Impact of functional genomics and proteomics on radionuclide imaging

Reflections on the theory of "silver bullet" octreotide tracers: implications for ligand-receptor interactions in the age of peptides, heterodimers, receptor mosaics, truncated receptors, and multifractal analysis

The classical attitude of Nuclear Medicine practitioners on matters of peptide-receptor interactions has maintained an intrinsic monogamic character since many years. New advances in the field of biochemistry and even in clinical Nuclear Medicine have challenged this type of thinking, which prompted me to work on this review. The central issue of this paper will be the use of somatostatin analogs, i.e., octreotide, in clinical imaging procedures as well as in relation to neuroendocirne tumors. Newly described characteristics of G-protein coupled receptors such as the formation of receptor mosaics will be discussed. A small section will enumerate the regulatory processes found in the cell membrane. Possible new interpretations, other than tumor detection, based on imaging procedures with somatostatin analogs will be presented. The readers will be taken to situations such as inflammation, nociception, mechanosensing, chemosensing, fibrosis, taste, and vascularity where somatostatin is involved. Thyroid-associated orbitopathy will be used as a model for the development of multi-agent therapeutics. The final graphical summary depicts the multifactorial properties of ligand binding.

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.

Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)

Emission tomography provides three-dimensional, quantitative images of the distribution of radiotracers used to mark physiological, metabolic, or pathological processes. Quantitative single photon emission computed tomography (SPECT) requires correction for the image-degrading effects due to photon attenuation and scatter. Phantom experiments have shown that radioactive concentrations can be assessed within some percentage of the true value when relevant corrections are applied. SPECT is widely spread, and radiotracers are available that are easy to use and comparably inexpensive. Compared with other methods, SPECT suffers from a lower spatial resolution, and the time required for image acquisition is longer than for some alternative methods. In contrast to some other methods, SPECT allows simultaneous imaging of more than one process, e.g., both regional blood flow and ventilation, for the whole lung. SPECT has been used to explore the influence of posture and clinical interventions on the spatial distribution of lung blood flow and ventilation. Lung blood flow is typically imaged using macroaggregates of albumin. Both radioactive gases and particulate aerosols labeled with radioactivity have been used for imaging of regional ventilation. However, all radiotracers are not equally suited for quantitative measurements; all have specific advantages and limitations. With SPECT, both blood flow and ventilation can be marked with radiotracers that remain fixed in the lung tissue, which allows tracer administration during conditions different from those at image registration. All SPECT methods have specific features that result from the used radiotracer, the manner in which it is administered, and how images are registered and analyzed.

Gene therapy imaging in patients for oncological applications

Thus far, traditional methods for evaluating gene transfer and expression have been shown to be of limited value in the clinical arena. Consequently there is a real need to develop new methods that could be repeatedly and safely performed in patients for such purposes. Molecular imaging techniques for gene expression monitoring have been developed and successfully used in animal models, but their sensitivity and reproducibility need to be tested and validated in human studies. In this review, we present the current status of gene therapy-based anticancer strategies and show how molecular imaging, and more specifically radionuclide-based approaches, can be used in gene therapy procedures for oncological applications in humans. The basis of gene expression imaging is described and specific uses of these non-invasive procedures for gene therapy monitoring illustrated. Molecular imaging of transgene expression in humans and evaluation of response to gene-based therapeutic procedures are considered. The advantages of molecular imaging for whole-body monitoring of transgene expression as a way to permit measurement of important parameters in both target and non-target organs are also analyzed. The relevance of this technology for evaluation of the necessary vector dose and how it can be used to improve vector design are also examined. Finally, the advantages of designing a gene therapy-based clinical trial with imaging fully integrated from the very beginning are discussed and future perspectives for the development of these applications outlined.

'Omics'-based imaging in cancer detection and therapy

Genomics, proteomics and metabolomics, which can be also summarized as 'omics', have become increasingly inter-related with imaging. Gene expression profiling may be assessed using high-density microarrays for the detection of overexpression patterns, followed by the development of histochemical assays. Next, antibodies to the gene-corresponding proteins (for example, receptors) can be produced, leading to serum immunoassays for follow-up, as well as antibody-guided in vivo imaging or therapy. In vivo imaging for cancer detection and/or therapy can be performed by applying nonlabeled antibodies, by using radiolabeled antibodies for detection using single-photon tomography or positron emission tomography (PET), or by other tracers, for example, for magnetic resonance imaging tomography (MRI, MRT). Protein profiles from protein chips can be derived from mass maps obtained through mass spectrometry (MS). Electrophoretic separation of proteins has also been combined with MS to produce a two-dimensional assignment of proteins within a complex mixture. Overexpression of tumor-related proteins can be used for the development of antibodies to develop noninvasive assays that can be used in the screening of risk groups as a basis for further investigation by invasive imaging methods. Metabolomic profiling by nuclear magnetic resonance spectroscopy can be applied for the detection of biomarkers of the metabolome. Metabolite profiles in cells, tissues, and organisms can be generated with nuclear magnetic resonance spectroscopy and MS. Metabolic information provided by magnetic resonance spectroscopic imaging (MRSI) combined with the anatomical information provided by MRI can significantly improve the assessment of cancer location and extent, and cancer aggressiveness. Biomarkers found by MRSI can lead to new PET tracers. This article provides examples and discusses some of the recent achievements to bring forward novel strategies for the diagnosis and therapy of cancer.

PET in abdominal pathology: advantages and limitations

New oncologic procedures are currently more focused on the biological features of tumors. The ideal objective is the administration of personalized effective treatments for each patient that affects not just the location and spread of disease but also special metabolic characteristics of tumoral cells. Radiologic diagnostic methods are extremely important in the management of the patient for staging, restaging, and evaluation of treatment response, and clinicians are avid for some additional functional and metabolic information. Further, they need more dynamic methods for follow-up. Nuclear Medicine and positron emission tomography (PET) in many cases can meet this requirement, although it is not perfect, at least at the present time. Currently 2-((18)F)fluoro-2-desoxi-D: -glucose positron emission tomography is being widely used for oncologic purposes. Its information can be very useful in abdominal diseases and must be taken into account with the results of radiologic imaging. Thus, many changes in the choice of treatment are seen. However, it is very important to know that sometimes there is a lack of specificity that has to be considered.