Sensitive and selective tumor imaging with novel and highly activatable fluorescence probes

Biocompatible nanomicelles for sensitive detection and photodynamic therapy of early-stage cancer

The lack of sensitive detection techniques and agents for early-stage tumors, which are characterized by small size, juvenile blood vessels and scarce secreted markers, has hampered timely cancer therapy and human well-being. Herein, the natural product pyropheophorbide-a (PPa) and FDA-approved Pluronic F127 are organized to develop F127-PPa nanomicelles with favorable size, red-shifted fluorescence and decent biocompatibility. After intravenous (i.v.) injection, the F127-PPa nanomicelles could not only accurately identify early-stage xenografted tumors, but also sensitively detect cancer metastasis in lungs through near-infrared (NIR) fluorescence imaging. The fluorescence signals are consistent with radionuclide imaging, photoacoustic (PA) imaging and bioluminescence imaging of tumors, consolidating the reliability of using F127-PPa nanomicelles for sensitive cancer diagnosis in a non-invasive and low-cost manner. Moreover, the fluorescence intensity of small tumors is linearly correlated with the tumoral mass ranging from 10 to 120 mg with a fluorescence coefficient of 4.5 × 10⁷ mg^-1. Under the guidance of multimodal imaging, the tumors could be thoroughly eradicated by F127-PPa under laser irradiation due to efficient reactive oxygen species (ROS) generation. These findings may provide clinically translatable agents and strategies for sensitive diagnosis of early-stage tumors and timely cancer therapy.

Versatile fluorophores for bioimaging applications: π-expanded naphthalimide derivatives with skeletal and appendage diversity

Four novel fluorescent cores bearing a transformable functional group based on a π-expanded naphthalimide including a fused pyranone or furan ring have been prepared.

A light-up endoplasmic reticulum probe based on a rational design of red-emissive fluorogens with aggregation-induced emission

Fine-tuning the interaction between electron donors and acceptors generates a red-emissive AIEgen which was further developed into an ER targeting imaging probe for specific ER imaging with high selectivity.

Turn on Fluorescent Probes for Selective Targeting of Aldehydes

Two different classes of fluorescent dyes were prepared as a turn off/on sensor system for aldehydes. Amino derivatives of a boron dipyrromethene (BDP) fluorophore and a xanthene-derived fluorophore (rosamine) were prepared. Model compounds of their product with an aldehyde were prepared using salicylaldehyde. Both amino boron dipyrromethene and rosamine derivatives are almost non-fluorescent in polar and apolar solvent. However, imine formation with salicylaldehyde on each fluorophore increases the fluorescence quantum yield by almost a factor of 10 (from 0.05 to 0.4). These fluorophores are therefore suitable candidates for development of fluorescence-based sensors for aldehydes.

A self-reporting AIE probe with a built-in singlet oxygen sensor for targeted photodynamic ablation of cancer cells

A probe for the in situ monitoring of singlet oxygen generation during targeted theranostic photodynamic therapy is developed based on a photosensitizer with aggregation-induced emission (AIE) characteristics and conjugated to a fluorogenic rhodol dye via a singlet oxygen cleavable linker.

The real-time monitoring of reactive oxygen species (ROS, particularly singlet oxygen) generation during photodynamic therapy is a great challenge due to the extremely short half-life and small radius of action. To tackle this issue, we herein report a bioprobe composed of a red emissive photosensitizer (PS) with aggregation-induced emission (AIE) characteristics and a fluorogenic green emissive rhodol dye conjugated via a singlet oxygen cleavable aminoacrylate (AA) linker. The probe emits red fluorescence in water, and the red emissive PS can be used for probe self-tracking. Upon image-guided light irradiation, the generated singlet oxygen cleaves the AA linker to yield green fluorescence turn-on of rhodol, which offers real-time and in situ monitoring of singlet oxygen generation during photodynamic ablation of cancer cells, providing a strategy for the early evaluation of the therapeutic effect.

Rational design for cooperative recognition of specific nucleobases using β-cyclodextrin-modified DNAs and fluorescent ligands on DNA and RNA scaffolds

We propose a binary fluorimetric method for DNA and RNA analysis by the combined use of two probes rationally designed to work cooperatively. One probe is an oligonucleotide (ODN) conjugate bearing a β-cyclodextrin (β-CyD). The other probe is a small reporter ligand, which comprises linked molecules of a nucleobase-specific heterocycle and an environment-sensitive fluorophore. The heterocycle of the reporter ligand recognizes a single nucleobase displayed in a gap on the target labeled with the conjugate and, at the same time, the fluorophore moiety forms a luminous inclusion complex with nearby β-CyD. Three reporter ligands, MNDS (naphthyridine-dansyl linked ligand), MNDB (naphthyridine-DBD), and DPDB (pyridine-DBD), were used for DNA and RNA probing with 3'-end or 5'-end modified β-CyD-ODN conjugates. For the DNA target, the β-CyD tethered to the 3'-end of the ODN facing into the gap interacted with the fluorophore sticking out into the major groove of the gap site (MNDS and DPDB). Meanwhile the β-CyD on the 5'-end of the ODN interacted with the fluorophore in the minor groove (MNDB and DPDB). The results obtained by this study could be a guideline for the design of binary DNA/RNA probe systems based on controlling the proximity of functional molecules.

Hyperspectral imaging and quantitative analysis for prostate cancer detection

Hyperspectral imaging (HSI) is an emerging modality for various medical applications. Its spectroscopic data might be able to be used to noninvasively detect cancer. Quantitative analysis is often necessary in order to differentiate healthy from diseased tissue. We propose the use of an advanced image processing and classification method in order to analyze hyperspectral image data for prostate cancer detection. The spectral signatures were extracted and evaluated in both cancerous and normal tissue. Least squares support vector machines were developed and evaluated for classifying hyperspectral data in order to enhance the detection of cancer tissue. This method was used to detect prostate cancer in tumor-bearing mice and on pathology slides. Spatially resolved images were created to highlight the differences of the reflectance properties of cancer versus those of normal tissue. Preliminary results with 11 mice showed that the sensitivity and specificity of the hyperspectral image classification method are 92.8% to 2.0% and 96.9% to 1.3%, respectively. Therefore, this imaging method may be able to help physicians to dissect malignant regions with a safe margin and to evaluate the tumor bed after resection. This pilot study may lead to advances in the optical diagnosis of prostate cancer using HSI technology.

Activatable optical imaging with a silica-rhodamine based near infrared (SiR700) fluorophore: a comparison with cyanine based dyes

Optical imaging is emerging as an important tool to visualize tumors. However, there are many potential choices among the available fluorophores. Optical imaging probes that emit in the visible range can image superficial tumors with high quantum yields; however, if deeper imaging is needed then near-infrared (NIR) fluorophores are necessary. Most commercially available NIR fluorophores are cyanine based and are prone to nonspecific binding and relatively limited photostability. Silica-containing rhodamine (SiR) fluorophores represent a new class of NIR fluorophores, which permit photoactivation via H-dimer formation as well as demonstrate improved photostability. This permits higher tumor-to-background ratios (TBRs) to be achieved over longer periods of time. Here, we compared an avidin conjugated with SiR700 (Av-SiR700) to similar compounds based on cyanine dyes (Av-Cy5.5 and Av-Alexa Fluor 680) in a mouse tumor model of ovarian cancer metastasis. We found that the Av-SiR700 probe demonstrated superior quenching, enabling activation after binding-internalization to the target cell. As a result, Av-SiR700 had higher TBRs compared to Av-Cy5.5 and better biostability compared to Av-Alexa Fluor 680.

Anti-angiogenic activity and intracellular distribution of epigallocatechin-3-gallate analogs

Angiogenesis, a process of construction of new blood capillaries, is crucial for tumor progression and metastasis. Our previous studies demonstrated that a component of green tea, epigallocatechin-3-gallate (EGCG), suppressed angiogenesis and subsequent tumor growth. In this study, to elucidate the detailed mechanism of the anti-angiogenic effect of EGCG and to enhance the antiangiogenic activity of EGCG, we designed and synthesized EGCG derivatives and examined their biological effect and intracellular localization in human umbilical vein endothelial cells (HUVECs). EGCG derivatives aminopentyl dideoxyEGCG and aminopentyl dideoxygallocatechin-3-gallate (cis-APDOEGCG and trans-APDOEGCG) had an enhanced inhibitory effect on the proliferation when used at more than 30 µM. To elucidate antiangiogenic effect of EGCG, we used a 1 µM concentration for subsequent experiments where no effect on proliferation was observed. These EGCG derivatives showed a stronger inhibitory effect on migration, invasion, and tube formation by HUVECs than the non-derivatized EGCG. Furthermore, the derivatives induced a change in the distribution of F-actin and subsequent morphology of the HUVECs. Next, we synthesized fluorescent TokyoGreen-conjugated EGCG derivative (EGCG-TG) and observed the distribution in HUVECs under a confocal laser scanning microscope. Abundant fluorescence was observed in the cells after a 3-h incubation, and was localized in mitochondria as well as in cytoplasm. These results suggest that EGCG was incorporated into the HUVECs, that a portion of it entered into their mitochondria.

Rational chemical design of the next generation of molecular imaging probes based on physics and biology: mixing modalities, colors and signals

In recent years, numerous in vivo molecular imaging probes have been developed. As a consequence, much has been published on the design and synthesis of molecular imaging probes focusing on each modality, each type of material, or each target disease. More recently, second generation molecular imaging probes with unique, multi-functional, or multiplexed characteristics have been designed. This critical review focuses on (i) molecular imaging using combinations of modalities and signals that employ the full range of the electromagnetic spectra, (ii) optimized chemical design of molecular imaging probes for in vivo kinetics based on biology and physiology across a range of physical sizes, (iii) practical examples of second generation molecular imaging probes designed to extract complementary data from targets using multiple modalities, color, and comprehensive signals (277 references).

New fluorescent trans-dihydrofluoren-3-ones from aldol-Robinson annulation-regioselective addition involved one-pot reaction

An unexpected discovery of new trans-4-acetyl-1,9-dimethyl-4,4a-dihydro-3H-fluoren-3-ones from one pot reactions of benzaldehydes and acetylacetone is described. The synthetic mechanism and stereochemistry were discussed. These new derivatives exhibit good fluorescent properties in solutions.

Binding of NIR-conPK and NIR-6T to astrocytomas and microglial cells: evidence for a protein related to TSPO

PK 11195 and DAA1106 bind with high-affinity to the translocator protein (TSPO, formerly known as the peripheral benzodiazepine receptor). TSPO expression in glial cells increases in response to cytokines and pathological stimuli. Accordingly, [¹¹C]-PK 11195 and [¹¹C]-DAA1106 are recognized molecular imaging (MI) agents capable of monitoring changes in TSPO expression occurring in vivo and in response to various neuropathologies.

Here we tested the pharmacological characteristics and TSPO-monitoring potential of two novel MI agents: NIR-conPK and NIR-6T. NIR-conPK is an analogue of PK 11195 conjugated to the near-infrared (NIR) emitting fluorophore: IRDye 800CW. NIR-6T is a DAA1106 analogue also conjugated to IRDye 800CW.

We found that NIR-6T competed for [³H]-PK 11195 binding in astrocytoma cell homogenates with nanomolar affinity, but did not exhibit specific binding in intact astrocytoma cells in culture, indicating that NIR-6T is unlikely to constitute a useful MI agent for monitoring TSPO expression in intact cells. Conversely, we found that NIR-conPK did not compete for [³H]-PK 11195 binding in astrocytoma cell homogenate, but exhibited specific binding in intact astrocytoma cells in culture with nanomolar affinity, suggesting that NIR-conPK binds to a protein distinct, but related to, TSPO. Accordingly, treating intact astrocytoma cells and microglia in culture with cytokines led to significant changes in the amount of NIR-conPK specific binding without corresponding change in TSPO expression. Remarkably, the cytokine-induced changes in the protein targeted by NIR-conPK in intact microglia were selective, since IFN-γ (but not TNFα and TGFβ) increased the amount of NIR-conPK specific binding in these cells.

Together these results suggest that NIR-conPK binds to a protein that is related to TSPO, and expressed by astrocytomas and microglia. Our results also suggest that the expression of this protein is increased by specific cytokines, and thus allows for the monitoring of a particular subtype of microglia activation.

H-type dimer formation of fluorophores: a mechanism for activatable, in vivo optical molecular imaging

In vivo molecular imaging with target-specific activatable "smart" probes, which yield fluorescence only at the intended target, enables sensitive and specific cancer detection. Dimerization and fluorescence quenching has been shown to occur in concentrated aqueous solutions of various fluorophores. Here, we hypothesized that fluorophore dimerization and quenching after conjugation to targeting proteins can occur at low concentration. This dimerization can be exploited as a mechanism for fluorescence activation. Rhodamine derivatives were conjugated to avidin and trastuzumab, which target D-galactose receptor and HER2/neu antigen, respectively. After conjugation, a large proportion of R6G and TAMRA formed H-type dimers, even at low concentrations, but could be fully dequenched upon dissociation of the dimers to monomers. To demonstrate the fluorescence activation effect during in vivo fluorescence endoscopic molecular imaging, a highly quenched probe, avidin-TAMRA, or a minimally quenched probe, avidin-Alexa488, was administered into mice with ovarian metastases to the peritoneum. The tumors were clearly visualized with avidin-TAMRA, with low background fluorescence; in contrast, the background fluorescence was high for avidin-Alexa488. Thus, H-dimer formation as a mechanism of fluorescence quenching could be used to develop fluorescence activatable probes for in vivo molecular imaging.

Noninvasive Imaging of Liver Repopulation following Hepatocyte Transplantation

Near infrared fluorescence (NIRF) optical imaging is a technique particularly powerful when studying in vivo processes at the molecular level in preclinical animal models. We recently demonstrated liver irradiation under the additional stimulus of partial hepatectomy as being an effective primer in the rat liver repopulation model based on hepatocyte transplantation. The purpose of this study was to assess optical imaging and the feasibility of donor cell expansion tracking in vivo using a fluorescent probe. Livers of dipeptidylpeptidase IV (DPPIV)-deficient rats were preconditioned with irradiation. Four days later, a partial hepatectomy was performed and wild-type (DPPIV+) hepatocytes were transplanted into recipient livers via the spleen. Repopulation by transplanted DPPIV+ hepatocytes was detected in vivo with Cy5.5-conjugated DPPIV antibody using the eXplore Optix™ System (GE HealthCare). Results were compared with nontransplanted control animals and transplanted animals receiving nonspecific antibody. Optical imaging detected Cy5.5-specific fluorescence in the liver region of the transplanted animals, increasing in intensity with time, representing extensive host liver repopulation within 16 weeks following transplantation. A general pattern of donor cell multiplication emerged, with an initially accelerating growth curve and later plateau phase. In contrast, no specific fluorescence was detected in the control groups. Comparison with ex vivo immunofluorescence staining of liver sections confirmed the optical imaging results. Optical imaging constitutes a potent method of assessing the longitudinal kinetics of liver repopulation in the rat transplantation model. Our results provide a basis for the future development of clinical protocols for suitable fluorescent dyes and imaging technologies.