Molecular probes for the in vivo imaging of cancer

High-Resolution Magnetic Resonance Angiography of Tumor Vasculatures with an Interlocking Contrast Agent

The comprehensive evaluation of tumor vasculature that is crucial for the development, expansion, and spread of cancer still remains a great challenge, especially the three-dimensional (3D) evaluation of vasculatures. In this study, we proposed a magnetic resonance (MR) angiography strategy with interlocking stratagem of zwitterionic Gd-chelate contrast agents (PAA-Gd) for continuous monitoring of tumor angiogenesis progression in 3D. Owing to the zwitterionic structure and nanoscale molecular diameter, the longitudinal molar relaxivity (r1) of PAA-Gd was 2.5 times higher than that of individual Gd-chelates on a 7.0 T MRI scanner, resulting in the higher-resolution visualization of tumor vasculatures. More importantly, PAA-Gd has the appropriate blood half-life (69.2 min), emphasizing the extended imaging window compared to the individual Gd-chelates. On this basis, by using PAA-Gd as the contrast agent, the high-resolution, 3D depiction of the spatiotemporal distribution of microvasculature in solid tumors formed by different cell lines over various inoculation times has been obtained. This method offers an effective approach for early tumor diagnosis, development assessment, and prognosis evaluation.

The Development of a Smart Magnetic Resonance Imaging and Chemical Exchange Saturation Transfer Contrast Agent for the Imaging of Sulfatase Activity

The molecular imaging of biomarkers plays an increasing role in medical diagnostics. In particular, the imaging of enzyme activity is a promising approach, as it enables the use of its inherent catalytic activity for the amplification of an imaging signal. The increased activity of a sulfatase enzyme has been observed in several types of cancers. We describe the development and in vitro evaluation of molecular imaging agents that allow for the detection of sulfatase activity using the whole-body, non-invasive MRI and CEST imaging methods. This approach relies on a responsive ligand that features a sulfate ester moiety, which upon sulfatase-catalyzed hydrolysis undergoes an elimination process that changes the functional group, coordinating with the metal ion. When Gd3+ is used as the metal, the complex can be used for MRI, showing a 25% decrease at 0.23T and a 42% decrease at 4.7T in magnetic relaxivity after enzymatic conversion, thus providing a "switch-off" contrast agent. Conversely, the use of Yb3+ as the metal leads to a "switch-on" effect in the CEST imaging of sulfatase activity. Altogether, the results presented here provide a molecular basis and a proof-of-principle for the magnetic imaging of the activity of a key cancer biomarker.

In Vivo Evaluation of Gallium-68-Labeled IRDye800CW as a Necrosis Avid Contrast Agent in Solid Tumors

Necrosis only occurs in pathological situations and is directly related to disease severity and, therefore, is an important biomarker. Tumor necrosis occurs in most solid tumors due to improperly functioning blood vessels that cannot keep up with the rapid growth, especially in aggressively growing tumors. The amount of necrosis per tumor volume is often correlated to rapid tumor proliferation and can be used as a diagnostic tool. Furthermore, efficient therapy against solid tumors will directly or indirectly lead to necrotic tumor cells, and detection of increased tumor necrosis can be an early marker for therapy efficacy. We propose the application of necrosis avid contrast agents to detect therapy-induced tumor necrosis. Herein, we advance gallium-68-labeled IRDye800CW, a near-infrared fluorescent dye that exhibits excellent necrosis avidity, as a potential PET tracer for in vivo imaging of tumor necrosis. We developed a reliable labeling procedure to prepare [68Ga]Ga-DOTA-PEG4-IRDye800CW ([68Ga]Ga-1) with a radiochemical purity of >96% (radio-HPLC). The prominent dead cell binding of fluorescence and radioactivity from [68Ga]Ga-1 was confirmed with dead and alive cultured 4T1-Luc2 cells. [68Ga]Ga-1 was injected in 4T1-Luc2 tumor-bearing mice, and specific fluorescence and PET signal were observed in the spontaneously developing tumor necrosis. The ip injection of D-luciferin enabled simultaneous bioluminescence imaging of the viable tumor regions. Tumor necrosis binding was confirmed ex vivo by colocalization of fluorescence uptake with TUNEL dead cell staining and radioactivity uptake in dichotomized tumors and frozen tumor sections. Our presented study shows that [68Ga]Ga-1 is a promising PET tracer for the detection of tumor necrosis.

Biomarker selection and imaging design in cancer: A link with biochemical pathways for imminent engineering

Malignant cells reprogram metabolic pathways to meet the demands of growth and proliferation. These altered manners of metabolism are now identified as hallmarks of cancer. Studies have revealed tumor cells alter specific pathways such as glycolysis, fatty acid synthesis and amino acid synthesis to support their proliferation. In this review, we provide a theoretical framework to understand metabolic reprogramming and the mechanisms accompanying distorted metabolism to tumor progression. How these alterations will be assisting in cancer diagnostics and advances in standard techniques in marker identification and imagining are also discussed.

Single Photon Emission Computed Tomography Tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g., peptide, antibody fragment) and a γ-radiation-emitting radionuclide (e.g., ^99mTc, ¹²³I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design, these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

Selective photothermal killing of cancer cells using LED-activated nucleus targeting fluorescent carbon dots

The development of effective theranostic probes in cancer therapy is hampered due to issues with selectivity and off-target toxicity. We report the selective LED-photothermal ablation of cervical (HeLa) cancer cells over human dermal fibroblasts (HDF) using a new class of green-emissive fluorescent carbon dots (FCDs). The FCDs can be easily prepared in one pot using cheap and commercial starting materials. Physico-chemical characterization revealed that a surface coating of 2,5-deoxyfructosazine on a robust amorphous core gives rise to the nanomaterial's unique properties. We show that intracellular uptake mostly involves passive mechanisms in combination with intracellular DNA interactions to target the nucleus and that cancer cell selective killing is likely due to an increase in intracellular temperature in combination with ATP depletion, which is not observed upon exposure to either the "naked" core FCDs or the surface components individually. The selectivity of these nanoprobes and the lack of apparent production of toxic metabolic byproducts make these new nanomaterials promising agents in cancer therapy.

Optical and x-ray technology synergies enabling diagnostic and therapeutic applications in medicine

X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radio-optical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine.

Functional probes for cardiovascular molecular imaging

Cardiovascular diseases (CVDs) are a severely threatening disorder and frequently cause death in industrialized countries, posing critical challenges to modern research and medicine. Molecular imaging has been heralded as the solution to many problems encountered in individuals living with CVD. The use of probes in cardiovascular molecular imaging is causing a paradigmatic shift from regular imaging techniques, to future advanced imaging technologies, which will facilitate the acquisition of vital information at the cellular and molecular level. Advanced imaging for CVDs will help early detection of disease development, allow early therapeutic intervention, and facilitate better understanding of fundamental biological processes. To promote a better understanding of cardiovascular molecular imaging, this article summarizes the current developments in the use of molecular probes, highlighting some of the recent advances in probe design, preparation, and functional modification.

Magnetic iodixanol - a novel contrast agent and its early characterization

AIMS

Contrast-induced nephropathy is a commonly encountered problem in clinical practice. The purpose of the study was to design and develop a novel contrast agent, which could be used to prevent contrast-induced nephropathy in the future.

METHODS

In total, 20-220nm magnetic nanoparticles were conjugated with iodixanol, and their radio-opacity and magnetic properties were assessed thereafter. Scanning electron microscopy pictures were acquired. Thereafter, the nanoparticles conjugate was tested in cell culture (HUVEC cells), and Quantibody^® assay was studied after cell treatment in 1:5 dilutions for 48h, compared with control.

RESULTS

The conjugate preparation had an adequate radio-opacity. A 4mm magnetic bubble was attached to a bar magnet and the properties were studied. The magnetic bubble maintained its structural integrity in all angles including antigravity position. Scanning electron microscopy showed magnetic nanoparticles in all pictures and the particles are of 100-400nm agglomerates with primary particle sizes of roughly 20nm. 1:5 diluted particles had no effect on secretion of IL-1a, IL-1b, IL-4, IL-10, IL-13 and TNFa. Particles increased secretion of IL-8 from 24h and 48h. Secretion of IFNg was also increased when particles were added to the cells as early as 1h. Likewise, IL-6 was strongly secreted by HUVEC treated with particles from 24h incubation time. In contrast, the secretion of MCP-1 was slightly reduced on HUVEC treated with particles.

CONCLUSION

There is potential for a novel iodixanol-magnetic nanoparticle conjugate to be used in cineradiography. Further investigations need to be performed to study its performance in vitro and in vivo.

Raltegravir blocks the infectivity of red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL in the setting of post-exposure prophylaxis in NOD/SCID/Jak3-/- mice transplanted with human PBMCs

Employing NOD/SCID/Jak3-/- mice transplanted with human PBMCs (hNOJ mice) and replication-competent, red-fluorescent-protein (mCherry; mC)-labeled HIV-1JR-FL (HIVmC), we examined whether early antiretroviral treatment blocked the establishment of HIV-1 infection. The use of hNOJ mice and HIVmC enabled us to visually locate infection foci and to examine the early dynamics of HIVmC infection without using a large amount of antiretroviral unlike in non-human primate models. Although when raltegravir (RAL) administration was begun 1 day after intraperitoneal (ip) inoculation of HIVmC, no plasma p24 or plasma HIV-1-RNA (pRNA) were detected in 10 of 12 hNOJ (hNOJmCRAL+) mice as assessed on the last day of the 14-day continuous twice-daily RAL administration, all 10 untreated hNOJmC (hNOJmCRAL-) mice became positive for p24 and pRNA and had significantly swollen lymph nodes in peritoneal cavity and abundant p24+/mC+/CD3+/CD4+ T cells and p24+/mC+/CD68+ monocytes/macrophages were identified in their omenta and mesenteric lymphoid tissues/lymph nodes upon necropsy of the mice on day 14. In 12 hNOJmCRAL+ mice, no significantly swollen lymph nodes were seen compared to hNOJmCRAL- mice; however, in the omentum of the 2 hNOJmCRAL+ mice that were positive for pRNA and in site RNA, mC+/p24+/CD3+/CD83+ cells were identified, suggesting that viral breakthrough occurred later in the observation period. The present data suggest that the use of hNOJ mouse model and HIVmC may shed light on the study of early-phase dynamics of HIV-1 infection and cellular events in post-exposure/pre-exposure prophylaxis.

In Situ Ligation of High- and Low-Affinity Ligands to Cell Surface Receptors Enables Highly Selective Recognition

This paper reports an entirely unexplored concept of simultaneously recognizing two receptors using high- and low-affinity ligands through ligating them in situ on the target cell surface. This de novo approach is inspired by the pretargeting strategy frequently applied in molecular imaging, and has now evolved as the basis of a new paradigm for visualizing target cells with a high imaging contrast. A distinct advantage of using a labeled low-affinity ligand such as glycan is that the excess labeled ligand can be washed away from the cells, whereas the ligand bound to the cell, even at the milli molar affinity level, can be anchored by a bioorthogonal reaction with a pretargeted high-affinity ligand on the surface. Consequently, nonspecific background is minimized, leading to improved imaging contrast. Importantly, despite previously unexplored for molecular imaging, a notoriously weak glycan/lectin interaction can now be utilized as a highly selective ligand to the targets.

Early phase dynamics of traceable mCherry fluorescent protein-carrying HIV-1 infection in human peripheral blood mononuclear cells-transplanted NOD/SCID/Jak3-/- mice

We attempted to elucidate early-phase dynamics of HIV-1 infection using replication-competent, red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL (HIVJR-FLmC) and NOD/SCID/Jak3-/- mice transplanted with Individual-A's human peripheral blood mononuclear cells (hPBMC)(hNOJ mice). On day 7 following HIVJR-FLmC inoculation, mCherry-signal-emitting infection foci were readily identified in the subserosa of 10 of 10 HIVJR-FLmC-inoculated hNOJ mice, although infection foci were not located without the mCherry signal in unlabeled HIV-1JR-FL-inoculated mice (n = 6). Even on day 14, infection foci were hardly located in the unlabeled HIV-1JR-FL-inoculated mice, while in all of 7 HIVJR-FLmC-inoculated hNOJ mice examined, mCherry-signal-emitting lymph nodes were easily identified, in which active viral replication was present. On day 14, a significantly larger number of mesenteric lymph nodes were seen in HIVJR-FLmC-exposed hNOJ mice than in HIVJR-FLmC-unexposed mice (P = 0.0025). The weights of mesenteric lymph nodes of those HIVJR-FLmC-exposed hNOJ mice were also greater than those of HIVJR-FLmC-unexposed mice (P = 0.0005). When hNOJ mice were inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, significantly greater viremia was seen than in cell-free HIVJR-FLmC-inoculated hNOJ mice as examined on day 7. In the lymph nodes of those mice inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, a substantial number of Individual-B's HIVJR-FLmC-infected cells were identified together with Individual-A's cells as examined on day 14. The present HIVJR-FLmC-infected mouse model represents the first system reported using traceable HIVJR-FLmC and human target cells, not using SIV or simian cells, which should be of utility in studies of early-phases of HIV-1 transmission and in evaluating the effects of potential agents for post-exposure and pre-exposure prophylaxis.

Site-selective installation of BASHY fluorescent dyes to Annexin V for targeted detection of apoptotic cells

Fluorophores are indispensable for imaging biological processes. We report the design and synthesis of azide-tagged boronic acid salicylidenehydrazone (BASHY) dyes and their use for site-selective labelling of Annexin V. The Annexin V-BASHY conjugate maintained function and fluorescence as demonstrated by the targeted detection of apoptotic cells.

Intraoperative Fluorescence Imaging for Personalized Brain Tumor Resection: Current State and Future Directions

INTRODUCTION

Fluorescence-guided surgery is one of the rapidly emerging methods of surgical "theranostics." In this review, we summarize current fluorescence techniques used in neurosurgical practice for brain tumor patients as well as future applications of recent laboratory and translational studies.

METHODS

Review of the literature.

RESULTS

A wide spectrum of fluorophores that have been tested for brain surgery is reviewed. Beginning with a fluorescein sodium application in 1948 by Moore, fluorescence-guided brain tumor surgery is either routinely applied in some centers or is under active study in clinical trials. Besides the trinity of commonly used drugs (fluorescein sodium, 5-aminolevulinic acid, and indocyanine green), less studied fluorescent stains, such as tetracyclines, cancer-selective alkylphosphocholine analogs, cresyl violet, acridine orange, and acriflavine, can be used for rapid tumor detection and pathological tissue examination. Other emerging agents, such as activity-based probes and targeted molecular probes that can provide biomolecular specificity for surgical visualization and treatment, are reviewed. Furthermore, we review available engineering and optical solutions for fluorescent surgical visualization. Instruments for fluorescent-guided surgery are divided into wide-field imaging systems and hand-held probes. Recent advancements in quantitative fluorescence-guided surgery are discussed.

CONCLUSION

We are standing on the threshold of the era of marker-assisted tumor management. Innovations in the fields of surgical optics, computer image analysis, and molecular bioengineering are advancing fluorescence-guided tumor resection paradigms, leading to cell-level approaches to visualization and resection of brain tumors.

Evaluation of the microscopic dose enhancement for nanoparticle-enhanced Auger therapy

The aim of this study is to investigate the dosimetric characteristics of nanoparticle-enhanced Auger therapy. Monte Carlo (MC) simulations were performed to assess electron energy spectra and dose enhancement distributions around a nanoparticle. In the simulations, two types of nanoparticle structures were considered: nanoshell and nanosphere, both of which were assumed to be made of one of five elements (Fe, Ag, Gd, Au, and Pt) in various sizes (2-100 nm). Auger-electron emitting radionuclides (I-125, In-111, and Tc-99m) were simulated within a nanoshell or on the surface of a nanosphere. For the most promising combination of Au and I-125, the maximum dose enhancement was up to 1.3 and 3.6 for the nanoshell and the nanosphere, respectively. The dose enhancement regions were restricted within 20-100 nm and 0-30 nm distances from the surface of Au nanoshell and nanosphere, respectively. The dose enhancement distributions varied with sizes of nanoparticles, nano-elements, and radionuclides and thus should be carefully taken into account for biological modeling. If the nanoparticles are accumulated in close proximity to the biological target, this new type of treatment can deliver an enhanced microscopic dose to the target (e.g. DNA). Therefore, we conclude that Auger therapy combined with nanoparticles could have the potential to provide a better therapeutic effect than conventional Auger therapy alone.

Dual-Modality Optical/PET Imaging of PARP1 in Glioblastoma

PURPOSE

The current study presents [(18)F]PARPi-FL as a bimodal fluorescent/positron emission tomography (PET) agent for PARP1 imaging.

PROCEDURES

[(18)F]PARPi-FL was obtained by (19)F/(18)F isotopic exchange and PET experiments, biodistribution studies, surface fluorescence imaging, and autoradiography carried out in a U87 MG glioblastoma mouse model.

RESULTS

[(18)F]PARPi-FL showed high tumor uptake in vivo and ex vivo in small xenografts (< 2 mm) with both PET and optical imaging technologies. Uptake of [(18)F]PARPi-FL in blocked U87 MG tumors was reduced by 84 % (0.12 ± 0.02 %injected dose/gram (%ID/g)), showing high specificity of the binding. PET imaging showed accumulation in the tumor (1 h p.i.), which was confirmed by ex vivo phosphor autoradiography.

CONCLUSIONS

The fluorescent component of [(18)F]PARPi-FL enables cellular resolution optical imaging, while the radiolabeled component of [(18)F]PARPi-FL allows whole-body deep-tissue imaging of malignant growth.

Mini-review: fluorescence imaging in cancer cells using dye-doped nanoparticles

Fluorescence imaging has gained increased attention over the past two decades as a viable means to detect a variety of cancers.

Microarray based screening of peptide nano probes for HER2 positive tumor

Peptides are excellent biointerface molecules and diagnostic probes with many advantages such as good penetration, short turnover time, and low cost. We report here an efficient peptide screening strategy based on in situ single bead sequencing on a microarray. Two novel peptides YLFFVFER (H6) and KLRLEWNR (H10) specifically binding to the tumor biomarker human epidermal growth factor receptor 2 (HER2) with aKD of 10(-8) M were obtained from a 10(5) library. Conjugated to nanoparticles, both the H6 and H10 probes showed specific accumulation in HER2-positive tumor tissues in xenografted mice by in vivo imaging.

Trends in fluorescence image-guided surgery for gliomas

Mounting evidence suggests that a more extensive surgical resection is associated with an improved life expectancy for both low-grade and high-grade glioma patients. However, radiographically complete resections are not often achieved in many cases because of the lack of sensitivity and specificity of current neurosurgical guidance techniques at the margins of diffuse infiltrative gliomas. Intraoperative fluorescence imaging offers the potential to improve the extent of resection and to investigate the possible benefits of resecting beyond the radiographic margins. Here, we provide a review of wide-field and high-resolution fluorescence-imaging strategies that are being developed for neurosurgical guidance, with a focus on emerging imaging technologies and clinically viable contrast agents. The strengths and weaknesses of these approaches will be discussed, as well as issues that are being addressed to translate these technologies into the standard of care.

Dual-function theranostic nanoparticles for drug delivery and medical imaging contrast: perspectives and challenges for use in lung diseases

Theranostic nanoparticles with both therapeutic and imaging abilities have the promise to revolutionize diagnosis, therapy, and prognosis. Early and accurate detection along with swift treatment are the most important steps in the successful treatment of any disease. Over the last decade, a variety of nanotechnology-based platforms have been created in the hope of improving the treatment and diagnosis of a wide variety of diseases. However, significant hurdles still remain before theranostic nanoparticles can bring clinical solutions to the fight against chronic respiratory diseases. Some fundamental issues such as long-term toxicity, a precise understanding of the accumulation, degradation and clearance of these particles, and the correlation between basic physicochemical properties of these nanoparticles and their in vivo behavior have to be fully understood before they can be used clinically. To date, very little theranostic nanoparticle research has focused on the treatment and diagnosis of chronic respiratory illnesses. Nanomedicine approaches incorporating these theranostic nanoparticles could potentially be translated into clinical advances to improve diagnosis and treatment of these chronic respiratory diseases and enhance quality of life for the patients.

Endoscopic molecular imaging of cancer

White light endoscopy has proven to be a very powerful tool in oncology. There is still, however, a need for better endoscopic techniques to overcome the current limitations of white light optics. New technologies that allow higher sensitivity, improved microanatomy and molecular characterization have been available for in vitro microscopy and are now being translated into in vivo endoscopy. Endoscopic molecular imaging is still in its infancy but holds the promise for enhancing sensitivity for early lesions, thus allowing earlier diagnosis and enabling early image-guided endoscopic intervention. A key feature of endoscopic molecular imaging is its increased sensitivity and specificity, which will be illustrated in this article, as well as describing perspectives on its future use in oncologic surgery.

Chitosan-triphosphate nanoparticles for encapsulation of super-paramagnetic iron oxide as an MRI contrast agent

Super-paramagnetic iron oxide nanoparticles (SPIONPs) were encapsulated at various concentrations within chitosan-triphosphate (SPIONPs-CS) nanoparticles using an ionotropic gelation method. The encapsulation of SPIONPs within CS nanoparticles enhanced their dispersion ability in aqueous solution, with all particles being lower than 130 nm in size and having highly positive surface charge. The SPIONPs-CS nanoparticles exhibited crystalline structure and super-paramagnetic behavior, as seen in non-encapsulated SPIONPs. The morphology of SPIONPs-CS nanoparticles showed that they almost spherical in shape. The effect of phantom environments (culture medium and 3% agar solution) on either T1 or T2 weighted MRI was investigated using a clinical 1.5T MRI scanner. The results revealed that 3% agar solution showed relaxation values higher than the culture medium, leading to a significant decrease in the MR image intensity. Our results demonstrated that the SPIONPs-CS nanoparticles can be applied as tissue-specific MRI contrast agents.

Rational design of a triple reporter gene for multimodality molecular imaging

Multimodality imaging using noncytotoxic triple fusion (TF) reporter genes is an important application for cell-based tracking, drug screening, and therapy. The firefly luciferase (fl), monomeric red fluorescence protein (mrfp), and truncated herpes simplex virus type 1 thymidine kinase SR39 mutant (ttksr39) were fused together to create TF reporter gene constructs with different order. The enzymatic activities of TF protein in vitro and in vivo were determined by luciferase reporter assay, H-FEAU cellular uptake experiment, bioluminescence imaging, and micropositron emission tomography (microPET). The TF construct expressed in H1299 cells possesses luciferase activity and red fluorescence. The tTKSR39 activity is preserved in TF protein and mediates high levels of H-FEAU accumulation and significant cell death from ganciclovir (GCV) prodrug activation. In living animals, the luciferase and tTKSR39 activities of TF protein have also been successfully validated by multimodality imaging systems. The red fluorescence signal is relatively weak for in vivo imaging but may expedite FACS-based selection of TF reporter expressing cells. We have developed an optimized triple fusion reporter construct DsRedm-fl-ttksr39 for more effective and sensitive in vivo animal imaging using fluorescence, bioluminescence, and PET imaging modalities, which may facilitate different fields of biomedical research and applications.

Optical imaging as an expansion of nuclear medicine: Cerenkov-based luminescence vs fluorescence-based luminescence

Integration of optical imaging technologies can further strengthen the field of radioguided surgery. Rather than using two separate chemical entities to achieve this extension, hybrid imaging agents can be used that contain both radionuclear and optical properties. Two types of such hybrid imaging agents are available: (1) hybrid imaging agents generated by Cerenkov luminescence imaging (CLI) of β-emitters and (2) hybrid imaging agents that contain both a radioactive moiety and a fluorescent dye. One major challenge clinicians are now facing is to determine the potential value of these approaches. With this tutorial review we intend to clarify the differences between the two approaches and highlight the clinical potential of hybrid imaging during image-guided surgery applications.

Single photon emission computed tomography tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g. peptide, antibody fragment) and a γ-radiation emitting radionuclide (e.g. (99m)Tc, (123)I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

MRI of prostate stem cell antigen expression in prostate tumors

BACKGROUND

The prostate stem cell antigen (PSCA) is broadly overexpressed on the surface of prostate cancer cells.

MATERIALS & METHODS

Anti-human PSCA monoclonal antibody (mAb 7F5) was bound to Fe(3)O(4)/Au (GoldMag) nanoparticles to serve as a PSCA-specific molecular MRI probe (mAb 7F5@GoldMag) for in vivo detection of prostate cancer cells. First, the efficacy of the antibody immobilization for the binding was assessed. Next, PC-3 (human prostate cancer cell line with PSCA overexpression) tumor-bearing mice were injected with mAb 7F5@GoldMag for MRI measurements while using mouse anti-human IgG bound to the particles (IgG@GoldMag) to serve as a nonspecific control. MRI examinations were conducted before and after injection of these probes at 6, 12 and 24 h; T2-weighted signal intensity within the tumors was measured.

RESULTS

Targeted binding of the mAb 7F5@GoldMag probe to PC-3 tumors was verified with optical images and MRI; selective binding was not observed for the nonspecific IgG@GoldMag probe.

CONCLUSION

MRI measurements suggest the promising efficacy of this new approach for targeted molecular imaging of prostate tumors.

In vivo imaging of immunotoxin treatment using Katushka-transfected A-431 cells in a murine xenograft tumour model

PURPOSE

Preclinical in vivo analyses of treatment responses are an important prerequisite to evaluate new therapeutics. Molecular in vivo imaging in the far red (FR)/near infra red (NIR) is a promising method, as it enables measurements at different time points in individual animals, thereby reducing the number of animals required, while increasing statistical significance. Here, we show the establishment of a method to monitor response to treatment using fluorescent cells, expressing the epidermal growth factor receptor (EGFR), a target already used in therapy.

METHODS

We transfected A-431 tumour cells with the far red-emitting protein Katushka (Kat2), resulting in strong fluorescence allowing for the monitoring of tumour growth when implanted in BALB/c nu/nu mice with a CRi Maestro in vivo imager. We targeted A-431 cells with a previously reported immunotoxin (IT), consisting of the anti-EGFR antibody single-chain variable fragment (scFv) 425, fused to Pseudomonas aeruginosa Exotoxin A' (ETA'). In addition, EGFR expression was verified using the 425(scFv) conjugated to a NIR dye BG-747 through a SNAP-tag linker.

RESULTS

The results show the feasibility to evaluate response to treatment in vivo by FR imaging, while at the same location detecting EGFR expression. Treatment with 425(scFv)-ETA' resulted in decelerated tumour growth, while not affecting the overall health of the animals. This is in contrast to treatment with Doxorubicin, which, although decreasing the tumour size, resulted in poor health.

CONCLUSIONS

We developed a novel method to non-invasively determine treatment responses by in vivo imaging of multiple parameters which showed the efficacy of 425(scFv)-ETA'.

A molecular imaging primer: modalities, imaging agents, and applications

Molecular imaging is revolutionizing the way we study the inner workings of the human body, diagnose diseases, approach drug design, and assess therapies. The field as a whole is making possible the visualization of complex biochemical processes involved in normal physiology and disease states, in real time, in living cells, tissues, and intact subjects. In this review, we focus specifically on molecular imaging of intact living subjects. We provide a basic primer for those who are new to molecular imaging, and a resource for those involved in the field. We begin by describing classical molecular imaging techniques together with their key strengths and limitations, after which we introduce some of the latest emerging imaging modalities. We provide an overview of the main classes of molecular imaging agents (i.e., small molecules, peptides, aptamers, engineered proteins, and nanoparticles) and cite examples of how molecular imaging is being applied in oncology, neuroscience, cardiology, gene therapy, cell tracking, and theranostics (therapy combined with diagnostics). A step-by-step guide to answering biological and/or clinical questions using the tools of molecular imaging is also provided. We conclude by discussing the grand challenges of the field, its future directions, and enormous potential for further impacting how we approach research and medicine.

NEAR-INFRARED DYES: Probe Development and Applications in Optical Molecular Imaging

The recent emergence of optical imaging has brought forth a unique challenge for chemists: development of new biocompatible dyes that fluoresce in the near-infrared (NIR) region for optimal use in biomedical applications. This review describes the synthesis of NIR dyes and the design of probes capable of noninvasively imaging molecular events in small animal models.

Development of membrane type-1 matrix metalloproteinase-specific activatable fluorescent probe for malignant tumor detection

Membrane type-1 matrix metalloproteinase (MT1-MMP) is a protease that activates pro-MMP-2 and pro-MMP13, which are related to tumor malignancy. Therefore, probes that specifically image MT1-MMP would be useful for malignant tumor diagnosis. In the present study, we prepared rhodamine X-conjugated anti-MT1- MMP antibody (anti-MT1-MMP mAb-ROX) as an activatable fluorescent probe and evaluated its usefulness for MT1-MMP-specific imaging. Anti-MT1-MMP mAb-ROX was obtained in a quenched form with approximately three ROX molecules per mAb. Its fluorescence intensity increased approximately 14-fold in the presence of detergent, which is suitable for activatable systems. C6 glioma cells and MCF-7 human breast adenocarcinoma cells were used as MT1-MMP-positive and MT1-MMP-negative models, respectively. The fluorescence intensity of C6 cells treated with anti-MT1-MMP mAb-ROX, but not ROX-conjugated isotype control antibody (NC Ab-ROX), increased with time and was significantly higher than that of MCF-7 cells at 6 h (P < 0.001). The fluorescence intensity of cells treated with anti-MT1-MMP mAb-ROX was also suppressed by pre-treatment with a MT1-MMP endocytosis inhibitor (P < 0.05). Furthermore, the probes were intravenously administered to C6 and MCF-7 xenografted mice. The tumor-to-muscle (T/M) ratio of the anti-MT1-MMP mAb-ROX group was 15.1 ± 3.2 at 48 h and was significantly higher than that of the NC Ab-ROX group (T/M ratio = 4.6 ± 3.0, P < 0.05) in C6 xenografted mice, while the T/M ratio of the anti-MT1-MMP mAb-ROX and NC Ab-ROX groups was not different in MCF-7 xenografted mice. These findings suggest that anti-MT1-MMP mAb-ROX is a promising probe for specifically detecting MT1-MMP-expressing tumors.

Tumor targeting and imaging using cyclic RGD-PEGylated gold nanoparticle probes with directly conjugated iodine-125

Radioactive iodine-labeled, cyclic RGD-PEGylated gold nanoparticle (AuNP) probes are designed and synthesized for targeting cancer cells and imaging tumor sites. These iodine-125-labeled cRGD-PEG-AuNP probes are stable in various conditions including a range of pHs and high salt and temperature conditions. These probes can target selectively and be taken up by tumor cells via integrin αvβ3-receptor-mediated endocytosis with no cytotoxicity. The probes show a significant increase in the avidity of αvβ3 integrin compared to the corresponding free cRGD peptides. In-vivo SPECT/CT imaging results show that the iodine-125-labeled cRGD-PEG-AuNP probes can target the tumor site as soon as 10 min after injection, and also that cyclic RGD peptides are needed for efficient and long-term in-vivo monitoring. The results suggest that the probes circulate through the whole body, including renal filtration, and are excretable. These promising results show that radioactive-iodine-labeled gold nanoprobes have potential for highly specific and sensitive tumor imaging or for use as angiogenesis-targeted SPECT/CT imaging probes.

Multiplex photoacoustic molecular imaging using targeted silica-coated gold nanorods

The establishment of multiplex photoacoustic molecular imaging to characterize heterogeneous tissues requires the use of a tunable, thermally stable contrast agent targeted to specific cell types. We have developed a multiplex photoacoustic imaging technique which uses targeted silica-coated gold nanorods to distinguish cell inclusions in vitro. This paper describes the use of tunable targeted silica-coated gold nanorods (SiO(2)-AuNRs) as contrast agents for photoacoustic molecular imaging. SiO(2)-AuNRs with peak absorption wavelengths of 780 nm and 830 nm were targeted to cells expressing different cell receptors. Cells were incubated with the targeted SiO(2)-AuNRs, incorporated in a tissue phantom, and imaged using multiwavelength photoacoustic imaging. We used photoacoustic imaging and statistical correlation analysis to distinguish between the unique cell inclusions within the tissue phantom.

Target-cancer-cell-specific activatable fluorescence imaging probes: rational design and in vivo applications

Conventional imaging methods, such as angiography, computed tomography (CT), magnetic resonance imaging (MRI), and radionuclide imaging, rely on contrast agents (iodine, gadolinium, and radioisotopes, for example) that are "always on." Although these indicators have proven clinically useful, their sensitivity is lacking because of inadequate target-to-background signal ratio. A unique aspect of optical imaging is that fluorescence probes can be designed to be activatable, that is, only "turned on" under certain conditions. These probes are engineered to emit signal only after binding a target tissue; this design greatly increases sensitivity and specificity in the detection of disease. Current research focuses on two basic types of activatable fluorescence probes. The first developed were conventional enzymatically activatable probes. These fluorescent molecules exist in the quenched state until activated by enzymatic cleavage, which occurs mostly outside of the cells. However, more recently, researchers have begun designing target-cell-specific activatable probes. These fluorophores exist in the quenched state until activated within targeted cells by endolysosomal processing, which results when the probe binds specific receptors on the cell surface and is subsequently internalized. In this Account, we present a review of the rational design and in vivo applications of target-cell-specific activatable probes. In engineering these probes, researchers have asserted control over a variety of factors, including photochemistry, pharmacological profile, and biological properties. Their progress has recently allowed the rational design and synthesis of target-cell-specific activatable fluorescence imaging probes, which can be conjugated to a wide variety of targeting molecules. Several different photochemical mechanisms have been utilized, each of which offers a unique capability for probe design. These include self-quenching, homo- and hetero-fluorescence resonance energy transfer (FRET), H-dimer formation, and photon-induced electron transfer (PeT). In addition, the repertoire is further expanded by the option for reversibility or irreversibility of the signal emitted through these mechanisms. Given the wide range of photochemical mechanisms and properties, target-cell-specific activatable probes have considerable flexibility and can be adapted to specific diagnostic needs. A multitude of cell surface molecules, such as overexpressed growth factor receptors, are directly related to carcinogenesis and thus provide numerous targets highly specific for cancer. This discussion of the chemical, pharmacological, and biological basis of target-cell-specific activatable imaging probes, and methods for successfully designing them, underscores the systematic, rational basis for further developing in vivo cancer imaging.

Affinity peptide for targeted detection of dysplasia in Barrett's esophagus

BACKGROUND & AIMS

Dysplasia is a premalignant condition in Barrett's esophagus that is difficult to detect on endoscopy because of its flat architecture and patchy distribution. Peptides are promising for use as novel molecular probes that identify cell surface targets unique to disease and can be fluorescence-labeled for detection. We aim to select and validate an affinity peptide that binds to esophageal dysplasia for future clinical studies.

METHODS

Peptide selection was performed using phage display by removing nonspecific binders using Q-hTERT (intestinal metaplasia) cells and achieving specific binding against OE33 (esophageal adenocarcinoma) cells. Selective binding was confirmed on bound phage counts, enzyme-linked immunosorbent assay (ELISA), flow cytometry, competitive inhibition, and fluorescence microscopy. On stereomicroscopy, specific peptide binding to dysplasia on endoscopically resected specimens was assessed by rigorous registration of fluorescence intensity to histology in 1-mm intervals.

RESULTS

The peptide sequence SNFYMPL was selected and showed preferential binding to target cells. Reduced binding was observed on competition with unlabeled peptide in a dose-dependent manner, an affinity of K(d) = 164 nmol/L was measured, and peptide binding to the surface of OE33 cells was validated on fluorescence microscopy. On esophageal specimens (n = 12), the fluorescence intensity (mean ± SEM) in 1-mm intervals classified histologically as squamous (n = 145), intestinal metaplasia (n = 83), dysplasia (n = 61), and gastric mucosa (n = 69) was 46.5 ± 1.6, 62.3 ± 5.8, 100.0 ± 9.0, and 42.4 ± 3.0 arb units, respectively.

CONCLUSIONS

The peptide sequence SNFYMPL binds specifically to dysplasia in Barrett's esophagus and can be fluorescence labeled to target premalignant mucosa on imaging.

Image-guided surgery using invisible near-infrared light: fundamentals of clinical translation

The field of biomedical optics has matured rapidly over the last decade and is poised to make a significant impact on patient care. In particular, wide-field (typically > 5 cm), planar, near-infrared (NIR) fluorescence imaging has the potential to revolutionize human surgery by providing real-time image guidance to surgeons for tissue that needs to be resected, such as tumors, and tissue that needs to be avoided, such as blood vessels and nerves. However, to become a clinical reality, optimized imaging systems and NIR fluorescent contrast agents will be needed. In this review, we introduce the principles of NIR fluorescence imaging, analyze existing NIR fluorescence imaging systems, and discuss the key parameters that guide contrast agent development. We also introduce the complexities surrounding clinical translation using our experience with the Fluorescence-Assisted Resection and Exploration (FLARE™) imaging system as an example. Finally, we introduce state-of-the-art optical imaging techniques that might someday improve image-guided surgery even further.

Imaging the life and death of tumors in living subjects: Preclinical PET imaging of proliferation and apoptosis

Cancer is characterized by deregulation of cell proliferation and altered cell death apoptosis, which constitutes, in almost all instances, the minimal common platform upon which all neoplastic evolution occurs. The most implicit and clinically attractive anticancer strategies, therefore, consist of eliminating tumor cells by preventing their expansion and ultimately inducing cell death apoptosis. In this context, the non-invasive molecular assessment of tumor cell proliferation and apoptosis status using PET imaging constitutes a major strategy in preclinical studies to assess the efficacy of new anticancer therapeutics using small animal PET imaging, and in clinical settings for the monitoring of treatment responses in patients. For this purpose, a variety of PET tracers targeting specific molecular entities allowing the non-invasive measurement of biological processes, including cell proliferation and apoptosis, are under development for use in preclinical studies and clinical trials to non-invasively image in vivo the lifeline of tumors.

Molecular imaging and targeted therapies

Targeted therapeutic and imaging agents are becoming more prevalent, and are used to treat increasingly smaller segments of the patient population. This has lead to dramatic increases in the costs for clinical trials. Biomarkers have great potential to reduce the numbers of patients needed to test novel targeted agents by predicting or identifying non-response early-on and thus enriching the clinical trial population with patients more likely to respond. Biomarkers are characteristics that are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers can be used to predict response to specific therapies, predict response regardless of therapy, or to monitor response once a therapy has begun. In terms of drug development, predictive biomarkers have the greatest impact, as they can be used as inclusion criteria for patient segmentation. Prognostic markers are used routinely in clinical practice but do not provide direction for the use of targeted therapies. Imaging biomarkers have distinct advantages over those that require a biopsy sample in that they are "non-invasive" and can be monitored longitudinally at multiple time points in the same patient. This review will examine the role of functional and molecular imaging in predicting response to specific therapies; will explore the advantages and disadvantages of targeting intracellular or extracellular markers; and will discuss the attributes of useful targets and methods for target identification and validation.