Activatable imaging probes with amplified fluorescent signals

Probes for optical imaging: new developments

Recent developments of fluorescent probes beyond approved indocyanine green (ICG) - itself increasingly spreading into new imaging applications like lymphatic mapping, arthritis imaging and tumor surgery - exploit various photophysical and biochemical mechanisms to monitor molecular events with higher specificity and accuracy. Emphasizing nanoparticulate formulations, targeted conjugates, activatable probes, probes with a sensor function and multimodality probes, this review discusses advantages and limitations of each type of probe, thereby critically assessing the desired translation into the clinic.:

A dual-emission Förster resonance energy transfer nanoprobe for sensing/imaging pH changes in the biological environment

A dual-emission nanoprobe that can sense changes in the environmental pH is designed based on the concept of pH-responsive Förster resonance energy transfer induced by the conformational transition of an associating polyelectrolyte, N-palmitoyl chitosan, bearing a donor (Cy3) or an acceptor (Cy5) moiety. We demonstrate that the developed pH-responsive nanoprobe can be used to ratiometrically image and thus discriminate the pH changes in the biological environment at different length scales.

Near-infrared fluorescence imaging using a protease-specific probe for the detection of colon tumors

BACKGROUND/AIMS

Early tumor detection is crucial for the prevention of colon cancer. Near-infrared fluorescence (NIRF) imaging using a target-activatable probe may permit earlier disease detection. Matrix metalloproteinases (MMPs) participate in tumorigenesis and tumor growth. The aim of this study was to determine whether NIRF imaging using an MMP-activatable probe can detect colon tumors at early stages.

METHODS

WE UTILIZED TWO MURINE COLON CANCER MODELS: a sporadic colon cancer model induced by azoxymethane (AOM), and a colitis-associated cancer model induced by a combination of AOM and dextran sodium sulfate (DSS). Colonic lesions were analyzed by histologic examination, Western blotting, immunohistochemical staining, and NIRF imaging using an MMP-activatable probe.

RESULTS

Multiple variable-sized tumors developed in both models and progressed from adenomas to adenocarcinomas over time. At the early stage of the AOM/DSS model, diffuse inflammation was observed within the tumors. MMP expression increased progressively through normal, inflammation, adenoma, and adenocarcionoma stages. NIRF signal intensities were strongly correlated with each tumor stage from adenoma to adenocarcinoma. NIRF imaging also distinguished tumors from inflamed mucosa.

CONCLUSIONS

NIRF imaging using a protease-activatable probe may be a useful tool for early tumor detection. This approach could translate to improve the endoscopic detection of colon tumors, especially in patients with inflammatory bowel disease.

Near-infrared fluorescent nanoprobes for cancer molecular imaging: status and challenges

Near-infrared fluorescence (NIRF) imaging promises to improve cancer imaging and management; advances in nanomaterials allow scientists to combine new nanoparticles with NIRF imaging techniques, thereby fulfilling this promise. Here, we present a synopsis of current developments in NIRF nanoprobes, their use in imaging small living subjects, their pharmacokinetics and toxicity, and finally their integration into multimodal imaging strategies. We also discuss challenges impeding the clinical translation of NIRF nanoprobes for molecular imaging of cancer. Whereas utilization of most NIRF nanoprobes remains at a proof-of-principle stage, optimizing the impact of nanomedicine in cancer patient diagnosis and management will probably be realized through persistent interdisciplinary amalgamation of diverse research fields.

Protease sensing with nanoparticle based platforms

Nanoparticulate systems in various unique configurations are highly effective at detecting protease activity both in vivo and in vitro. In this article, we have summarised the conventional modern methods for monitoring protease activity, and critically appraised recent advances in protease-responsive nanosensors.

Exogenous Molecular Probes for Targeted Imaging in Cancer: Focus on Multi-modal Imaging

Cancer is one of the major causes of mortality and morbidity in our health care system. Molecular imaging is an emerging methodology for the early detection of cancer, and the development of exogenous molecular probes that can be labeled for multi-modality imaging is critical to this process. Today, molecular imaging is at crossroad, and new targeted imaging agents are expected to broadly expand our ability to detect pre-malignant lesions. This integrated imaging strategy will permit clinicians to not only localize lesions within the body, but also to visualize the expression and activity of specific molecules. This information is expected to have a major impact on diagnosis, therapy, drug development and understanding of basic cancer biology. At this time, a number of molecular probes have been developed by conjugating various labels to affinity ligands for targeting in different imaging modalities. This review will describe the current status of exogenous molecular probes for optical, nuclear and MRI imaging platforms. Furthermore, we will also shed light on how these techniques can be used synergistically in multi-modal platforms and how these techniques are being employed in current research.

Peptide-based probes for targeted molecular imaging

Targeted molecular imaging techniques have become indispensable tools in modern diagnostics because they provide accurate and specific diagnosis of disease information. Conventional nonspecific contrast agents suffer from low targeting efficiency; thus, the use of molecularly targeted imaging probes is needed depending on different imaging modalities. Although recent technologies have yielded various strategies for designing smart probes, utilization of peptide-based probes has been most successful. Phage display technology and combinatorial peptide chemistry have profoundly impacted the pool of available targeting peptides for the efficient and specific delivery of imaging labels. To date, selected peptides that target a variety of disease-related receptors and biomarkers are in place. These targeting peptides can be coupled with the appropriate imaging moieties or nanoplatforms on demand with the help of sophisticated bioconjugation or radiolabeling techniques. This review article examines the current trends in peptide-based imaging probes developed for in vivo applications. We discuss the advantage of and challenges in developing peptide-based probes and summarize current systems with respect to their unique design strategies and applications.

Molecular imaging of in vivo gene expression

Molecular imaging provides spatial and temporal information on cellular changes that occur during development and in disease. MRI and optical imaging of reporter genes allows for the visualization of promoter activity, protein-protein interactions, protein stability and the tracking of individual proteins and cells. Reporter genes can be genetically encoded in transgenic animals or detected through the administration of an exogenous contrast agent. Advances in molecular imaging of reporter genes have led to the development of imaging probes that detect changes in endogenous cellular changes. The ability to use contrast agents coupled with functional information on cellular events will allow for sensitive assessment of individual patient therapies, leading to an accurately tailored treatment regimen.

Polymeric nanoparticle-based activatable near-infrared nanosensor for protease determination in vivo

We report here a new protease activatable strategy based on a polymer nanoparticle platform. This nanosensor delivers chemically labeled matrix metalloproteinase (MMP)-activatable fluorogenic peptides to the specific MMPs of interest in vivo. Intravenous administration of the nanosensor in an MMP-positive SCC-7 xenograft tumor and a colon cancer mouse model verified the enzyme specificity of the nanosensor in vivo. The design platform of the nanosensor is flexible and can be fine-tuned for a wide array of applications such as the detection of biomarkers, early diagnosis of disease, and monitoring therapeutic efficacy.

PET Imaging of Angiogenesis

Angiogenesis is a highly-controlled process that is dependent on the intricate balance of both promoting and inhibiting factors, involved in various physiological and pathological processes. A comprehensive understanding of the molecular mechanisms that regulate angiogenesis has resulted in the design of new and more effective therapeutic strategies. Due to insufficient sensitivity to detect therapeutic effects by using standard clinical endpoints or by looking for physiological improvement, a multitude of imaging techniques have been developed to assess tissue vasculature on the structural, functional and molecular level. Imaging is expected to provide a novel approach to noninvasively monitor angiogenesis, to optimize the dose of new antiangiogenic agents and to assess the efficacy of therapies directed at modulation of the angiogenic process. All these methods have been successfully used preclinically and will hopefully aid in antiangiogenic drug development in animal studies. In this review article, the application of PET in angiogenesis imaging at both functional and molecular level will be discussed. For PET imaging of angiogenesis related molecular markers, we emphasize integrin alpha(v)beta(3), VEGF/VEGFR, and MMPs.