radiation weighting factors were extracted for the beam intensities.

Conclusion

The results show that taking the effect of hypoxia into account would cause the reduction of average doses delivered to the tumour tissues up to 1.54 times. In this regard, the required dose is reduced by 1.63 times in the healthy tissues before the tumour. This will result in an effective protection of healthy tissues around the tumour.

Using positron-emission tomography-computed tomography for predicting radiotherapy-induced tumor regression in carcinoma esophagus in an Indian population

Carcinoma esophagus is a common malignancy of the Indian subcontinent. The role of positron-emission tomography–computed tomography (PET-CT) in the assessment of response to radiotherapy has been widely studied and accepted. However, its precise use as a predictive tool for actual histopathological response to radiotherapy needs further evaluation, especially in an Indian population. The aim of this study was to identify a quantum of metabolic response on PET-CT that can also predict for a good pathological response. Forty-four patients of carcinoma esophagus treated with neoadjuvant chemoradiotherapy followed by surgery were included in the study. All patients underwent a PET-CT before starting treatment as well as at 4–6 weeks after completion of radiotherapy. The percentage change in pre and posttreatment maximum standardized uptake value (SUV_max) value (ΔSUV%) of the primary tumor was correlated against histopathological tumor regression grade (TRG) as per the Mandard's system. Seventy-five percent of the patients with a significant metabolic response, i.e., a ΔSUV% of 60% or more, also had a good pathological response to treatment. Thus, by considering a ΔSUV% of 60%, we could predict for a good pathological response (TRG of 1 or 2) to chemoradiotherapy in our patient set with a sensitivity of 95.45% and a specificity of 72.72%.

Characterization of Brain Inflammation, Apoptosis, Hypoxia, Blood-Brain Barrier Integrity and Metabolism in Venezuelan Equine Encephalitis Virus (VEEV TC-83) Exposed Mice by In Vivo Positron Emission Tomography Imaging

Traditional pathogenesis studies of alphaviruses involves monitoring survival, viremia, and pathogen dissemination via serial necropsies; however, molecular imaging shifts this paradigm and provides a dynamic assessment of pathogen infection. Positron emission tomography (PET) with PET tracers targeted to study neuroinflammation (N,N-diethyl-2-[4-phenyl]-5,7-dimethylpyrazolo[1,5-a]pyrimidine-3-acetamide, [¹⁸F]DPA-714), apoptosis (caspase-3 substrate, [¹⁸F]CP-18), hypoxia (fluormisonidazole, [¹⁸F]FMISO), blood–brain barrier (BBB) integrity ([¹⁸F]albumin), and metabolism (fluorodeoxyglucose, [¹⁸F]FDG) was performed on C3H/HeN mice infected intranasally with 7000 plaque-forming units (PFU) of Venezuelan equine encephalitis virus (VEEV) TC-83. The main findings are as follows: (1) whole-brain [¹⁸F]DPA-714 and [¹⁸F]CP-18 uptake increased three-fold demonstrating, neuroinflammation and apoptosis, respectively; (2) [¹⁸F]albumin uptake increased by 25% across the brain demonstrating an altered BBB; (3) [¹⁸F]FMISO uptake increased by 50% across the whole brain indicating hypoxic regions; (4) whole-brain [¹⁸F]FDG uptake was unaffected; (5) [¹⁸F]DPA-714 uptake in (a) cortex, thalamus, striatum, hypothalamus, and hippocampus increased through day seven and decreased by day 10 post exposure, (b) olfactory bulb increased at day three, peaked day seven, and decreased day 10, and (c) brain stem and cerebellum increased through day 10. In conclusion, intranasal exposure of C3H/HeN mice to VEEV TC-83 results in both time-dependent and regional increases in brain inflammation, apoptosis, and hypoxia, as well as modest decreases in BBB integrity; however, it has no effect on brain glucose metabolism.

A 3D microvascular network model to study the impact of hypoxia on the extravasation potential of breast cell lines

Hypoxia is a common feature of the tumor microenvironment. Accumulating evidence has demonstrated hypoxia to be an important trigger of tumor cell invasion or metastasizes via hypoxia-signaling cascades, including hypoxia-inducible factors (HIFs). Microfluidic model can be a reliable in vitro tool for systematically interrogating individual factors and their accompanying downstream effects, which may otherwise be difficult to study in complex tumor tissues. Here, we used an in vitro model of microvascular networks in a microfluidic chip to measure the extravasation potential of breast cell lines subjected to different oxygen conditions. Through the use of HIF-1α knock-down cell lines, we also validated the importance of HIF-1α in the transmigration ability of human breast cell lines. Three human breast cell lines derived from human breast tissues (MCF10A, MCF-7 and MDA-MB-231) were used in this study to evaluate the role of hypoxia in promoting metastasis at different stages of cancer progression. Under hypoxic conditions, HIF-1α protein level was increased, and coincided with changes in cell morphology, viability and an elevated metastatic potential. These changes were accompanied by an increase in the rate of extravasation compared to normoxia (21% O₂). siRNA knockdown of HIF-1α in hypoxic tumors significantly decreased the extravasation rates of all the cell lines tested and may have an effect on the function of metastatic and apoptotic-related cellular processes.

PET/MR Imaging of the Pancreas

PET/MR imaging has the potential to markedly alter pancreatic care in both the malignant, and premalignant states with the ability to perform robust, high-resolution, quantitative molecular imaging. The ability of PET/MR imaging to monitor disease processes, potentially correct for motion in the upper abdomen, and provide novel biomarkers that may be a combination of MR imaging and PET biomarkers, offers a unique, precise interrogation of the pancreatic milieu going forward.

Clinical imaging of hypoxia: Current status and future directions

Tissue hypoxia is a key feature of many important causes of morbidity and mortality. In pathologies such as stroke, peripheral vascular disease and ischaemic heart disease, hypoxia is largely a consequence of low blood flow induced ischaemia, hence perfusion imaging is often used as a surrogate for hypoxia to guide clinical diagnosis and treatment. Importantly, ischaemia and hypoxia are not synonymous conditions as it is not universally true that well perfused tissues are normoxic or that poorly perfused tissues are hypoxic. In pathologies such as cancer, for instance, perfusion imaging and oxygen concentration are less well correlated, and oxygen concentration is independently correlated to radiotherapy response and overall treatment outcomes. In addition, the progression of many diseases is intricately related to maladaptive responses to the hypoxia itself. Thus there is potentially great clinical and scientific utility in direct measurements of tissue oxygenation. Despite this, imaging assessment of hypoxia in patients is rarely performed in clinical settings. This review summarises some of the current methods used to clinically evaluate hypoxia, the barriers to the routine use of these methods and the newer agents and techniques being explored for the assessment of hypoxia in pathological processes.

Polymorphisms in HIFs and breast cancer sutarsceptibility in Chinese women: a case-control study

Hypoxia-inducible factors (HIFs) play a crucial role in cancer progression. Several epidemiological studies have demonstrated that HIFs polymorphisms can influence the susceptibility of multiple cancers. However, the relationship of HIFs polymorphisms (rs11549467 and rs17039192) and breast cancer (BC) risk was still unknown. Thus, we performed a case-control study based on 560 BC patients and 583 healthy controls to explore the association between them. Our results indicated a boardline connection between HIF-1 rs11549467 and BC risk (AG compared with GG: OR = 1.61, 95% CI = 1.05–2.49, P=0.03; AG + AA compared with GG: OR = 1.64, 95% CI = 1.08–2.51, P=0.02; AG compared with GG + AA: OR = 1.61, 95% CI = 1.04–2.48, P=0.03; OR = 1.64, 95% CI = 1.09–2.45, P=0.02), while HIF-2 rs17039192 had no influence on breast cancer. Considered the comparison of sample size and potential heterogeneity of previous case–control studies, we concluded that HIF-1 rs11549467 has a marginal effect on BC risk. Further well-designed studies with larger sample size were required.

Oxygen Sensing, Hypoxia Tracing and in Vivo Imaging with Functional Metalloprobes for the Early Detection of Non-communicable Diseases

Hypoxia has been identified as one of the hallmarks of tumor environments and a prognosis factor in many cancers. The development of ideal chemical probes for imaging and sensing of hypoxia remains elusive. Crucial characteristics would include a measurable response to subtle variations of pO2 in living systems and an ability to accumulate only in the areas of interest (e.g., targeting hypoxia tissues) whilst exhibiting kinetic stabilities in vitro and in vivo. A sensitive probe would comprise platforms for applications in imaging and therapy for non-communicable diseases (NCDs) relying on sensitive detection of pO2. Just a handful of probes for the in vivo imaging of hypoxia [mainly using positron emission tomography (PET)] have reached the clinical research stage. Many chemical compounds, whilst presenting promising in vitro results as oxygen-sensing probes, are facing considerable disadvantages regarding their general application in vivo. The mechanisms of action of many hypoxia tracers have not been entirely rationalized, especially in the case of metallo-probes. An insight into the hypoxia selectivity mechanisms can allow an optimization of current imaging probes candidates and this will be explored hereby. The mechanistic understanding of the modes of action of coordination compounds under oxygen concentration gradients in living cells allows an expansion of the scope of compounds toward in vivo applications which, in turn, would help translate these into clinical applications. We summarize hereby some of the recent research efforts made toward the discovery of new oxygen sensing molecules having a metal-ligand core. We discuss their applications in vitro and/or in vivo, with an appreciation of a plethora of molecular imaging techniques (mainly reliant on nuclear medicine techniques) currently applied in the detection and tracing of hypoxia in the preclinical and clinical setups. The design of imaging/sensing probe for early-stage diagnosis would longer term avoid invasive procedures providing platforms for therapy monitoring in a variety of NCDs and, particularly, in cancers.

Modeling of FMISO [F18] nanoparticle PET tracer in normal-cancerous tissue based on real clinical image

Hypoxia as one of the principal properties of tumor cells is a reaction to the deprivation of oxygen. The location of tumor cells could be identified by assessment of oxygen and nutrient level in human body. Positron emission tomography (PET) is a well-known non-invasive method that is able to measure hypoxia based on the FMISO (Fluoromisonidazole) tracer dynamic. This paper aims to study the PET tracer concentration through convection-diffusion-reaction equations in a real human capillary-like network. A non-uniform oxygen pressure along the capillary path and convection mechanism for FMISO transport are taken into account to accurately model the characteristics of the tracer. To this end, a multi-scale model consists of laminar blood flow through the capillary network, interstitial pressure, oxygen pressure, FMISO diffusion and FMISO convection transport in the extravascular region is developed. The present model considers both normal and tumor tissue regions in computational domain. The accuracy of numerical model is verified with the experimental results available in the literature. The convection and diffusion types of transport mechanism are employed in order to calculate the concentration of FMISO in the normal and tumor sub-domain. The influences of intravascular oxygen pressure, FMISO transport mechanisms, capillary density and different types of tissue on the FMISO concentration have been investigated. According to result (Table 4) the convection mechanism of FMISO molecules transportation is negligible, but it causes more accuracy of the proposed model. The approach of present study can be employed in order to investigate the effects of various parameters, such as tumor shape, on the dynamic behavior of different PET tracers, such as FDG, can be extended to different case study problems, such as drug delivery.

Oxygen Supplementation Ameliorates Tibial Development via Stimulating Vascularization in Tibetan Chickens at High Altitudes

Tibetan chickens (TBCs) living in high-altitude hypoxic environment, are characterized by delayed growth and small size as compared to low-altitude broiler chickens. Increasing evidences signify the beneficial effect of oxygen (O₂) supplementation in animal's body for regulating their body growth and organ development. However, it is still unclear that whether O₂ supplementation has an ameliorative and protective role in TBCs living at high altitude. In this study, we first found that O₂ supplementation not only increased the survival rate but also promoted the growth of TBCs associated with bone development. Importantly, we observed that the increase of vascular distribution in the tibial hypertrophic zone could contribute to promote growth and development of the tibia, which is highly correlated with the up-regulated expression level of vascular endothelial growth factor (VEGF)-A and VEGF receptor-1 (VEGFR1). Additionally, hypoxia inducible factor (HIF)-1ɑ also has a stimulative elevation by O₂ supplementation. These results were confirmed by histology, immunohistochemistry, qRT-PCR and Western blotting techniques. Altogether, these findings demonstrated that the up-regulation of VEGFA and its receptors are accompanied by proangiogeneic factor (HIF-1α) expression, which were required for angiogenesis to meliorate tibia development of TBCs in hypoxia-induced bone suppression that occurred during O₂ supplementation. Thus, O₂ supplementation may serve as a good applicant for promoting and meliorating bone development in juvenile high-altitude animals.

Intra-arterially infused carbon dioxide-saturated solution for sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model

The present study aimed to evaluate the efficacy of an intra-arterially infused carbon dioxide (CO2)-saturated solution in sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model. Forty VX2 liver tumor-bearing Japanese white rabbits were randomly divided into four groups and infused via the proper hepatic artery with a saline solution (control group), CO2-saturated solution (CO2 group), cisplatin solution (cisplatin group), or CO2-saturated solution and cisplatin solution (combined group). The tumor volume (TV) and the relative tumor volume (RTV), RTV = (TV on day 3 or 7)/(TV on day 0) x 100, were calculated using contrast-enhanced computed tomography. Hypoxia-inducible factor-1α (HIF‑1α) and carbonic anhydrase IX (CA IX) staining were used to evaluate cellular hypoxia. Cleaved caspase-3 and cleaved caspase-9 were analyzed to assess tumor apoptosis. The mean RTV on days 3 and 7 were 202.6±23.7 and 429.2±94.8%, respectively, in the control group; 172.2±38.1 and 376.5±61.1% in the CO2 group; 156.1±15.1 and 269.6±45.2% in the cisplatin group; and 118.3±28.1 and 210.3±55.1% in the combined group. RTV was significantly lower in the CO2 group than in the control group (day 3; P<0.05), and in the combined group than in the cisplatin group (days 3 and 7; P<0.05). HIF-1α and CA IX suppression, and increased cleaved caspase-3 and cleaved caspase-9 expression, were detected in the CO2 and combined groups, compared with the other two groups. An intra-arterially infused CO2-saturated solution inhibits liver VX2 tumor growth and sensitizes the anticancer effect of cisplatin.

KEMTUB012-NI2, a novel potent tubulysin analog that selectively targets hypoxic cancer cells and is potentiated by cytochrome p450 reductase downregulation

PURPOSE

There is an urgent need to develop effective therapies and treatment strategies to treat hypoxic tumors, which have a very poor prognosis and do not respond well to existing therapies.

METHODS

A novel hypoxia-targeting agent, KEMTUB012-NI2, was synthesized by conjugating a 2-nitroimidazole hypoxia-targeting moiety to a synthetic tubulysin, a very potent antimitotic. Its hypoxic selectivity and mode of action were studied in breast cancer cell lines.

RESULTS

KEMTUB012-NI2 exhibited a similar selectivity for hypoxic cells to that of tirapazamine, a well-established hypoxia-targeting agent, but was >1,000 times more potent in cell cytotoxicity assays. The hypoxia-targeting mechanism for both KEMTUB012-NI2 and tirapazamine was selective and mediated by one-electron reductases. However, while cytochrome p450 reductase (POR) downregulation could inhibit tirapazamine cytotoxicity, it actually sensitized hypoxic cells to KEMTUB012-NI2.

CONCLUSION

KEMTUB012-NI2 is a potent new agent that can selectively target hypoxic cancer cells. The hypoxia selectivity of KEMTUB012-NI2 and tirapazamine appears to be differentially activated by reductases. Since reductases are heterogeneously expressed in tumors, the different activation mechanisms will allow these agents to complement each other. Combining POR downregulation with KEMTUB012-NI2 treatment could be a new treatment strategy that maximizes efficacy toward hypoxic tumor cells while limiting systemic toxicity.

Hypoxia imaging and radiotherapy: bridging the resolution gap

Oxygen distribution is a major determinant of treatment success in radiotherapy, with well-oxygenated tumour regions responding by up to a factor of three relative to anoxic volumes. Conversely, tumour hypoxia is associated with treatment resistance and negative prognosis. Tumour oxygenation is highly heterogeneous and difficult to measure directly. The recent advent of functional hypoxia imaging modalities such as fluorine-18 fluoromisonidazole positron emission tomography have shown promise in non-invasively determining regions of low oxygen tension. This raises the prospect of selectively increasing dose to hypoxic subvolumes, a concept known as dose painting. Yet while this is a promising approach, oxygen-mediated radioresistance is inherently a multiscale problem, and there are still a number of substantial challenges that must be overcome if hypoxia dose painting is to be successfully implemented. Current imaging modalities are limited by the physics of such systems to have resolutions in the millimetre regime, whereas oxygen distribution varies over a micron scale, and treatment delivery is typically modulated on a centimetre scale. In this review, we examine the mechanistic basis and implications of the radiobiological oxygen effect, the factors influencing microscopic heterogeneity in tumour oxygenation and the consequent challenges in the interpretation of clinical hypoxia imaging (in particular fluorine-18 fluoromisonidazole positron emission tomography). We also discuss dose-painting approaches and outline challenges that must be addressed to improve this treatment paradigm.

Early and delayed evaluation of solid tumours with 64Cu-ATSM PET/CT: a pilot study on semiquantitative and computer-aided fractal geometry analysis

OBJECTIVE

The aim of this study was to analyse early and delayed acquisition on copper-64 diacetyl-bisN4-methylthiosemicarbazone (Cu-ATSM) PET/CT in a small cohort of patients by comparing semiquantitative and computer-aided fractal geometry analyses.

PATIENTS AND METHODS

Five cancer patients, including non-small-cell lung cancer and head and neck cancer, were investigated with Cu-ATSM PET/CT. Participants received an intravenous injection of Cu-ATSM according to body size and were imaged 60 min (early) and 16 h (delayed) later on hybrid PET/CT. Reconstructed images were visualized on advanced workstations for the definition of semiquantitative parameters: standardized uptake value (SUV)max, SUVratio-to-muscle, SUVmean, hypoxic volume (HV) and hypoxic burden (HB=HV×SUVmean). DICOM data retrieved from both scans were analysed using an ad-hoc computer program to determine the mean intensity value, SD, relative dispersion, three-dimensional histogram fractal dimension and three-dimensional fractal dimension.

RESULTS

All tumour lesions showed increased uptake of Cu-ATSM at early evaluation, with a median SUVratio-to-muscle of 4.42 (range: 1.58-5.62), a median SUVmax of 5.3 (range: 1.9-7.3), a median SUVmean of 2.8 (range: 1.5-3.9), a median HV of 41.6 cm (range: 2.8-453.7) and a median HB of 161.5 cm (range: 4.4-1112.5). All semiquantitative data obtained at 1 h were consistent with the parameters obtained on delayed imaging (P>0.05). A borderline statistically significant difference was found only for SUVmax of the muscle (P=0.045). Fractal geometry analysis on DICOM images showed that all parameters at early imaging showed no statistically significant difference with late acquisition (P>0.05).

CONCLUSION

Our findings support the consistency of Cu-ATSM PET/CT images obtained at early and delayed acquisition for the assessment of tumour lesions.

Visualization of exosome-mediated miR-210 transfer from hypoxic tumor cells

Cancer cells actively release exosomes carrying specific cellular components, such as proteins, mRNA, and miRNA, to communicate with various cells in the tumor microenvironment. We visualized exosome-mediated transfer of miR-210 from hypoxic breast cancer cells to neighboring cells using a miR-210 specific reporter system. By in vitro and in vivo visualization, we found that exosomes with miR-210 were transferred to cells in the tumor microenvironment and that miR-210 was involved in expression of vascular remodeling related genes, such as Ephrin A3 and PTP1B, to promote angiogenesis. These results indicate that cellular components, such as miRNAs from hypoxic cancer cells, spread to adjacent cancer cells in the tumor microenvironment via exosomes and influence tumor progression.

Recent development of luminescent rhenium(i) tricarbonyl polypyridine complexes as cellular imaging reagents, anticancer drugs, and antibacterial agents

This Perspective summarizes recent advances in the biological applications of luminescent rhenium(i) tricarbonyl polypyridine complexes.

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.

Development of a mathematical model to estimate intra-tumor oxygen concentrations through multi-parametric imaging

Background

Tumor hypoxia is involved in every stage of solid tumor development: formation, progression, metastasis, and apoptosis. Two types of hypoxia exist in tumors—chronic hypoxia and acute hypoxia. Recent studies indicate that the regional hypoxia kinetics is closely linked to metastasis and therapeutic responses, but regional hypoxia kinetics is hard to measure. We propose a novel approach to determine the local pO₂ by fusing the parameters obtained from in vivo functional imaging through the use of a modified multivariate Krogh model.

Methods

To test our idea and its potential to translate into an in vivo setting through the use of existing imaging techniques, simulation studies were performed comparing the local partial oxygen pressure (pO₂) from the proposed multivariate image fusion model to the referenced pO₂ derived by Green’s function, which considers the contribution from every vessel segment of an entire three-dimensional tumor vasculature to profile tumor oxygen with high spatial resolution.

Results

pO₂ derived from our fusion approach were close to the referenced pO₂ with regression slope near 1.0 and an r² higher than 0.8 if the voxel size (or the spatial resolution set by functional imaging modality) was less than 200 μm. The simulation also showed that the metabolic rate, blood perfusion, and hemoglobin concentration were dominant factors in tissue oxygenation. The impact of the measurement error of functional imaging to the pO₂ precision and accuracy was simulated. A Gaussian error function with FWHM equal to 20 % of blood perfusion or fractional vascular volume measurement contributed to average 7 % statistical error in pO₂.

Conclusion

The simulation results indicate that the fusion of multiple parametric maps through the biophysically derived mathematical models can monitor the intra-tumor spatial variations of hypoxia in tumors with existing imaging methods, and the potential to further investigate different forms of hypoxia, such as chronic and acute hypoxia, in response to cancer therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12938-016-0235-5) contains supplementary material, which is available to authorized users.

Synthesis and preclinical characterization of 1-(6'-deoxy-6'-[18F]fluoro-β-d-allofuranosyl)-2-nitroimidazole (β-6'-[18F]FAZAL) as a positron emission tomography radiotracer to assess tumor hypoxia

Positron emission tomography (PET) using fluorine-18 (¹⁸F)-labeled 2-nitroimidazole radiotracers has proven useful for assessment of tumor oxygenation. However, the passive diffusion-driven cellular uptake of currently available radiotracers results in slow kinetics and low tumor-to-background ratios. With the aim to develop a compound that is actively transported into cells, 1-(6'-deoxy-6'-[¹⁸F]fluoro-β-d-allofuranosyl)-2-nitroimidazole (β-[¹⁸F]1), a putative nucleoside transporter substrate, was synthetized by nucleophilic [¹⁸F]fluoride substitution of an acetyl protected labeling precursor with a tosylate leaving group (β-6) in a final radiochemical yield of 12±8% (n=10, based on [¹⁸F]fluoride starting activity) in a total synthesis time of 60min with a specific activity at end of synthesis of 218±58GBq/μmol (n=10). Both radiolabeling precursor β-6 and unlabeled reference compound β-1 were prepared in multistep syntheses starting from 1,2:5,6-di-O-isopropylidene-α-d-allofuranose. In vitro experiments demonstrated an interaction of β-1 with SLC29A1 and SLC28A1/2/3 nucleoside transporter as well as hypoxia specific retention of β-[¹⁸F]1 in tumor cell lines. In biodistribution studies in healthy mice β-[¹⁸F]1 showed homogenous tissue distribution and excellent metabolic stability, which was unaffected by tissue oxygenation. PET studies in tumor bearing mice showed tumor-to-muscle ratios of 2.13±0.22 (n=4) at 2h after administration of β-[¹⁸F]1. In ex vivo autoradiography experiments β-[¹⁸F]1 distribution closely matched staining with the hypoxia marker pimonidazole. In conclusion, β-[¹⁸F]1 shows potential as PET hypoxia radiotracer which merits further investigation.

Prognostic Evaluation of Disease Outcome in Solid Tumors Investigated With 64Cu-ATSM PET/CT

PURPOSE

Cu-ATSM is a very promising PET radiopharmaceutical for tumor imaging of hypoxia. One of the advantages of this compound compared with other hypoxia-avid tracers is the high tumor-to-background signal offered, which guaranties facilitated tumor delineation. This study analyzes optimal semiquantitative and quantitative parameters obtained by Cu-ATSM PET/CT in the same cohort of patients with special focus on their correlation to disease outcome.

PATIENTS AND METHODS

A prospective recruitment of 18 consecutive patients (M:F, 13:5; mean age, 60.7 years) with locally advanced non-small cell lung cancer (n = 7) or head and neck cancer (HNC) was performed. Each participant received 105 to 500 MBq of tracer according to body size and was scanned in a 3-dimensional mode PET/CT 60 minutes after tracer injection. PET images were reconstructed and visualized on a GE Advanced 4.6 workstation for the definition of semiquantitative and quantitative parameters: SUVmax, SUVratio-to-muscle, hypoxic tumor volume (HTV), and hypoxic burden (HB = HTV × SUVmean). These data were subsequently correlated to disease outcome, expressed in terms of progression-free survival calculated on a follow-up period with a median of 14.6 months.

RESULTS

All patients showed a moderately to highly increased uptake of Cu-ATSM in tumor lesions, with a mean SUVmax of 5.2 (range, 1.9-8.3) and mean SUVratio of 4.4 (range, 1.6-6.8). In addition, a broad range of HTV and HB was defined as mean values of 99.3 cm (range, 2.5-453.7 cm) and 301 (4.2-1134), respectively. Receiver operating characteristic analysis identified as reference cutoffs with respect to disease outcome with the following values: SUVmax >2.5 (AUC, 0.57; sensitivity, 88.9%; specificity, 50%), SUVratio ≤4.4 (AUC, 0.60; sensitivity, 50; specificity, 83.3%), HTV >160.7 cm (AUC, 0.61; sensitivity, 55.6%; specificity, 75%), and HB >160.7 (AUC, 0.67; sensitivity, 58.3%; specificity, 83.3%). In our cohort, HB showed a statistically significant difference in terms of mean values on the analysis of variance test with respect to disease progression (P = 0.04). On univariate analysis, Cox regression confirmed these findings and showed a significant correlation to progression-free survival for HB (P = 0.05) and HTV (P = 0.02).

CONCLUSIONS

In our cohort, the definition of optimal semiquantitative and quantitative parameters on Cu-ATSM PET/CT seems feasible and in line with previously published data. However, when considering the prognostic role with respect to disease outcome, the more robust parameters are represented by HTV and HB.