Novel fluorophores as building blocks for optical probes for in vivo near infrared fluorescence (NIRF) imaging

Association of Indocyanine Green with Chitosan Oleate Coated PLGA Nanoparticles for Photodynamic Therapy

Indocyanine green (ICG) is a safe dye widely used in the biomedical field. Its photodynamic effect (PDT), originating from laser irradiation at 803 nm, opens interesting perspectives in theranostic applications. To overcome its low water stability, ICG can be shielded with nanoparticles (NPs). In this work, previously developed NPs based on poly lactic-co-glycolic acid (PLGA) coated with chitosan oleate (CS-OA) and loaded with resveratrol as a hydrophobic model drug have been proposed as an ICG carrier. These systems have been selected for their observed immunostimulatory properties. The possible loading of the dye by adsorption onto NP surface by electrostatic interaction was studied here in comparison with the encapsulation into the PLGA core. The ICG-chitosan (CS) interaction has been characterized by spectrophotometry, spectroscopy and in-cell in vitro assays. Fluorescence quenching was observed due to the ionic interaction between ICG and CS and was studied considering the dye:polymer stoichiometry and the effect of the NP dilution in cell culture medium (DMEM). The NP systems have been compared in vitro, assessing their behaviour in Caco-2 cell lines. A reduction in cell viability was observed after irradiation of ICG associated with NPs, evident also for the samples loaded by adsorption. These findings open the opportunity to exploit the association of PDT’s effect on ICG with the properties of CS-OA coated NPs, whose immunostimulatory effect can be associated with PDT mechanism in cancer therapy.

Targeted Near-Infrared Fluorescence Imaging With Iodized Indocyanine Green in Preoperative Pulmonary Localization: Comparative Efficacy, Safety, Patient Perception With Hook-Wire Localization

Background

Precise preoperative localization is of great importance to improve the success rate and reduce the operation time of VATS surgery. This study aimed to assess the efficacy, safety, patient perception between CT-guided indocyanine green (ICG) preoperative localization of lung nodule and hook-wire localization.

Methods

65 patients with 85 clinically suspicious pulmonary nodules underwent ICG preoperative localization in this study, and 92 patients with 95 nodules localized by conventional hook-wire served as controls. Both hook-wire localization and ICG injection were performed under CT guidance. Successful targeting rate, success rate in the operative field, incidence rate of complications and respiratory pain score were recorded and compared.

Results

The successful targeting rate for both groups is 100%, however, due to hook-wire dislodgement, the success rate in the VATS operation field of the hook-wire group (95.6%) is lower than that of the ICG group (100%), with no significant difference(p=0.056). The overall complication rate of the hook-wire group (37.0%) is significantly higher than the ICG group (35.4%) (p=0.038). The mean respiratory pain score of the hook-wire group is 3.70 ± 1.25, which is significantly higher than that of the ICG group (2.85 ± 1.05) (p<0.001).

Conclusions

ICG composed with contrast mixture are superior to the conventional hook-wire preoperative lung nodule localization procedure, with a lower complication rate, lower pain score, and relatively higher success rate. ICG is a promising alternative method for pulmonary nodule preoperative localization.

Photophysical Properties of Indocyanine Green in the Shortwave Infrared Region

With the growing development of new contrast agents for optical imaging using near-infrared and shortwave infrared (SWIR) wavelengths, it is essential to have consistent bench-marks for emitters in these regions. Indocyanine green (ICG), a ubiquitous and FDA-approved organic dye and optical imaging agent, is commonly employed as a standard for photophysical properties and biological performance for imaging experiments at these wavelengths. Yet, its reported photophysical properties across organic and aqueous solvents vary greatly in the literature, which hinders its ability to be used as a consistent benchmark. Herein, we measure photophysical properties in organic and aqueous solvents using InGaAs detection (~950-1,700 nm), providing particular relevance for SWIR imaging.

Substitution pattern controlled aggregation-induced emission in donor-acceptor-donor dyes with one and two propeller-like triphenylamine donors

We present a comparative study of the spectroscopic properties of the donor-acceptor-donor substituted dyes triphenylamine-allylidenemalononitrile-julolidine (TMJ) and triphenylamine-allylidenemalononitrile-triphenylamine (TMT), bearing one and two propeller-like triphenylamine donor moieties, in solvents of varying polarity and viscosity and in the aggregated and solid state. Our results reveal control of the aggregation-induced spectroscopic changes and the packing motifs of the dye molecules in the solid state by the chemical nature and structure of the second nitrogen-containing donor, i.e., a planar and a rigid julolidine or a twisted triphenyl group. Assuming that the TMT and TMJ aggregates show a comparable arrangement of the molecules to the respective crystals, these different molecular interactions in the solid state are responsible for aggregation induced emission (AIE) in the case of TMT and its absence for TMJ. Moreover, a versatile strategy for the fluorescence enhancement of only weakly emissive AIE dyes is shown, turning these dyes into bright nanoscale fluorescent reporters by using them as stains for preformed polymer particles.

Water Soluble Porphyrin for the Fluorescent Determination of Cadmium Ions

Porphyrins are highly conjugated molecules that perform wide variety of functions in biological systems. They absorb strongly in the visible region and they are excellent fluorophores that emit in the visible region. If the meso or β positions of porphyrins are properly substituted, emission in the NIR region is facilitated. The fluorescence property of porphyrins can be used in sensing applications. Here, we report the synthesis of a water soluble porphyrin that emits in the NIR region and this molecule is used in the fluorescent determination of cadmium ion, which is an environmental pollutant and affects the health of living organisms adversely. 5,10,15,20-tetrakis(4-hydroxy-3,5-dimethoxyphenyl)porphyrin (THMPP), which is water soluble was synthesised from 5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin (TMPP) by partial demethylation, which in turn was synthesized by mixture acid method. The donor-acceptor interaction of THMPP-Cd²⁺ system displays a dynamic fluorescence quenching through the electron transfer (ET) mechanism. Developed method showed a linear response toward Cd²⁺ in the concentration range of 0.25 μM to 2 μM. The limit of detection was found to be 0.1499 μM. THMPP exhibited excellent selectivity towards Cd (II) in presence of other metal ions like Hg²⁺, Mn²⁺, Mg²⁺, Co²⁺ in 1:100, Zn²⁺, Cu²⁺, Ni²⁺ in 1:10 and Na⁺, K⁺ in 1:1 M ratio.

Fluorescence Guidance in Surgical Oncology: Challenges, Opportunities, and Translation

Surgical resection continues to function as the primary treatment option for most solid tumors. However, the detection of cancerous tissue remains predominantly subjective and reliant on the expertise of the surgeon. Surgery that is guided by fluorescence imaging has shown clinical relevance as a new approach to detecting the primary tumor, tumor margins, and metastatic lymph nodes. It is a technique to reduce recurrence and increase the possibility of a curative resection. While significant progress has been made in developing this emerging technology as a tool to assist the surgeon, further improvements are still necessary. Refining imaging agents and tumor targeting strategies to be a precise and reliable surgical strategy is essential in order to translate this technology into patient care settings. This review seeks to provide a comprehensive update on the most recent progress of fluorescence-guided surgery and its translation into the clinic. By highlighting the current status and recent developments of fluorescence image-guided surgery in the field of surgical oncology, we aim to offer insight into the challenges and opportunities that require further investigation.

A fast and effective determination of the biodistribution and subcellular localization of fluorescent immunoliposomes in freshly excised animal organs

Background

Preclinical research implementing fluorescence-based approaches is inevitable for drug discovery and technology. For example, a variety of contrast agents developed for biomedical imaging are usually evaluated in cell systems and animal models based on their conjugation to fluorescent dyes. Biodistribution studies of excised organs are often performed by macroscopic imaging, whereas the subcellular localization though vital, is often neglected or further validated by histological procedures. Available systems used to define the subcellular biodistribution of contrast agents such as intravital microscopes or ex vivo histological analysis are expensive and not affordable by the majority of researchers, or encompass tedious and time consuming steps that may modify the contrast agents and falsify the results. Thus, affordable and more reliable approaches to study the biodistribution of contrast agents are required. We developed fluorescent immunoliposomes specific for human fibroblast activation protein and murine endoglin, and used macroscopic fluorescence imaging and confocal microscopy to determine their biodistribution and subcellular localization in freshly excised mice organs at different time points post intravenous injection.

Results

Near infrared fluorescence macroscopic imaging revealed key differences in the biodistribution of the respective immunoliposomes at different time points post injection, which correlated to the first-pass effect as well as the binding of the probes to molecular targets within the mice organs. Thus, a higher accumulation and longer retention of the murine endoglin immunoliposomes was seen in the lungs, liver and kidneys than the FAP specific immunoliposomes. Confocal microscopy showed that tissue autofluorescence enables detection of organ morphology and cellular components within freshly excised, non-processed organs, and that fluorescent probes with absorption and emission maxima beyond the tissue autofluorescence range can be easily distinguished. Hence, the endoglin targeting immunoliposomes retained in some organs could be detected in the vascular endothelia cells of the organs.

Conclusions

The underlying work represents a quick, effective and more reliable setup to validate the macroscopic and subcellular biodistribution of contrast agents in freshly excised animal organs. The approach will be highly beneficial to many researchers involved in nanodrug design or in fluorescence-based studies on disease pathogenesis.

Magnetic resonance imaging/fluorescence dual modality protocol using designed phosphonate ligands coupled to superparamagnetic iron oxide nanoparticles

A simple and versatile methodology to tailor the surface of superparamagnetic iron oxide nanoparticles (SPIONs), and render additional fluorescence capability to these contrast agents, is reported. The dual modality imaging protocol was developed by designing multi-functional scaffolds with a combination of orthogonal moieties for aqueous dispersion and stealth, to covalently link them to SPIONs, and carry out post-functionalization of nanoparticles. SPIONs stabilized with ligands incorporating surface-anchoring phosphonate groups, ethylene glycol backbone for aqueous dispersion, and free surface exposed OH moieties were coupled to near-infrared dye Cy5.5A. Our results demonstrate that design of multi-tasking ligands with desired combination and spatial distribution of functions provides an ideal platform to construct highly efficient dual imaging probes with balanced magnetic, optical and cell viability properties.

Indocyanine green delivery systems for tumour detection and treatments

Indocyanine green (ICG) is a cyanine compound that displays fluorescent properties in the near infrared region. This dye is employed for numerous indications but nowadays its major application field regards tumour diagnosis and treatments. Optical imaging by near infrared fluorescence provides news opportunities for oncologic surgery. The imaging of ICG can be useful for intraoperative identification of several solid tumours and metastases, and sentinel lymph node detection. In addition, ICG can be used as an agent for the destruction of malignant tissue, by virtue of the production of reactive oxygen species and/or induction of a hyperthermia effect under irradiation. Nevertheless, ICG shows several drawbacks, which limit its clinical application. Several formulative strategies have been studied to overcome these problems. The rationale of the development of ICG containing drug delivery systems is to enhance the in vivo stability and biodistribution profile of this dye, allowing tumour accumulation and resulting in better efficacy. In this review, ICG containing nano-sized carriers are classified based on their chemical composition and structure. In addition to nanosystems, different formulations including hydrogel, microsystems and others loaded with ICG will be illustrated. In particular, this report describes the preparation, in vitro characterization and in vivo application of ICG platforms for cancer imaging and treatment. The promising results of all systems confirm their clinical utility but further studies are required prior to evaluating the formulations in human trials.

Dual delivery of biological therapeutics for multimodal and synergistic cancer therapies

Cancer causes >8.2 million deaths annually worldwide; thus, various cancer treatments have been investigated over the past decades. Among them, combination drug therapy has become extremely popular, and treatment with more than one drug is often necessary to achieve appropriate anticancer efficacy. With the development of nanoformulations and nanoparticulate-based drug delivery, researchers have explored the feasibility of dual delivery of biological therapeutics to overcome the current drawbacks of cancer therapy. Compared with the conventional single drug therapy, dual delivery of therapeutics has provided various synergistic effects in addition to offering multimodality to cancer treatment. In this review, we highlight and summarize three aspects of dual-delivery systems for cancer therapy. These include (1) overcoming drug resistance by the dual delivery of chemical drugs with biological therapeutics for synergistic therapy, (2) targeted and controlled drug release by the dual delivery of drugs with stimuli-responsive nanomaterials, and (3) multimodal theranostics by the dual delivery of drugs and molecular imaging probes. Furthermore, recent developments, perspectives, and new challenges regarding dual-delivery systems for cancer therapy are discussed.

Fluorescence-quenching of a liposomal-encapsulated near-infrared fluorophore as a tool for in vivo optical imaging

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous number of imaging techniques currently available and the progress in instrumentation, there is still a need for highly sensitive probes that are suitable for in vivo imaging. One typical problem of available preclinical fluorescent probes is their rapid clearance in vivo, which reduces their imaging sensitivity. To circumvent rapid clearance, increase number of dye molecules at the target site, and thereby reduce background autofluorescence, encapsulation of the near-infrared fluorescent dye, DY-676-COOH in liposomes and verification of its potential for in vivo imaging of inflammation was done. DY-676 is known for its ability to self-quench at high concentrations. We first determined the concentration suitable for self-quenching, and then encapsulated this quenching concentration into the aqueous interior of PEGylated liposomes. To substantiate the quenching and activation potential of the liposomes we use a harsh freezing method which leads to damage of liposomal membranes without affecting the encapsulated dye. The liposomes characterized by a high level of fluorescence quenching were termed Lip-Q. We show by experiments with different cell lines that uptake of Lip-Q is predominantly by phagocytosis which in turn enabled the characterization of its potential as a tool for in vivo imaging of inflammation in mice models. Furthermore, we use a zymosan-induced edema model in mice to substantiate the potential of Lip-Q in optical imaging of inflammation in vivo. Considering possible uptake due to inflammation-induced enhanced permeability and retention (EPR) effect, an always-on liposome formulation with low, non-quenched concentration of DY-676-COOH (termed Lip-dQ) and the free DY-676-COOH were compared with Lip-Q in animal trials.

Rational design of fluorophores for in vivo applications

Several classes of small organic molecules exhibit properties that make them suitable for fluorescence in vivo imaging. The most promising candidates are cyanines, squaraines, boron dipyrromethenes, porphyrin derivatives, hydroporphyrins, and phthalocyanines. The recent designing and synthetic efforts have been dedicated to improving their optical properties (shift the absorption and emission maxima toward longer wavelengths and increase the brightness) as well as increasing their stability and water solubility. The most notable advances include development of encapsulated cyanine dyes with increased stability and water solubility, squaraine rotaxanes with increased stability, long-wavelength-absorbing boron dipyrromethenes, long-wavelength-absorbing porphyrin and hydroporphyrin derivatives, and water-soluble phthalocyanines. Recent advances in luminescence and bioluminescence have made self-illuminating fluorophores available for in vivo applications. Development of new types of hydroporphyrin energy-transfer dyads gives the promise for further advances in in vivo multicolor imaging.

Fluorescent molecular imaging: technical progress and current preclinical and clinical applications in urogynecologic diseases

Many molecular imaging probes have been developed in recent years that hold great promise for both diagnostic and therapeutic functions in urogynecologic disease. Historically, optical probe designs were based on either endogenous or exogenous fluorophores. More recently, organic fluorophore probes have been engineered to target specific tissues and emit fluorescence only upon binding to targets. Several different photochemical mechanisms of activation exist. This review presents a discussion of the history and development of molecular imaging probe designs and provides an overview of successful preclinical and clinical models employing molecular probes for in vivo imaging of urogynecologic cancers.

Liposomal encapsulation of a near-infrared fluorophore enhances fluorescence quenching and reliable whole body optical imaging upon activation in vivo

In the past decade, there has been significant progress in the development of water soluble near-infrared fluorochromes for use in a wide range of imaging applications. Fluorochromes with high photo and thermal stability, sensitivity, adequate pharmacological properties and absorption/emission maxima within the near infrared window (650-900 nm) are highly desired for in vivo imaging, since biological tissues show very low absorption and auto-fluorescence at this spectrum window. Taking these properties into consideration, a myriad of promising near infrared fluorescent probes has been developed recently. However, a hallmark of most of these probes is a rapid clearance in vivo, which hampers their application. It is hypothesized that encapsulation of the near infrared fluorescent dye DY-676-COOH, which undergoes fluorescence quenching at high concentrations, in the aqueous interior of liposomes will result in protection and fluorescence quenching, which upon degradation by phagocytes in vivo will lead to fluorescence activation and enable imaging of inflammation. Liposomes prepared with high concentrations of DY-676-COOH reveal strong fluorescence quenching. It is demonstrated that the non-targeted PEGylated fluorescence-activatable liposomes are taken up predominantly by phagocytosis and degraded in lysosomes. Furthermore, in zymosan-induced edema models in mice, the liposomes are taken up by monocytes and macrophages which migrate to the sites of inflammation. Opposed to free DY-676-COOH, prolonged stability and retention of liposomal-DY-676-COOH is reflected in a significant increase in fluorescence intensity of edema. Thus, protected delivery and fluorescence quenching make the DY-676-COOH-loaded liposomes a highly promising contrast agent for in vivo optical imaging of inflammatory diseases.

Multiplexed in vivo fluorescence optical imaging of the therapeutic efficacy of photodynamic therapy

In our study we wanted to elucidate a time frame for in vivo optical imaging of the therapeutic efficacy of photodynamic therapy (PDT) by using a multiplexed imaging approach for detecting apoptosis and vascularization. The internalization of the photosensitizer Foslip(®) into tongue-squamous epithelium carcinoma cells (CAL-27) was examined in vitro and in vivo. For detecting apoptosis, annexin V was covalently coupled to the near-infrared dye DY-734 and the spectroscopic properties and binding affinity to apoptotic CAL-27 cells were elucidated. CAL-27 tumor bearing mice were treated with PDT and injected 2 days and 2 weeks thereafter with DY-734-annexin V. PDT-induced changes in tumor vascularization were detected with the contrast agent IRDye(®) 800CW RGD up to 3 weeks after PDT. A perinuclear enrichment of Foslip(®) could be seen in vitro which was reflected in an accumulation in CAL-27 tumors in vivo. The DY-734-annexin V (coupling efficiency 30-50%) revealed a high binding affinity to apoptotic compared to non-apoptotic cells (17.2% vs. 1.2%) with a KD-value of 20 nm. After PDT-treatment, the probe showed a significantly higher (p <0.05) contrast in tumors at 2 days compared to 2 weeks after therapy (2-8 h post injection). A reduction of the vascularization could be detected after PDT especially in the central tumor areas. To detect the therapeutic efficacy of PDT, a multiplexed imaging approach is necessary. A detection of apoptotic cells is possible just shortly after therapy, whereas at later time points the efficacy can be verified by investigating the vascularization.

Carborhodol: a new hybrid fluorophore obtained by combination of fluorescein and carbopyronine dye cores

Asymmetric hybrid fluorophores are built from the structural elements of two (or even more) symmetric dyes and can develop valuable new features which their parents do not possess. A new hybrid carborhodol dye was obtained by the combination of fluorescein and carbopyronine fluorophores. The brightly fluorescent hybrid dye with a linker and reactive group was prepared in 12 steps with overall yield of 1.6%. In aqueous solutions, it has absorption and emission maxima at 586 and 613 nm, respectively. Antibodies labeled with a carborhodol dye possess broad absorption and emission bands so that the effective Stokes shift is increased (compared with small Stokes shifts of the parent dyes) and the fluorescence quantum yield of 39% at a degree of labeling of 5.2. Two samples of secondary antibodies labeled with carborhodol and the benchmark red-emitting rhodamine dye (KK114) were used in two-color imaging experiments with excitation at 514-532 (carborhodol dye) and 633-640 nm (KK114). When emitted light was detected above 650 nm, the novel carborhodol dye provided a lower crosstalk than spectrally similar emitters (e. g., Atto594; crosstalk 40-60% with KK114 under the same conditions). The optical resolution of ca. 80 nm was attained using the new dye in stimulated emission depleted (STED) microscopy. The relatively short fluorescence lifetime in conjugates with antibodies (τ = 1.2-1.6 ns) suggests the possibility of dual FLIM with numerous dyes having τ values in the range of 3-5 ns. All of these features make the carborhodol fluorophore a valuable addition to the family of the red-emitting fluorescent dyes.

Biomembrane interactions of functionalized cryptophane-A: combined fluorescence and 129Xe NMR studies of a bimodal contrast agent

Fluorescent derivatives of the (129)Xe NMR contrast agent cryptophane-A were obtained by functionalization with near infrared fluorescent dyes DY680 and DY682. The resulting conjugates were spectrally characterized, and their interaction with giant and large unilamellar vesicles of varying phospholipid composition was analyzed by fluorescence and NMR spectroscopy. In the latter, a chemical exchange saturation transfer with hyperpolarized (129)Xe (Hyper-CEST) was used to obtain sufficient sensitivity. To determine the partitioning coefficients, we developed a method based on fluorescence resonance energy transfer from Nile Red to the membrane-bound conjugates. This indicated that not only the hydrophobicity of the conjugates, but also the phospholipid composition, largely determines the membrane incorporation. Thereby, partitioning into the liquid-crystalline phase of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was most efficient. Fluorescence depth quenching and flip-flop assays suggest a perpendicular orientation of the conjugates to the membrane surface with negligible transversal diffusion, and that the fluorescent dyes reside in the interfacial area. The results serve as a basis to differentiate biomembranes by analyzing the Hyper-CEST signatures that are related to membrane fluidity, and pave the way for dissecting different contributions to the Hyper-CEST signal.

A novel sulfonated prosthetic group for [18F]-radiolabelling and imparting water solubility of biomolecules and cyanine fluorophores

Synthesis and some applications of a novel [(18)F]-fluorinated prosthetic group based on the promising sultone radiochemistry and suitable for the labelling of amine-containing (bio)chemical compounds are described. The combined sequential use of two easy and efficient conjugation reactions namely the fluoride ring-opening of a 1,3-propanesultone moiety and the aminolysis of an N-hydroxysuccinimidyl ester is the key component of this original radiolabelling strategy. The mild reaction conditions and the release of a free sulfonic acid moiety as a result of the [(18)F]-induced sultone ring-opening reaction, both make this [(18)F]-conjugation method suitable for the radiofluorination of fragile and hydrophobic biomolecules and fluorophores, particularly by making the separation of the targeted [(18)F]-tagged sulfonated compound from its starting precursor easier and thus faster. The ability of this unusual prosthetic group to readily introduce the radioisotope within complex (bio)molecular architectures has been demonstrated by (1) the preparation of the first [(18)F]-labelled cyanine 5.5 (Cy 5.5) dye, a suitable precursor for the construction of hybrid positron emission tomography/near-infrared fluorescence (PET/NIRF) imaging probes and (2) the radiolabelling of a biologically relevant peptide bearing a single lysine residue.

Multiwavelength time-resolved detection of fluorescence during the inflow of indocyanine green into the adult's brain

Optical technique based on diffuse reflectance measurement combined with indocyanine green (ICG) bolus tracking is extensively tested as a method for clinical assessment of brain perfusion in adults at the bedside. Methodology of multiwavelength and time-resolved detection of fluorescence light excited in the ICG is presented and advantages of measurements at multiple wavelengths are discussed. Measurements were carried out: 1. on a physical homogeneous phantom to study the concentration dependence of the fluorescence signal, 2. on the phantom to simulate the dynamic inflow of ICG at different depths, and 3. in vivo on surface of the human head. Pattern of inflow and washout of ICG in the head of healthy volunteers after intravenous injection of the dye was observed for the first time with time-resolved instrumentation at multiple emission wavelengths. The multiwavelength detection of fluorescence signal confirms that at longer emission wavelengths, probability of reabsorption of the fluorescence light by the dye itself is reduced. Considering different light penetration depths at different wavelengths, and the pronounced reabsorption at longer wavelengths, the time-resolved multiwavelength technique may be useful in signal decomposition, leading to evaluation of extra- and intracerebral components of the measured signals.

pH-stimuli-responsive near-infrared optical imaging nanoprobe based on poly(γ-glutamic acid)/poly(β-amino ester) nanoparticles

pH-stimuli-responsive near-infrared optical imaging nanoprobes are designed and synthesized in this study in a facile one-step synthesis process based on the use of the biocompatible and biodegradable polymer poly(γ-glutamic acid) (γ-PGA)/poly(β-amino ester) (PBAE). PBAE has good transfection efficiency and promotes degradation properties under acidic conditions. This pH-responsive degradability can be used for the effective release of encapsulating materials after cellular uptake. As an optical imaging probe, indocyanine green (ICG) is an FDA-approved near-infrared fluorescent dye with a quenching property at a high concentration. In this regard, we focus here on the rapid degradation of PBAE in an acidic environment, in which the nanoparticles are disassembled. This allows the ICG dyes to show enhanced fluorescence signals after being releasing from the particles. We demonstrated this principle in cellular uptake experiments. We expect that the developed pH-stimuli-responsive smart nanoprobes can be applied in intracellular delivery signaling applications.

Spectroscopically Well-Characterized RGD Optical Probe as a Prerequisite for Lifetime-Gated Tumor Imaging

Labeling of RGD peptides with near-infrared fluorophores yields optical probes for noninvasive imaging of tumors overexpressing αvβ3 integrins. An important prerequisite for optimum detection sensitivity in vivo is strongly absorbing and highly emissive probes with a known fluorescence lifetime. The RGD-Cy5.5 optical probe was derived by coupling Cy5.5 to a cyclic arginine–glycine–aspartic acid–d-phenylalanine–lysine (RGDfK) peptide via an aminohexanoic acid spacer. Spectroscopic properties of the probe were studied in different matrices in comparison to Cy5.5. For in vivo imaging, human glioblastoma cells were subcutaneously implanted into nude mice, and in vivo fluorescence intensity and lifetime were measured. The fluorescence quantum yield and lifetime of Cy5.5 were found to be barely affected on RGD conjugation but dramatically changed in the presence of proteins. By time domain fluorescence imaging, we demonstrated specific binding of RGD-Cy5.5 to glioblastoma xenografts in nude mice. Discrimination of unspecific fluorescence by lifetime-gated analysis further enhanced the detection sensitivity of RGD-Cy5.5-derived signals. We characterized RGD-Cy5.5 as a strongly emissive and stable probe adequate for selective targeting of αvβ3 integrins. The specificity and thus the overall detection sensitivity in vivo were optimized with lifetime gating, based on the previous determination of the probes fluorescence lifetime under application-relevant conditions.

Optical imaging of CCK₂/gastrin receptor-positive tumors with a minigastrin near-infrared probe

PURPOSE

A variety of tumors in different organs with good accessibility to near-infrared light express the cholecystokinin-2 (CCK₂)/gastrin receptor. Therefore, the applicability of fluorescence optical imaging was assessed using a novel peptide probe.

MATERIALS AND METHODS

This study was approved by the regional animal committee. Our optical peptide probe (DY-minigastrin) was synthesized by coupling a hemicyanine dye to a gastrin derivative peptide (minigastrin). In vitro CCK₂/gastrin receptor identification was performed in receptor-positive HT-29 and negative A-375 cells using flow cytometry, laser scanning microscopy, and macroscopic near-infrared fluorescent (NIRF) imaging. For in vivo studies, tumor cells were implanted into mice, and DY-minigastrin in presence or absence of nonlabeled minigastrin (control of signaling specificity) was applied intravenously. Fluorescence signals in tumors and organs were recorded and statistically analyzed.

RESULTS

Flow cytometry, laser scanning microscopy, and in vitro macroscopic imaging of cell pellets revealed a distinct accumulation of our minigastrin probe in HT-29 cells, showing distinct probe internalization. In vivo NIRF whole-body animal imaging, again, demonstrated a clear depiction of HT-29 tumors, which was reversed by blocking with nonlabeled minigastrin. Semi-quantitative fluorescence analysis and histologic observations were in agreement with these observations. A distinct probe organ distribution was observed.

CONCLUSIONS

Our observations indicate that DY-minigastrin-based NIRF optical imaging of CCK₂/gastrin receptor protein is feasible. Because of its widespread occurrence in different tumor types, endoscopic, laparoscopic, and tomographic receptor imaging could be accomplished in the near future.

Optical imaging in vivo with a focus on paediatric disease: technical progress, current preclinical and clinical applications and future perspectives

To obtain information on the occurrence and location of molecular events as well as to track target-specific probes such as antibodies or peptides, drugs or even cells non-invasively over time, optical imaging (OI) technologies are increasingly applied. Although OI strongly contributes to the advances made in preclinical research, it is so far, with the exception of optical coherence tomography (OCT), only very sparingly applied in clinical settings. Nevertheless, as OI technologies evolve and improve continuously and represent relatively inexpensive and harmful methods, their implementation as clinical tools for the assessment of children disease is increasing. This review focuses on the current preclinical and clinical applications as well as on the future potential of OI in the clinical routine. Herein, we summarize the development of different fluorescence and bioluminescence imaging techniques for microscopic and macroscopic visualization of microstructures and biological processes. In addition, we discuss advantages and limitations of optical probes with distinct mechanisms of target-detection as well as of different bioluminescent reporter systems. Particular attention has been given to the use of near-infrared (NIR) fluorescent probes enabling observation of molecular events in deeper tissue.

Water-solubilisation and bio-conjugation of a red-emitting BODIPY marker

The synthesis and preliminary bio-conjugation studies of a novel water-soluble red-emitting di-styryl BODIPY dye are disclosed. Aggregation behaviour of this compound under physiological conditions was suppressed by specific introduction of a di-sulfonated peptide-based linker at the meso phenyl substituent, sultonated styryl arms and short polyethyleneglycol chains at the boron center. Thus, a good quantum yield of 22% in PBS for this red-emitting BODIPY was obtained. Introduction of an activated ester function enabled successful bio-conjugation to monoclonal antibodies and proteins.