Near infrared optical applications in molecular imaging

A Vector Nanoplatform for the Bioimaging of Deep-Seated Tumors

Today, in preclinical studies, optical bioimaging based on luminescence and fluorescence is indispensable in studying the development of neoplastic transformations, the proliferative activity of the tumor, its metastatic potential, as well as the therapeutic effect of antitumor agents. In order to expand the capabilities of optical imaging, sensors based on the bioluminescence resonance energy transfer (BRET) mechanism and, therefore, independent of an external light source are being developed. A targeted nanoplatform based on HER2-specific liposomes whose internal environment contains a genetically encoded BRET sensor was developed in this study to visualize deep-seated tumors characterized by overexpression of human epidermal growth factor receptor type 2 (HER2). The BRET sensor is a hybrid protein consisting of the highly catalytic luciferase NanoLuc (an energy donor) and a LSSmKate1 red fluorescent protein with a large Stokes shift (an energy acceptor). During the bioimaging of disseminated intraperitoneal tumors formed by HER2-positive SKOV3.ip1cells of serous ovarian cystadenocarcinoma, it was shown that the developed system is applicable in detecting deep-seated tumors of a certain molecular profile. The developed system can become an efficient platform for optimizing preclinical studies of novel targeted drugs.

Optically active organic and inorganic nanomaterials for biological imaging applications: A review

Recent advancements in the field of nanotechnology have enabled targeted delivery of drug agents in vivo with minimal side effects. The use of nanoparticles for bio-imaging has revolutionized the field of nanomedicine by enabling non-invasive targeting and selective delivery of active drug moieties in vivo. Various inorganic nanomaterials like mesoporous silica nanoparticles, gold nanoparticles, magnetite nanoparticles graphene-based nanomaterials etc., have been created for multimodal therapies with varied multi-imaging modalities. These nanomaterials enable us to overcome the disadvantages of conventional imaging contrast agents (organic dyes) such as lack of stability in vitro and in vivo, high reactivity, low-quantum yield and poor photo stability. Inorganic nanomaterials can be easily fabricated, functionalised and modified as per requirements. Recently, advancements in synthesis techniques, such as the ability to generate molecules and construct supramolecular structures for specific functionalities, have boosted the usage of engineered nanomaterials. Their intrinsic physicochemical properties are unique and they possess excellent biocompatibility. Inorganic nanomaterial research has developed as the most actively booming research fields in biotechnology and biomedicine. Inorganic nanomaterials like gold nanoparticles, magnetic nanoparticles, mesoporous silica nanoparticles, graphene-based nanomaterials and quantum dots have shown excellent use in bioimaging, targeted drug delivery and cancer therapies. Biocompatibility of nanomaterials is an important aspect for the evolution of nanomaterials in the bench to bedside transition. The conduction of thorough and meticulous study for safety and efficacy in well-designed clinical trials is absolutely necessary to determine the functional and structural relationship between the engineered nanomaterial and its toxicity. In this article an attempt is made to throw some light on the current scenario and developments made in the field of nanomaterials in bioimaging.

Non-invasive detection and differentiation of apoptotic and necroptotic cell death in vitro

Cell death plays an important role in the development of multicellular organisms and the maintenance of adult homeostasis. However, traditional methods of cell death detection can damage cells and tissues. Here, we report the use of near-infrared (NIR) spectroscopy for non-invasively distinguishing between cell death types. We found a difference between normal, apoptotic, and necroptotic mouse dermal fibroblast cells in the wavelength range of 1100-1700 nm. In particular, the differences in scattering of NIR light between cells at different states are enough to be distinguished. This feature was exploited by measuring the attenuation coefficient (δμ), which specifies the ease at which light can pass through a substance. The results showed that δμ can be used to distinguish between different types of cell death. Therefore, this study proposes a new, non-invasive, and fast method to differentiate cell death types without the additional fluorescent labeling.

Fluorescence Imaging of Breast Tumors and Gastrointestinal Cancer

Optical imaging offers a high potential for noninvasive detection and therapy of cancer in humans. Recent advances in instrumentation for diffuse optical imaging have led to new capabilities for the detection of cancer in highly scattering tissue such as the female breast. In particular, fluorescence imaging was made applicable as a sensitive technique to image molecular probes in vivo. We review recent developments in the detection of breast cancer and fluorescence-guided surgery of the breast by contrast agents available for application on humans. Detection of cancer has been investigated with the unspecific contrast agents "indocyanine green" and "omocianine" so far. Hereby, indocyanine green was found to offer high potential for the differentiation of malignant and benign lesions by exploiting vessel permeability for macromolecules as a cancer-specific feature. Tumor-specific molecular targeting and activatable probes have been investigated in clinical trials for fluorescence-guided tumor margin detection. In this application, high spatial resolution can be achieved, since tumor regions are visualized mainly at the tissue surface. As another example of superficial tumor tissue, imaging of lesions in the gastrointestinal tract is discussed. Promising results have been obtained on high-risk patients with Barrett´s esophagus and with ulcerative colitis by administering 5-aminolevulinic acid which induces accumulation of protoporphyrin IX serving as a tumor-specific fluorescent marker. Time-gated fluorescence imaging and spectroscopy are effective ways to suppress underlying background from tissue autofluorescence. Furthermore, recently developed tumor-specific molecular probes have been demonstrated to be superior to white-light endoscopy offering new ways for early detection of malignancies in the gastrointestinal tract.

Basic concepts of optical measuring of bone thickness with IR-beam

This paper describes a new concept for measuring bone thickness via optically analyzing of hard tissue. In many surgical disciplines effecting bone treatment, like oral and maxillofacial surgery or otolaryngology, the knowledge of existing bone material is very important in order not to hurt anatomically sensitive structures. The existing bone material can be determined preoperatively using imaging procedures. However, the surgeon has no information about the residual bone thickness during the intervention. As a consequence of this, the distance between the tip of his instrument and sensitive structures is also unknown. Therefore, it would be very useful, if the bone thickness could be measured concurrently to the bone ablation. In this work, bone was irradiated with IR-Light and the reflection was detected. It would be examined, if there was an interrelation between bone thickness and reflection and how it could be measured. The results of the experiments show, that by means of this method it is possible to detect different bone thicknesses for a bone thickness < 1 mm.

Time-domain in vivo near infrared fluorescence imaging for evaluation of matriptase as a potential target for the development of novel, inhibitor-based tumor therapies

Proteolytic enzymes expressed on the surface of tumor cells, and thus easily accessible to external interventions, represent useful targets for anticancer and antimetastatic therapies. In our study, we thoroughly evaluated matriptase, a trypsin-like transmembrane serine protease, as potential target for novel inhibitor-based tumor therapies. We applied time-domain near infrared fluorescence (NIRF) imaging to characterize expression and activity of matriptase in vivo in an orthotopic AsPC-1 pancreatic tumor model in nude mice. We show strong and tumor-specific binding of intravenously injected Cy5.5 labeled antimatriptase antibody (MT-Ab*Cy5.5) only to primary AsPC-1 tumors and their metastases over time within living mice, taking into account fluorescence intensities and fluorescence lifetimes of the applied probes. Specific binding of MT-Ab*Cy5.5 to tumor sites was confirmed by ex vivo NIRF imaging of tumor tissue, NIRF microscopy and by coregistration of the in vivo acquired NIRF intensity maps to anatomical structures visualized by flat-panel volume computed tomography (fpVCT) in living mice. Moreover, using an activatable synthetic substrate S*DY-681 we could clearly demonstrate that matriptase is proteolytically active in vitro as well as in vivo in tumor-bearing mice, and that application of synthetic active-site inhibitors having high affinity and selectivity toward matriptase can efficiently inhibit its proteolytic activity for at least 24 hr. We thus successfully applied NIRF imaging in combination with fpVCT to characterize matriptase as a promising molecular target for inhibitor-based cancer therapies.

In vivo tumor detection in small animals by hematoporphyrin-mediated fluorescence imaging

OBJECTIVE

Noninvasive in vivo imaging of human tumors implanted in mice provides a reliable and economic tool for the investigation of tumor progression and metastasis and of the effectiveness of the antiblastic drugs on them. The purpose of this study is to report on the performance achievable by the well-known and extensively investigated HP-FRI (HematoPorphyrin (HP)-mediated Fluorescence Reflectance Imaging) when a high-quality image-acquisition device is used.

BACKGROUND DATA

Previous articles of ours showed that HP-FRI still represents a useful, simple and reliable optical imaging technique to detect surface tumors. Therefore, it is particularly suitable to be used in combination with other imaging modalities in a multimodal imaging system endowed with diagnostic capabilities much better than each separate modality.

MATERIALS AND METHODS

Six-week-old Crl:CD-1 nude mice were subcutaneously inoculated with tumor cells. Tumor-bearing mice were irradiated in vivo by a frequency-doubled pulsed Nd:YAG laser (lambda = 532 nm). A cooled CCD digital camera recorded fluorescence light emitted by HP injected in mice through a cut-on long-wavelength pass filter.

RESULTS

The system we developed allows in vivo imaging of surface tumors on small animals with a large field of view, high photometric sensitivity, adequate space resolution, and short measurement time. The estimated spatial resolution is 730 microm for a fluorescence source placed about 0.5 mm under the mouse skin. The first exploration of the capabilities of this HP-FRI setup on few mice shows that it allows the detection of (a) both types of investigated tumors, (b) early stage and late stage but visually unrecognizable tumors, (c) the gross structure of tumors, and (d) the discrimination of necrotic and nonnecrotic tumor regions.

Multicolor in vivo targeted imaging to guide real-time surgery of HER2-positive micrometastases in a two-tumor coincident model of ovarian cancer

One of the primary goals of oncological molecular imaging is to accurately identify and characterize malignant tissues in vivo. Currently, molecular imaging relies on targeting a single molecule that while overexpressed in malignancy, is often also expressed at lower levels in normal tissue, resulting in reduced tumor to background ratios. One approach to increasing the specificity of molecular imaging in cancer is to use multiple probes each with distinct fluorescence to target several surface antigens simultaneously, in order to identify tissue expression profiles, rather than relying on the expression of a single target. This next step forward in molecular imaging will rely on characterization of tissue based on fluorescence and therefore will require the ability to simultaneously identify several optical probes each attached to different targeting ligands. We created a novel 'coincident' ovarian cancer mouse model by coinjecting each animal with two distinct cell lines, HER2+/red fluorescent protein (RFP)- SKOV3 and HER2-/RFP+ SHIN3-RFP, in order to establish a model of disease in which animals simultaneously bore tumors with two distinct phenotypes (HER2+/RFP-, HER2-/RFP+), which could be utilized for multicolor imaging. The HER2 receptor of the SKOV3 cell line was targeted with a trastuzumab-rhodamine green conjugate to create green tumor implants, whereas the RFP plasmid of the SHIN3 cells created red tumor implants. We demonstrate that real-time in vivo multicolor imaging is feasible and that fluorescence characteristics can then serve to guide the surgical removal of disease.

Molecular imaging as a tool for translating breast cancer science

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

Engineering of SiO2-Au-SiO2 sandwich nanoaggregates using a building block: single, double, and triple cores for enhancement of near infrared fluorescence

We have developed a simple and flexible chemical method to synthesize orderly metallic nanoaggregates using a designed SiO 2-Au core-shell building block. The number of the building blocks in a nanoaggregate is tunable from one to three. These metal nanostructures can generate an enlarged localized electromagnetic field through surface plasmon resonance and enhance the optical signals of the photoactive molecules within this electromagnetic field. Aggregates of metallic nanoparticles provide a higher signal enhancement than well-dispersed nanoparticles combined. The level of signal enhancement is determined by the number of building blocks in a nanoaggregate. The signal enhancement of the nanoaggregates has been verified with a near-infrared (NIR) dye. In the NIR region, biological samples have low background signals and deeper penetration of radiation. The application of these NIR enhanced metal nanostructures will open a significant approach for sensitive detection of biological samples.

In vivo molecular imaging to diagnose and subtype tumors through receptor-targeted optically labeled monoclonal antibodies

Molecular imaging of cell surface receptors can potentially diagnose tumors based on their distinct expression profiles. Using multifilter spectrally resolved optical imaging with three fluorescently labeled antibodies, we simultaneously imaged three different cell surface receptors to distinguish tumor types noninvasively. We selected tumors overexpressing different subtypes of EGFR receptor: HER-1 (A431) and HER-2 (NIH3T3/HER2(+)), or interleukin-2 receptor alpha-subunit receptor (IL-2Ralpha; SP2/Tac). After tumor establishment, a cocktail of three fluorescently labeled monoclonal antibodies was injected: cetuximab-Cy5 (targetingHER-1), trastuzumab-Cy7(HER-2),anddaclizumab-AlexaFluor-700 (IL-2Ra). Optical fluorescence imaging was performed after 24 hours with both a red filter set and three successive filter sets (yellow, red, and deep red). Spectrally resolved imaging of 10 mice clearly distinguished A431, NIH3T3/HER2(+), and SP2-Tac tumors based on their distinct optical spectra. Three-filter sets significantly increased the signal-to-background ratio compared to a single-filter set by reducing the background signal, thus significantly improving the differentiation of each of the receptors targeted (P < .022). In conclusion, following multifilter spectrally resolved imaging, different tumor types can be simultaneously distinguished and diagnosed in vivo. Multiple filter sets increase the signal-to-noise ratio by substantially reducing the background signal, and may allow more optical dyes to be resolved within the narrow limits of the near-infrared spectrum.

Multimodal nanoprobes for radionuclide and five-color near-infrared optical lymphatic imaging

Current contrast agents generally have one function and can only be imaged in monochrome; therefore, the majority of imaging methods can only impart uniparametric information. A single nanoparticle has the potential to be loaded with multiple payloads. Such multimodality probes have the ability to be imaged by more than one imaging technique, which could compensate for the weakness or even combine the advantages of each individual modality. Furthermore, optical imaging using different optical probes enables us to achieve multicolor in vivo imaging, wherein multiple parameters can be read from a single image. To allow differentiation of multiple optical signals in vivo, each probe should have a close but different near-infrared emission. To this end, we synthesized nanoprobes with multimodal and multicolor potential, which employed a polyamidoamine dendrimer platform linked to both radionuclides and optical probes, permitting dual-modality scintigraphic and five-color near-infrared optical lymphatic imaging using a multiple-excitation spectrally resolved fluorescence imaging technique.

Nanoparticles for bioimaging

The emergence of synthesis strategies for the fabrication of nanosized contrast agents is anticipated to lead to advancements in understanding biological processes at the molecular level in addition to progress in the development of diagnostic tools and innovative therapies. Imaging agents such as fluorescent dye-doped silica nanoparticles, quantum dots and gold nanoparticles have overcome many of the limitations of conventional contrast agents (organic dyes) such as poor photostability, low quantum yield, insufficient in vitro and in vivo stability, etc. Such particulates are now being developed for absorbance and emission in the near infrared region, which is expected to allow for real time and deep tissue imaging via optical routes. Other efforts to facilitate deep tissue imaging with pre-existing technologies have lead to the development of multimodal nanoparticles which are both optical and MRI active. The main focus of this article is to provide an overview of properties and design of contrast agents such as dye-doped silica nanoparticles, quantum dots and gold nanoparticles for non-invasive bioimaging.

Neuro-oncological applications of optical spectroscopy

Advances in optics and molecular imaging have occurred rapidly in the past decade. One technique poised to take advantage of these developments is optical spectroscopy (OS). All optical spectroscopic techniques have in common tissue interrogation with light sources ranging from the ultraviolet (UV) to the infrared (IR) ranges of the spectrum, and collection of information on light reflected (reflectance spectroscopy) or light interactions with tissue and emergence at different wavelengths (fluorescence and Raman spectroscopy). OS can provide information regarding intrinsic tissue optical properties such as tissue structure, nuclear density, and the presence or absence of endogenous or exogenous fluorophores. Among other applications, this information has been used to distinguish tumor from normal brain tissues, to detect tumor margins in intrinsic, infiltrating gliomas, to identify radiation damage to tissues, and to assess tissue viability and predict the onset of apoptosis in vitro and in vivo. Potential applications of OS include detection of specific central nervous system (CNS) structures, such as brain nuclei, identification of cell types by the presence of specific neurotransmitters, and the detection of optically labeled cells or drugs during therapeutic interventions. All have potential utility in neuro-oncology, have been investigated in our laboratories, and will be the subject of this review.

Behavioral Profiling of Human Transitional Cell Carcinoma Ex vivo

Outcome studies of many types of cancer have revealed that tumors of indistinguishable histologic appearance may differ significantly in aggressiveness and in their response to therapy. A strategy that would enable early identification of patients at high risk for disease progression and allow screening of multiple therapeutic agents simultaneously for efficacy would improve clinical management. We have developed an orthotopic organ culture model of bladder cancer in which quantum dot-based fluorescent imaging approaches are used to obtain quantitative measurements of tumor cell behavior. Human transitional cell carcinoma (TCC) cells are labeled with quantum dot nanoparticles, and the cells instilled into the rat bladder in vivo, after which the bladder is excised and cultured ex vivo. Cell implantation, proliferation, and invasion into the organ wall are monitored using epifluorescence imaging and two-photon laser scanning confocal microscopy. Using this approach, we were able to assign distinct phenotypes to two metastatic bladder cancer cell lines based on different patterns of invasiveness into the bladder wall. We also showed that established tumor cell masses regressed following intravesical administration of the chemotherapeutic drug thiotepa. Collectively, these findings suggest that this assay system, which we have named EViTAS (for ex vivo tumor assay system), can recapitulate salient aspects of tumor growth in the host and is amenable to behavioral profiling of human cancer.