Recent advances in imaging endogenous or transferred gene expression utilizing radionuclide technologies in living subjects: applications to breast cancer

STAT6 - polymorphisms, haplotypes and epistasis in relation to atopy and asthma

BACKGROUND

STAT6 has an important role in the IL-4 / IL-13 signalling pathway. Genome - wide association studies have shown that particular polymorphism (SNP) or haplotype variants of STAT6 as well as epigenetic gene modifications are associated with IgE level and asthma in childhood.

METHODS

A review of the available literature was performed to map out the function and signalling pathway of STAT6, studies of STAT6 SNPs association with susceptibility to asthma and atopy, covering the years 1997 - 2012 were summarized, and the value of epigenetic and epistatic influences on STAT6 and their relevance to the development of the studied phenotype (atopy or asthma) were determined.

RESULTS

There are 2 SNPs (rs71802646 and rs320411) with clinical association and proven functional effect on STAT6 expression. The effect of STAT6 SNPs cumulates in haplotypes and more potently during interaction with SNPs in the genes from the signalling pathway (IL4, IL4Ra, and IL13). Expression of STAT6 is also influenced by DNA methylation. Atopy is traditionally believed to be maternally inherited but there is one report about paternally overtransmitted STAT6 haplotype (TCA haplotype, built from rs324011, rs3024974 and rs4559 SNPs).

CONCLUSIONS

STAT6 polymorphisms and their combinations have an important influence on IgE level and development of asthma. However, the interaction between SNPs in the IL-4 / IL-13 signalling pathway is of greater impact. Hypermethylation of the STAT6 promoter is also significant in the regulation of STAT6 expression and this fact opens possibilities for targeting therapy in asthma.

Radiotracer breast cancer imaging: Beyond FDG and MIBI

Radiotracer imaging with MIBI and FDG have shown the benefit of the functional imaging of breast cancer. Newer radiopharmaceuticals targeted to particular aspects of breast cancer biology will likely play an important role in directing more specific and individualized breast cancer treatment. Future studies will need to test the ability of SPECT and PET imaging to detect breast cancer, but also to assess target expression, identify resistance factors, and measure early response to treatment. This will require protocols designed to test the predictive capability of imaging in the setting of a therapy trial, a new paradigm for breast cancer imaging, for which radiotracer imaging is ideally suited.

Image-guided nanosystems for targeted delivery in cancer therapy

Current challenges in early detection, limitations of conventional treatment options, and the constant evolution of cancer cells with metastatic and multi-drug resistant phenotypes require novel strategies to effectively combat this deadly disease. Nanomedical technologies are evolving at a rapid pace and are poised to play a vital role in diagnostic and therapeutic interventions - the so-called "theranostics" - with potential to advance personalized medicine. In this regard, nanoparticulate delivery systems can be designed with tumor seeking characteristics by utilizing the inherent abnormalities and leaky vasculature of solid tumors or custom engineered with targeting ligands for more specific tumor drug targeting. In this review we discuss some of the recent advances made in the development of multifunctional polymeric nanosystems with an emphasis on image-guided drug and gene delivery. Multifunctional nanosystems incorporate variety of payloads (anticancer drugs and genes), imaging agents (optical probes, radio-ligands, and contrast agents), and targeting ligands (antibodies and peptides) for multi-pronged cancer intervention with potential to report therapeutic outcomes. Through advances in combinatorial polymer synthesis and high-throughput testing methods, rapid progress in novel optical/radiolabeling strategies, and the technological breakthroughs in instrumentation, such as hybrid molecular and functional imaging systems, there is tremendous future potential in clinical utility of theranostic nanosystems.

Radiolabeled oligonucleotides for antisense imaging

Oligonucleotides radiolabeled with isotopes emitting γ-rays (for SPECT imaging) or positrons (for PET imaging) can be useful for targeting messenger RNA (mRNA) thereby serving as non-invasive imaging tools for detection of gene expression in vivo (antisense imaging). Radiolabeled oligonucleotides may also be used for monitoring their in vivo fate, thereby helping us better understand the barriers to its delivery for antisense targeting. These developments have led to a new area of molecular imaging and targeting, utilizing radiolabeled antisense oligonucleotides. However, the success of antisense imaging relies heavily on overcoming the barriers for its targeted delivery in vivo. Furthermore, the low ability of the radiolabeled antisense oligonucleotide to subsequently internalize into the cell and hybridize with its target mRNA poses additional challenges in realizing its potentials. This review covers the advances in the antisense imaging probe development for PET and SPECT, with an emphasis on radiolabeling strategies, stability, delivery and in vivo targeting.

Breast imaging: A survey

Breast cancer is the second leading cause of death in women. It occurs when cells in the breast start to grow out of proportion and invade neighboring tissues or spread throughout the body. Mammography is one of the most effective and popular modalities presently used for breast cancer screening and detection. Efforts have been made to improve the accuracy of breast cancer diagnosis using different imaging modalities. Ultrasound and magnetic resonance imaging have been used to detect breast cancers in high risk patients. Recently, electrical impedance imaging and nuclear medicine techniques are also being widely used for breast cancer screening and diagnosis. In this paper, we discuss the capabilities of various breast imaging modalities.

Use of radionuclides in cancer research and treatment

Cancer occurs as a result of misregulation of cell growth, which appears to be a consequence of alteration in the function of oncogenes and tumour suppressor genes. Ionising radiation has been used, since the discovery of X-rays in 1896 by Roentgen, both in cancer research and treatment of the disease. The main purpose of cancer research is to understand the molecular alterations involved in the development and progression of the disease in order to improve diagnosis and develop personalised therapies, by focusing on the features of the tumoral cell and the biological events associated to carcinogenesis. Radioisotopic techniques have been used routinely for in vitro research in the molecular and cellular biology of cancer for more than 20 years and are in the process of being substituted by alternative non-radioactive techniques. However in vivo techniques such as irradiation of cells in culture and/or experimental animal models and radioactive labelling are in development, due in part to advances in molecular imaging technologies. The objective of this review is to analyse in an integrative way the applications of ionising radiation in cancer research and therapy. It had been divided into two parts. The first one will approach the techniques applied to cancer research and the second will summarise how ionising radiation is applied to the treatment of neoplastic disease.

Molecular imaging as a tool for translating breast cancer science

The ability to measure biochemical and molecular processes underlies progress in breast cancer biology and treatment. These assays have traditionally been performed by analysis of cell culture or tissue samples. More recently, functional and molecular imaging has allowed the in vivo assay of biochemistry and molecular biology, which is highly complementary to tissue-based assays. This review briefly describes different imaging modalities used in molecular imaging and then reviews applications of molecular imaging to breast cancer, with a focus on translational work. It includes sections describing work in functional and physiological tumor imaging, imaging gene product expression, imaging the tumor microenvironment, reporter gene imaging, and cell labeling. Work in both animal models and human is discussed with an eye towards studies that have relevance to breast cancer treatment in patients.

Human breast tumor cells express multimodal imaging reporter genes

OBJECTIVE

Human ZR75-1 cells were among the first few characterized estrogen-dependent mammary gland carcinoma cell lines and had been utilized in various studies for the pro- or antitumor effect of xenoestrogens and antiestrogens. The objective of this study was to establish a breast tumor model in ZR75-1 cells bearing multimodal reporter genes to allow noninvasive imaging of tumor growth using fluorescence and nuclear imaging platforms.

METHODS AND RESULTS

Enhanced green fluorescent protein (eGFP) cDNA was fused at the C-terminus with herpes simplex virus type 1 thymidine kinase (HSV1-tk) to form the fusion reporter gene (eGFP-tk). In vitro proliferation, migration, and invasion assays revealed that eGFP-tk-transfected ZR75-1 cells exhibited decreased proliferation rate, migratory activity, and invasion ability compared to the wild-type cells. The functional HSV1-tk enzymatic activity in stably transfected cells were confirmed by in vitro ganciclovir (GCV) sensitivity and [123I]2-fluoro-2-deoxy-1-beta-D-arabinofuranosyl-5-iodouracil (FIAU) accumulation assays. In vivo fluorescence and nuclear imaging were performed on nude mice bearing multiple subcutaneous xenografts established from ZR75-1-eGFP-tk and wild-type cells. Optical imaging was able to detect the green fluorescence of eGFP-tk tumor. The eGFP-tk reporter gene-specific imaging was achieved by single photon emission computed tomography (SPECT) using [123I]FIAU as a radiotracer and demonstrated decreased FIAU uptake in eGFP-tk tumor by GCV treatment. Probably due to a flare reaction after GCV treatment, micro-positron emission tomography (micro-PET) imaging using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) could not demonstrate decreases in FDG uptake. However, in vitro metabolic assay also revealed that eGFP-tk cells transiently increased [3H]-deoxyglucose uptake in response to GCV treatment.

CONCLUSIONS

This study confirmed the usefulness of eGFP-tk in many applications by providing, in vitro and in vivo, the sensitive and reporter gene-specific imaging. ZR75-1-eGFP-tk cells that are ready to incorporate in various imaging platforms constitute a useful model in breast cancer research.

Molecular imaging: reporter gene imaging

Non-invasive in-vivo molecular genetic imaging developed over the past decade and predominantly utilises radiotracer (PET, gamma camera, autoradiography), magnetic resonance and optical imaging technology. Molecular genetic imaging has its roots in both molecular biology and cell biology. The convergence of these disciplines and imaging modalities has provided the opportunity to address new research questions, including oncogenesis, tumour maintenance and progression, as well as responses to molecular-targeted therapy. Three different imaging strategies are described: (1) "bio-marker" or "surrogate" imaging; (2) "direct" imaging of specific molecules and pathway activity; (3) "indirect" reporter gene imaging. Examples of each imaging strategy are presented and discussed. Several applications of PET- and optical-based reporter imaging are demonstrated, including signal transduction pathway monitoring, oncogenesis in genetic mouse models, endogenous molecular genetic/biological processes and the response to therapy in animal models of human disease. Molecular imaging studies will compliment established ex-vivo molecular-biological assays that require tissue sampling by providing a spatial and a temporal dimension to our understanding of disease development and progression, as well as response to treatment. Although molecular imaging studies are currently being performed primarily in experimental animals, we optimistically expect they will be translated to human subjects with cancer and other diseases in the near future.

Breast Cancer Treatment in the Era of Molecular Imaging

Molecular imaging employs molecularly targeted probes to visualize and often quantify distinct disease-specific markers and pathways. Modalities like intravital confocal or multiphoton microscopy, near-infrared fluorescence combined with endoscopy, surface reflectance imaging, or fluorescence-mediated tomography, and radionuclide imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are increasingly used for small animal high-throughput screening, drug development and testing, and monitoring gene therapy experiments. In the clinical treatment of breast cancer, PET and SPECT as well as magnetic resonance-based molecular imaging are already established for the staging of distant disease and intrathoracic nodal status, for patient selection regarding receptor-directed treatments, and to gain early information about treatment efficacy. In the near future, reporter gene imaging during gene therapy and further spatial and qualitative characterization of the disease can become clinically possible with radionuclide and optical methods. Ultimately, it may be expected that every level of breast cancer treatment will be affected by molecular imaging, including screening.

[Molecular imaging with new PET tracers]

In the recent years, positron emission tomography (PET) has gained more and more importance, especially in oncology for primary staging, as well as for response evaluation. The glucose analogon (18)F-FDG is the most widely used tracer up to now. In this paper, we review the applications of newly developed, more specific PET tracers. These tracers allow for imaging of a variety of biological processes, such as hypoxia and proliferation. The expression of different receptors can be visualized, like the somatostatin receptor 2 and the integrin alphavbeta3. Moreover, gene expression can be imaged as well. While most of these approaches are currently in the first phases of clinical evaluation, imaging of hypoxia and proliferation might be integrated into the daily routine in the near future.

Tumor-specific positron emission tomography imaging in patients: [18F] fluorodeoxyglucose and beyond

Biochemical and molecular imaging of cancer using positron emission tomography (PET) plays an increasing role in the care of cancer patients. Most clinical work to date uses the glucose analogue [(18)F]fluorodeoxyglucose (FDG) to detect accelerated and aberrant glycolysis present in most tumors. Although clinical FDG PET has been used largely to detect and localize cancer, more detailed studies have yielded biological insights and showed the utility of FDG as a prognostic marker and as a tool for therapeutic response evaluation. As cancer therapy becomes more targeted and individualized, it is likely that PET radiopharmaceuticals other than FDG, aimed at more specific aspects of cancer biology, will also play a role in guiding cancer therapy. Clinical trials designed to test and validate new PET agents will need to incorporate rigorous quantitative image analysis and adapt to the evolving use of imaging as a biomarker and will need to incorporate cancer outcomes, such as survival into study design.

Non-invasive in vivo optical imaging of the lacZ and luc gene expression in mice

The bacterial lacZ gene encoding for beta-galactosidase (beta-gal) is a common reporter gene used in transgenic mice. Nonetheless, the absence of fluorigenic substrates usable in live animals greatly hampered the non-invasive follow-up of this reporter gene expression. We used far-red fluorescence for imaging beta-Gal expression in live cells in vitro or in vivo. The 9H-(1,3-dichloro-9,9-dimethylacridin- 2-one-7-yl) beta-D-galactopyranoside substrate was used to monitor beta-Gal expression as a reporter of tumor growth, or of the physiological levels of an endogenous gene or of gene transfer in lung. A quantitative evaluation of this method as well as a comparison of its sensitivity with Firefly Luciferase-based bioluminescence was also performed. In vivo measurements showed that 10(3) beta-Gal tumor cells located under the skin were detectable. In deeper organs like lung, as little as 5 ng of beta-Gal or Luciferase enzymes per mg of proteins were measured, confirming that both techniques reached similar sensibilities. Nonetheless, quantitative comparison of beta-Gal levels measured with far-red imaging or with a standardized enzymatic evaluation after killing revealed that the 2D-fluorescent reflectance imaging method is submitted to a color-dependent disparity of the organs and cannot supply quantitative measurements but that a simple correction can be applied.

Current and future use of positron emission tomography (PET) in breast cancer

Positron emission tomography (PET) is a radiotracer imaging method that is increasingly used in both the clinical care of breast cancer patients and in translational breast cancer research. This review emphasizes current and future clinical applications of PET to breast cancer, and highlights some translational research using PET to elucidate the clinical biology of breast cancer. PET principles are reviewed, followed by a review of current applications of (18)F-fluorodeoxyglucose (FDG) to clinical breast cancer care. Finally we review work done with other radiopharmaceuticals beyond FDG designed to image a number of aspects of breast cancer biology, emphasizing those most likely to enter clinical trials in the near future.

Small animal positron emission tomography in food sciences

Positron emission tomography (PET) is a 3-dimensional imaging technique that has undergone tremendous developments during the last decade. Non-invasive tracing of molecular pathways in vivo is the key capability of PET. It has become an important tool in the diagnosis of human diseases as well as in biomedical and pharmaceutical research. In contrast to other imaging modalities, radiotracer concentrations can be determined quantitatively. By application of appropriate tracer kinetic models, the rate constants of numerous different biological processes can be determined. Rapid progress in PET radiochemistry has significantly increased the number of biologically important molecules labelled with PET nuclides to target a broader range of physiologic, metabolic, and molecular pathways. Progress in PET physics and technology strongly contributed to better scanners and image processing. In this context, dedicated high resolution scanners for dynamic PET studies in small laboratory animals are now available. These developments represent the driving force for the expansion of PET methodology into new areas of life sciences including food sciences. Small animal PET has a high potential to depict physiologic processes like absorption, distribution, metabolism, elimination and interactions of biologically significant substances, including nutrients, 'nutriceuticals', functional food ingredients, and foodborne toxicants. Based on present data, potential applications of small animal PET in food sciences are discussed.

Weaving single photon imaging into new drug development

The specific aim of this review is to assess the potential contribution of single photon emitting radiopharmaceutical technologies to new drug development. For each phase of therapeutic drug development, published literature was sought that shows single photon emitters can add value by quantifying pharmacokinetics, visualizing mechanisms of drug action, estimating therapeutic safety indices, or measuring dose-dependent pharmacodynamic effects. Not any published reports were found that describe using nuclear medicine techniques to help manage the progress of a new drug development program. As a consequence, most of the case in favor of weaving single photon imaging into the process had to be built on extrapolations from studies that showed feasibility post hoc. The strongest evidence of potential value was found for drug candidates that hope to influence diseases characterized by cell proliferation or cell death, particularly in the fields of oncology, cardiology, nephrology, and inflammation. Receptor occupancy studies were observed to occasionally offer unique advantages over analogous studies with positron emission tomography (PET). Enough hard data sets were found to justify the costs of using single photon imaging in a variety of new drug development paradigms.

Evolving role of positron emission tomography in breast cancer imaging

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) has been used for detection, staging, and response monitoring in breast cancer patients. Although studies have proven its accuracy in detection of the primary tumor and axillary staging, its most important current clinical application is in detection and defining the extent of recurrent or metastatic breast cancer and for monitoring response to therapy. PET is complementary to conventional methods of staging in that it provides better sensitivity in detecting nodal and lytic bone metastases; however, it should not be considered a substitute for conventional staging studies, including computed tomography and bone scintigraphy. FDG uptake in the primary tumor carries prognostic information, but the underlying biochemical mechanisms responsible for enhanced glucose metabolism have not been completely elucidated. Future work using other PET tracers besides FDG will undoubtedly help our understanding of tumor biology and help tailor therapy to individual patient by improving our ability to quantify the therapeutic target, identify drug resistance factors, and measure and predict early response.

Molecular imaging in breast cancer

Since the 1960s, bone scanning has played a major role in the management of breast cancer. In the last decade, however, the role of radionuclide molecular imaging has expanded significantly in the clinical management of breast cancer because of fluorodeoxyglucose positron emission tomography, mammoscintigraphy, and sentinel lymph node techniques. Molecular imaging also is instrumental in drug development,gene therapy, and in basic science research of breast cancer. This article provides a comprehensive review of the role of molecular imaging of breast cancer in clinical practice and reports on the current state of research in this field.

In vivo imaging of beta-galactosidase activity using far red fluorescent switch

beta-Galactosidase (beta-gal) has been widely used as a transgene reporter enzyme, and several substrates are available for its in vitro detection. The ability to image beta-gal expression in living animals would further extend the use of this reporter. Here we show that DDAOG, a conjugate of beta-galactoside and 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) (DDAO), is not only a chromogenic beta-gal substrate but that the cleavage product has far-red fluorescence properties detectable by imaging. Importantly, the cleavage substrate shows a 50-nm red shift, enabling its specific detection in a background of intact probe, a highly desirable feature for in vivo imaging. Specifically, we show that beta-gal-expressing 9L gliomas are readily detectable by red fluorescence imaging in comparison with the native 9L gliomas. We furthermore show that herpes simplex virus amplicon-mediated LacZ gene transfer into tumors can be transiently and thus serially visualized over time. The results indicated that in vivo real-time detection of beta-gal activity is possible by fluorescence imaging technology.

Positron emission tomography in diagnosis and management of invasive breast cancer: current status and future perspectives

[18F]fluorodeoxyglucose positron emission tomography (FDG-PET) is a metabolic imaging modality that has increasing applications in oncology, neurology, and cardiology. Among the oncology applications, breast cancer is one of the most extensively studied diseases. FDG-PET has been performed for diagnosis, staging, and restaging of invasive breast cancer and for monitoring responsiveness to therapies. At the present time, the results of FDG-PET in detection of primary breast cancer and axillary staging are mixed and inconclusive. However, results demonstrating the superiority of FDG-PET over anatomic imaging modalities in detection of distant metastasis, recurrence, and monitoring therapies are relatively well documented. These applications have been accepted by medical professionals and the public, as evidenced by a recent decision by the Centers for Medicare and Medicaid Services (formerly Health Care Financing Agency) to provide coverage for the procedure. Future trends in this exciting area include development of novel breast cancer-specific PET radiopharmaceuticals and use of dedicated breast PET technologies for scans of breast/axillary lesions. PET/computed tomography technology, which combines anatomic and molecular/biochemical information, is also rapidly proliferating and should help to further improve the management of patients with breast cancer. The role of FDG-PET in breast cancer is increasing and evolving, and this metabolic imaging modality, in conjunction with newer tracers and other anatomic imaging methods, should improve diagnosis and management of patients with breast cancer

Radiotracers for positron emission tomography imaging

Over the past 30 years, advances in radiotracer chemistry and positron emission tomography instrumentation have merged to make positron emission tomography a powerful scientific tool in the biomedical sciences. However, despite the increasing reliance of the biomedical sciences on imaging and the new needs for functional information created by the sequencing of the human genome, the development of new radiotracers with the specificity and kinetic characteristics for quantitative analysis in vivo remains a slow process. In this article, we focus on advances in the development of the radiotracers involved in neurotransmission, amino acid transport, protein synthesis, and DNA synthesis. We conclude with a brief section on newer radiotracers that image other molecular targets and conclude with a summary of some of the scientific and infrastructure needs that would expedite the development and introduction of new radiotracers into biomedical research and the practice of medicine.

In vivo imaging of gene and cell therapies

Molecular imaging can be broadly defined as the in vivo characterization and measurement of biological processes at the cellular and molecular level. In contrast to commonly used clinical imaging, it sets forth to probe the molecular abnormalities that are the basis of disease, rather than imaging the end effects of these molecular alterations. Development of new imaging technologies requires a multidisciplinary collaboration between biologists, chemists, physicists, and imaging scientists to create novel agents, signal amplification strategies, and imaging techniques that successfully address these questions. In this article we attempt to present some of the recent developments and show how molecular imaging can be used, at least experimentally, to assess specific molecular targets for gene- and cell-based therapies. In particular, we place emphasis on the development and use of experimental small-animal models, which are particularly inclined toward this approach, primarily in combination with magnetic resonance (MR), radionuclide, and optical imaging. In the future, specific imaging of disease targets will allow earlier detection and characterization of disease, as well as earlier and direct molecular assessment of treatment efficacy.