Luminescent nanoparticles and their applications in the life sciences

Nanoparticles have recently emerged as an important group of materials used in numerous disciplines within the life sciences, ranging from basic biophysical research to clinical therapeutics. Luminescent nanoparticles make excellent optical bioprobes significantly extending the capabilities of alternative fluorophores such as organic dyes and genetically engineered fluorescent proteins. Their advantages include excellent photostability, tunable and narrow spectra, controllable size, resilience to environmental conditions such as pH and temperature, combined with a large surface for anchoring targeting biomolecules. Some types of nanoparticles provide enhanced detection contrast due to their long emission lifetime and/or luminescence wavelength blue-shift (anti-Stokes) due to energy upconversion. This topical review focuses on four key types of luminescent nanoparticles whose emission is governed by different photophysics. We discuss the origin and characteristics of optical absorption and emission in these nanoparticles and give a brief account of synthesis and surface modification procedures. We also introduce some of their applications with opportunities for further development, which could be appreciated by the physics-trained readership.

Fluorescence correlation spectroscopy: past, present, future

In recent years fluorescence correlation spectroscopy (FCS) has become a routine method for determining diffusion coefficients, chemical rate constants, molecular concentrations, fluorescence brightness, triplet state lifetimes, and other molecular parameters. FCS measures the spatial and temporal correlation of individual molecules with themselves and so provides a bridge between classical ensemble and contemporary single-molecule measurements. It also provides information on concentration and molecular number fluctuations for nonlinear reaction systems that complement single-molecule measurements. Typically implemented on a fluorescence microscope, FCS samples femtoliter volumes and so is especially useful for characterizing small dynamic systems such as biological cells. In addition to its practical utility, however, FCS provides a window on mesoscopic systems in which fluctuations from steady states not only provide the basis for the measurement but also can have important consequences for the behavior and evolution of the system. For example, a new and potentially interesting field for FCS studies could be the study of nonequilibrium steady states, especially in living cells.

Bringing chemistry to life

Bioorthogonal chemistry allows a wide variety of biomolecules to be specifically labeled and probed in living cells and whole organisms. Here we discuss the history of bioorthogonal reactions and some of the most interesting and important advances in the field.

In situ ligation: a decade and a half of experience

The in situ ligation (ISL) methodology detects apoptotic cells by the presence of characteristic DNA double-strand breaks. A labeled double-stranded probe is ligated to the double-strand breaks in situ on tissue sections. Like the popular TUNEL assay, ISL detects cells in apoptosis based on the ongoing destruction of DNA by apoptotic nucleases. In comparison to TUNEL, it is more specific for apoptosis versus other causes of DNA damage, both repairable damage and necrosis. In the decade and a half since its introduction, ISL has been used in several hundred publications. Here we review the development of the method, its current status, and its uses and limitations.

FRET for lab-on-a-chip devices - current trends and future prospects

This review focuses on the use of Förster Resonance Energy Transfer (FRET) to monitor intra- and intermolecular reactions occurring in microfluidic reactors. Microfluidic devices have recently been used for performing highly efficient and miniaturised biological assays for the analysis of biological entities such as cells, proteins and nucleic acids. Microfluidic assays are characterised by nanolitre to femtolitre reaction volumes, which necessitates the adoption of a sensitive optical detection scheme. FRET serves as a strong 'spectroscopic ruler' for elucidating the tertiary structure of biomolecules, as the efficiency of the non-radiative energy transfer is extremely sensitive to nanoscale changes in the separation between donor and acceptor markers attached to the biomolecule of interest. In this review, we will review the implementation of various microfluidic assays which employ FRET for diverse applications in the biomedical field, along with the advantages and disadvantages of the various approaches. The future prospects for development of microfluidic devices incorporating FRET detection will be discussed.

The future of medical imaging

The organisers of this conference have kindly provided me with the forum to look forward and examine the future of medical imaging. My view of the future is informed by my own research directions; thus, I illustrate my vision of the future with results from my own research, and from the research that has motivated me over the last few years. As such, the results presented are specific to the field of breast imaging; however, I believe that the trends presented have general applicability, and hope that this discourse will motivate new research. My vision of the future can be summarised in accordance with three broad trends: (1) increased prevalence of low-dose tomographic X-ray imaging; (2) continuing advances in functional and molecular X-ray imaging; and (3) novel image-based biomarker discovery.

Advances in radionuclide molecular imaging in myocardial biology

Molecular imaging is a new and evolving field that employs a targeted approach to noninvasively assess biologic processes in vivo. By assessing key elements in specific cellular processes prior to irreversible end-organ damage, molecular tools will allow for earlier detection and intervention, improving management and outcomes associated with cardiovascular diseases. The goal of those working to expand this field is not just to provide diagnostic and prognostic information, but rather to guide an individual's pharmacological, cell-based, or genetic therapeutic regimen. This article will review molecular imaging tools in the context of our current understanding of biological processes of the myocardium, including angiogenesis, ventricular remodeling, inflammation, and apoptosis. The focus will be on radiotracer-based molecular imaging modalities with an emphasis on clinical application. Though this field is still in its infancy and may not be fully ready for widespread use, molecular imaging of myocardial biology has begun to show promise of clinical utility in acute and chronic ischemia, acute myocardial infarction, congestive heart failure, as well as in more global inflammatory and immune-mediated responses in the heart-like myocarditis and allogeneic cardiac transplant rejection. With continued research and development, molecular imaging promises to be an important tool for the optimization of cardiovascular care.

Current advancement in radiation therapy for uterine cervical cancer

Radiation therapy is one of the effective curative treatments for uterine cervical cancer. However poor clinical results for the advanced stages require further improvement of the treatment. Intensive studies on basic and clinical research have been made to improve local control, primarily important for long term survival in radiation therapy. Regarding current advancement in radiation therapy for uterine cervical cancer, the following three major subjects are pointed out; technological development to improve dose distribution by image guided radiation therapy technology, the concomitant anticancer chemotherapy with combination of radiation therapy, and radiation biological assessment of the radiation resistance of tumors. The biological factors overviewed in this article include hypoxia relating factors of HIF-1alpha, SOD, cell cycle parameters of pMI, proliferation factors of Ki67, EGFR, cerbB2, COX-2, cycle regulation proteins p53, p21, apoptosis regulation proteins Bcl2 and Bax and so on. Especially, the variety of these radiation biological factors is important for the selection of an effective treatment method for each patient to maximize the treatment benefit.

Optical molecular imaging in atherosclerosis

Current imaging techniques focus on evaluating the anatomical structure of blood vessel wall and atherosclerotic plaque. These techniques fail to evaluate the biological processes which take place in the vessel wall and inside the plaque. Novel imaging techniques like optical imaging can evaluate the biological and cellular processes inside the plaque and provide information which can be vital for better patient risk stratification. This review highlights the various optical imaging techniques and their application in assessing biological processes in atherosclerosis.

[Diagnosis and therapy monitoring applying methods of molecular medicine]

New experimental approaches are presented which are implemented in rheumatology research. DNA microarray technology and proteome analysis are two new methods which are applied to gain a global survey over the gene expression at the RNA and protein level under various conditions. Based on these methods of molecular medicine important functional proteins in the pathogenesis of rheumatoid arthritis (RA) as well as clinical relevant genetic polymorphisms shall be identified. New insights are expected which will help in the differentiation of clinical entities and in the search for new therapeutic strategies in the treatment of RA.

A crowdsourcing evaluation of the NIH chemical probes

Between 2004 and 2008, the US National Institutes of Health Molecular Libraries and Imaging initiative pilot phase funded 10 high-throughput screening centers, resulting in the deposition of 691 assays into PubChem and the nomination of 64 chemical probes. We crowdsourced the Molecular Libraries and Imaging initiative output to 11 experts, who expressed medium or high levels of confidence in 48 of these 64 probes.

Nuclear imaging of cancer cell therapies

A promising role of cellular therapies in cancer treatment is reflected by the constantly growing number of clinical trials with adoptively transferred cells. Direct and indirect cell labeling for the nuclear imaging of transferred cells has been proven reliable for imaging adoptive cellular therapies. Both methods show their advantages and limitations. Direct labeling is a relatively easy, inexpensive, and well-established methodology. Indirect labeling using a reporter gene imaging paradigm allows for reliable, stable, and harmless visualization of cellular trafficking, persistence, proliferation, and function at the target site. It is expected that new human-derived reporter genes will be rapidly translated into clinical applications that require repetitive imaging for the effective monitoring of various genetic and cellular therapies.

Can gallium-68 compounds partly replace (18)F-FDG in PET molecular imaging?

The development of gallium-68 -1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid ((68)Ga-DOTA) compounds was made possible due to the chemistry of (68)Ga, which matches the pharmacokinetics of many peptides, specially the chelators DOTA and DOTAderivatives with the formation of stable (68)Ga (3+) complexes. The availability of this tracer from a germanium-68-gallium-68 generator with a relatively long half-life makes it attractive to use in busy nuclear medicine departments, particularly those with limited access to cyclotrons. The recent clinical experience with (68)Ga-peptides includes imaging neuroendocrine tumours particularly carcinoid, as well as neuroectodermal tumours such as phaeochromocytoma and paraganglioma. In vitro and animal testing are still progressing alongside clinical studies, with promising results in the use of (68)Ga-DOTA-rhenium-cyclized alpha-melanocyte stimulating hormone (MSH) and (68)Ga-DOTA-napamide (NAP) in melanoma, (68)Ga-DOTA-PEG(4)-BN(7-14) (PESIN) for the imaging of bombesin receptor- positive tumours and (68)Ga-ethylene dicysteine-metronidazole (EC-MN) for imaging tumour hypoxia. In addition to tumours, (68)Ga- DOTA peptide inhibitor of vascular peptide protein 1(VAP-P1) is being assessed for imaging inflammatory reaction. An additional value following a positive scan is the use of beta emitters labelled to the same peptides for radionuclide treatment. In conclusion, the recent introduction of (68)Ga-peptides, made available by a convenient (68)Ga/(68)Ge generator, could greatly contribute to the management of a wide range of clinical conditions including tumours and inflammation.

Molecular imaging of vessels in mouse models of disease

Vascular imaging of angiogenesis in mouse models of disease requires multi modal imaging hardware capable of targeting both structure and function at different physical scales. The three dimensional (3D) structure and function vascular information allows for accurate differentiation between biological processes. For example, image analysis of vessel development in angiogenesis vs. arteriogenesis enables more accurate detection of biological variation between subjects and more robust and reliable diagnosis of disease. In the recent years a number of micro imaging modalities have emerged in the field as preferred means for this purpose. They provide 3D volumetric data suitable for analysis, quantification, validation, and visualization of results in animal models. This review highlights the capabilities of microCT, ultrasound and microPET for multimodal imaging of angiogenesis and molecular vascular targets in a mouse model of tumor angiogenesis. The basic principles of the imaging modalities are described and experimental results are presented.

New horizons in prostate cancer imaging

Prostate cancer is the most common non-cutaneous malignancy among American men. Imaging has recently become more important in detection of prostate cancer since screening techniques such as digital rectal examination (DRE), prostate specific and transrectal ultrasound guided biopsy have considerable limitations in diagnosis and localization of prostate cancer. In this manuscript, we reviewed conventional, functional and targeted imaging modalities used in diagnosis and local staging of prostate cancer with exquisite images.

Imaging oncogene expression

This review briefly outlines the importance of molecular imaging, particularly imaging of endogenous gene expression for noninvasive genetic analysis of radiographic masses. The concept of antisense imaging agents and the advantages and challenges in the development of hybridization probes for in vivo imaging are described. An overview of the investigations on oncogene expression imaging is given. Finally, the need for further improvement in antisense-based imaging agents and directions to improve oncogene mRNA targeting is stated.

Nanoparticles for optical molecular imaging of atherosclerosis

Molecular imaging contributes to future personalized medicine dedicated to the treatment of cardiovascular disease, the leading cause of mortality in industrialized countries. Endoscope-compatible optical imaging techniques would offer a stand-alone alternative and high spatial resolution validation technique to clinically accepted imaging techniques in the (intravascular) assessment of vulnerable atherosclerotic lesions, which are predisposed to initiate acute clinical events. Efficient optical visualization of molecular epitopes specific for vulnerable atherosclerotic lesions requires targeting of high-quality optical-contrast-enhancing particles. In this review, we provide an overview of both current optical nanoparticles and targeting ligands for optical molecular imaging of atherosclerotic lesions and speculate on their applicability in the clinical setting.

The impact of gene expression on 18F-FDG kinetics; a new chapter for diagnostic nuclear medicine

Nuclear medicine procedures are the methods of choice for the assessment of the tracer kinetics in a volume over time. Fluorine-18 fluoro-deoxyglucose ((18)F-FDG) is primarily a marker of tumor viability and the kinetics of (18)F-FDG reflects major biological factors like angiogenesis and proliferation. The correct interpretation of (18)F- FDG tracer kinetics demands the knowledge about the association of quantitative positron emission tomography (PET) data and gene expression. The use of gene arrays is helpful to obtain expression data for a large number of genes from tissue samples. However, limited data are available about quantitative (18)F-FDG data and gene array results. Studies in primary liver cancer patients revealed that the (18)F-FDG uptake was associated with genes related to tumor cell adhesion and tumor invasion. We noted in patients with giant cell tumors a correlation of the (18)F-FDG uptake, as measured by the standardized uptake value (SUV) and the cell division cycle 2 (cdc2) gene expression. The effect of therapeutic interventions is dependent on the agent used for treatment. In gastrointestinal stromal tumors the change in (18)F-FDG uptake is most likely due to an antiproliferative effect. However, this may be different in other tumor types and for other treatment protocols, therefore dedicated studies of the (18)F-FDG kinetics and gene expression are needed. Based on the recent data available in colorectal tumors and gene expression, we were able to demonstrate that at least two key genes of the angiogenesis, vascular endothelial growth factor (VEGF-A) and angiopoietin-2, have a major impact on the tracer kinetics. Furthermore, regression functions for the (18)F-FDG kinetics and gene expression data facilitate the calculation of parametric images of the gene expression, reflecting the spatial distribution of angiogenesis in a colorectal tumor. Currently the development of information management systems for the prediction of clinical relevant information in individual patients is in progress to retrieve the optimum on information from individual (18)F-FDG patient examinations to support individualization of treatment management.

Molecular imaging of cardiovascular disease using ultrasound

Molecular imaging using probes that specifically home to function- or disease-specific targets is a promising tool for both basic research investigations as well as clinical diagnostics. Ultrasound-based molecular imaging utilizes acoustically active particles (contrast agents) bearing targeting ligands that specifically bind to a molecule of interest. In the presence of an ultrasound field, the bound particles are detectable as a persistent contrast effect during ultrasound imaging. Different types of targeted contrast agents have been reported, most of which share in common the presence of a gas encapsulated by a shell of varying chemical formulation. These agents, or "microbubbles," are typically 2 to 4 mum in diameter, and have a natural resonance frequency that corresponds to the frequencies used in diagnostic echocardiography. This attribute makes it possible to induce microbubble resonance and non-linear oscillation at diagnostic ultrasound frequencies, leading to acoustic emissions from the microbubbles that can be detected as specific signals during two dimensional ultrasound imaging. Targeting ligands that have been attached to microbubbles include monoclonal antibodies, peptides, and the naturally occurring ligands for the receptor of interest, such as vascular endothelial growth factor. Because the contrast agents stay within the intravascular space, they are ideally suited for detection of endothelial epitopes, such as leukocyte adhesion molecules or angiogenesis receptors. Ultrasound molecular imaging with targeted contrast agents has been used to detect inflammation association with ischemia/reperfusion (ischemic memory), cardiac transplant rejection, early atherosclerosis, and angiogenesis. Application to tumor angiogenesis has also been reported using peptides that specifically bind to angiogenic tumor endothelium. Translation of ultrasound molecular imaging to the clinical arena will require optimization of contrast agent design to maximize specific binding, and customization of imaging systems to sensitively detect the binding events.

Where is it heading? Single-particle tracking of single-walled carbon nanotubes

Single-particle tracking of individual single-walled carbon nanotubes (SWNTs) using their near-infrared band gap fluorescence is a powerful tool for understanding how these Brownian rods diffuse and interact with various molecular force potentials, including living systems. Pioneered by the Weisman laboratory at Rice University, the method is one of the only available to study single SWNT molecules in solution over extended periods since SWNTs have no apparent irreversible photobleaching threshold at moderate fluence and no intrinsic blinking mechanism. Recent progress by Tsyboulski et al. shows how real-time measurement of rotational and transitional diffusivities can provide information about rod length and mechanical properties. Recently, Jin et al. used single-particle tracking to map the trajectories of SWNTs as they are incorporated into and expelled from NIH-3T3 cells in real time. The technique has provided the first evidence of nanoparticle exocytosis in this case and demonstrates an expulsion rate that closely matches the endocytosis rate. The ability to track and to analyze single molecules in this way may lead to new technologies that utilize as their platform a single, freely diffusing nanotube.

Molecular imaging with optics: primer and case for near-infrared fluorescence techniques in personalized medicine

We compare and contrast the development of optical molecular imaging techniques with nuclear medicine with a didactic emphasis for initiating readers into the field of molecular imaging. The nuclear imaging techniques of gamma scintigraphy, single-photon emission computed tomography, and positron emission tomography are first briefly reviewed. The molecular optical imaging techniques of bioluminescence and fluorescence using gene reporter/probes and gene reporters are described prior to introducing the governing factors of autofluorescence and excitation light leakage. The use of dual-labeled, near-infrared excitable and radio-labeled agents are described with comparative measurements between planar fluorescence and nuclear molecular imaging. The concept of time-independent and -dependent measurements is described with emphasis on integrating time-dependent measurements made in the frequency domain for 3-D tomography. Finally, we comment on the challenges and progress for translating near-infrared (NIR) molecular imaging agents for personalized medicine.